CHAPTER 2 ELK POINT CARBONATE RESERVOIRS

Transcription

1 CHAPTER 2 ELK PONT CARBONATE RESERVORS N.L. Andersn, Dept. f Gelgical Sciences, Ohi University; RJ. Brwn, (Crdinatr), Dept. f Gelgy & Gephysics, University f Calgary; D.J. Gendzwill, Dept. f Gelgical Sciences, University f Saskatchewan; RC. Hinds, Dept. f Gelgy, University f Pretria; RM. Lundberg, Lundberg Gdwin & Curts, Gephysical Cnsultants NTRODUCTON The Elk Pint Gp is the earliest f several cyclthems in Middle Devnian time, each cnstituting a transgressive and a regressive phase f the Devnian sea. The stratigraphy (Fig. 2.1) and gelgical histry f the Elk Pint Gp are synthesized frm Hargeaves et al. (1960), Graystn et al. (1964), McCamis and Griffith (1967), Bassett and Stut (1967), Langtn and Chin (1968), Barss et a\. (1970), Hriskevich, (1970), Maiklem (1971), Klvan (1974), Gendzwill, (1978), Perrin (1982), Hills et al. (1984), Williams (1984), Campbell (1987), Gendzwill and Wilsn (1981), and AGAT Labratries (1987, 1988). This gelgy is described briefly in the ntrductin t this vlume, where it is nted that the Elk Pint Gp cnsists f carbnates, evaprites and clastics and that the carbnates and carse clastics frm the principal reservir facies. Clastic reservirs are discussed in Chapter 1 (Basal Palezic Clastic Reservirs). Eamples presented in this chapter include five different types f Elk Pint carbnate build-ups, thse f the Rainbw Mbr, Upper Keg River Reef Mbr and Zama Mbr (nrthwestern Alberta), the Keg River Fm (nrth-central Alberta) and the Winnipegsis Fm (suthern Saskatchewan). Figure 2.2 shws the general lcatins f these different carbnate build-ups in the Middle Devnian Elk Pint basin. They cnstitute the principal and mst prspective f the Elk Pint carbnates. All five were depsited within evaprite basins: the Winnipegsis Fm as pinnacles and atlls within the main Elk Pint basin; the Rainbw and Upper Keg River Reef members (Keg River Fm) as pinnacles and atlls within the Black Creek basin (an Elk Pint subbasin); the Keg River Fm (Sene area) as patch reefs n the fringing Keg River Fm shelf, and the Zama Mbr (Keg River Fm) as a widespread shaling facies within the nrthern part f the Black Creek basin (Fig. 2.3). Prductin frm the Rainbw, Upper Keg River Reef and Zama members dwarfs that frm the Keg River Fm (Sene) r Winnipegsis Fm, hwever, due t recent imprtant discveries and current eplratin interest, eamples f these latter tw reservir types have a natural place in this chapter. The five types cvered, including fur Keg River types plus the Winnipegsis type, are rughly time-equivalent. The reefs f the Rainbw Mbr, Upper Keg River Reef Mbr and the munds f the Winnipegsis Fm grew n their underlying platfrm facies as the transgressing Elk Pint seas deepened. Alng the basin margins the Keg River/Winnipegsis fringing shelf develped cncurrently. Shreward f the shelf edge, in the nrtheastern Peace River arch r Sene area, Keg River Fm patch reefs develped, typically n r abve prminent basement structures. Keg River and Winnipegsis reef grwth terminated initially in the main Elk Pint basin and subsequently within the Black Creek basin as circulatin became restricted and hypersaline cnditins develped. All f these reefs were encased in interlayered evaprites and carbnates. Typically, the Winnipegsis Fm munds were envelped by thick salts and thin interbedded anhydrites f the Prairie Evaprite Fm (r Prairie Fm). The lw-relief Keg River Fm patch reefs (Sene area) were verlain by interlayered salts, dlmites and anhydrites (Muskeg Fm). Reefs f the Rainbw and Upper Keg River Reef members were surrunded by the thick basinal salt f the Black Creek Mbr and an verlying successin f interlayered carbnates and anhydrites f the upper Muskeg Fm. The Zama Mbr, a shaling carbnate facies, f the upper Muskeg Fm, was distributed within the nrthern part f the Black Creek basin and typically is prductive where draped acrss reefs f the Upper Keg River Reef Mbr. slated reefs f the Rainbw Mbr, Upper Keg River Reef Mbr and Winnipegsis Fm are herein classified as stratigraphic traps. The classificatin f the Winnipegsis build-ups as munds r as reefs is discussed further in Part B f this chapter. Althugh, pstdepsitinal structure, due t differential cmpactin and basinal subsidence, influences the distributin f hydrcarbns (generally the thickest gas and/r il clumns are lcated within the updip rims f the atlls), this effect is cnsidered secndary t the reservir-seal relatinship f the reef t ff-reef sediments. n cntrast, the Keg River Fm patch reefs and the Zama Mbr shaling facies are cnsidered t be structural traps, as these sediments are generally prductive nly where draped acrss underlying Precambrian basement structures and the Upper Keg River Reef Mbr, respectively. Althugh prsity and permeability within these latter tw units are stratigraphically cntrlled, the ff-structure facies generally being tighter, these effects are cnsidered as secndary t the drape resulting frm differential cmpactin (McCamis and Griffith, 1967). A brad spectrum f Elk Pint Gp carbnate reservirs is spanned by the eamples analyzed within this chapter. The carbnate facies are bth bihermal and bistrmal, the trapping mechanisms bth stratigraphic and structural, and the build-ups range frm munds, whse status as reefs is still in sme dubt, t patches, pinnacles and atlls f diverse mrphlgies. Similarly, the seismic signatures f these evaprite-basin carbnate reservirs are diverse (Andersn and Brwn, 1987). Fr instance, velcity pull-up is interpreted fr all five reef types but is the result f varius causes. Beneath the Rainbw and Upper Keg River Reef members, pull-up is attributed primarily t drape n hrizns abve the reef (indeed, the reefal facies is typically f lwer velcity than the adjacent ff-reef sediment). Pull-up beneath the Keg River Fm patch reefs is als attributed t drape. Belw the Winnipegsis Fm, such relief is principally due t the higher velcity f the reef relative t the adjacent ff-reef facies. The magnitude f structural drape als changes appreciably, being a functin, nt nly f differential cmpactin but als, f the timing and etent f salt disslutin in the vicinity f the reefs. (The term cmpactin, as used here, refers t all pstdepsitinal vlume changes, whether physically r chemically induced, ecept fr salt disslutin which, due t its fundamentally different nature as well as its magnitude and significance, is treated as a separate mechanism). Fr eample, clsure alng the Slave Pint Fm acrss the Rainbw Mbr eamples is up t 30 m. n cntrast, the Prairie Evaprite Fm is lcally 40 m lwer n-reef than ff-reef. n bth eamples, pst-reef structures result frm a cmbinatin f differential cmpactin and salt disslutin. The cntrast between the seismic signatures f the reef and ff-reef facies is as variable as the estimates f velcity pull-up and time-structural drape. Fr eample, the seismic images f the Winnipegsis Fm are relatively easy t distinguish frm thse f the Prairie Evaprite Fm. n cntrast, the seismic images f the Zama ACKNOWLEDGEMENTS This wrk has been partially supprted by the Natural Sciences and Engineering Research Cuncil f Canada thrugh an perating grant t R.J. Brwn. 27

2 c w ~' (,9 ZAMA ~ ~ GROUP FORMATON MEMBER Z <! Z Z <! z (J") 'G: z «> w > :i '" z > w WOOD BEND (WQODBEND JUPEROW (,~r:,,::? SC,;~r;",s RVER <1 SOURS g;.rver DAVDSON ;;~f jl-!',-ower SOURS w c SLAVE POiNT SLAVE PONT :i r=='tc,r"l,,=",ncc2rn~evf!ce~r~ WATT WATERWAYS SULPHUR MuSKEG GROUP) ~f--r j ~ ~ W 00'" w<! WATERWAYS WATT MUSKEG MOUNTAN BSTCHO ANHYDRTE ~_;~ ~AMA MOUNTAN PONT ANHYDR,TE BLACK CL ~\ RAN- UPPEr LACj{ BOW f--- h:p~_;~~-k ~~~:1-- --jc",,,r,"p~~i-"0"{,? 'EGR ~'G R: ~. KEG RVER LOWER KEG RVER LOWER g:::.:: KEG RVER KEG RVER: ~ ~ L;j e--j '-----l----'-----'-- ~ 1!..LJ CH NC HAGA CH NCHAGA RANBOW LAKE SOUiH SASKATCHEWAN FORMATON MEMBER GROUP FORMATON MEMBER_ DAWSON BAY SECOND RED HED PRAiRE WNNPEGOSS ASHERN ~ ~ f-er-nceosl-~na-l-akle-ake--+--e~-~~;-tna-lak-leak---je~~ Figure 2.1. Stratigraphic crrelatin chart fr part f the Devnian f nrthern Alberta and suthern Saskatchewan. Frmatins fr the general Sene area f nrth-central Alberta cnfrm clsely t thse f the Rainbw Lake area but nt the subdivisins int members. Mbr and the adjacent Muskeg Fm sediment cannt be, as a rule, differentiated visually. n the remainder f this chapter, the Keg River carbnates, essentially f Alberta, that is the Rainbw, Upper Keg River Reef ~ U ~ '" <! CO CO " > Z! 0 a. WASHNGTON ALBERTA eallan! (WNNPEGOSS FM) CANADA USA ROCANLLE-,; NORTH DAKOTA Figure 2.2. Map f the Elk Pint basin shwing the lcatin f the eamples discussed in this chapter. The dashed bundary represents an ersinal edge (mdified after Hlter, 1969, Maiklem, 1971 and Williams, 1984). DSHELF CARBONATE 1>;%0$>1 SLCCLASTCS LH NTEROR BASN Figure 2.3. Palegegraphy f the Canadian prtin f the Elk Pint basin in Keg River time (mdified after Campbell, 1987 and Nelsn, 1970). and Zama members and the Keg River Fm itself, are treated in Part A. The Winnipegsis carbnates, essentially f Saskatchewan, are discussed in Part B. PART A: KEG RVER CARBONATES N.L. Andersn, R.J. Brwn, R.C. Hinds RANBOW R.5 12 LL FELD: and NN Keg Pls River HHH, The Rainbw field is situated in the sutheastern part f the Black Creek basin (Fig. 2.2). Oil prductin (Table 2.1) is principally frm the Rainbw Mbr (Fig. 2.1). These reefs are stratigraphic traps, twering up t 200 m abve the Lwer Keg River Mbr platfrm and standing encased in the relatively impermeable interlayered dlmites and anhydrites f the Muskeg Fm. Figure 2.4 shws bth the apprimate lcatin f the eample seismic line, the lcatin f the si wells f the gelgical crss-sectin (Fig. 2.5) and the estimated areal etent f the Rainbw Mbr biherms at the Keg River HHH, LL and NN pls. Fur f the si wells tied t the seismic line (Fig. 2.6) and incrprated int the gelgical crss-sectin penetrate full reef; the ther tw stand abandned. R.4W61':110 1:109 Figure 2.4. Area cntaining the Keg River HHH, LL and NN pls. Pl utlines, the si wells incrprated int the gelgical crss-sectin and the apprimate lcatin f the seismic sectin are shwn. 34 Table 2.1. Prductin data fr the area f the Keg River HHH, LL and NN pls, Rainbw field (curtesy f Virtual Cmputing Services Ltd.) \/ELl G ~ ' "110-4~ O S ~ ~ ~6 ' ~ FELD Rair>bk ~.inbw Rainbw FELD Rainb<>w ~ainbw ~eir"!bw Rainbw ~.inbw ~ainbw Rainbw Rainbw Rair"!bw RainbW Rainbw Rainbw GEOLOGCAL Keg Ri~.c K2K Keg ~iver H~H Keg Keg ~ivec Keg Ri~ec ~iver Keg River PROOUC~:; ZCJ(E teg Ri~er Ll ~eg River <N 'iver lqq ~e9 River Keg Ri~er K2K (eg River Keg R ;~er LL Keg Ri~er Keg River LL Keg ~iver Keg ~i~er LL ~eg Riv<!c PROOUC1CJl( DAlE 06/M 09/67 12/63 01/!l6 09/67 10/67 08/67 00/00 04/67 10/84 11/63 10/63 10/67 03/86 Keg ~iver X Keg Rivec 12/84 a5/~ 03/67 _. OF \/ELlS ~eg River CROSS-SECTON 14, , , , , , , , ,159.2 S9, , , ,658.5 CUMULATVE PROOUCTj~ Oil (,,3) Gas (E0,,3) ~aler (,,3) 103, , , , ,950.7 ClJlllATV: ~TlOll ,lS , , , ,41l3.5 23, , , , , , , , , ,n2.9 32, , , , , ;; (.,3) Gas (E3.,3) ~"le; (""l 203, , , , , , , , , , , ,073.1 Where n ff-reef well cntrl is available, the mrphlgy f the interreef areas, as illustrated in the crss-sectin, is inferred frm the seismic data. The entire line is within the cnfines f the Black Creek basin. Tw f these Keg River pls were tested by tw wells each and the third, the LL pl, by si wells (Fig. 2.7). The NN-pl reef is likely a small pinnacle with a basal diameter f less than 1 km and withut any prnunced raised rim (Langtn and Chin, 1968). n cntrast, the larger LL-pl reef culd be termed an atll. Hwever, there is n seismic evidence f a raised reef rim, a feature characteristic f differential cmpactin between the rganic rim and the interir lagnal facies. Therefre the LL pl is classified as a large pinnacle reef. As cntured, the HHH pl is part f the Hay River barrier, described variusly as a carbnate bank r as a chain f islated reefs (Hriskevich, 1967). The deepest hrizn identified n the gelgical crss-sectin (Fig. 2.5), the Chinchaga Fm, verlies the Precambrian, the Basal Red Beds f the flanks f the Peace River and Tathlina arches, and 28

