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Modeling Burial, Thermal History, and Hydrocarbon Generation in North GOM Petroleum Systems

This study evaluates the hydrocarbon potential, organic maturation, and burial and thermal history of the North Gulf of Mexico petroleum systems. It focuses on the Smackover source rock and assesses secondary hydrocarbon migration. The study also includes modeling of formation temperature and heat flow, and the calculation of thermal conductivity. The results provide insights into the volumes of oil and gas generated and expelled.

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Modeling Burial, Thermal History, and Hydrocarbon Generation in North GOM Petroleum Systems

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  1. North GOM Petroleum Systems: Modeling the Burial and Thermal History, Organic Maturation, and Hydrocarbon Generation and Expulsion Roger J. Barnaby 2006 GCAGS MEETING

  2. Previous studies of northern GOM crude oils: composition, 13C, document Type II algal kerogen in Smackover major source • Evaluate source rock hydrocarbon potential and maturity • Smackover geochemistry (TOC, kerogen) • Model burial history • Model thermal history • Model hydrocarbon maturation, generation and expulsion • Key controls • Timing and burial depths • Volumes of oil and gas • Assess secondary hydrocarbon migration Objectives

  3. MONROE UPLIFT N. LA SALT BASIN Primary control for basin modeling 140 key wells (red) 44 sample wells (blue) 30 additional wells being analyzed SABINE UPLIFT CRETACEOUS SHELF MARGIN 50 mi

  4. Burial History: Depositional and Erosion Events Geological time scale: Berggren et al. 1995 Formation ages: Salvador 1991 Galloway et al. 2000 Mancini and Puckett 2002; 2003 Mancini et al 2004

  5. Miocene Jackson Oligocene Hosston Wilcox Austin Paluxy Midway Tuscaloosa Cotton Valley Wash/Fred Mooringsport Glen Rose Sligo Smackover

  6. Burial History • Reconstructed from present-day sediment thickness after correcting for compaction • Compaction due to sediment loading • Maximum paleo water depths < few 100 meters, no correction for water loading • Paleobathymetry • Sea level through time

  7. Porosity-Depth Relationships Limestone Shale Exponential Compaction f = f0 exp (-Kz) Where: f = porosity f0 = Initial porosity K = compaction factor z = depth Sandstone

  8. 3 3 2 2 1 1 Burial History: Decompaction t1 Remove 2 & 3 Decompact 1 t2 Add 2 Partially compact 1 t3 Add 3 Compact 2 and 1 Present-day depths y’1 1 2 y’2 1 y1 y2

  9. Burial History: Compacted vs Non-compacted Non-compacted Compacted

  10. Lithology (Wilcox) CALCULATE DECOMPACTION -lithology from digital logs End member lithologies -SS, SH, LS, ANH Log-derived lithology -mixture of end members Compaction parameters for mixed lithology – weighted arithmetic average

  11. Lithology (Upper Glen Rose)

  12. Miocene Jackson Oligocene Hosston Wilcox Austin Paluxy Midway Tuscaloosa Cotton Valley Wash/Fred Mooringsport Glen Rose Sligo Smackover

  13. Burial History

  14. 2 Jackson Miocene Oligocene Wilcox Austin Hosston Midway Mooringsport Wash/Fred Cotton Valley Glen Rose Sligo Tuscaloosa Smackover

  15. Burial History

  16. Thermal History • Modeling formation temperature • Heat flow approach: temperature function of basement heat flow, thermal conductivity overlying sediment • Present-day heat flow • Well BHTs • Surface temp = 20oC • Thermal conductivity • Porosity and lithology are major variables controlling thermal conductivity • In-situ thermal conductivity computed by BasinMod

  17. Heat Flow Calculation W W T2-T1 (103 .deg K) = x y2-y1 (meters) meter (103. deg K) meters2 Heat Flow Temperature Gradient Thermal Conductivity T1, y1 T2, y2

