The Permo-Triassic story of the Sindbad/Sesam well (Nordland Ridge)

Transcription

1 The Permo-Triassic story of the Sindbad/Sesam well (Nordland Ridge) Thomas Tvedt, E.ON Exploration & Production Norge AS FORCE seminar - Underexplored Plays 8-9th April, 2015

2 Presentation outline Brief Introduction to the Permian and Triassic geology in the area Introduction to the targets of the Sesam/Sindbad well Triassic Sindbad amplitude anomaly observations Sindbad modeling Sindbad results Permian Sesam depth prognosis Sesam results 2

3 The Permo-Triassic story of the Sindbad/Sesam well (Nordland Ridge) PL350: Awarded in 2004, Relinquished in 2012 Partners: E.ON E&P Norge AS (operator) Statoil PGNiG E.ON E&P Norge AS drilled a Triassic and a Permian prospect in 2011/12 on the Sør High of the Nordland Ridge in the Norwegian Sea. The intent was to test an amplitude anomaly in the Triassic section Sindbad (6507/6-4S) on the long path down to the Permian prospect Sesam (6507/6-4A). Both wells were unfortunately dry but gave a better understanding of the Triassic and Permian and shedding light on the need for higher resolution data. 3

4 Location Sindbad/Sesam 4

5 Permian Palaeogeography Warm water platform carbonates Nordland Ridge & East Greenland Organic rich source rock basins Jameson Land & Helgeland Basin Evidence of HC generation and migration Fluid inclusions in exploration wells and outcrops Shows in shallow research boreholes Modified from Stemmerik 1997

6 Permian outcrop Wegener Halvø, East Greenland 80 m 6

7 Palaeogeographic Maps and Tectonics Griesbachian - Rhätian Post-rift phase 3 (Norian-Rhätian) represents termination of the late Triassic tectonic event. Progradation of extensive fluvial system in the end of this phase is related to an uplift of the Norwegian Mainland. Gradual increase in the humidity of the climate. Modified from Müller et al. 2005

8 Triassic Unit TR5 Sedimentology and Depositional Environment Late Permian to Triassic Litho-Chronostratigraphy Tr5 Idealised chronostratigraphy illustrates basin fill history of the Mid-Norwegian shelf and East Greenland Expected reservoir unit in Sindbad comprises part of Unit Tr5 Unit Tr5 is of Norian to Rhätian age- Post rift phase 3 Lower boundary defined by the last occurrence of thin evaporitic beds (Tr4) before going into dominant continental palyno-facies of Tr5. Lower part of unit (>300m) is deposited in shallow and extensive mud-dominated lacustrine basin Upper part of unit (Sindbad level) consists of thick sandstones beds interbedded with mudstone and thin coals Upper part of Tr5 deposited in a fluvial system dominated by moderate to high sinuous channels Tr5 unit represents an overall coarsening upward trend from a mudstone-rich lacustrine flood-basin to a sand-dominated fluvial environment Modified from Müller et al. 2005

9 TWT Sesam & Sindbad NW SE Former PL350 in 6507/6 East of Skarv field (Sindbad) (Sesam) Saga well, 1986 Sindbad Biogenic gas Åre Fm Grey Beds Red Beds Dolomite/Anhydrite Sesam Sindbad Sesam Depth surface of Top Permian Depth surface of Top Sindbad with RMS amplitude overlain 9

10 Seismic angle stacks Near angle 5-15 degrees Far angle degrees NW SE NW Stronger amplitude response up-dip from the 6-1 well on both nears and fars Strong degradation of frequency content from near to far angle SE

11 Pre-stack offset gathers from 6507/6-1 to Sindbad NW 6507/6-4S 6507/6-1 SE Seabed BCU Sindbad level Red is hard Offset m Evaporite

12 12 - Pre-stack angle gathers from 6507/6-1 to Sindbad 6507/6-4S 6507/6-1 BCU Sindbad level Evaporite NW Red is hard Angles 5-41 degrees SE

13 RMS maps on full offset seismic Upper event Lower event (Sindbad) (Sindbad) Saga well, 1986 Saga well, 1986 Data-room September 2010 Geoscience Dpt Depth contours 3 km Depth contours 13

14 AVO modeled gathers fluid substitution 6507/6-1 Alternating sand/shale Brighter response for HC, fairly flat AVO InSitu OIL GAS

15 1 brine 2 light oil 3 heavy oil 4 - gas AVO product for 4 scenarios NW SE

16 6507/6-4S vs 6507/6-1 comparison 6507/6-4S 6507/6-1 AI AI Sandier section in Sindbad, slightly more distinct shale packages but thin and possibly below tuning Slightly more marked AI contrast

17 PR 6507/6-4S modeling Color-coded hard stringers coinciding with carbonate flags AI Synthetic modeling of Sindbad logs show slight brightening with offset

18 Estimate velocity model below Evaporites NW SE Nearby well did not penetrate Permian marker Very little reflectivity or established markers within the Red beds below the Evaporites Nearest Permian velocity control several hundred km s to north Sindbad Biogenic gas Åre Fm Grey Beds Red Beds Dolomite/Anhydrite Sesam 18

19 VSP Overlay on Depth seismic Long section to drill from Triassic evaporites to Permian marker without correlatable reflectors Anisotropic PreSDM Estimates of anisotropy uncertain Red line indicates actual Top Carbonate (4119m TVDSS)

20 Top Permian depth Interpreted top carbonate came in deeper than expected (+261m TVD). Possible explanations: Incorrect anisotropy estimation for BCU to Top Anhydrite Three intervals tested leading to a decision to choose a relatively high delta. However the Top carbonate came in close to the isotropic velocity depth model. Interval between Top Anhydrite and Top carbonate more or less isotropic. Weak lower Triassic reflector in offset well not correlatable to Sesam well (basis for delta value below Top Anhydrite). Isotropic PreSDM shows close to same (slightly less) thickness between Top Anhydrite and Top Carbonate as encountered in the well. Smaller thickness in the isotropic PreSDM means that the tomographic velocity was too low (negative delta is not realistic). Stacking velocity has a large uncertainty for reflectors at 4km depth. Velocity difference between 6-1 well and 6-4A. Presence of high velocity stringers in 6-4A that in isolation are below tomographic resolution The velocity model is not honouring the dip of the events and reflects a compaction trend. Lithology below TD of offset well was unknown in terms of velocity. It contained considerable marl content and anhydrite stringers. 20

21 Well Tie Chronostratigraphic correlation 21

22 Conclusions Sindbad tested an amplitude anomaly in the Grey beds of the Triassic on the Sør High of the Nordland Ridge. False positive AVO effect due to tuning and/or calcite stringers. Higher N/G than at 6507/6-1, indicating possible channel penetration. Although dry, the Sesam well penetrates a full Upper Permian sequence including the P/T boundary and underlying Lower Permian/Carboniferous rocks. The lower part of the sequence can be correlated to clastic rocks penetrated in shallow IKU drill cores recovered close to the Norwegian mainland. Depth conversion in regions with little/no well control remain challenging! Charge and seal remain the key risks of the Triassic and the Permian on the Nordland Ridge in the Norwegian Sea. 22

23 Acknowledgements The presenter thanks E.ON E&P Norge AS for permission to present this work. The presenter also thanks current and former colleagues for their contributions to the work performed in PL350, in addition to former license partners Statoil and PGNiG. Also thanks to the Organising Committee of the FORCE seminar «Underexplored plays» for the opportunity to share the results of the Sindbad/Sesam well on the Sør High of the Nordland Ridge. 23