3 0 R 5 <0'" ~~ ",, ~----l''''''''''''''' 00 en =N,-;- R 4W6 000 :rldtdf'-- 0.~-::cc--==~ ~ -"...--,1: 110,,~i : -1/70 i -1/60 10 ~, Figure 2.7. Structure map (in metres relative t mean sea level) f the Keg River Fm tp. This and the subsequent structure maps were cnstructed frm bth well-lg and available seismic cntrl. the Cld Lake Fm. The Basal Red Beds and Cld Lake Fm are cmprised f lw-velcity clastics and salts, respectively, which cntrast markedly with the higher-velcity Chinchaga and Precambrian units. Cnsequently, bth the tp f the Cld Lake and the base f the Basal Red Beds generate prminent high-amplitude st;~ismic events. rhe Chinchaga Fm was penetrated by nly ne f the fur wells n the gelgical crss-sectin (Fig. 2.5) and the reginal trend shwn was estimated frm seismic data and reginal well cntrl. The Lwer Keg River Mbr was als penetrated nly nce. Hwever, this lw-amplitude event culd nt be crrelated cnfidently acrss the seismic sectin and is arbitrarily shwn t be parallel t the Chinchaga Fm (Fig. 2.5). Since the boljl1d~'les f the Chinchaga, Muskeg, and Slave Pint frm~tins are mre r less parallel n the seismic sectin, this etraplatin is reasnab'e. The Lwer Keg River J'v1br is verlain by either the Rainbw Mbr r its ff-reef time-equivalent, the Upper K,'g River Mbr. As illustrated n the crss-sectin (Fig. 2.5), the reefal facies stands as much as 170 m abve the platfrm. At their bases tbese biherms are flanked by the interreef Upper Keg River Mbr which, nearer the basin depcentre, cnsists typically f deep water lutites and reef talus As thcse ff-reef sedimeuts have nt heen penetrated in the study area, neither their thickness nr their lithlgy can be cnfirmed, nr can they be crrelated acrss the seismic sectin. They are shwn n the crshectin t be slightly thinner tban near the basin depcentre, where they are typically 51) m thick. These strata are prbably mre prus and permeable in the vicinity f the reefs, due t the shallwer water and greater availability f reef detritus, than nearer the basin depcentre. Near the depeentre f the Black Creek basin, the ljpper Keg River Mbr is cmmnly verlain by remnants up t 80 m thick f the Black Creek Mbr salt. These salts were riginally widespread thrughut the basin but are nw areally restricted due t pstdepsitinal disslutin. The mst etensive disslutin has ccurred arund the Rainbw Mbr build-ups and in the shallwer parts f the basin. Salt was depsited abut the periphery f the reefs in direct cntact with prus permeable sediment, either reef r reef-detrital facies, as well as in the shallwer parts f the basin where it is believed t have been underlain by sediments that are mre prus and permeable than the deep-water lutites nearer the basin depcentre (Andersn, 1986; Brwn et a., 1989). Presumably, salt disslutin was caused by waters perclating thrugh these prus and permeable strata. Salt disslutin is interpreted as having ccurred in sme lcatins mre r less cntinuusly since shrtly after depsitin. The Black Creek salt cannt be seen n the seismic sectin (Fig. 2.6) nr is it present in any f the wells in the study area. Analysis f this seismic data suggt:sts that either the Black Creek salt was never depsited in this part f the basin r else disslutin ccurred during Muskeg time. Our ratinale fr this is utlined belw. Since the Black Creek Mbr was depsited nly in interreefal areas, the pstdepsitinal disslutin f this salt wuld accentuate the clsure subsequently develped ver the reefs and due primarily t differential empjctin. Fr eample, jf evaprites arund the periphery f a reef were disslved after the depsitin f the Slave Pint Fm, then drape alng the Slave Pint Fm (Fig. 2.8) culd be attributed t bth differential cmpactin and salt disslutin. n cntrilst, if salts were nt depsited r if they were disslved prir t Slave Pint time, then clsure acrss the reef at the Slave Pint level culd nly be attnbuted t differential cmpactin. Andersn (1986), in a detailed seismic study f several Rainbw Mbr reefs, cncluded that differential cmpactin f the reef and ff-reef facies has typically resulted in 15 t 25 m f clsure at the Slave Pint Fm level. Clsure in ecess f this range is generally attributable t pst-slave Pint salt disslutin. The Muskeg Fm, like the Slave Pint Fm, drapes aerss the Rainbw MbT biherms by 15 t 25 m (Fig. 2.5), in gd agreement Figure 2.8. Structure map f the tp f the Slave Pint 'm (as Fig. 2.7) with Andersn (1986). This suggests that, if salts were depsited within the study area, they were disslved relatively early, i.e. during Muskeg 'm time. t shuld be kept in mind that structural relief alng bth the Muskeg and Slave Pint frmatins has been inferred frm the seismic data. The Muskeg Fm, in this area, cnsists f interlayered dlmite and anhydrite with an average interval velcity greater than that f the encased reefs. As shwn in the crss-sectin (Fig. 2.5), the Muskeg Fm is verlain by the Watt Muntain 'm, the Slave Pint Fm and the Wabamun Gp. All f these hrizns, ecept fr the Wabamun, drape by up t 25 m acrss the biherms due t differential cmpactin and this clsure was prbably nt accentuated by any late phases f salt disslutin. Drape at the Wabamun tp (Fig. 2.9) averages nly abut 5 m. The magnitude f drape acrss the reefs is f significance t the interpretatin f the seismic sectin. Fr eample, nte that the Chinchaga Fm in the 6-4 well is verlain by abut 410 m f high-velcity (typically abut 6000 mjs) sediment cmprising the Slave Pint/Chinchaga interval. Off-reef, the Slave Pint/Chinchaga interval is abut 20 m thinner whereas the verlying lw-velcity (typically abut 3300 mjs) Frt Simpsn Fm and Beaverhill Lake Gp shales are abut 20 m thicker. This thickening f the high-velcity carbnate sectin and accmpanying thinning f the verlying lw-velcity shale sectin n-reef, generate a significant cmpnent f velcity pull-up beneath the reef. -1-, -30 r-----=-" p "" " 2 35 SESMC SECTON "" 'i----:::/' i.~--,-_.l ~_ i --~l:109 Figure 2.9. Structure map f the tp f the Wabamun Fm (as Fig. 2.7) The seismic line (Fig. 2.6) crsses the Keg River HHH,. and NN pls. These data were recrded in 1981 using single -kg charges at depths f 15 m, a 2414-m split spread, 201-m sht intervals, and a 50.3-m grup interval. n Figure 2.l0, a 10 synthetic seismgram fr the 6-4 well (Fig. 2.4) is presented whereas Figure 2.11 shws a 20 synthetic seismic sectin. The field sectin (Fig. 2.6) and the synthetic sectin (Fig. 2.11) crrelate weil at and beneath the Slave Pint event but mistie by abut 15 ms at the Wabamun. Such a pr crrelatin ver the Wabamun/Slave Pint interval n lder vintage lgs in the Rainbw area is cmmn and is attrihuted t prhlems inherent in lgging the Frt Simpsn Fm shales. n this regard, Andersn et al. (1988a) illustrated the inaeeuracv f lder 1960's snic lgs thrugh the Frt Simpsn Fm which can invlve tw-way traveltime errrs f the rder f 20 ms r mre. This is significant in light f the lact that bserved thinning f the Wabamun/Slave Pint imerval f the rder f 15 ms is ne f the tw principal criteria fr gephysically interpreting Rainbw Mbr reefs (Andersn and Bre", n, 1987). The lwest reflectins dentified n the seismic sectin (Fig. 2.6), the Cld Lake and Precambrian events, have nt been penetrated by any f the wells f the gelgical crss-sectin (Fig. 2.5) hut are established reginal mjrkers and,1re therefre cnfidently identified. The amplitudes f these <,vents and their crrespnding ischrn values are mre r less unifrm acrss the seismic sectin, suggesting that during the Middle D,'vnian the Precambrian was lcally a 29

4 ,. KLOMETRES , ,-'T-:r , ~r r_- 'l~.,..._--..., '"'""':!""' r_~---, 2-6, SLAVE PONT MUSKEG en w a: ~ w ::E KEG RVER LOWER KEG RVER CHNCHAGA Figure 2.5. Gelgical crss-sectin, fr the line f wells f Figure 2.4 (Keg River HHH, LL and NN pls). RLEY N. ANDERSON 30

5 KLOMETRES 3! , , WABAMUN 0.4 en c 0.5 w 0.6 z en RETON ~~.-~ ~ BEAVERHLL LK. SLAVE PONT MUSKEG CHNCHAGA COLD LAKE PRECAMBRAN Figure 2.6. Nrmal-plarity seismic sectin, fr the seismic line f Figure 2.4 (Keg River HHH, LL and NN pls). ANADAN C DENTAL PETR LEUM LTD. 31 R: N. ANDER ~ ---J

6 ",;::_'JC~V " j sec Figure Synthetic seismgram fr the W6 well (curtesy f GMA Ltd.) W6 surface f relatively little relief. Significant structure wuld have caused lateral variatins in the thickness f the Cld Lake/precambrian interval and crrespnding changes in bth the ischrn values and seismic image. Bth the Cld Lake and Precambrian events are abut 5 ms high beneath the reefs. The Chinchaga event is f lw amplitude and mre r less parallel t the Cld Lake and Precambrian reflectins, suggesting that the bserved 5 ms f lcalized relief is velcity-generated. Neither the verlying Lwer Keg River, Upper Keg River nr Rainbw events can be crrelated with cnfidence acrss the seismic sectin. And even thugh the average interval velcity f the verlying Muskeg Fm is higher than that f the prus reef, the cntact des nt generate a prnunced reflectin, perhaps because f the hetergeneity f the reef and/r its relatively small areal etent. The seismic images f the Rainbw and Muskeg frmatins are likewise difficult t differentiate visually. The seismic images f the reefs cnsist f lw- t mderate-amplitude discntinuus reflectins, whereas the image f the Muskeg Fm is cmprised f events with sme lateral cntinuity. Such cntinuity may be indicative f nndepsitin f the Black Creek Mbr r f an early phase f disslutin. Typically, where etensive pst-muskeg salt disslutin has ccurred, the seismic image f the Muskeg Fm cnsists f discntinuus reflectins. c ~ ts ' ~ :J U) ts ill ts._, "'~ ~., e ts :::J ~ ~ =l._ CO CO ~ Distance (METRES) ! L t --f= E 001 y-- 6 CO ~ >- CO--=! ~ ~ =t= =-_c- ==?_:::::::3 CO - i: -,---~~., 7 ~~~ ;1'-,,_,_-,--_. Velcity Density Velcity Density (m/s) (kg/nil) (m/s) (kg/nil) (1 ) Precambrian (2) Basa l Red Beds (3) Ernestina lake (4) Cld lake (5 ) Ch inchaga (6) lwer Keg River (7) Upper Keg River (8) Muskeg (9) \.latt Muntain (10) Slave Pint (11) Beaverhill lake (12) Rainbw (13) Upper Keg River (14) Rainbw (15) Upper Keg River (16) Rainbw Figure Synthetic seismic sectin generated frm the gelgical crss-sectin (Fig. 2.5) using a zer-phase nrmal-plarity, 30-Hz, Ricker wavelet (curtesy f GMA Ltd.). As mentined previusly, the Muskeg and Slave Pint events are apprimately parallel and shw abut 10 t 12 ms f relief acrss the reef, indicating that little, if any, salt disslutin has ccurred in pst-slave Pint time. As shwn in the gelgical crss-sectin (Fig. 2.5), this 10 t 12 ms f drape translates int structure f 15 t 20 m. The carbnate marker in the Frt Simpsn shale als drapes acrss the reefs (by abut 5 ms) whereas n drape can be detected alng the Wabamun event. S the seismic evidence is cnsistent with the well lgs, bth indicating that the high-velcity (abut 6000 m/s) Slave Pint/Chinchaga interval is rughly 20 m thicker n-reef than ff-reef, and that the lw-velcity (abut 3300 m/s) Frt Simpsn/Slave Pint interval is rughly 20 m thicker ff-reef than n-reef. The tw-way traveltime thrugh 20 m f Frt Simpsn shale is abut 5 ms greater than thrugh an equivalent thickness f the underlying carbnates, cnsistent with the bserved pull-up belw the reefs n the Cld Lake and Precambrian events. Thus, drape at the Slave Pint Fm level is evidently the principal cause f this pull-up. ndeed, as nted, the Rainbw Mbr has a lwer average interval velcity than the anhydrites and dlmites f the ff-reef Muskeg Fm and this, if anything, partially negates pull-up due t structural drape. RANBOW FELD: Keg River PP Pl The Keg River PP pl is gegraphically situated in the Rainbw area f Alberta, near the eastern edge f the Black Creek basin (Fig. 2.12). Prductin at the Keg River PP pl is frm a small pinnacle reef f the Rainbw Mbr sealed by the impermeable interlayered dlmites and anhydrites f the Muskeg Fm (Fig. 2.1) and classified herein as a stratigraphic trap. This reef reservir was penetrated by the W6M well which is incrprated int the gelgical crss-sectin (Fig. 2.13), alng with the GG-pl reef, penetrated by the W6M well. On this crss-sectin, the stratigraphic and mrphlgical relatinships between these Rainbw Mbr reefs and the adjacent sedimentary sectin are illustrated. Figure 2.12 shws the PP and GG pls, the eastern edge f the Black Creek Mbr salt remnant, the western edge f the Hay River barrier and the apprimate lcatins f bth the seismic line and the five wells incrprated int the gelgical crss-sectin. The seismic sectin (Fig. 2.14) crsses the ape f the Rainbw Mbr reef f the PP pl but lies t the nrth f the Keg River GG-pl build-up. Prductin data fr the Keg River PP-pl study area are presented in Table 2.2. ~~~_-,_~_R.5W6 "0, 2= L.-4:$.~=-.L_R~~ ~ELl 9-30'109-4"", ,"", ',~ ~ '5~ ~ '50' '5~ '5\16 9' ,~6 15-2' 109-5~6 9-26'109-,006 flelo Rainbw Rainbw R"inbw Rai~bw FJELD Rainbw Rainbw Rainbw Painbw Rainbw Rai r>bw Rair>bw Rainbw GEOLOGCAL Keg Rivec rry Keg River R< Keg River PP ~llg -... ~ Keg Ri.er ~eg Z~E Keg River Rivec Keg Rive, Keg River PP P 01 PROOUCJ~G Z~E Of..ellS P~OOUCJO~ DATE ~e~ Rivr GG ~e~ Ri...c u2/67 ~e~ P've, GG ~eg Rivec 11/66 ~eg Ri... pp ~eg Rive, 08/83 Keg Piv~, PP Keg Riv.c 02/68 CROSS SECTON , ,982. 2, ,'46. 20, , ' CiJ'UUTVE cq yy p ~~~j : , , , , 1".0 50'.2 2, , , , , , , , ,153.4 a.82.6 S, , ,, , , ,2G , ,01,6.8 38, ,31S.9 PROOUCTD~ Oil (.,3) Gas (E3 m» ~alec (.,3) 119, ,25S.2 190,669.S , CUlt.JlAVl' PRCXlUCTQj Oil (.,3) Gas (E3.,3) ~.t"' (.,3) U 495, , , L_~"'!.'-_~--' Figure Keg River PP-pl study area. Pl utlines, the five wells incrprated int the gelgical crss-sectin and the lcatin f the seismic line are shwn. Table 2.2. Prductin data fr the area f the Keg River PP pl, Rainbw field (curtesy f Virtual Cmputing Services Ltd.) 1, , , ,9 a.87.4 The gelgical crss-sectin (Fig. 2.13) etends frm the eastern edge f a remnant f Black Creek salt (the well) twards the western edge f the Hay River barrier (the well) and incrprates the 1-21 ff-reef well and the 3-23 PP-pl reef well. As illustrated in Figure 2.2, the Hay River barrier separates the 32

7 Black Creek basin frm the main Elk Pint basin t the east. This barrier has been variusly pstulated t be either a cntinuus carbnate bank r a chain f islated reefs with interreef carbnates (Hriskevich, 1970). The Rainbw Mbr and the carbnates f bth the Hay River and Presqu'ile barriers are stratigraphically differentiated, the latter being referred t as undivided Keg River Fm. This cnventin is fllwed in the study area in spite f the clse primity f the Rainbw Mbr reef f the PP pl t the interpreted edge f the Hay River barrier and despite the uncertainty as t the eact rigin f the barrier lcally. Herein the Lwer Keg River Mbr is referred t as the platfrm facies fr the Rainbw Mbr reefs whereas the Keg River Fm carbnates f the Hay River barrier are undifferentiated. The lwest labelled hrizns n the gelgical crss-sectin, the Precambrian and the Cld Lake Fm, are penetrated by nly the 3-23 well (Fig. 2.13). Due t lack f additinal deep well cntrl, these hrizns are drafted parallel t the verlying Chinchaga Fm. The slpes, as shwn, are cnsistent with reginal gelgical trends and the seismic data. n particular, acrss the seismic sectin the Chinchaga/Precambrian interval is mre r less unifrm with respect t bth time-thickness and seismic image, suggesting that the Precambrian was a surface f relatively lw relief during the early Devnian. The verlying Chinchaga Fm is penetrated by tw f the wells n the crss-sectin. The etraplated slpe is cnsistent with reginal gelgical trends and the seismic data. As shwn, the Chinchaga apprimately parallels the Lwer Keg River Mbr, the platfrm facies fr the Rainbw Mbr. These verlying Rainbw Mbr reefs are thught t have develped n the Lwer Keg River Mbr n lcalized tpgraphic highs, pssibly due t underlying basement structure, faulting, disslutin f the Cld Lake Fm salt and/r rganic munds. Hwever, such pstulated features, if present, are t subtle t be cnfidently delineated n the basis f the limited well and seismic cntrl and this hrizn is therefre mapped n the gelgical crss-sectin as mre r less flat. The Lwer Keg River Mbr is verlain by either the Rainbw Mbr r, in ff-reef areas, by the Upper Keg River Mbr (Figs. 2.1 and 2.13). n this area, the respective tps f these members cnstitute the Keg River Fm tp, whse structure is illustrated in Figure The Lwer Keg River Mbr has nt been etraplated beneath the interpreted edge f the undifferentiated Keg River Fm carbnates f the Hay River barrier. As shwn in Figure 2.13, the Rainbw Mbr Figure Structure map f the tp f the Keg River Fm (as Fig. 2.7). pinnacle reef at the PP pl, with an estimated basal diameter f less than 1 km, rises sme 180 m abve the platfrm. T the west, near the basin depcentre, these reefs attain thicknesses f ver 200 m. The greater thicknesses nearer the basin depcentre reflect the depth f water in the Black Creek basin at the end f Keg River time. n this area, the Hay River barrier edge is mapped as immediately t the east f the Rainbw Mbr PP pl reef (Fig. 2.12). The ff-reef time-equivalent f the Rainbw Mbr and the Hay River barrier carbnates in the Rainbw area is the Upper Keg River Mbr, cnsisting typically f relatively impermeable deep-water lutites. n the vicinity f the reefs and near the margins f the barrier, significant reef talus is present, prbably accmpanied by increased verall permeability and pssibly influencing the present-day distributin f the Black Creek Mbr salt (Figs and 2.13). The Black Creek Mbr, the basal unit f the Muskeg Fm (Fig. 2.1), is thught t have been widely distributed in interreef areas within the Black Creek basin. These salts have been subjected t etensive pstdepsitinal disslutin and nw eist nly as remnants, sme f which are up t 80 m thick. Well and seismic cntrl indicate that such residual salt is present nly in the westernmst part f the area (Fig. 2.12). Hwever, salt is als believed t have been depsited east f the Hay River barrier, arund the reefs thrughut this area. This thesis is supprted by seismic and well-lg data which indicate that the Slave Pint/ Muskeg (inclusive) interval ff-reef and east f the barrier is thickest where salt remnants are present, implying that disslutin has ccurred in pst-slave Pint time. The pattern f salt disslutin in the Rainbw area indicates that leaching was mst etensive in the vicinity f the reefs and near the bank margins. n these areas, the Upper Keg River Mbr, being cmprised partially f reef talus, is prbably relatively prus and permeable. As wuld be anticipated, the Slave Pint Fm drapes acrss the Rainbw Mbr reef, the Hay River barrier and the residual salt. Drape acrss the salt is due t pst-slave Pint disslutin, whereas drape acrss the carbnate buildup is due bth t differential cmpactin and t leaching. nterpreted structure at the Slave Pint and Wabamun levels, as shwn in Figures 2.16 and 2.17, is based n bth well and seismic cntrl. SESMC SECTON The apprimate lcatin f the seismic sectin is shwn n Figure These seismic data (Fig. 2.14) were recrded in 1981 using a 2-kg surce at a depth f 15 m, a 1632-m split spread, a Figure Structure map f the tp f the Slave Pint Fm (as Fig. 2.7). Figure Structure map f the tp f the Wabamun Grup (as Fig. 2.7). 136-m surce interval and a 34-m grup interval. Figures 2.18 and 2.19 shw 1D synthetic seismic traces fr n-reef (3-23) and ff-reef (14-18) wells, indicating the crrelatin between the subsurface stratigraphy and prminent seismic events. These features are related with even mre clarity in the 2D synthetic seismic sectin f Figure The lwest hrizn identified n this sectin, the Precambrian, crrelates with a lw-amplitude laterally cntinuus peak. The amplitude f this event interferes with and is significantly affected by the high-amplitude peak riginating frm the Ernestina Lake Fm. As shwn in Figure 2.13, at the 3-23 well lcatin these hrizns are separated by nly abut 30 m (abut 12 ms). Similarly, the Cld LakelErnestina Lake interval is sufficiently small (abut 40 m r 10 ms) that the respective reflectins interfere. Yet bth f these high-amplitude events, and indeed the Precambrian reflectin as well, have mre r less unifrm amplitudes acrss the seismic sectin, being nly slightly lwer beneath the Black Creek salt remnant than elsewhere. The lwer amplitudes beneath the salt are prbably due t greater seismic attenuatin thrugh the salts than thrugh an equivalent thickness f 0.2 =-.,., - - Ricker 0 P~C H 28 "'s, 28 H, Pev r '<0'''' "EFL COF -t:- - DEPTh KB - 10~O i VCLOClTY ~ 0 0 h ;<R''Fff'F=:::::: Gething Barll! "",++--",l-t-'-'=----- Wabamun w...++~-- Ft. Simpsn ~...LL-t-'-~-Beavertlin Lake ~ - S:~~=E= =-- Muskeg Slave Pint _~._JJ_ "'""w ~_ ~~~!~~ 6~::~K>l~g River :::- Cld Lake - H-t Ernlstlna Lake ~.- J :: Precambrian i 1:::- Figure Synthetic seismgram fr the W6 n-reef well (curtesy f GMA Ltd.). 33

