Tectonics and Hydrocarbon System, East Gobi Basin, Mongolia Gary Prost, ConocoPhillips Canada, Calgary
Project Objectives (a joint project of Gulf Canada and ROC Oil) What structures can be expected in these basins, and what age are they? Where is the best quality reservoir? When did hydrocarbons generate; where did they migrate? What hydrocarbon type can be expected? What volumes were generated?
Work Program - Map East Gobi basin using regional Landsat images - Map subbasins using enlarged satellite images and airphotos - Reconnaissance field mapping - Evaluate seismic data, well logs, cuttings, outcrop samples, and literature - Model the hydrocarbon system
Location Map, East Gobi Basin Mongolia Unegt. Sainshand Sainshand ZB TE Khovsgol Zuunbayan 46 o 44 o The East Gobi basin of southeast Mongolia consists of several subbasins Mongolia W. Gobi E. Gobi Songliao China 5 1 km 42 o China Ordos Erlian 16 o 18 o 11 o
Quaternary Tertiary Cretaceous Jurassic Permian- Devonian Upper Lower Upper Middle Maastrichtian Campanian Campanian Santonian Santonian Turonian Cenomanian Albian Aptian Barremian Hauterivian Valanginian Tithonian Kimmeridgian Bathonian... O.. o....... O o ------------...---............ --------... -----------... -----------... ----------- ------------... ------------ ----------- --------... ----------- _ ------------ - --- -- --------...... -------- - --- -- -... -----------.. ------------...O.. o... ------------... ---- --- --....... ~~~~~++ ~~~~+++ Undifferentiated Nemegt Baruungoyot Bayanshiree Sainshand or Baruunbayan Zuunbayan Tsagaan Tsav Sharlyn Upper Lower Bituminous Khamar Khoovor Tavan Tolgoy Seal Reservoir Seal Reservoir Seal Source Reservoir Seal Stratigraphy, East Gobi Basin Seals are lacustrine shales of the Zuunbayan, and Sainshand formations The reservoir consists of fluvial and alluvial sands in the Tsagaan Tsav and Zuunbayan formations Source rock is the Bituminous member of the Zuunbayan Fm.
Landsat Index Row 28 Path 128 47 46 The area of interest is covered by 5 Landsat TM images Row 3 Row 29 Path 129 Sainshand Zuunbayan Mongolia China 45 44 43 Color and B/W images at 1:1, served as a base for mapping (next slide) 17 18 19 11 111 112
Remote Sensing and Mapping town Ukhaa Anticline field airstrip Zuunbayan Anticline 1 km 1:1, Landsat TM image
Remote Sensing and Mapping Hutuul Uus area Fine detail can be mapped where airphotos are available. 1:32, Russian Airphotos
Field Mapping Minor fold, Hutuul Uus area The field program provided map detail Confirmed satellite and airphoto work Allowed measurement of kinematic indicators
Satellite + Field Map, Unegt Subbasin next slide Hutuul Uus (previous slide) Zuunbayan area Subbasins can be mapped in fair detail
Enlarged portion of the Unegt subbasin Light-colored Paleozoic granites identified on satellite images and confirmed in the field Next Slide
Seismic across NE Zuunbayan fault The Zuunbayan Fault has both normal and reverse displacement along strike, suggesting strike-slip faulting and/or varying degrees of inversion
Seismic over Zuunbayan field The Zuunbayan anticline is a result of inversion on pre-existing east-northeast-trending normal faults
Seismic lines, Tsagaan Els field mid-cretaceous unconformity Tsagaan Els structure shows pre-mid-cretaceous inversion Present-day structure Flattened on Middle Cretaceous Unconformity
Lower Cretaceous inversion mid-cretaceous unconformity Northwest-directed out-of-the-basin thrusting, northern Unegt basin
Beachballs are a lower hemisphere projection of a Schmidt net showing poles of shortening and extension. White areas indicate zone of shortening. Kinematic Measurements * * * * * * Unegt Subbasin Zuunbayan Tsagaan Els * * * * Multiple fault plane orientations, lineations, and striations were mapped at each site * At several locations two solutions are required to avoid simultaneous extension and shortening in the same direction
Kinematic Summary 1 2 3 5 Tectonic Events Are Identified Pre-Jurassic left-lateral strike slip on NE-trending faults Late Jurassic - Early Cretaceous normal faulting along east-west trends Late Early Cretaceous shortening & inversion along existing east-west & NE trends 4 Mid-Cretaceous uplift & erosion 5 Post Mid-Cretaceous east-west shortening & right-lateral strike slip along northeast faults
9 Temp (C) 16 Depth (m) Hydrocarbon Systems Modeling Thermal gradient from BHTs is 4.5 o C/1 m Heat Flow 2.6 Heat flow ranges from 2.6 to 2.25 HFU, with five peaks corresponding to volcano-tectonic events 2.2 14 Age (my)
Source Rock Isopach 19 19 3 19 19 3 44 5 44 5 And Maturity 11 11 11 3 11 3.8 Sainshand Sainshand.4 Isopach (m) (m) 44 444 4 44 443 44 442 44 1.4.8 2. 5 1.2 1.2 1.6.8.4 1 km.8.8 1.2 ZB TE 5 5 1.2 1 1.6 1 mi 1.2.8 5 5 1 5.8.4-5 -5 5-1 5-1 >1 >1.4.4.8.8 1.2 1.2 1.6 1.6
1 Migration Paths, 14 Ma 1-1 -2-1 -1-1 -1-1 -2 1-1 1-1 trap no outcrop Zuunbayan Deep basin Deep basin Deep basin Tsagaan Els trap
1 Migration Paths 5 Ma 1 Total Hydrocarbon Volume Accumulated: 256 MMbo -2-1 Deep basin -1-1 -1 Deep basin Deep basin -1-2 trap 1-1 -1 1-1 trap no outcrop Tsagaan Els Zuunbayan
1 2 Present Day Migration Paths 1 1-1 1 2 S Sainshand -1-1 -1-1 NB ZB 1-1 -2-1 -1-2 1 TE EZB KK SU Unegt Sub-basin Zuunbayan Sub-basin Paleozoic outcrop -1 1 1 44 5 44 4 44 3 44 2 19 3 11 Total Hydrocarbon Volume Paleozoic outcrop Accumulated: 652 MMbo -2-2 U -3-2 BM4
Event Diagram Sharlyn Tsagaan Tsav Zuunbayan Bayanshiree Nemegt Deposition Source Khamar Khoovor Bituminous Mbr Zuunbayan Undifferentiated Baruungoyot Reservoir Tsagaan Tsav Zuunbayan Sainshand Seal Tectonics Generation and Migration North-South Extension and Rifting Tilted Fault Block Traps North-South Shortening Thrusted Fold Traps East-West Shortening Fold Traps Early Peak Late
Conclusions Paleozoic Granite Five structural episodes are recognized: 1) pre-jurassic NE shortening 2) Mid-Jurassic to Early Cretaceous rifting on NE trends 3) late Early Cretaceous NS shortening 4) middle Cretaceous uplift and erosion 5) EW shortening and right-lateral offset on NE faults Imagery identifies light-colored intrusives that may serve as a source of high-quality reservoir
Conclusions The bituminous member Zuunbayan Fm. should be mature over much of the deep Unegt and Zuunbayan subbasins Oil generation began at 11 Ma, peaked 1-9 Ma, and continues to present As much as 86 B BOE may have been generated; at least 65 MMBO accumulated (156 MMBO discovered) The locals are real friendly