  18. Calculated vs Measured BHTs BHTs Calculated Heat Flow = 50 mW/m2

  19. Thermal History: Paleoheat Flow b = 2.0 170130026300 • Constant vs. rift model b = 1.75 b = 1.5 b = 1.25 b = 1.0 N. LA Beta 1.25 ≤ b≤ 2.0 b = 2 Crust Moho 30 km Subcrustal lithosphere 120 km Nunn et al 1984 Dunbar & Sawyer 1987 Aesthenosphere

  20. Thermal History: Lithospheric Stretching b = 1.25 b = 1.5 b = 1.75 Dunbar and Sawyer 1987 b = 2.0

  21. MONROE UPLIFT Surface %Ro (expected) 17067006100 Trend B 170612011700 Trend A Thermal History Late K Igneous Event SABINE UPLIFT 50 mi

  22. Moody (1949)

  23. Heat Flow History and Thermal Maturity, Monroe Uplift Late K thermal event 170670006100 (J-2) 6000 ft Optimum match between BHTs and %Ro and modeled values using rift model with Late Cretaceous thermal event

  24. Heat Flow: 170 Ma

  25. Heat Flow: 119 Ma

  26. Heat Flow: 95 Ma

  27. Heat Flow: 17 Ma

  28. Maturity Modeling • Thermal maturity (%Ro) calculated using kinetic model from LLNL • Standard type II kerogen • 1D steady-state heat flow at model base, heat transfer from conduction 170692023300

  29. Thermal History: Paleoheat Flow • Thermal maturity constrained by %Ro 170692023300 48 mW/m2, rift model, modeled maturity reasonably matches TAI and %Ro

  30. 170152087800 170812037000 171190164100 170812042100 170692007200 170692008800

  31. Calculated %Ro vs. Measured

  32. Smackover Maturity Present-day 95 Ma Present-day

  33. Hydrocarbon Generation & Expulsion Smackover: oil-prone Type II kerogen TOC data updip wells only Extrapolated downdip Ran models with range TOC

  34. OIL-WATER SYSTEM WATER-WET LITHOLOGIES 100 OIL SOURCE ROCKS Swirr K OIL INCREASINGLY MOBILE 10 TYPICAL RESERVOIRS RELATIVE PERMEABILITY: OIL/WATER PHASES EQUALLY MOBILE 1 0.1 WATER INCREASINGLY MOBILE Ex: saturation threshold = 0.20 0.01 0.7 0.4 0.0 OIL SATURATION Pepper (1991)

  35. Oil Expulsion Volumetrics 109 bbls oil

  36. Expulsed Oil Volumetrics Constant heat flow (present-day) Rift heat flow model peak expulsion (108 to 103 my) (late Early Cretaceous) TOC = 2 x RKZ Saturation Threshold = 0.15

  37. Gas Generation and Expulsion Secondary gas Primary gas Average GOR, North Louisiana = 12,500, up to 500,000 or more

  38. Expelled Gas (Primary + Secondary) TOC = 2%, saturation threshold = 0.2, rift heat flow w/ K event

  39. Timing of gas expulsion Saturation threshold = 0.2 TOC = 1% Heat flow model with rifting and late K event 1.00 0.80 Cumulative Expulsed Gas Fraction 0.60 0.40 0.20 0.00 140 120 100 80 60 40 20 0 M.a.

  40. N. LA Petroleum System 200 150 100 50 Jurassic Cretaceous Tertiary Time Scale Petroleum Systems Events E M L E L Source Rock Reservoir Rocks Overburden Rocks Uplift oil Generation-Expulsion gas Secondary Migration Trap Salt Critical Moments

  41. Conclusions • Geochemical data and basin modeling indicate that Smackover mature for oil and gas • Peak oil expulsion late Early Cretaceous, persisted into Late Cretaceous • Most gas is secondary • Peak gas expulsion early to middle Tertiary • Cumulative production accounts for less than1.0% of total expulsed volumes of oil and gas • Estimates in published literature 1-3%

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