8 1 KLOMETRES SLAVE PONT WATT MOUNTAN MUSKEG KEG RVER (J) w a: t w :e LOWER KEG R CHNCHAGA COLD LAKE ERNESTNA LK. PRECAMBRAN Figure Gelgical crss-sectin fr the line f wells f Figure 2.12 (Keg River PP pl). PL T:.LEY S OATASHARE.NTERNAT NAL LTD. AUTH R: N. ANDERSON R.C. HNDS 34

9 u, KLOMETRES 3,, ~OO , ETHNG 0.4 WABAMUN en 0.5 z w 0.6 RETON 0.7 RETON MARKER c en 0.8 tt--"ceaverhll LK LAVE PONT USKEG ~HNCHAGA COLD LAKE :--PRECAMBRAN H R: N. ANDERSON R.C. HNDS

10 ~ Distance (METRES). 0 0_ 2 _ 6 Ric",e, 0 Phase 28 Ms, 28 Hz Rev, N'~ ' -~@~:<+-- --'lm~.m\ _ - REFL COEF. DEPTH KB \/[LOCTY K f t /se c " 'r."h=t=h=t:==== Gething - Banff --Tt" +--l H'~ = ~ _~= _=_30_00_._~,,=,,==!-':'-=C..-.~ ~ - ~ 0 4 ::._.f+l l+f+-t _;40_001_1! J.JJ r 0.6 ~ Wabamun F. Simpsn _._ 1-f'f..!~.~"1=R+~-Beaverhill lake --il~~.'~ -= ~ 5000 '.. i -H +-~ "e Muskeg Pit G 5 - _.- _~_._.-----t-- -_ 0_ 8 _ 1 ) : i =.._.-~-_._._._ J.;.--+-=- 1~~=::::: Black Creek '19' - Upper Keg River Figure Synthetic seismgram fr the W6 ff-reef well (curtesy f GMA Ltd.). carbnates and/r anhydrites. This mre r less unifrm amplitude suggests that during the Middle Devnian the Precambrian surface had little relief lcally. Significant relief wuld have resulted in appreciable variatins in the thicknesses f the Basal Red Beds, Ernestina Lake Fm and Cld Lake Fm and laterally varying interference effects alng their respective seismic events. The verlying Chinchaga event is f lw amplitude, is laterally cntinuus and is mre r less parallel t the Precambrian, Ernestina Lake and Cld Lake reflectins. n cntrast, the Lwer Keg River event cannt be crrelated cnfidently acrss the seismic sectin. Thus, even if either the Rainbw Mbr r Hay River barrier develped n structures at the Lwer Keg River level, they cannt be discerned n these seismic data. The basal Devnian events are time-structurally higher beneath the Rainbw Mbr reef and the western edge f the Hay River barrier than t the west. This relatinship indicates that these build-ups may have lcalized n an upthrwn structure f Lwer Keg River age. Similar time-structural relief is bserved at the Wabamun and basal Cretaceus levels, which may be real and due t ersin r t drape ver the Keg River ~ ;;; ~ w ~ " ~ ~ w e ~ ;; ~ ~ 0 0 ~ ~ N "' z u. u '". ~ " > ::-:-8:: i! ; ,----~~.~--, Velcity Densi ty Velcity Density (m/s) (kg/m3) (mls) (kg/m3) (1) PrecarTtlrian (2) Basa l Red Beds (3) Ernestina lake (4) Cld lake (5) Chinchaga (6) Lwer Keg River (7) Upper Keg River (8) Black Creek (9) Muskeg (10) Watt Muntain (11) Slave Pint (12) Beaverhill Lake (13) Rainbw (14) Upper Keg River (15) Rainbw (16) Upper Keg River (17) Rainbw Figure Synthetic seismic sectin generated frm the gelgical crss-sectin (Fig. 2.13) using a zer-phase nrmal-plarity, 30-Hz, Ricker wavelet (curtesy f GMA Ltd.).! ".9 Fm build-ups. On the ther hand, these features may be nly apparent and due t statics prblems. As nted, it is difficult t crrelate the Lwer Keg River event cnfidently acrss the seismic line. Within the basin, this hrizn underlies either the Rainbw Mbr r its ff-reef time-equivalent, the Upper Keg River Mbr, bth f which have acustic impedances similar t that f the platfrm unit. Where the Keg River Fm carbnates f the Hay River barrier are present, any lateral equivalent f the Lwer Keg River Mbr wuld be similarly difficult t discern. The high-amplitude Slave Pint event drapes acrss the residual salt and the Keg River Fm build-ups. Drape acrss the salt is whlly due t pst-slave Pint disslutin f the Black Creek Mbr, whereas drape acrss the carbnate build-up is als partly attributed t differential cmpactin f the Keg River Fm and an equivalent thickness f ff-reef sediment. The drape f the high-amplitude Wabamun event acrss the Keg River Fm build-ups is believed t be real and is attributed t differential cmpactin f reef and ff-reef sediments, pssibly accentuated by pst-devnian disslutin f the Black Creek Mbr. The diffractin pattern bserved near the eastern edge f these remnant salts (Fig. 2.14, arund trace 450) suggests that pst Wabamun leaching has ccurred. Whether disslutin triggered fault displacement at the Wabamun level, r vice versa, cannt be discerned frm these data. Andersn (1986) reprted a 20-km lng seismically mappable lineament at the Wabamun level acrss a salt remnant in the Rainbw basin and etensive assciated disslutin, suggesting fault-triggered leaching, at least in that case. With respect t the present seismic line, the diffractin culd emanate frm an ersinal feature such as that bserved near trace 400. The reflectin frm the tp f the Upper Keg River Mbr is als difficult t map, ecept where the Black Creek Mbr salt is sufficiently thick (abut 15 m) t be seismically visible. n these areas, the high-velcity Upper Keg River Mbr carbnates are readily distinguished frm the relatively lw-velcity salts. Elsewhere, the Upper Keg River Mbr is verlain by anhydrites and dlmites f the Muskeg Fm, whse acustic impedances are nt very different frm thse f the Upper Keg River Mbr. The Rainbw Mbr and the Keg River Fm carbnates f the Hay River barrier are similarly difficult t differentiate frm the encmpassing Muskeg Fm. The acustic-impedance cntrasts between these units are small and the seismic images f all three units, where salt is absent, cnsist f lw-amplitude discntinuus reflectins. ZAMA KRV'5V' ---gelgical crss-sectin seismic line FELD: KRV, KRW, and KRG Pls R4W6 i KRP2P Prductin at the Zama KRV, KRW, KRP2P and KRG pls (Fig. 2.21) is frm the bihermal Upper Keg River Reef Mbr and the verlying bistrmal Zama Mbr. n the ntrductin t this Atlas the relatinship between these reefs (stratigraphic traps encased in relatively impermeable interlayered dlmites and anhydrites) and the verlying Zama Mbr is discussed. The KRV, KRW, KRP2P and KRG pls are gegraphically lcated in the nrthern part f the Black Creek basin, an area frequently referred t as either the Zama basin r the Zama area (Fig. 2.21). Dispersed thrughut this area are numerus islated pinnacle reefs, cllectively termed the Upper Keg River Reef Mbr (McCamis and Griffith, 1967). These reefs are lithlgically R.5 Figure Zama study area. Pl classificatins, the wells incrprated int gelgic crss-sectins A and B and the lcatins f the tw crrespnding seismic lines are shwn. 36

11 differentiated frm the Rainbw reefs f the Rainbw area (suthern Black Creek basin) by the presence f the Zama Mbr, a widespread shaling carbnate facies which is present in the Zama area and absent in the Rainbw area. The Zama Mbr is structurally clsed acrss the Upper Keg River Reef Mbr as a result f differential cmpactin f the reefs and the ff-reef Muskeg Fm facies. This was pssibly accentuated by disslutin f the Black Creek Mbr salt in pst-zama time. A typical biherm f the Upper Keg River Reef Mbr, illustrating the mrphlgical and stratigraphic relatinships between these pinnacles and the adjacent sedimentary sectin, is incrprated int the reginal crss-sectin in the ntrductin t this vlume. A plan view f the hydrcarbn pls in the study area and the apprimate lcatins f the seismic and gelgical crss-sectins are shwn in Figure Prductin frm the eample pls is frm bth the Upper Keg River Reef and Zama members. Table 2.3 summarizes prductin data fr the Zama area. GEOLOGCAL CROSS-SECTONS All f the wells incrprated int the gelgical crss-sectins f Figures 2.22 and 2.24 penetrate Upper Keg River Reef Mbr biherms and tie the seismic line as indicated. The mrphlgy f the interreef area has been inferred frm the seismic data (Figs and 2.25). 1be deepest hrizn identified n these gelgical crss-sectins is the Precambrian, which is verlain, in turn, by the Basal Red Beds, the Cld Lake Fm and the Chinchaga Fm. Since the well (Fig. 2.24) is the nly ne t penetrate all f these strata, their reginal dips culd nt be determined frm the ehibited well lgs. Rather, they were estimated frm an analysis f mre reginal well cntrl and the seismic sectin. The seismic data suggest that bth the Precambrian (an ersinal surface) and the verlying strata are reasnably well represented as planar surfaces. The Basal Red Beds are verlain by the Cld Lake Fm, the tp f which generates a high-amplitude reflectin, a diagnstic marker in analysis f the verall seismic signatures f the Upper Keg River Reef Mbr. The Chinchaga Fm underlies the Lwer Keg River Mbr platfrm. Althugh this platfrm is shwn t be flat acrss the gelgical crss-sectins (Figs and 2.24), it is cnceivable that the reefs develped n slight tpgraphic highs n the platfrm, pssibly lcalized crinid meadws (Langtn and Chin, 1968), which cannt be reslved seismically. Table 2.3. Prductin data fr the Zama study area (curtesy f Virtual Cmputing Services Ltd.) )i 1;-; 117 /,"" La"'" «(', R'ver, Kg,ivc- C2.'" 2G,'-0.9,1 &;6,9 9,676.8 '~~'~'-="i~-i.";-'--i1====-~la~-,-, ~'_"'J~"'~"cr~"-=c-,'_KOg.:...'_i"c_'+_C"_!?4-j,_?,G_n,_,_~'':''''''~'',--' -,--"'-,-0'':''''---11 ; " lg-l!?-4." 2;,,"', '.OS,;"er U2U 'eg Ri','e- (2/00 66, ,191,.6 3,691.0 :3/07 1, ,085.5, '0, ~ 14 _ ,943.2 ''j cc The Upper Keg River Reef Mbr build-ups shwn n the gelgical crss-sectins are rughly circular in plan view, with seismically estimated basal diameters f abut ne kilmetre. They rise abut 100 m abve the platfrm facies. Typically, these islated biherms d nt ehibit seismically recgnizable raised rims and are therefre classified as pinnacles. Mst f these reefs have been tested by nly ne well (additinal wells wuld prvide crrbrative >,823.2 estimates f relief) and it is ften difficult t differentiate the reef tps seismically frm the Zama Mbr (Figs and 2.25). The Upper Keg River Reef Mbr and the interreef sediment are verlain by interlayered dlmites and anhydrites f the Muskeg Fm. Thrughut much f the Zama area (and pssibly within the study area) the interreef sediment was riginally verlain by up t 80 m f salt f the Black Creek Mbr, which, if indeed depsited within this area, has subsequently been disslved. The distributin f the Black Creek salts is prbably related t the nature f the underlying interreef sediment. The Black Creek Mbr is mre widespread in the Rainbw Area where it verlies the deep-water Upper Keg River Mbr. n the Zama area, the salts were depsited abve the mre prus reef detritus and have since been etensively disslved (McCamis and Griffith, 1967). Bth the Upper Keg River Reef Mbr build-ups and the Black Creek Mbr salts were verlain by interlayered dlmites and anhydrites. Within the area the Zama Mbr rests mre r less directly upn the Upper Keg River Reef Mbr, whereas ff-reef its stratigraphic lcatin is uncertain. f thick salts were initially depsited and subsequently disslved, the Zama Mbr r lateral equivalent may presently verlie interreef sediments. Alternatively, if salts were never depsited, structural relief alng the Zama Mbr may parallel that alng the Slave Pint Fm, depending n the depth f water in which the ff-reef Zama Mbr was depsited. Estimates f clsure at the Zama Mbr acrss these reefs range frm a minimum f 30 m (relief alng the verlying Slave Pint Fm) t a maimum f 100 m (assuming that, as a result f salt disslutin, the Zama Mbr rests uncnfrmably abve a thin veneer f interreef detritus). Well cntrl wuld be required t cnstrain these clsure estimates since the Zama Mbr cannt be reslved cnfidently acrss the seismic line. n cntrast, clsure alng the Slave Pint Fm can be estimated seismically and is n the rder f 30 m. This relief is attributed bth t the differential cmpactin f reef and ff-reef sediments and t pst-slave Pint disslutin f the Black Creek Mbr salts. n a detailed study f several reefs f the Upper Keg River Reef Mbr, Andersn (1986) cncluded that differential cmpactin prbably generated between 15 and 25 m f the relief bserved alng the Slave Pint Fm hrizn. f these estimates are realistic, then 5 t 15 m f salt was prbably disslved in pst-slave Pint Fm time within the area. Andersn (1986) als cncluded, n the basis f seismic data, that salt disslutin within the Black Creek basin likely ccurred frm shrtly after depsitin t as late as pst-mississippian time. Therefre, significantly mre disslutin-induced structure culd be present at the Zama Mbr level than alng the Slave Pint Fm. SESMC SECTONS Figure 2.21 shws the apprimate lcatins f the seismic lines relative t the pls. These data (Figs and 2.25) were recrded in 1981 using dynamite (single charges f 2 kg at S-m depths), a 1200-m split spread, a 100-m shtpint spacing and a 50-m grup interval. A 2D synthetic sectin crrespnding t line A (Figs and 2.23) appears as Figure 2.26 whereas Figure 2.27 shws a 10 synthetic crrespnding t the well f line B (Figs and 2.25). The tw time-structurally lwest reflectins identified n the seismic sectins (Figs and 2.25) are the Precambrian and Cld Lake events. These tw high-amplitude reflectins are f unifrm amplitude acrss the seismic sectins and ehibit cnsistent ischrn values, suggesting that the Precambrian and the Cld Lake hrizns are essentially flat. The slight decrease in amplitude alng these events beneath the tw reefs is attributed t differential attenuatin within reef and ff-reef sediment and nt t any lateral variatins in either thickness r lithlgy. Furthermre, the lcal time-structural highs beneath these reefs (abut 8 ms) is ascribed entirely t velcity pull-up and nt t any basement tpgraphy. The lw-amplitude reflectin frm the Chinchaga Fm is cnfidently crrelated acrss the seismic sectin, whereas the Lwer Keg River event is nt. The uncertainty as t the nature f the interreef sediment (detritus, Muskeg Fm dlmites r anhydrites) makes the uncntrlled crrelatin f the Lwer Keg River event tenuus at best. The Chinchaga event parallels the Cld Lake event, supprting the incrpratin f flat interfaces n the gelgical crss-sectin and the cnclusin that the bserved lcal time-structural highs beneath the reefs are velcity-generated. The seismic image f the reefs (shaded purple in Figs and 2.25) is cmprised f relatively lw-amplitude discntinuus reflectins bunded by the lw-amplitude Lwer Keg River and Upper Keg River Reef events. The seismic image f the ff-reef Muskeg Fm similarly cnsists f lw-amplitude discntinuus events which are difficult t distinguish visually frm the seismic image f the reef. The discntinuus incherent character f the seismic image f the Muskeg Fm is mre cnsistent with the cncept f pstdepsitinal salt disslutin and assciated cllapse than with nndepsitin. f Black Creek Mbr salt had nt been depsited in the area, the seismic image f the Muskeg Fm wuld likely have a mre unifrm reflectin pattern. 37

