North GOM Petroleum Systems: Modeling the Burial and Thermal History, Organic Maturation, and Hydrocarbon Generation and Expulsion

Transcription

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, 13 C, document Type II algal kerogen in Smackover major source Objectives 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

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 CRETACEOUS SHELF MARGIN 50 mi

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

5 Hosston Wilcox Miocene Oligocene Cotton Valley

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7 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

8 depth (ft) Porosity-Depth Relationships 0 porosity Limestone Shale Exponential Compaction f = f 0 exp (-Kz) Sandstone Where: f = porosity f 0 = Initial porosity K = compaction factor z = depth 20000

9 depth (ft) Burial History: Decompaction Present-day depths 3 t1 Remove 2 & 3 Decompact 1 1 y 1 y 2 t2 Add 2 Partially compact 1 2 t3 Add 3 Compact 2 and y 1 y 2 1 porosity

10 Burial History: Compacted vs Non-compacted Depth (ft) Time (Ma) Non-compacted Compacted

11 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

12 Lithology (Upper Glen Rose)

13 Hosston Wilcox Miocene Oligocene Cotton Valley

14 Burial History

15 2 Miocene Oligocene Hosston Wilcox Cotton Valley

16 Burial History

17 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 = 20 o C Thermal conductivity Porosity and lithology are major variables controlling thermal conductivity In-situ thermal conductivity computed by BasinMod

18 Heat Flow Calculation W meters 2 = T 2 -T 1 (10 3. deg K) y 2 -y 1 (meters) x W meter (10 3. deg K) T 1, y 1 Heat Flow Temperature Gradient Thermal Conductivity T 2, y 2

19 Calculated vs Measured BHTs BHTs Calculated Heat Flow = 50 mw/m 2

20 Thermal History: Paleoheat Flow Constant vs. rift model Heat Flow (mw/m2) b = b = b = 1.5 b = Litho=120 Litho=96 Litho=80 Litho=68 Litho=60 b = Time (Ma) Moho b = 2 Crust Aesthenosphere Subcrustal lithosphere 30 km 120 km N. LA Beta 1.25 b 2.0 Nunn et al 1984 Dunbar & Sawyer 1987

21 Thermal History: Lithospheric Stretching b = 1.25 Dunbar and Sawyer 1987 b = 2.0

22 MONROE UPLIFT Depth (ft) Thermal History Late K Igneous Event %Ro (measured) Surface %Ro (expected) mi

23 Moody (1949)

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

25 Heat Flow: 170 Ma

26 Heat Flow: 119 Ma

27 Heat Flow: 95 Ma

28 Heat Flow: 17 Ma

29 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

30 48 mw/m2, rift model, modeled maturity reasonably matches TAI and %Ro Thermal History: Paleoheat Flow Thermal maturity constrained by %Ro

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32 %Ro (calc) Calculated %Ro vs. Measured y = x R 2 = %Ro (meas)

33 Smackover Maturity Present-day 95 Ma Present-day

34 N Hydrocarbon Generation & Expulsion Smackover: oil-prone Type II kerogen TOC data updip wells only Extrapolated downdip Ran models with range TOC TOC (%)

35 RELATIVE PERMEABILITY: OIL/WATER 100 OIL-WATER SYSTEM WATER-WET LITHOLOGIES 10 K Sw irr OIL SOURCE ROCKS OIL INCREASINGLY MOBILE 1 PHASES EQUALLY MOBILE 0.1 Ex: saturation threshold = 0.20 WATER INCREASINGLY MOBILE OIL SATURATION Pepper (1991)

36 Oil Expulsion Volumetrics 10 9 bbls oil

37 cum. billion bbls Expulsed Oil Volumetrics Constant heat flow (present-day) Series1 Series4 Rift heat flow model 500 peak expulsion (108 to 103 my) (late Early Cretaceous) M.a. TOC = 2 x RKZ Saturation Threshold = 0.15

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

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

40 Cumulative Expulsed Gas Fraction Timing of gas expulsion Saturation threshold = 0.2 TOC = 1% Heat flow model with rifting and late K event M.a

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

42 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 than 1.0% of total expulsed volumes of oil and gas Estimates in published literature 1-3%