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