12 .-----' KLOMETRES SLAVE PONT MUSKEG ZAMA KEG RVER LOWER KEG R. CHNCHAGA Figure Gelgical crss-sectin A, Zama study area (Fig. 2.21). L...!=!!DR..!!:A!.!...!...~: L.~~~~----:.:..:R:.=.L=..:EY=-..:S~D~AT.!...!:!,;AHARE NTERNAT NAL LTD. N. ANDERS N 38

13 KLOMETRES ; 605 5~5! ~~lrw ABAMUN c tj) 0.7 tj) z w 0.8 SLAVE PONT 0.9 PRECAMBRAN R: N. ANDER N

14 KLOMETRES ::= SLAVE PONT MUSKEG en w a:: tw :E ZAMA KEG RVER LOWER KEG R. CHNCHAGA COLD LAKE ED BEDS RECAMBRAN Figure Gelgical crss-sectin B, Zama study area (Fig. 2.21). 40 DATA HARE NTERNAT NAL LTD. N. ANDER N

15 HH H'", "'" 11!,,' 't' KLOMETRES 2!! , U) c z 0 w U) 0.7 SLAVE PONT PRECAMBRAN Figure Nrmal-plarity seismic sectin B, Zama study area (Fig. 2.21). 41 E N. ANDER N

16 , 1 j1ilill ii!! '' L_,, ~ till;,"' 1*~ -, ~ ~l\ffil1 d! ; r= --=j \i11:, 1 e~ ',,~ 14 =r " -, f--=-( 1.2 s S - f ' c=- - ~ -~ =--c3 (1) PrecaJTbri an (3) Cld lake (5) lwer Keg River (7) Muskeg (9) Watt Muntain (11) Beaverhill Lake (13) Upper Keg River (15) Upper Keg River (17) Upper Keg River Velcity (m/s) \ Density (kg/m3) 2650 (2) Basal Red Beds (4) Chinchaga (6) Upper Keg River (8) Muskeg (10) Slave Pint (12) Upper Keg River (14) Upper Keg River (16) Upper Keg River Velcity (m/s) Density (kg/m3) Figure Synthetic seismic sectin generated frm gelgical crss-sectin A (Fig. 2.22) using a zer-phase nrmal-plarity, 30-Hz, Ricker wavelet (curtesy f GMA Ltd.) ,,,, i1icker 0 Ph~se 28 Ms, 28 Hz Re', r Nc' '" 1D W6 REFl DEPTH DENSTY COEF KB gm. cc ~ 1000 i =-1 :-1 V"-cOCTY K t sec i ~ 0.0 Wabamun ~ ~B+t+_=---Ft. Simpsn -,_,-- 02 ~, = ~H-f+i+t i~,'-'----'-_ 0.4 _,.$_= ~-'-'-'-!-'-=_'--~Beaverhill lake i~ " ~_:. 6 ~~~:e~int ', i,',, _'_ '--~- - - Chinchaga, = i,' 1 " = Cld Lake - i ' -- =-- Precambrian ~,-, ,-lm_~ilw~ ',~ uppe~:';(l, River. _ Lwer Keg RVer Figure Synthetic seismgram fr the 1O W6M well (curtesy f GMA Ltd.). The verlying Slave Pint event is lcally abut 20 ms higher n-reef than ff-reef, crrespnding t actual structure f the rder f 30 m (using a 3000 m/s average interval velcity fr the verlying 600 m f Frt Simpsn Fm and Beaverhill Lake Gp shales). This lateral velcity cntrast (between such ff-reef shales and 30 m f n-reef Slave Pint Fm carbnates, with velcities arund 6000 m/s) wuld pull-up the underlying events by abut 10 ms. The difference between the estimated 10 ms f pull-up and the bserved 8 ms f pull-up is prbably due t the lateral velcity cntrast between the high-velcity ff-reef Muskeg Fm sediment and the lwer-velcity reef. ndeed, the velcity cntrast between reef and ff-reef sediments tends t push dwn the events underlying the reef. n this eample, the bserved pull-up is entirely attributable t lateral variatins in the thickness f lithlgical units verlying the reef and ff-reef sediments. Significantly less relief is bserved alng the carbnate marker in the Frt Simpsn Fm which is abut 5 ms higher n-reef than ff-reef. Higher in the sectin, the Wabamun event des nt appear t drape at all, indicating that little r n salt disslutin ccurred in pst-devnian time and that the prcessed seismic line is nt significantly affected by statics prblems. "fic ","ny PANNY PJ~. FELD During Keg River time the Panny field f the Sene area was part f the fringing shelf surrunding the Elk Pint basin in nrthern Alberta (Fig. 2.28). The Keg River Fm here cnsists f carbnates f varying argillaceus cntent. Lcally, mre argillaceus carbnates predminate in the lwer Keg River Fm sectin whereas cleaner carbnates are predminant in the upper part f the frmatin. A schematic crss-sectin f the Sene-Peace River arch area is displayed in Figure Fr further backgrund n the gelgy f this area, see Campbell (1987), Andersn et al. (1988b) and Cant (1988). The Keg River Fm is the principal reservir facies in this study area and is typically prductive where structurally clsed acrss underlying Precambrian highs. These highs are the result f pre-devnian tectnism and subsequent ersin with, pssibly, later stages f faulting in sme areas. The reservir facies is capped by the basal anhydrite unit f the Muskeg Fm. Prductin data fr the Panny area is summarized in Table 2.4. Figure 2.30 shws a prtin f the Panny field, the apprimate rientatin f the tw eample seismic lines and the lcatins f the fur wells incrprated int the tw gelgical crss-sectins. Three f the fur wells (1-3, 3-11 and 3-5) were drilled int clsed Precambrian structures. Wells 1-3 and 3-11 prduce frm the Keg River Fm whereas 3-5 was abandned. The furth well (4-5) was drilled int a flank lcatin and als abandned. Lg suites fr these Table 2.4. Prductin data fr the Panny study area (curtesy f Virtual Cmputing Services Ltd.) '5 i eve CU'l..AT;." PROOUCTOH ~'i 1"J) Ga,; (E3.,3) later (.,3),~,,,a,7 l,ns.9 6,288.7 ffj BASN GEOLOGCAL ~ SHELF MARGN -;~~~~=; -=----= =--- ~~&t f------j Will CROSS-SECTONS u MDDLE SHELF NNER SHELF Tl02 Ta' R22W4M Figure Map f the fields and facies f the Sene area (after Campbell, 1987). wells are shwn n the gelgical crss-sectins f Figures 2.31 and The crrespnding seismic sectins are presented in Figures 2.32 and 2.34, respectively. The deepest hrizn identified n the gelgical crss-sectins f Figures 2.31 and 2.33 is the Precambrian. As illustrated, relief n this surface is typically n the rder f 50 t 100 m. Anmalus 42

17 PNNAC.E MESOSA.NE PATCH REEF SLCC.ASTC WEDGE 1:96 LOWER KEG RVER MEMBER 'NTERREEF _-----""'1 - ~~::::-~~~. " " " " " " " " ", " " " " " " " LOWER ELK PONT ", ", " " " " " SUBGROUP.' '.. " > " ~~~-;r~. " " " " " " " " PRECAMBRAN'... " " "" " " """'" " " " " " ",, A' " ", "" " " "J( " " " " " "' " " " " " " " " " " " " " " ",. " " " l " " '", ", Figure Schematic gelgical crss-sectin thrugh the general Campbell, 1987), Sene-Peace River arch area, Keg River t Precambrian interval (after 30,------,----- R.6W5 UEPOO ----~ j- ( ), \L/. \ G pl --- gelgical crss-sectin ll seismic line L -----" , ,1:96, ni ~~/ +- /, " r D pl Figure Panny study area, Pl utlines, the wells incrprated int the gelgical crss-sectins 1 and 2 and the lcatins f the tw crrespnding seismic sectins are shwn, 36 1:95 structural highs, such as thse beneath the 1-3, 3-11 (Fig, 2.31) and 3-5 (Fig, 2.33) wells are prevalent thrughut the Panny area, Generally, such structures are mapped frm the seismic data as being lcally areally clsed, a pattern cnsistent bth with the idea f an ersinal surface and with that f a surface fractured by cnjugate sets f faults (Andersn et al, 1988b), As illustrated (Figs, 2.31 and 2.33), the basal Palezic clastics and Keg River Fm sediments thin significantly frm ff-structure t n-structure lcatins, supprting the thesis that relief at the Precambrian level is ersinal in rigin, Structural relief in interwell areas is inferred by the authrs frm the crrespnding seismic lines. Within the study area, the Precambrian is verlain by basal Palezic clastics and the Keg River Frn. Structure maps f these tw hrizns are shwn in Figures 2.35 and 2.36, respectively, As mentined abve, the Keg River Fm is generally thinnest abve Precambrian highs and thicker ff-structure, Fr eample, the Keg River Fm in the 3-5 and 4-5 wells is 4 and 45 m thick, respectively (Fig, 2.33), n additin, the Precambrian in the 3-5 well is 80 m structurally higher than in the 4-5 well, s that the tp f the Keg River Fm in the 3-5 well is abut 40 m higher than in the 4-5 well and is structurally clsed, Relief alng the tp f the Keg River Fm is principally attributed t the differential cmpactin f the n-structure and ff-structure Palezic sectin (Andersn et al, 1988b) althugh sme wrkers believe that later stages f faulting played a significant rle. Figure 235. Structure map f the tp f the basal Palezic clastics (as Fig, 2,7). 1:95 As determined frm the lg suite fr the 4-5 well (Fig, 2.33) the Keg River Fm in the area cnsists f carbnate with a variable degree f argillaceus cntent The mre argillaceus carbnates predminate in the lwer Keg River Fm sectin and cleaner bistrmal carbnates are predminant in the upper prtin, Typically, these upper carbnates are prductive where they are structurally clsed acrss the underlying Precambrian, such as in the 3-11 and 3-5 wells (Figs, 2.31 and 2.33), As evidenced by these tw wells, the mre argillaceus carbnates f the lwer Keg River Fm are generally absent where the Precambrian is anmalusly high, The Keg River Fm in the Panny area is verlain by the Muskeg Fm, principally an interlayered sequence f salts and anhydrites, As shwn in Figures 2.31 and 2.33, the basal anhydrite f this frmatin seals the Keg River Fm reservir facies, Althugh this basal anhydrite has a slightly higher velcity and density than the underlying Keg River Fm, the cntact between the tw units cannt be mapped n the seismic data, Hwever, the cntact between this basal anhydrite and the verlying salt can be delineated seismically and is frequently referred t as the near-keg River event As shwn n Figures 2.31 and 2.33, the basal salt/anhydrite cntact is mre r SESMC SECTONS ----' ~-L-=---- '0 1:95 Figure 236. Structure map f the tp f the Keg River Fm (as Fig, 2,7), less parallel t the anhydri te!keg River Fm cntact These crss-sectins als shw that the Muskeg Fm, the Slave Pint Fm (Fig, 2.37) and the Beaverhill Lake Gp drape acrss the anmalus Precambrian structures, Th is is attributed t differential cmpactin f the Palezic sectin, Figure 2.30 shws the lcatin f the seismic sectins (Figs, 2.32 and 2.34), The 96-trace 24-fld seismic data were recrded in 1982, using a Vibrseis surce, a 1530-m split spread, 120-m sht spacing and a 24-m grup interval. Figure 2.38 is a D synthetic seismgram fr the 3-11 well As illustrated, the synthetic and the field data (Fig, 2.32) crrelate well at the Precambrian, near-keg River (r basal anhydrite), Slave Pint and retn events. The Wabamun event, nt shwn n the synthetic, is cnfidently identified acrss bth seismic lines n the basis f reginal crrelatins, The Wabamun event is usually nt displayed n synthetics in the Panny area as casing is usually set belw this hrizn prir t lgging, 43

18 , KLOMETRES 2! (J) w a: w :E SLAVE PONT MUSKEG TOP SALT BASAL SALT BASALANHYDRTE KEG RVER -wasal CLASTCS -800 Figure Gelgical crss-sectin 1, Panny study area (Fig. 2.30). RLEY DATA HARE NTERNAT NAL LTD. N. ANDERSON R.J. BR WN 44

19 u KLOMETRES """',"""'"'!'TTTTlT''''''''''''''''~ m"t1m"1t1m"1t1m"1t1m"1t1"".",..,m tj) c z 0 (J w tj) -WABAMUN ':;;;-RETON " mmtmmmmttttttlmlt-_ SLAVE PONT MUSKEG BASAL ANHYDRTE -PRECAMBRAN Figure Nrmal-plarity seismic sectin 1, Panny study area (Fig. 2.30). MA EXPL A 45 P NVER

20 ! KLOMETRES 2! r ~,..._~: - :~r =:;;=_ ,...-.., BEAVERHLL LAKE (J) w a: w :E SLAVE PONT MUSKEG TOP SALT -800 Figure Gelgical crss-sectin 2, Panny study area (Fig. 2.30). : N. ANDER ON R.J. BROWN ~~~~brte KEG RVER BASAL CLASTCS PRECAMBRAN 46

21 KLOMETRES 2!! en c z 0 0 WABAMUN RETON w en SLAVE PONT -MUSKEG 0.8 BASAL ANHYDRTE -PRECAMBRAN R: N. ANDER N

22 \ ~-=------'-----' ' t 96 Figure Structure map f the tp f the Slave Pint Fm (as Fig. 2.7). c c Ric'e- 0 Phas. 25 Ms, 28 r'z Re -, r N' rr ~ _4~:) _'_'-----'-- J'scL~ ~~_,_c--'t RE'~ COEF ijept" KB VELCCFY Figure Synthetic seismgram fr the W5M well (curtesy f GMA Ltd.). Figures 2.39 and 2.40 shw snic-lg crss-sectins and crrespnding synthetic seismic sectins. These mdels demnstrate hw the amplitudes f the Precambrian and near-keg River events change as a functin f relief alng the Precambrian with crrespnding thinning f the verlying clastics (Fig. 2.39) r anhydrite (Fig. 2.40). As the Keg River Fm is typically prductive where draped acrss clsed Precambrian highs, the recgnitin f ".. ~ l - Q, -- E 0 J.1-,1 ), ),~,~.~.~'~;t'~"~',r) ~',',' ~.... ~ )0, ". ", '., ) :' '., ;. " ~ " t._~ y,) ) ') 'j ) ) '. ) :> ) >') ) ~ :).~ " ~.~~~~.»~~~~~~)~~~~~~ -=- 8.i _~.~~l.._;~ (~_~_'a.!~~.:..l.~ ~~;~~i...~~.~~j..--,,---,,--sla V E._~,, ~<c:_<.:.~":::-,<-:--<~,---:..-~?~r_,.,:_~<=-:.c..<c~~~ ~,:.-.._~,> ~~ i.! PO tnt J ~ ) J j j ) ) ) 1 } ) ) ) ) ] 1 ) ) ), )0,'" -, ).. _.. ~. ;. --~ '~,-. ~. ~-. '-. ;.,-. ').).. :.. )t-~--anh'r'drte ill. : ' :~l~t!t"~')-) PRECAMBRAN Figure Snic-lg mdel and crrespnding synthetic seismic sectin illustrating the effect f thinning f the basal anhydritelprecambrian sectin (curtesy f GMA Ltd.). the seismic signatures f such features is critical. On the synthetic seismic sectins the amplitudes f bth the Precambrian and near-keg River events are higher ff-structure than n-structure. As discussed belw, these lateral amplitude changes are principally interference effects related t the n-structure thinning f bth the basal Palezic clastic sectin and the basal Muskeg anhydritelprecambrian interval. n Figure 2.39 the thicknesses f the basal Muskeg anhydrite and Keg River intervals are kept cnstant whereas that f the basal Palezic clastics is varied frm 65 m (abut a half-wavelength) t zer. Optimal tuning f the reflectins frm the tp and base f these clastics ccurs at thicknesses near 32 m (abut a quarter-wavelength). At thicknesses less than an eighth f a wavelength (abut 16 m) the basal Palezic clastics cannt be reslved with cnfidence. At zer thickness the Precambrian is verlain by the Keg River Fm. n Figure 2.40 the thickness f the basal Muskeg anhydritelprecambrian sectin is decreased prprtinately frm 80 m (abut a half-wavelenth) t zer. Optimal tuning f the near-keg River and Precambrian events ccurs at a thickness f a half-wavelength (abut 80 m); maimum destructive interference ccurs at a thickness f a quarter-wavelength (abut 40 m). As this mdelled thickness cntinues t decrease, the Precambrian and near-keg River events becme increasingly tuned t ne anther. At zer thickness, the Precambrian is mdelled as directly verlain by this basal Muskeg Fm salt. As discussed belw, this relatinship is nt knwn t ccur in practice. n the interpreted seismic sectins, the lwest event identified, the reflectin frm the Precambrian surface, is time-structurally highest in the vicinity f trace 185 (Fig. 2.32) and trace 207 (Fig. 2.34), which cincide with the lcatins f the prducing 3-11 and 3-5 wells, respectively. Fr cmparative purpses, nte that the Precambrian event at traces 41 and 301 (Fig. 2.32) is 18 and 8 ms lwer, respectively, than at trace 185. At traces 61 and 281 (Fig. 2.34) the Precambrian event is abut 40 and 20 ms lwer, respectively, than at trace 207. As shwn n the gelgical crss-sectins (Figs and 2.33), these time-structural highs crrelate with anmalus relief alng the Precambrian surface. Hwever, it shuld be recalled that the structure n the gelgical crss-sectins in interwell areas was estimated by analysis f the seismic data. As anticipated, bth the near-keg River and Slave Pint events drape acrss these Precambrian highs. The Slave PintlPrecambrian time-thickness decreases significantly (ca. 20 t 30 ms) frm ff-structure t n-structure lcatins, indicating that the Slave Pintlbasal Palezic (inclusive) interval thins significantly frm ff-structure t n-structure psitins. n additin, the verlying Wabamun event des nt appear t drape acrss these Precambrian highs. As anticipated frm an analysis f the suite f synthetic mdels, anmalus structures alng the Precambrian hrizn manifest themselves as lateral amplitude changes and by time-structural relief alng the Precambrian and near-keg River events. Mre specifically, the amplitudes f bth the Precambrian and near-keg River events are significantly lwer n-structure [near traces 185 (Fig. 2.32) and 207 (Fig. 2.34)] than ff-structure. As demnstrated thrugh mdelling (Figs t 2.41), these lwer amplitudes are interference effects caused by the n-structure thinning f the basal Palezic clastic sectin and f the basal Muskeg anhydrite/basal clastic (inclusive) sectin. n the vicinity f the 3-5 well (Fig. 2.34, trace 207), where the basal Muskeg Fm anhydritelprecambrian interval is thin (abut 35 m r slightly under a quarter-wavelength), the amplitude f the intervening peak is etremely lw, supprting the premise f destructive interference. n the vicinity f the 3-11 well (Fig. 2.32, trace 185) the sectin is abut 45 m thick (slightly greater than a quarter-wavelength) and the amplitude f the intervening peak is marginally higher. Presumably, with increasing relief at the Precambrian level, the amplitude f the peak wuld decrease t the pint where the near-keg River and Precambrian events wuld visually merge. Where the basal Muskeg anhydrite and the Keg River Fm sediments are absent (presumably due t nndepsitin acrss Precambrian structure as in the W5M well f the fllwing eample) the verlying Muskeg salts are etensively disslved. The resultant cllapse features are readily identified n seismic sectins. Recgnitin f clsed Precambrian structure is vital t successful eplratin fr Keg River Fm reservirs in the Panny area. Typically, the Keg River Fm is draped acrss these structures as a result f differential cmpactin f lwer Palezic sediments. Prspective Precambrian structures can be identified seismically where: 1) time-structural relief ccurs alng the Precambrian, near-keg River and Slave Pint events; 2) n-structure time-thinning f the Precambrian/Slave Pint and Slave Pint/Wabamun intervals ccurs; and 3) n-structure decreases ccur in the amplitude f bth the Precambrian and near-keg River events, withut assciated salt-cllapse features. TROUT FELD The gelgical backgrund fr the Trut field f nrth-central Alberta clsely parallels that f the nearby Panny field. The Keg River Fm, the principal reservir facies in the Trut area, is prductive where it is structurally clsed acrss r against the flanks f underlying Precambrian highs and the reservir facies are capped by the basal anhydrite unit f the Muskeg Fm. Prductin frm the 48

23 velcity Density Velcity Density (rn/s) (kg/m3) (m/s) (kg/m3) (1 ) Precarrtlr i an (2) Basal Clastics (3) Keg River (4) Keg River (5 ) Basal Anhydrite (6) Salt (7) Anhydrite (8) Salt (9) Anhydri te (10) Sal t Trut field has als been established frm the underlying basal Palezic sandstnes. These sediments are als prductive where structurally clsed acrss r against the flanks f anmalus Precambrian structures. Prductin data fr the Trut field are presented as Table 2.5. GEOLOGCAL ~HL '5 n ~5 n ~ ~ ~5 11-\5-69-3~5 15 '5 89 3~S 'ELO Trut Trut Trut lrut :rut Trut Trut Trut Trut Trut Trut :,..ut CROSS-SECTON Figure 2.42 is a map f the suthern Trut area shwing the apprimate lcatins f the eample seismic line and f the three wells incrprated int the gelgical crss-sectin (Fig. 2.43). Only ne f the three, the well (cmpleted in 1987), currently prduces frm the Keg River Fm, whereas, the ther tw were abandned. As illustrated in Figure 2.43, the 1-31 well is ff-structure where the Keg River Fm is wet. n cntrast, the 2-10 well is n-structure, and here the Keg River Fm is absent, presumably because f nndepsitin. Table 2.5. Prductin data fr the Trut study area (curtesy f Virtual Cmputing Services Ltd.),c PROOUC~G ZONE Keg ~iver- PROOUCTO~ DATE 02/88 Unassi9ned KE9 River 10/87 K~9 River K K"9 River 06/87 Una"sign"" Keg River 09/87 Granite \lash A Gr-anite \lash 01/67 K~g River M Keg River 02/87 U,assigned Kg River J W~assigned Whessigned U~ass;gn"" Unassigned Keg River Keg River Keg River Keg River Keg River 01/88 Q3/67 01/88 12/87 08/87 01/87 02/87 0/,/87 08/87 1, , ,'19.0 5,94.6 2,919.3 '65,1 11'.2 7, l:l)hulatve PROOUCT1ON Oi l (003) GaS (E3 m3) ~ater- (m3) J " ,3 1, " S ',220.1 The lwest hrizn identified n this gelgical crss-sectin is the Precambrian. n the Trut area, as fr the Panny area, this is a surface f cnsiderable relief, and basement highs are generally mapped frm seismic data as being lcally areally clsed. As depicted in Figure 2.43, the basal Palezic clastics and Keg River Fm sediments thin frm ff-structure t n-structure, being depsitinally absent in the 2-10 well, cnsistent with the thesis that relief at the Precambrian is ersinal in rigin. Nte that this bserved thinning frm ff-structure t n-structure will generate a crrespnding lateral variatin in the reflectin (Fig. 2.44) frm the Precambrian hrizn. Reactivatin f basement faulting [after the end f Elk Pint time (Fig. 2.1)] des nt have t be invked t eplain the lws n certain Beaverhill Lake markers (e.g., the Slave Pint). These features are accunted fr, in ur interpretatin, by cllapse fllwing disslutin f Muskeg salts, which ccurred mainly during Beaverhill Lake time (Fig. 2.43). R.4 R.3 WS UNASSGNED UNASSGNED UNASSGNED K G RVER L UNASSGNED..UNASSGNED UNASSGNED. KEGR. UNASS6NED UNASSGNED UNASSGNED.,UNASSGNED "';'UNAS4GNED E ' E uniassgned U~ASSGNED..; 2-1 ~~- - U+SSrGNED 4, KEjG RVER K, i UNAS GNED UN4SSGNED, it.89 As discussed abve, bth the basal Palezic clastics and the Keg River Fm thin frm ff-structure t n-structure and in etreme cases can be depsitinally absent. As a result f differential cmpactin, bth f the crrespnding tps are typically clsed acrss r against the flanks f Precambrian structures. Such clsure is illustrated at the well (Fig. 2.45). Once again, the near-keg River event, crrespnding t the cntact between the basal Muskeg anhydrite and the verlying salt, is seismically mre prminent than the Keg River event itself. As was the case fr the Panny field, this salt/basal anhydrite cntact mre r less parallels the basal anhydrite/keg River Fm cntact (Fig. 2.43). n places, as evidenced by the 2-10 well, the Precambrian is depsitinally bald with respect t the basal Palezic clastics, the Keg River Fm and the basal prtin f the Muskeg Fm. n these areas, interlayered salts and anhydrites were depsited directly n the Precambrian. Typically, such salts have been pstdepsitinally disslved. Disslutin in the 2-10 well is interpreted as having R.4 R.3 WS [/,," ~fs-~ i ~~o-'c-'rt \-t ,. i"" (11) Anhydri te (12) Salt (13) Muskeg (14) Watt Muntain (15) Slave Pint (16) Beaverhill lake (17) Ft. Si~sn (18) Keg River Figure Synthetic seismic sectin generated frm the gelgical crss-sectin (Fig. 2.33) using a zer-phase nrmal-plarity, 3D-Hz, Ricker wavelet (curtesy f GMA Ltd.). ' U-89-W ~5 2-3'-69-3~S '5 Trut l,ut Trut 1c ut ',ut T,ut c'mssign"" U~assigned ~.ssigned Keg Rive; [ Ke~ River ~ Ke~ Ri ver ~ (e~ River- 0 Ke~ River C Keg Rive, Keg River Keg Rive, Keg River Keg River Keg River Keg River 11/67 0'/88 1'/87 02/1lB 02/86 1J/e7 12/86 01/B7 10/87 12/87 071B7 12/ S 10, ,. 2,,91.6 5, , ,9' ' , , ,236, " 1-31 gelgical crss-sectin seismic line ~~-~~ ~------JT.88 Figure Trut study area. Pl utlines, the three wells incrprated int the gelgical crss-sectin and the lcatin f the seismic line are shwn. '-~~--+~--~~- Figure 2.7) ~ T. 88 Structure map f the tp f the Keg River Fm (as Fig. 49

24 ! KLOMETRES 2! BEAVERHLL LAKE MARKER en wa: t w :E SLAVE PONT - WATT MOUNTAN -MUSKEG _ BASAL ANHYDRTE -KEG RVER BASAL PALEOZOC CLASTCS - PRECAMBRAN -900 Figure Gelgical crss-sectin, Trut study area (Fig. 2.42). : RLE N. ANDERS N' R.J. BR WN 50

25 u KLOMETRES, ! en c z (J 0.4 WABAMUN 0.5 w en 0.6 -RETON 0.7 SLAVE PONT MUSKEG BASAL ANHYDRTE PRECAMBRAN Figure Nrmal-plarity seismic sectin, Trut study area (Fig. 2.42). R N ANADA R 51 MPANY R: N ANDERSON R.J. BROWN

26 ccurred principally during Beaverhill Lake time and t have been caused by waters perclating thrugh the weathered Precambrian (Andersn et a., 1988b). A~ depicted in Figure 2.43, prnunced cllapse features can be assciated with salt disslutin. The Muskeg Fm and the verlying Watt Muntain and Slave Pint frmatins typically drape acrss underlying Precambrian structure as a result f differential cmpactin. As illustrated in Figure 2.43, eceptins ccur in areas f etensive salt disslutin. A~ evidenced by the 2-10 well, and shwn in the Keg River and Slave Pint structure maps f Figures 2.45 and 2.46, these hrizns can be anmalusly lw where the Precambrian is anmalusly high. The seismic int~rpreter shuld be aware f this pssibility and avid prejudiciusly assuming that time-structure abve the Precambrian is simply a subdued replica f basement relief. 6 " t <, "(~~ \-" Figure Structure map f the tp f the Slave Pint Fm (as Fig. 2.7). SESMC SECTON The 120-trace 12-fld seismic data (Fig. 2.44) were recrded in 1979, using single 2,25-kg charges at depths f 15 m, a 1560-m split spread, l30-m sht spacing and a 26-m grup interval. As was the case fr the Panny eamples, the labelled events are cnfidently identified acrss the seismic sectin (Fig. 2.44) n the basis f ties t synthetic seismgrams and reginal crrelatins. Figures 2.39 and 2.40 (discussed in the previus sectin n the Panny field) demnstrate hw the amplitudes f the Precambrian and near-keg River events change as a functin f relief alng the Precambrian and assciated thinning f verlying units (basal Palezic clastics and basal Muskeg Fm anhydrite). These mdel relatinships are b,erved n the seismic line f Figure Fr instance, the amplitude f the Precambrian event decreases as structural relief increases. n the interval frm trace 141 t 191, where the Muskeg anhydrite directly verlies the Precambrian, this cntact can be cnfidently mapped nly by using snic-lg cntrl frm the 2-10 well. The amplitude f the near-keg River event is similarly higher ff-structure than n-structure. n the vicinity f trace 191, where the Muskeg Fm salts have been leached, this reflectin disappears cmpletely. The verlying Slave Pint event, n the ther hand, can be crrelated cnfidently acrss the entire seismic sectin. This event drapes acrss the underlying Precambrian. ecept where the Muskeg Fm salts have been disslved in pst-slave Pint time (Fig. 2.44, traces 141 t 191). n such places, the Slave Pint event is anmalusly lw, despite verlying a Precambrian high. The verlying Beaverhill Lake, retn and Wabamun events drape nly slightly acrss the Precambrian, suggesting that the disslutin f the Muskeg Fm salts ccurred, fr the mst part, prir t the end f Beaverhill Lake time. The eplratinist active in the Trut area shuld be familiar with certain structural relatinships, namely, that: 1) the Keg River Fm reservirs are present where these sediments either drape acrss r pinch ut against Precambrian structural highs; 2) generally the Slave Pint Fm drapes acrss Precambrian basement highs, ecept where Muskeg salts have been leached in pst-slave Pint time, in which case cllapse has reduced r negated such drape, and 3) disslutin f these salts cmmnly ccurs where the Precambrian is in direct cntact with the Muskeg Fm (i.e. bald with respect t the Keg River Fm). t is als very imprtant t be able t identify Precambrian structures n seismic data. Where salt disslutin has nt ccurred, this eercise cnsists merely f differentiating structural-relief effects frm statics prblems. Where leaching has ccurred, the eercise is mre cmple as the Slave Pint event is generally anmalusly lw where the Precambrian is high. As well, the Precambrian and near-keg River events in these areas are typically difficult, if nt impssible, t crrelate. This lack f lateral cntinuity is ften the key t differentiating znes f salt disslutin frm structural lws at the Precambrian level. Where the Precambrian is lw, bth this event and the near-keg River reflectin shuld be f relatively high amplitude. Other features characteristic f salt disslutin include diffractin patterns and etreme time-structural relief at the Slave Pint level. Cmpactin-generated structure at this level shuld be less abrupt. PART B: WNNPEGOSS D.J. CARBONATES Gendzwill, R.M. NTRODUCTON Lundberg Winnipegsis munds are accumulatins f carbnate rck, mstly dlmite, scattered thrugh the Middle Devnian Elk Pint basin. The munds are buried t 2600 m ecept fr the Manitba utcrp regin. They are the equivalents f the Keg River reefs f Alberta. but unlike the Keg River reefs, the Winnipegsis munds have never prduced much il. Winnipegsis munds have been the target f several petrleum eplratin prgrams with little success ecept fr a small discvery in Nrth Dakta and the Tableland discvery f suthern Saskatchewan. Nevertheless, these discveries, taken with the general lack f knwledge f these features, sustain interest in them as eplratin targets. The ecnmic significance f the Winnipegsis Fm has been mre imprtant t the ptash mining industry because the munds affect the ptash-bearing rcks that lie ver them in ways which may interfere with mining peratins. Tle Winnipegsis munds are crnmn in suthern Saskatchewan but little is knwn abut them. After mre than 40 years f eplratin in the prvince, very few f the munds have been tested with the drill and f thse tested nearly all have nly Ole drill-hle thrugh them. A~ a result, there is little reliable infrmatin, even their status as reef structures is in dubt and in this reprt they are referred t as munds. Hwever, many munds have been crssed by seismic prfiles and the seismic anmalies prvide the mst cmmn type f gelgical infrmatin fr these enigmatic features. Therefre, a descriptin f the seismic respnse t these features as they are nw understd may increase ur knwledge f them. THE ELK PONT GROUP The Elk Pint Gp in Saskatchewan (Fig. 2.1) includes the: 1) Ashern Fm, a basal shale unit; 2) Winnipegsis Fm, a dlmitized carbnate unit; and 3) the Prairie Evaprite, a thick rck salt unit lcally grading int anhydrite. Subsequent cyclthems are fund in the Manitba Gp which verlies the Elk Pint Gp but the halite units in the Manitba Gp are much thinner. The Elk Pint Gp was depsited in the Elk Pint basin, a brad shallw basin trending nrthwest-sutheast acrss mst f Saskatchewan and etending int Nrth Dakta, Manitba, and Alberta (Fig. 2.2). Mst f the nrtheast flank f this basin is nw truncated by ersin suth f the epsed Precambrian. The interir basin nw underlies much f sutheast and central Saskatchewan and a fringing carbnate shelf fills the edge f the basin in Manitba, Nrth Dakta, suthwest Saskatchewan, and Alberta (Fig. 2.47). Figure 2.48 shws the detailed stratigraphic clumn fr the Elk Pint and Manitba grups f central and sutheastern Saskatchewan. ASHERN WNNPEGOSS FORMATON The Ashern Fm, a red r grey argillaceus dlmite, is the lwest frmatin f the Elk Pint Gp. t lies uncnfrmably n the Silurian nterlake Fm and underlies all f suthern Saskatchewan but des nt eceed 18 m in thickness (Patersn, 1973). The Winnipegsis Fm verlies the Ashern Fm. FORMATON The Middle Devnian Winnipegsis Fm underlies nearly all f the sedimentary regin f Saskatchewan, ecept fr a regin f nndepsitin in the suthwest crner (Jnes, 1965). t crps ut in nly ne place, near the Clearwater River. ts subcrp is truncated by ersin, tgether with ther Devnian rcks, suth f the Precambrian Shield. The Winnipegsis Fm dips steadily suth, suthwest, r sutheast, reaching its greatest depth f abut 3000 m, 52

27 tt z HATFELD MBR '::0 0:;::... (/)«HARRS MBR :::> -:2 = 0:0: LOWER HARRS SALT upper DAVDSON SALT a::: :>0 DAVDSON MBR... ~ u. FRST RED BED HUBBARD SALT "'" >z = t- «0 00_ NEELY MBR z zl- 0«:S (/):2 "'" ;:0: BURR MBR «0 au. SECOND RED BED UJ PAT~E~,C~SLAKE P TA H f- Z 0: 0 Oz BELLE PLANE POTASH ««- :2 >1-0: UJ«UJ a: : UJ 0. u. :::> -0 ESTERHAZY POTASH :> UJ = a::: 9:u. «!::... 0: a: 0. 0 t-. Z SHELL LAKE MBR «ULL LK > = (/) (/) UJ... -z UJ ::.:: (/)0... 0_ '" g~~htkow a: a:... <:)1- w '" UJ :;;: UJ«~ ~ ~ SALT ;: a: 9::2 ::>z 0 0. ZOO Z..J <:0 ;: \(!ATNER ~u. MBR LOWER WNNPEGOSS samples. Hwever, thse in Nrth Dakta have been called reefs by Perrin (1982) and Precht (1986). Perrin (1982) has identified three types f reefs: "pinnacle" reefs in the deeper parts f the basin, "platfrm r shelf edge" reefs which frmed arund the margins f the basin, and "patch" reefs which frmed n the shelf platfrm r n the shelf margin. The upper Winnipegsis munds, studied by Gendzwill and Wilsn (1987), are distributed thrughut the basin interir in suthern Saskatchewan. The munds are cmparable t the pinnacle reefs f Perrin (1982). The greatest numbers f munds are fund in the Saskatn area where it is estimated that they underlie nearly 25% f the area. Few f the munds have been penetrated by even ne drill-hle but many have been recgnized by their seismic signature. The munds, as seen n seismic sectins, are usually between ne and si kilmetres wide. The knwn thickness f the upper Winnipegsis ranges up t 105 m (Jnes, 1965). The munds are cmpsed f dlmitized carbnate (Gendzwill and Wilsn, 1987). Detailed structure f individual munds is nt knwn but cmpsite lithlgies have been prpsed based n cres f different munds. Wilsn (1984) prpsed an internal subdivisin f the munds int fur principal units, a pelidal grainstne, a laminated mudstne, an rganic unit, and a fringing cap unit. Figure 2.49 shws a cnceptual mdel f a Winnipegsis mund. A B HARRS 110 HATFELO MEMBERS DAWSON BAY SECOND RED BED SALT f POTASH 500 m HORZONTAL FRNGNG CAP LAMNATED MUDSTONE PELODAL GRANSTONE LOWER WNNPEGOSS SCALE,m VERTCAL FRNGNG CAP SALT FLUD FLOW ~ ~ r;:f ""'(,<J )~:r~========= Figure Reginal map shwing the Elk Pint basin, thickness f the Winnipegsis, and sme knwn munds (dts). Cntur interval, 30 ft (9.1 m) (curtesy f Jackalpe Gelgical, Bulder, Clrad). in Saskatchewan, near the U.S. brder suthwest f Estevan. t was divided int a lwer member and upper member by Jnes (1965). The lwer Winnipegsis member, called a platfrm member, is cmpsed f dlmitized fssiliferus packstne. t cntains algal nclites, brachipds, and crinids in a prly srted matri but dlmitizatin bscures many f the fssils (Jnes, 1965). The lwer ASHERN FORMATON Figure 2.48 Detailed stratigraphy f the Elk Pint and Manitba grups f suthern Saskatchewan (mdified after Gendzwill and Wilsn, 1987). Winnipegsis is relatively thin in the interir prtin f the Elk Pint basin but reaches a thickness f 40 m in the fringing carbnate shelf prtin suth f Regina and Mse Jaw. The upper Winnipegsis is cmpsed f thick carbnate munds lying n tp f the lwer Winnipegsis. These munds have been described by Gendzwill and Wilsn (1987), Precht (1986), Wilsn (1984), Perrin (1982), Gendzwill (1978), Wardlaw and Reinsn (1971), Streetn (1971), Jnes (1965) and thers. Thse in central Saskatchewan have been referred t as munds rather than reefs because typical reef characteristics have nt been bserved in cre The mst etensive unit is the pelidal grainstne which directly verlies the lwer Winnipegsis. The pelidal grainstne ranges frm well-srted grainstne t a prly-srted wackestne. Several generatins f calcium carbnate cement have reduced the prsity f this unit t less than 7% in the cres eamined. Hwever, Precht (1986) qutes prsity as high as 20% in Shell Oil Creek 41-2, a Nrth Dakta well. Near the edges f the mund, the pelidal grainstne grades int a narrw rganic unit. The rganic unit is similar t the pelidal grainstne in many respects but it cntains frame-building rganisms such as crals, strmatprids, nclites, and shell fragments in amunts up t 30%. These fssils are usually brken and abraided and nne f the rganisms have been fund in grwth psitin. The pelidal grainstne is verlain by a laminated mudstne unit r a fringing cap unit. The laminated mudstne cnsists f a dense, fine-grained, light-t-medium brwn, etensively dlmitized lime mudstne. The prsity is very lw. The laminated mudstne Figure Structure f Winnipegsis munds in central Saskatchewan. A is the structure when depsited, B is the structure after burial and cmpactin. Diagrammatic chimney-cllapse structures are shwn (after Gendzwill and Wilsn, 1987). cntains an anhydrite fractin, which increases twards the tp and grades int the verlying Shell Lake anhydrite. Near the edges f the mund, the laminated mudstne and pelidal grainstne units are verlain by a fringing cap unit which is cmprised f pislites, pelids, and etensively dlmitized intraclasts with cncretinary catings in a micrite matri. The pislites are frequently fractured and brecciated. The fringing cap unit is nt fund in very many cres and it is thught t be cnfined t a marginal psitin arund the munds rather than entirely cvering them. 53

28 The fractured and brecciated nature f fssils in the rganic unit and the fringing cap unit suggests that these rcks were in a relatively high-energy envirnment where the sediments were frequently ripped up and redepsited. These sediments may have faced the sea whereas the laminated mudstnes were prtected. RATNER MEMBER Between the upper Winnipegsis munds, The Ratner member (Reinsn and Wardlaw, 1972) verlies the lwer Winnipegsis and flanks the upper Winnipegsis. The Ratner member cnsists f carbnate mudstne and/r anhydrite. Anhydrite is ften fund abve the Ratner member. The upper Winnipegsis and Ratner members are verlain by salt f the Prairie Evaprite Fm where that salt has nt been disslved and remved. PRARE EVAPORTE FORMATON The Prairie Evaprite Fm underlies much f suthern Saskatchewan (Hlter, 1969). t is divided int tw majr salt units, the lwer r Whitkw salt and the upper r Lefnard salt, separated by the Shell Lake anhydrite (Jrdan, 1967). An anhydrite layer f variable thickness is ften fund at the base f the Prairie Evaprite Fm and the Whitkw si,lt lies n it. The Whitkw, usually cmpsed f clean salt, fills the basin between the munds, whereas the Shell Lake anhydrite lies n the Whitkw salt, nearly cincident with the tps f the munds (Hlter, 1969). Because f the irregular nature f the Shell Lake anhydrite, Hlter (1969) des nt use it in his nmenclature. Hlter defines an upper and a lwer salt with the bundary at the base f the lwest ptash member. Hwever, the anhydrite prduces a persistent seismic reflectin in mdny areas s it is a useful marker in seismic stratigraphy. Near thenunds, the Shell Lake anhydrite is interlayered with a thin carbnate unit called the Quill Lake marker bed. thught t be ersinal debris derived frm the tps f the munds. The Shell Lake anhydrite reaches a maimum thickness f 35 m in central Saskatchewan but it is variable and is entirely absent n the sutheast. The upper r Lefnard salt is cmpsed mstly f halite with several thick beds f sylvinite ptash re near tp. The Patience Lake. Belle Plain, and Esterhazy ptash memh,~r:, are mined ill different areas f Saskatchewan. Thin belb "'H.\ partings f cifjgrnitic :~ha,le cntarninate the ilpper salt ~-'tas?1 beds in sme areas. Prairie Evaprite salt reaches a maimum thickness f 215 m sutheast f Saskatn. THE MANTOBA DAWSON BAY FORMATON SOURS RVER FORMATON COMPACTON OF WNNPEGOSS MOUNDS GROUP Overlying the Prairie Evaprite Fm is the Dawsn Bay Fm (Dunn, 1(82). The Secnd Red Bed, a dlmitic mudstne is at the base. The Secnd Red Bed is fllwed by the Burr Mbr, a fssiliferus limestne, and then the Neely Mbr anther limestne. The final member is the Hubbard salt, a thin salt which is present in limited areas. The Otal Dawsn Bay Fm thickness is abut 50 m. The Suris River Fm lies n the Dawsn Bay Fm. This cnstitutes anther cyclthem with the First Red Bed, a dlmitic mudstne at the base, fllwed by the Davidsn carbnate and the Davidsn halite. Abve the Davidsn is a thin anhydrite and anther salt called the Harris salt fllwed by the Harris carbnate. The Davidsn and Harris salts tgether with the interbedded anhydrite make up a thickness f 40 m (Kendall, 1(76) but this ccupies nly a prtin f the basin and has been remved by disslutin in many areas. Seismic and well-lg studies f the munds (Gendzwill, 1(78) have demnstrated that substantial subsidence ccurred ver the munds after burial. The subsidence has been accurately measured in surveyed elevatins f undergrund penings f ptash mines which frequently etend ver areas underlain by Winnipegsis munds_ n sme mines, subsidence has been bserved ver every knwn mund and the relief is as great as 40 m (Mackintsh and McVittie, 1(83). Subsidence is [Jt the same n all munds, nr is it unifrm n any single mund. Sme munds have n subsidence that can be identified, at least n seismic data. The subsidence, attributed t cmpactin f the munds (Gendzwill and Wihll, 1(87) rather than t disslutin f the verlying salt (Gend!v,,'ll, 1(78). The cmpactiijfl "ppears t have taken place by dewatering (especially f the laminated mudstne), dlmitizatin and styllitizatin. Pervasive fracturing f the dlmitic rck may have resulted frm defrmatin assciated with the vlume reductin. The subsidence ver the munds is a result f differential cmpactin where the prus carbnate munds are subject t cmpactin but the dense, nnprus salt which encases and surrunds them is incmpressible. Subsidence due t partial disslving f the salt ver a mund is thught t be unlikely because the anhydrite capping ver mst f the munds frms an impermeable seal which prtects the salt frm water in the prus carbnate. Only where the anhydrite is fractured r missing culd water in the munds attack the salt. The anhydrite may be fractured by subsidence arund the edge f a mund. Such restricted access t the salt thrugh a narrw fracture shuld result in a narrw zne f salt remval. Cllapse chimneys cntaining breccia frm frmatins abve the mine have been fund in the ptash mines. The dimensins range frm a few tens t a few hundreds f metres in width. Such chimneys are always fund ver Winnipegsis munds (Mackintsh and McVittie, 1(83) and are thught t be caused by disslutin f salt by water mving thrugh the fractured anhydrite caprck. The water culd have been derived frm the laminated mudstne as it cmpacted. The presence f subsidence ver a Winnipegsis mund is an indicatin f the age f diagenesis, with cmpactin (and assciated fluid mvements) ccurring as late as the yungest verlying stratum which displays subsidence. The absence f subsidence ver a Winnipegsis mund is an indicatin that either: 1) n cmpactin f the mund ccurred; r 2) all the cmpactin ccurred prir t depsitin f the first mappable rck layer abve the mund. There are at least three different mechanisms which culd be respnsible fr cmpactin f a mund and the subsidence wuld be similar fr any f them. Develpment f prsity within a mund may affect the speed f seismic waves. Thus, under favurable cnditins, it may be pssible t identify a seismic anmaly within r belw a mund which represents that prsity; but this wuld be quite different frm any subsidence effect. SALT REMOVAL BY DSSOLUTON Salt f the Prairie Evaprite Fm has been disslved by grundwater in many areas. The largest f these areas is the Saskatn reentrant in which a layer f salt up t 180 m thick has been remved frm mre than km 2 in a rughly triangular-shaped area between Swift Current, Regina, and Saskatn. n this area, the verlying frmatins have been let dwn and brecciated. Multi-stage salt remval, with sedimentary infill between rem','al episdes, has created sme cmplicated structures (Sawatzky et a., 1(59). Sediments may als drape ver Winnipegsis munds when the supprting salt is remved. This reginal salt remval appears t have been cntrlled by interstratal slutins mving alng the reginal hydraulic gradient frm suth t nrth. Prairie Evaprite Fm salt has been cmpletely r partially remved in many "salt-remval structures" in the interir f the huge salt layer. These range in size frm a few tens f metres in diameter fr "chimney cllapse" t several hundred square kilmetres, such as the "Rsetwn Lw". The amplitude f the synclinal depressin prduced may be as large as 200 m. The smallest f these are cntrlled by Winnipegsis munds as described abve and the larger nes are prbably cntrlled by either basement faults r intrasedimentary faults. Yunger salts such as the Hubbard Evaprite (Dawsn Bay 'm) and Davidsn Evaprite (Suris River Fm) are usually remved wherever the Prairie Evaprite Fm has been remved. The yunger salts may als have been remved in sme places where the Prairie Evaprite Fm salt remains, r, perhaps they were never depsited. Salt was remved in several episdes frm the Devnian t the present (Hlter, 1(69). Salt springs issuing in nrthern Saskatchewan ami Manitba and evidence presented by Gendzwill and Hajnal (1971) and Christiansen (1971) indicate that salt is being disslved tday. nterpretatin f sme seismic features, tgether with cmparisn f stratigraphy in ptash mines, prvides evidence that salt has bee Jl remved frm the tp f the Prairie Evaprite Fm in sme arcas, frm the bttm in ther areas, and smetimes frm bth tp and bttm, depending t sme degree n hw much salt has been remved and hw much disturbance has been caused. Salt remval frm the periphery f Rainbw reefs, frming a crude "rim syncline"., has bcen cited by Andersn (1986) as a diagnstic feature fr the recgnitin f such reefs in Alberta. Similar features have bc,-n nted near sme Winnipegsis munds but the feature seems t,) i-,l' less prevalent in Saskatchewan than in 54

29 Alberta. Narrw cllapse chimneys ver the munds, such as are fund in the ptash mines, seem t be mst cmmn but these are seldm visible n seismic data. Such small features are rarely crssed by widely spaced seismic lines and, if ne is crssed by chance, it wuld nt be recgnized if its dimensin is less than that f the Fresnel zne fr seismic waves. SESMC OF REFLECTON FEATURES DEVONAN ROCKS N SASKATCHEWAN The appearance f these rcks n seismic reflectin data is affected by their physical prperties and their stratigraphy. The rcks are mstly carbnates and salt with sme shale. The seismic speed thrugh these materials ranges frm abut 4400 m/s fr salt and sme shales t 6000 m/s fr dense dlmites and anhydrites. The speed fr prus carbnates is variable and depends n the prsity. With these speeds, a 50-Hz seismic wave is abut 100 m in length, s it is advantageus t use seismic frequencies as high as pssible in rder t imprve the reslutin. The actual structure f the seismgrams frequently appears t be cntrlled by "tuning effects". This is demnstrated by snic lgs which shw cyclic patterns f acustic speed. The physical length f the patterns may match seismic wavelengths, prviding cnstructive reinfrcement and large-amplitude reflectins. A secnd characteristic f these bedded carbnate rcks is their generally unifrm nature. On the scale f a seismic wave they are laterally unifrm fr lng distances and dips are gentle ecept fr lcal structures. The best seismic reflectrs in the Devnian rcks f Saskatchewan are the cntrasts between salt and carbnate rcks r between the thicker shale units and carbnates. Where a Winnipegsis mund eists, the therwise unifrm patterns f reflectivity are interrupted. There may be a slping reflectin frm the edge f the mund. The reflectin frm the base f the salt is changed because high-speed carbnate rck is present instead f lw-speed salt. f the Shell Lake Mbr anhydrite is present, the reflectin frm the anhydrite tends t interfere with that frm the mund in a manner that depends n the thickness f the anhydrite and the cnsequent strength f its reflectin, n the thickness f the Whitkw Mbr salt and n the height f the mund. Nrmally, the Shell Lake Mbr anhydrite is abut level with the tp f the munds. Where the Whitkw Mbr salt is substantially less than 100 m in thickness, the effect f the munds is that f a thin bed between tw prminent reflectrs: i.e. the anhydrite and the base f the Winnipegsis; s the visual effect n a seismgram is much reduced. Als, if there is a thick basal anhydrite in the Whitkw Mbr, it may cver r nearly cver a carbnate mund, reducing r even eliminating any seismic indicatin. Where the Shell Lake Mbr anhydrite des nt eist, the prblem is simpler. Anhydrite may verlie the mund but there is n interference because it is cnfrmable t the shape f the mund and the seismic anmaly lks like a mund: i.e. a bump in an therwise smth reflectin. f the mund is thin, the effect is less bvius; and if the ttal salt thickness is small, there will be interference frm the tp-f-salt reflectin similar t that frm the Shell Lake Mbr. A secnd feature that may be seen is subsidence f shallwer strata ver all r prtins f the mund. The subsidence is a result f the cmpactin f the mund and is mst bvius n the Dawsn Bay reflectin, with lesser effects n yunger strata. The subsidence time-structure may eceed 10 ms in amplitude. A third effect that may be seen is the decrease in seismic traveltime thrugh the high-speed carbnate mund, cmpared t that thrugh the lw-speed salt. This causes the s called "velcity pull-up" in which reflectins frm deeper strata appear slightly earlier under a mund than elsewhere. This may amunt t a time differential f as much as 15 ms fr central Saskatchewan munds. The time difference may even be used t check thickness estimates. The cmbinatin f subsidence abve and pull-up belw a mund creates a distinctive pinched appearance t the seismic reflectins which wuld therwise be straight and parallel. A furth criterin that may indicate Winnipegsis munds is a change in the seismic reflectin structure immediately under the mund. This ccurs because the reflectin frm the base f the salt is eliminated under a mund and is replaced by ther primary and multiple reflectins. Disslutin f salt frm the flanks f a mund has been used by Andersn (1986) t recgnize Rainbw reefs in Alberta but the effect seems t be less cmmn in Saskatchewan. When it ccurs, the result is a psitive structure instead f the mre usual negative subsidence structure in Saskatchewan. The pull-up anmaly may be analyzed by cmparing the seismic time thrugh the salt with the seismic time frm the tp f salt t sme marker bed belw (Fig. 2.50). The time thrugh the salt, Ts, is given by: T s = Zs V s ~ (Z - Zm)V s where Zs is salt thickness wherever it is measured, Z is the full thickness f the salt where there is n mund, Zm is the height f the mund abve nrmal salt base, Vs is the seismic speed thrugh salt T k (Ms) f T s (Ms) ~s--~ Vs Z..._--:1"---"" S Zm ---~ i ~-r K Figure Subsidence mdel shwing dimensins fr "velcity pull-up" study, and crssplt f times fr Tableland anmaly. tt s (1) Similarly the time t a deeper marker bed, Tk, is given by: Tk = (Z - Zm)V s + ZmV m + K where Vm is seismic speed thrugh the mund, and K traveltime t a deeper reflectr. Tk ~ (Z - Zm)V s + (Zm - S)V m + K. Differentiating (1) and (3) with respect t mund height gives: dts / dzm ~ -lv s dtk / dzm = -lv s + (1- ds / dzm)v m and dividing (5) by (4) prduces: dtk / dts = 1 + Vs (1 - ds / dzm)v m. dtk / dts = 1 + V s / Wm (1 + ds / dzm)1. (2) is additinal f subsidence S has ccurred due t cmpactin f the mund but n salt has been disslved, equatin (2) is mdified t: A similar analysis may be made with the assumptin that subsidence is due t salt remval instead f cmpactin f the carbnates. n that case the equatin is: These equatins may be used t estimate seismic speed and subsidence relatins f a mund anmaly by crsspltting the seismic times thrugh the salt (Ts ) with seismic times frm tp f salt t a marker bed (Tk ). The slpe f the line may be diagnstic. SESMOGRAMS OF WNNPEGOSS MOUNDS Three eamples f Winnipegsis munds in Saskatchewan are presented here, ne frm Estevan (sutheast area), ne frm Rcanville (east area), and ne frm Allan (central area). Figure 2.2 shws the general lcatin f these munds. Prcessing parameters fr the seismic sectins are shwn in Table 2.6. (3) (4) (5) (6) (7) 55

30 KLOMETRES A ~ PRARE EVAPORTE SALT en w cc... w ::E WHTKOW ANHYDRTE U.WNNPEGOSS DOLOMTE ASHERN SHALE NTERLAKE SONC NDUCTON NEUTRON POROSTY NDUCTON SONC POROSTY SONC NDUCTON SONC NDUCTON SONC NDUCT. Figure Well-lg sectin fr the Tableland mund Hme Oil Cmpany Ltd.). (Curtesy f R: D. GENDZWLL 56

31 Table 2.6. Acquisitin and prcessing parameters fr the three Winnipegsis seismic Jines DATA COLLECTON Date Sht Cntractr nstruments Filters Surce interval Receivers array interval DATA PROCESSNG Date Cntractr Demu Line Gemetry nst. Phase Amp. Crnp. Decnvlutin Trace Equal. Drift Statics interactive emp Srt Aut Statics Velcity Anal. Nrmal Mveut Hute Aut Statics Dip Mveut Mute Filter Stack Filter F.D. Migratin Filter RMS Gain Display Sep 1986 Western 1200 ms Minimum Phase Frequency 80 ms V w = V - Allan 610 m/s 1890 m/s 10/15-80/90 Hz 1200% 10/15-80/90 Hz Rcanville Sep 1983 Grant Geph. DFSV/48 ch ut/128 Hz Vibrseis Hz/8 s 134 ill Mark 10 Hz 9/33.5 m 33.5 m Sep 1986 Western 1200 ms Zer Phase Frequency 80 ms V w = V ~ 610 m/s 1890 m/s 1200% Hz 10/15-80/90 Hz L-...L.L- --' -- TABLELAND Tableland May 1985 Pineer Ep!. DFSV/120 ch 8/128 Hz Dynamite 1 kg/17 m 134 m Gespace 14 Hz 9/33.5 m 33.5 m Nv 1987 Western 2450 ms Minimum Phase Spiking 100 rus V w ~ 610 mls V m/s 1200% Hz ANOMALY Jan 1975 Century Geph. DFS/48 ch 12/124 Hz Dynamite 0.2 kg/18 m 134 ill Mark 14 Hz 9/33.5 m 33.5 m The Dme Scurry Tableland W2M well was drilled in t encuntered 116 m f Prairie Evaprite Fm salt ver 16 m f anhydrite and 34 m f Winnipegsis Fm dlmite. The well prduced 4956 m 3 f il and m 3 f gas until A 1985 eplratin prgram resulted in the drilling f Hme et a!. Tableland 8A W2M in 1986 and Hme SRO Tableland W2M in 1987, bth within 1300 m nrthwest f the first well n the same structure (Fig. 2.51). These tw wells encuntered 63 and 69 m f Winnipegsis Fm dlmite. T the end f 1987 these last wells prduced m 3 f il and m 3 f gas. Figure 2.52 shws the structure and a well-lg sectin fr the mund. Significant features include the thick prus (9-10%) dlmite f the mund and a thin (2 m) anhydrite capping. Off the mund, the Whitkw Mbr anhydrite thickens t 20 r 25 m and the prus dlmite is replaced by a thin (5-10 m), dense Ratner member. Figure 2.53 shws a gelgical crss-sectin interpreted frm seismic line AEN 85-2 (Fig. 2.54). This seismic sectin shws the Tableland mund anmaly. The recrding and prcessing parameters are shwn in Table 2.6. Figure 2.55 shws a cmpressed plt f the seismgram t emphasize the small features. The mst bvius feature is the mund anmaly itself which appears as a psitive structural feature with 10 t 15 ms f relief. The highest pint n the seismic anmaly appears t crrespnd t the thickest accumulatin f dlmite as fund in the hles 8A-22 and 9-22 (Fig. 2.52). The seismgram structure is cmpsed f a psitive reflectin peak crrespnding t the tp f the Winnipegsis Fm and a weaker SECOND _ WHTE SPECKS MSSSSPPAN BRDBEAR PRARE_ EVAPORTE - WNNPEG. SHALE -_ KLOMETRES 3, Dme Hme et al 11~14 Ba-22 Hl /<1 lh lq~,gl '' 6g 'H H ' '1',Qt.._O.S MANNVLLE ~~~~~~~~~~ Figure Cmpressed seismic plt fr Tableland seismic line AEN 85-2 emphasizing subsidence and pull-up features R.9 W.'-'""2 _ 1--"," s,?",9> \, \ \ \,, \,,,,,,, \- \ \ L :..--'''7\-~+4+tA~~l-+_-_T.2 U.'\\..-l~. 14 \ _ gelgical crss-se-ctin seismic line \ \ ~~ '--- \ SP... 53' Figure Map f cntured prsity thickness in Tableland mund (curtesy f Hme Oil Cmpany Ltd.). psitive peak crrespnding t the base f the Ashern Fm. Shrt-perid multiples may mdify the shape f these peaks. n the vicinity f the Hme 8A-22 well (trace 171) the amplitude f bth these reflectin peaks diminishes. The reduced amplitude may be due t the thinning f the anhydrite cver and the lwer seismic speed f the prus dlmite (bth features as shwn in the well lg), resulting in smaller cntrasts f acustic speed and reflectivity with the ther rck. A seismic anmaly at the nrth end f the line suggests the presence f anther mund. There is abut 4-5 ms f subsidence ver this mund. The subsidence may be eamined by using dividers t cmpare seismic traveltimes ver the mund with thse ff the mund r by flding the sectin and verlaying different parts t btain eact cmparisns. Such cmparisn shws that there is differential thickening in the interval hetween the Watrus Fm (Cretaceus) and Mississippian reflectins but little r nne between the Mississippian and Prairie Evaprite Fm. This suggests that significant subsidence ver this mund ccurred nly after the Mississippian and befre the depsitin f the Watrus Fm. As mst f the il in the Estevan area is fund in Mississippian rcks, ne may speculate that subsidence and il emplacement may have been simultaneus in the mund. The pull-up anmaly under the mund may be analyzed using equatins (6) and (7). These equatins cmpare seismic times frm the tp f salt t the base f salt (Ts ) with seismic times frm the tp f salt t a deeper marker (Tk ) which is suppsed t be flat. Figure 2.50 shws a crssplt f useable times picked frm the sectin at 100-m intervals. The best fit line t the pint scatter has a slpe f (dtk / dts ). Using well-lg data, the rati f Vs / v,,, is 0.77 and frm equatin (6) (the limestne-cmpactin mdel) we derive ds/dz m is Near the nrthwest end, the mund anmaly has relief (Zm) f 13 ms and near the sutheast end relief is abut 11 ms. Using times instead f thicknesses (let dzm = 13), the check fr ds (subsidence due t cmpactin) is: ms = 5.2 ms at the nrthwest and ms = 404 ms at the sutheast, which is in reasnable agreement with the visual estimate frm the seismgram f 4 ms. Using equatin (7) (the salt-remval mdel) we btain ds/ dzm = 0.66 and the check n ds (subsidence due t salt remval) gives ms = 8.6 ms at the nrthwest and ms = 7.3 ms at the sutheast. This is rather mre subsidence than the 4 ms seen n the seismgram s we d nt accept the premise f (7) which is that salt has been remved. 57

32 , KLOMETRES 1, A M$SSS'PPAN 1750 tn wa: w :E SUBSDENCE l t SUBSDENCE T. ~ 'RARE EVAPORTE NNPEGOSS 3250 PULLUP r NNPEG. Figu~ nterpretatin sketch fr Tableland seismic sectin AEN R. LUNDBER 58

33 LJ, KLOMETRES A ~.~ - MSSSSPPAN en c z -BRDBEAR - PRARE EVAPORTE WNNPEGOSS w en WNNPEG SHALE Figure Seismic sectin AEN 85-2 fr the Tableland Winnipegsis mund. 59

34 KLOMETRES en w a: - w 750 ::E l SUBSDENCE VELOCTY PULLUP ----j SUBSDENCE due t salt remval -----j ~ Distrtin under cllapse zne MANNVLLE SOURS RVER BRDBEAR PRARE EVAP ANHYDRTE. WNNPEGOSS WNNPEG PRECAMBRAN ~~~;~O nterpretatin sketch fr Rcanville seismic sectin D. GENDZWLL 60

35 u u KLOMETRES 1, l'lllllllllllllllllllllrr.' 0.3 tj) c z 0 0 w tj) 0.4 -MANNVLLE 0.5 -SOURS RVER -!BRDBEAR., 0.6 -!PRARE EVAP. -ANHYDRTE -lwnnpegoss nrrTrr77.11 ~~ PRECAMBRAN Figure Seismic sectin T fr the Racnville Winnipegsis mund. RP. F SA SKAT HEWAN R ANVLLE 01 WNNPEG 61 P O. GENOZWLL

36 ~ The interpretatin frm this is that all f the seismic pull-up anmaly can be eplained by bserved features f the mund. Subsidence ver the mund can best be eplained as due t cmpactin f the mund rather than thinning f the salt, and there is n structural anmaly under the mund within the reslutin f this interpretatin. Synthetic seismgrams have been cnstructed fr several f the snic lgs, (Fig. 2.56). Frm the lgs, the highest part f the Winnipegsis mund cntains 70 m f anhydrite and carbnate abve the Ashern Fm. Tw-way seismic time thrugh this mass is abut 25 ms, time enugh fr tw 80-Hz wavelets, and n the 90-Hz synthetic seismgram fr the well there appears sme detail in that interval crrespnding t detail n the snic lg. Unfrtunately, n similar detail appears n the seismgram even thugh the upper filter cutff is 80 Hz. Mst f the seismic energy is arund 50 t 60 Hz. Reduced amplitude f the seismic reflectins near 9-22 and 8A-22 may indicate reduced reflectivity cntrast but the lack f high-frequency cntent in the seismgram limits the amunt f detailed infrmatin. MSSSSPPAN BRDBEAR PRARE EVAPORTE 1.5 WNNPEGOSS WNNPEG SHALE - 91 ' SS ls :n " ~, '" Synthetics, ~ ft s Dme Scurry Tableland W2 Figure Cmparisn f synthetic seismgrams fr Tableland well , " '" ~, '" " '", '" : ROCANVLLE ANOMALY The Sylvite Ste. Marthe W1M well was drilled in 1969 as a ptash test. t encuntered 64 m f Prairie Evaprite Fm salt, 17 m f anhydrite, and 17 m f prus Winnipegsis Fm dlmite at the bttm f the well. Accrding t Hlter (1969), abut 130 m f salt was epected in this area. Nrmally, the thickness f the mund plus the remaining Prairie Evaprite Fm abve the mund is apprimately equal t the ttal thickness f nearby salt where there is n mund. Therefre, an additinal 32 m f Winnipegsis Fm culd lie belw the bttm f the hle. N tests ther than gephysical lgs were dne in the hle. The Shell Lake Mbr anhydrite eists here but mst hles nly penetrate t the ptash level. MANNVLLE-:....=.- SOURS J'~'.~"-' RVER-... ~ --- BRDBEAR- PRARE EVAPORTE~ _'1~, a KLOMETRES 3! Sylvite 14-5 ~"''''-'''--- WNNPEGOSS--e_'::=i:, ;r. [ : :::"gn +8 4\;:~-~ PRECAMBRAN-? e-!wi i!>~~ 5a~~ Figure Cmpressed seismic plt fr Rcanville seismic line T17-l.0 emphasizing subsidence and pull-up features A seismic prfile was sht near the well in 1969 but the Winnipegsis mund was nt clearly identifiable in the data. A secnd prfile was sht in 1982 and reprcessed with the result that the anmaly is clearer. Figure 2.57 shws an interpretatin f the seismgram in Figure 2.58 whereas Figure 2.59 shws a cmpressed plt emphasizing the small features f the data. The seismic line shws a gradual dip t the west f all strata and a thickening tward the west, especially f the deep Ordvician and Silurian strata. There is an increase in the rate f thickening f the Ordvician and Silurian rcks in the vicinity f the Winnipegsis mund. Therefre, it may be speculated that this mund grew at a place where the water depth changed. The Devnian rcks, ecept fr the salt, are cnsistent in thickness. The Cretaceus rcks thicken westward but nt as much as the Ordvician and Silurian. These gradual stratigraphic thickenings may be related t the develpment f the Willistn basin and the psitin f the study area near the margin f the basin. The synthetic seismgrams (Fig. 2.60) shw the strng reflectin cntrasts f the Suris River and Birdbear frmatins which tended t mask the deeper reflectins in sme earlier surveys. The anmaly representing the mund is mre difficult t interpret than ther mund anmalies in central Saskatchewan because there is n angular reflectin representing the flank f the mund n either side. The reflectin frm the tp f the mund is mre r less cntinuus n the east side with a reflectin identified as the Shell Lake Mbr. Cnsequently, there is n clearly identifiable seismic anmaly directly assciated with the mund. On the west side, the large-amplitude reflectin frm the tp f the mund suddenly diminishes. This change in amplitude may represent the edge f the mund build-up because the Shell Lake Mbr may be thinner and less reflective n the west side than n the east side. There is a "sag" n the east side f the mund which affects reflectins at all depths, apprimately between traces 245 and 26l. Hwever, unlike the effect f a near-surface lw-speed zne, the time-structure f the sag is nt the same at all depths, being nearly 20 ms belw the Prairie Evaprite Fm but less than 10 ms abve. Recently, a large depressin-and-cllapse structure in the Prairie Evaprite Fm was fund in an undergrund ptash mine near this lcatin s there is a real gelgical subsidence structure which is the prbable cause f this seismic anmaly. Changes in seismic speed thrugh the shallwer disturbed rcks apparently cause the time delay t reflectrs belw the Prairie Evaprite Fm. MANNVLLE SOURS VALLEY BRDBEAR PRARE EVAPORTE WNNPEGOSS WNNPEG SAND PRECAMBRAN.", ~ t ~----.:::..-l- --e_9!! ~! ~! ~ ~!ft/s 1'-'-'. ",~_, i 'T---;---;'--r---r-, - '--1,-- r ---J 500 i.> 1 ~ " ili, [? H " f-- -=z--:; _;--::iii =:=:==,",.,~=:j Sylvite S. Marthe '" 14-S-17-3QW1 '0"... Line T 17-1.rt==== Figure Cmparisn f synthetic seismgrams fr Rcanville well On the west side f the mund, the tp f the Prairie Evaprite Fm drps slightly and the seismic interval between tp and bttm is slightly thinner than it is n the east side, suggesting that the salt is thinner n the west than n the east, cntrary t the reginal trends. The effect f thinning f the salt adjacent t the mund seems t match the effect f velcity puil-up under the mund s the seismic time frm the tp f salt t markers belw the Winnipegsis is abut the same ver r west f the mund. The cmbined effect f the cllapse structure n the east and the salt thinning n the west is t create a psitive drape structure ver the mund. f cmpactin has ccurred it is nt recgnizable. A velcity pull-up anmaly is a distinctive feature. t is present n all the reflectrs belw the mund, mdified by the reginal dip and eaggerated by the subsidence n the east flank. Figure 2.59 shws these structures in high relief. The change in character f the seismgram under the mund is caused by a reductin in the high-frequency cntent f the signal, giving the appearance f a lwer-frequency signal belw the mund 2500 ~s 62

37 than n either side. The mst dminant seismic features f this mund seem t be the decrease in dminant frequency belw it and the velcity pull-up structure. ALLAN MOUND Drill-hle Altair Elstw W3M wa,; drilled by Altair Oil Ltd. in January 1960 in rder t test the Winnipegsis and nterlake frmatins. t encuntered 107 m f Prairie Evaprite Fm salt, 9 m f anhydrite, and 99 m f upper and lwer Winnipegsis dlmite, cminuing 104 m int the middle f the nterlake Fm. Drill-stem tests prduced 46 m f mud frm the Winnipegsis Fm and 235 m f muddy salt water frm the nterlake Fm. Ttal salt thickness in the area is 190 m in drill-hle U.S. Bra W3M, abut 3 km west f the drill-hle. The Shell Lake Mbr is present in A seismic prgram fr the nearby Allan ptash mine in 1975 utlined the Winnipegsis munds f the area, including the ne tested by Altair Elstw Figure 2.61 shws the seismic cverage and cnfiguratin f the munds. A descriptin f sme f these R1 R28 ---\" '!--rl-~ ---.~---;- --~- -\--1 'T,- lt- j 11 SESMC LNE WNNPEGOSS ANOMALY -_.. DSPLAYED SECTON T- _j--1-'1 e- t '" '!,'..~!,,., '! _~~L- ' 4_0_...~' /j;/~~-~") "'_"'~ ~ 1.,.!,... " ') 9 27., Q :...! ;' --: il i T =::!S;:tr,1$=,~t~'~i~...=.~=:T= ~lj,-: :::c! :..!{,1,~Sj+~-R-E-M-O+-l-AL-!-'!f-,! - 1 t,.!! /, STRUCTUR~!Ot ' t-+.i--i-----+rr-r-----t--+".'/ ',,: 7 : 12 1~ 7 V ;!! ", " _: L-~_.-'-----~--1---~---+-/.: L.~ R1 R29 R28 DRLL HOLES 0 Figure Allan area shwing seismic cverage and knwn Winnipegsis munds (after Gendzwill, 1978). data, including cmparisns f well-lg and mine elevatin prfiles, was given by Gendz\,vill (1978) but Figures 2.62 and 2.63 shwing the gelgical interpretatin and seismic sectin fr seismic line T have nt been previusly published. Figure 2.64 shws a detailed prtin f T with the snic and synthetic seismgram frm U.S. Bra 5A-22 which is abut 1 km west f the end f the line. N well has been drilled n this seismic line. Altair Elstw is apprimately 600 m nrth f trace 50 but there was n snic lg fr the well. The mund is apprimately 5 t 6 km lng by 3 t 4 km wide but is quite irregular in shape. A salt-remval structure 3 t 4 km wide lies a shrt distance east f the mund but the mund des nt ft/s, ~L. Allan Elstw W3..~ ~;;~;~ =r... ' SPECKLED SHALE BLARMORE DUPEROW DAVDSON EVAPORTE FRST RED BED PRARE EVAPORTE WNNPEGOSS Figure Cmparisn f synthetic seismgrams fr Allan well seem t be invlved in the structure. Other munds are lcated nearby. Frm maps f this type (Fig. 2.61) in the Saskatn area, the rati f length f seismic line underlain by mund t ttal length f seismic line sht in the area, suggests that abut 25% f the area is underlain by Winnipegsis munds. The Allan mund displays all f the features cnsidered t be characteristic. There is a clear reflectin frm the surface f the mund, including the slping flanks, but this mund has a structure with high rims n each side and a lw depressin in the middle. The net seismic line, 0.8 km t the nrth, shws a single brad anmaly s the tw bumps n T prbably represent tw lbes etending suth frm a single large mund. The high lbe has abut 40 ms f seismic relief crrespnding t 88 m f Winnipegsis thickening which is in reasnable agreement with the drilled thickness 600 m t the nrth. The reflectin frm the Shell Lake Mbr appears at abut the same height as the tp f the mund but the amplitude f the reflectin is smaller than that frm the tp f the mund, prbably because the anhydrite is t thin t prduce a strng reflectin. The anhydrite reflectin has an "nlap" relatinship t the mund. There is a cmpactin-subsidence anmaly f abut 10 t 15 ms in the strata ver this mund. The greatest amunt f subsidence appears at the tp f the Prairie Evaprite Fm and lesser amunts appear at shallwer depth. The subsidence is best displayed at the west end because salt remval effects interfere at the east end. Als at the west end f the mund, an irregular structure in the reflectin frm the tp f salt suggests that the ptash beds may be disturbed ver a limited area. Figure 2.65 shws these features with emphasized relief. A velcity pull-up anmaly under the mund mimics the shape f the mund. There is a change in the structure f the seismgram in the regin belw the mund. This character change is a result f a reductin in the amplitude f the higher-frequency cntent f the signal s that the anmaly appears t becme lwer in frequency, especially under the high rim segments. Abve the mund is a typical reflectin structure cmpsed f three reflectin peaks abut 25 ms apart and cnsistent laterally fr a lng distance. These represent, frm tp t bttm, the upper Davidsnllwer Harris salt, the First Red Bed, and the Secnd Red Bed/Prairie Evaprite. Near the east edge f the mund, the tpmst f these reflectins disappears and there is a crrespnding subsidence structure which appears in shallwer reflectins. This anmaly represents the remval by disslving f 26 m f upper BLARMORE DUPEROW _ ~_~ _ DAVDSON~-\~ EVAPORTE..:.' ~. FRST RED BED""- --- PRARE EVAP... WNNPEGOSS WNNPEG SAN0 -'"lri.. PRECAMBRAN~~~~!iii~ REFERENCES._...:-1L AGAT Labratries, Table f Frmatins f Saskatchewan (including the Willistn Basin and adjining areas), AGAT Labratries, Calgary_ Figure Cmpressed seismic plt fr Allan seismic line T emphasizing subsidence and pull-up features. Davidsn and lwer Harris halites in the Suris River Fm. This is a peripheral effect f the cmplete remval f the Prairie Evaprite Fm in the Clnsay (a nearby village) cllapse structure a shrt distance east f the displayed seismic line as shwn n Figure This anmaly was cnsidered an indicatin that water was r is circulating in the adjacent rcks. Accrding t Phillips (1983) the re reserves and mining plans fr the Allan ptash mine were changed, n the basis f this interpretatin, t avid the hazard f a ptential water inflw t the mine. Althugh the Davidsn Evaprite is disslved up t the eastern edge f the mund, the main Prairie Evaprite Fm salt is intact at the eastern edge and fr sme distance eastward s that the mund des nt seem t be directly related t the Clnsay cllapse structure., Table f Frmatins f Alberta, AGAT Labratries, Calgary. 63

38 , KLOMETRES 1, 250 UJ w a: ij 750 :E SUBSDENCE due t.. t DAVDSON _ riemval 500, J SUBSDENCE due t MOUND j SUBSDENCE 1 VELOCTY PULLUP SPECKLED SHALE BLARMORE DUPEROW ~~~k~d~av~~ds~~n~s~a~lt~1i~m~it_4 =_=_: A V10SON EVAP. = FRST RED BED PRARE EVAP. WNNPEGOSS WNNPEG Figure nterpretatin sketch fr Allan seismic sectin T PL T : D. GENDZWLL, PRECAMBRAN 64

39 , u u KLOMETRES ~ 0.4 ~ z w U) -SPECKLED SHALE DUPEROW DAVDSON EVAP. FRST RED BED PRARE EVAP. WNNPEGOSS , h All Figure Selsnuc secton 1' lr t e an mund. w...ljr~..l~ PRECAMBRAN mrupegsls 65 R: D. ENDZWLL

40 Andersn, N.L An integrated gephysical/gelgical analysis f the seismic signatures f sme western Canadian Devnian reefs. Unpublished Ph.D. thesis, University f Calgary, 333 p. and Brwn, RJ The seismic signatures f sme western Canadian Devnian reefs. Jurnal f the Canadian Sciety f Eplratin Gephysicists, v. 23, p ,, and Hinds, RC. 1988a. A critical lk at the questin f lateral velcity variatins ver Leduc Frmatin and Rainbw Member reefs. n: Bly, G.R. and Charest, M. (Eds.), Principles and Cncepts fr the Eplratin f Reefs in the Western Canada Basin. Canadian Sciety f Petrleum Gelgists, Shrt Curse Ntes, Sectin 7, p , 1988b. A seismic perspective n the Panny and Trut fields f nrth-central Alberta. Canadian Jurnal f Eplratin Gephysics, v. 24, p Barss, D.L., Cpland, AB., and Ritchie, W.O Gelgy f Middle Devnian reefs, Rainbw area, Alberta, Canada. n: Halbuty, M.T. (Ed.) Gelgy f Giant Petrleum Fields. American Assciatin f Petrleum Gelgists, Memir 14, p Bassett, H.G. and Stut, J.G Devnian f western Canada. n: Oswald, D.H. (Ed.), Prceedings f the First nternatinal Sympsium n the Devnian System, Alberta Sciety f Petrleum Gelgists, Calgary, v. 1, p Brwn, RJ., Andersn, N.L., and Hills, L.Y. (1989). Seismic interpretatin f Upper Elk Pint (Givetian) carbnate reservirs f western Canada. Gephysical Prspecting. Campbell, C.V Stratigraphy and facies f the Upper Elk Pint Subgrup, nrthern Alberta. n: Krause, EF. and Burrwes, O.G. (Eds.), Devnian Lithfacies and Reservir Styles in Alberta: Secnd nternatinal Sympsium n the Devnian System, Calgary, Canadian Sciety f Petrleum Gelgists, p Cant, D.J Reginal structure and develpment f the Peace River Arch, Alberta: A Palezic failed-rift system? Bulletin f Canadian Petrleum Gelgy, v. 36, p Christiansen, E.A Gelgy f the Crater Lake cllapse structure in sutheastern Saskatchewan. Canadian Jurnal f Earth Sciences, v. 8, p Dunn, c.e Gelgy f the Middle Devnian Dawsn Bay Frmatin in the Saskatn Ptash Mining District. Saskatchewan Energy and Mines, Reprt 194, 117 p. Gendzwill, D.J Winnipegsis munds and the Prairie Evaprite Frmatin f Saskatchewan - seismic study. American Assciatin f Petrleum Gelgists, Bulletin, v. 62, p and Hajnal, Z Seismic investigatin f the Crater Lake cllapse structure in sutheastern Saskatchewan. Canadian Jurnal f Earth Sciences, v. 8, p and Wilsn, N.L Frm and distributin f Winnipegsis munds in Saskatchewan. n: Petersn, J.A, Kent, D.M., Andersn, S.B., Pilatzke, RB. and Lngman, M.W. (Ed.), Willistn Basin; Anatmy f a Cratnic Oil Prvince. Rcky Muntain Assciatin f Gelgists, Denver, Clrad, p Graystn, L.D., Sherwin, D.E, and Allan, J.E Middle Devnian. n: McCrssan, RG. and Glaister, RP. (Eds.), Gelgical Histry f Western Canada, Alberta Sciety f Petrleum Gelgists, p Hargreaves, G.E., Hunt, AD., de Wit, R and Wrkman, L.E. (Eds.) Leicn f gelgic names in the western Canada sedimentary basin and Arctic Archipelag, Alberta Sciety f Petrleum Gelgists, 380 p.. Hills, L.V., Sangster, E.V. and Suneby, L.B. (Eds.) Leicn f Canadian Stratigraphy, vl. 2, Yukn Territry and District f Mackenzie, Canadian Sciety f Petrleum Gelgists. Hlter, M.E The Middle Devnian Prairie Evaprite f Saskatchewan. Saskatchewan Department f Mineral Resurces, Reprt 123, 133 p. Hriskevich, M.E Middle Devnian reefs f the Rainbw regin f nrthwestern Canada, eplratin and eplitatin. Prceedings f the Seventh Wrld Petrleum Cngress, v. 3, p Middle Devnian reef prductin, Rainbw area, Alberta, Canada. American Assciatin f Petrleum Gelgists, Bulletin, v. 54, p Jnes, L The Middle Devnian Winnipegsis Frmatin f Saskatchewan. Saskatchewan Department f Mineral Resurces, Reprt 98, 101 p. Jrdan, S.P Saskatchewan reef trend lks big. Oilweek, January 16, p Kendall, AC Bedded halites in the Suris River Frmatin (Devnian) Ptash mining district arund Saskatn. Saskatchewan Gelgical Survey, Summary f nvestigatins. 1976, p Klvan, J.E Develpment f western Canadian Devnian reefs and cmparisn with Hlcene analgues. American Assciatin f Petrleum Gelgists, Bulletin, v. 58, p Langtn, J.R and Chin, G.E Rainbw Member facies and related reservir prperties, Rainbw Lake, Alberta. Bulletin f Canadian Petrleum Gelgy, v. 16, p Mackintsh, AD. and McVittie, GA Gelgical anmalies bserved at the Cminc Ltd. Saskatchewan ptash mine. n: McKercher, RM. (Ed.), Ptash Technlgy, p Pergamn Press, nc. Maiklem, W.R Evaprative drawdwn - A mechanism fr water-level lwering and diagenesis in the Elk Pint Basin. Bulletin f Canadian Petrleum Gelgy, v. 19, p McCamis, J.G. and Griffith, L.S Middle Devnian facies relatinships, Zama area, Alberta. Bulletin f Canadian Petrleum Gelgy, v. 15, p Nelsn, S.J The face f time: The gelgical histry f western Canada. Alberta Sciety f Petrleum Gelgists, 135 p. 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