Roger J. Barnaby 2006 GCAGS MEETING North GOM Petroleum Systems: Modeling the Burial and Thermal History, Organic Maturation, and Hydrocarbon Generation and Expulsion Roger J. Barnaby 2006 GCAGS MEETING I plan to talk about one of the projects that I am working on at the LGS This work is being funded by the DOE, there actually are 2 complimentary projects: 3-yr study focussed on deep gas 5-yr study on oil resources Both studies involve same geographic area and same geological section, so there is considerable overlap among the two projects

Previous studies of northern GOM crude oils: composition, 13C, 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

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

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

N-S cross section from Monroe uplift south into basin Miocene Jackson Oligocene Hosston Wilcox Austin Paluxy Midway Tuscaloosa Cotton Valley Wash/Fred Mooringsport Glen Rose Sligo Smackover N-S cross section from Monroe uplift south into basin Vertical red lines represent well control, wells to south-- projected beyond TD to base Smackover based on limited seismic Unconformity top Jurassic- eroded into Cotton Valley Major unconformity top lower Cretaceous, removed up to 4500 ft of Lower Cretaceous strata, eroded down into Hosston Minor unconformities post-Austin Chalk, end Cretaceous Not modeled unconformity – early Eocene Sabine Eroded thickness estimated by projecting thickness trend updip from erosional truncation

In N. LA, up to 5000 ft Mid-Cenomanian uplift and erosion In Southern Arkansas – up to 10,000 ft Interpreted by Jackson and Laubach to reflect tectonic compression associated with Cordillerean thrust faulting

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

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

Burial History: Decompaction Remove 2 & 3 Decompact 1 t2 Add 2 Partially compact 1 t3 Add 3 Compact 2 and 1 Present-day depths y’1 3 2 1 1 3 2 1 2 y’2 1 y1 y2 Decompaction: Removes overburden, restores to original thickness using porosity-depth function Adds overburden, layer-by-layer, to reconstruct burial history

Burial History: Compacted vs Non-compacted Burial curve corrected for compaction is deeper than a non-compacted curve, although beginning and ending points same Does not change absolute degree of maturity at present day, but impacts timing of maturation, generation, and expulsion Compacted

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 Computed lithology from .las log files and mapped for each unit Using porosity-depth core data, determined porosity-depth relationships for decompaction End member lithologies Sandstone Shale Limestone Anhydrite For lithologic mixtures, computed arithmetic average for compaction parameters (initial porosity, reciprocal compaction factor)

Lithology (Upper Glen Rose)

N-S cross section from Monroe uplift south into basin Miocene Jackson Oligocene Hosston Wilcox Austin Paluxy Midway Tuscaloosa Cotton Valley Wash/Fred Mooringsport Glen Rose Sligo Smackover N-S cross section from Monroe uplift south into basin Vertical red lines represent well control, wells to south-- projected beyond TD to base Smackover based on limited seismic Unconformity top Jurassic- eroded into Cotton Valley Major unconformity top lower Cretaceous, removed up to 4500 ft of Lower Cretaceous strata, eroded down into Hosston Minor unconformities post-Austin Chalk, end Cretaceous Not modeled unconformity – early Eocene Sabine Eroded thickness estimated by projecting thickness trend updip from erosional truncation

Burial History Fastest subsidence rates late Jurassic and Early Cretaceous Deepest burial depth in early Cretaceous Mid-Cenomanian Uplift resulted in erosion of 4500 ft of Lower Cretaceous strata, incised down into Hosston Fm Tuscaloosa deposited on top of Hosston Austin and Upper Cretaceous deposited and removed Relatively slow subsidence in Late Cretaceous due to uplift Subsidence once again increased in early Paleocene Deposition shifted basinward following Eocene, hiatus

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

Burial History Fastest subsidence rates late Jurassic and Early Cretaceous Mid-Cenomanian and Late Cretaceous Uplift resulted in slower subsidence rates Subsidence increased in early Paleocene Subsidence continued through Miocene, although at slower rates Present-day depths are maximum burial depths

Thermal History Modeling formation temperature Present-day heat flow 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

Heat Flow Calculation = x Heat Flow Temperature Gradient Thermal T2-T1 (103 . deg K) W = x meters2 y2-y1 (meters) meter (103 . deg K) Heat Flow Temperature Gradient Thermal Conductivity T1, y1 Example with BHT (T2 & T1) at depths y2 & y1 Surface temp = 20deg C Steady State Heat flow = temperature gradient x thermal conductivity Used lithology-based petrophysical parameters to calculate thermal conductivity for lithology porosity temperature T2, y2

Calculated vs Measured BHTs Calculated BHTs compared to measured values Performed sensitivity analysis of thermal conductivity and compaction parameters to optimize fit between measured and calculated temperatures Calculated Heat Flow = 50 mW/m2

Thermal History: Paleoheat Flow Constant vs. rift model b = 2.0 170130026300 b = 1.75 b = 1.5 b = 1.25 b = 1.0 Using heat flow to model formation paleotemperatures Constant heat flow through time Rift model, higher heat flow post-rifting, heat flow decreases exponentially through time Rift Model: heat flow function of Beta factor (stretching and thinning of lithosphere) Beta=2, post-rifting lithosphere is half as thick as pre-rifting lithosphere Beta=1.5, post rifting lithosphere is two thirds as thick as pre-rifting lithosphere Northern LA, 1.0 < Beta < 2.0 b = 2 N. LA Beta 1.25 ≤ b ≤ 2.0 Crust Moho 30 km Subcrustal lithosphere 120 km Nunn et al 1984 Dunbar & Sawyer 1987 Aesthenosphere

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

Thermal History Late K Igneous Event SABINE UPLIFT Trend B Trend A MONROE UPLIFT 170152065500 170612011700 17067006100 170152087800 171190136200 Thermal History Late K Igneous Event SABINE UPLIFT 170692023300 Surface %Ro (expected) 17067006100 170612011700 Trend A Trend B 170692007200 50 mi

Moody (1949)

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

Heat Flow: 170 Ma

Heat Flow: 119 Ma

Heat Flow: 95 Ma

Heat Flow: 17 Ma

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 Maturity modeled as kinetic reaction, dependent on time and temperature Used LLNL kinetic parameters and equations for Type II marine kerogen 170692023300

Thermal History: Paleoheat Flow Thermal maturity constrained by %Ro 170692023300 Measured vitrinite data in 42 wells used to constrain modeled thermal maturity Fit between measured and modeled compared 48 mW/m2, rift model, modeled maturity reasonably matches TAI and %Ro

171190164100 170152087800 170812037000 170812042100 170692008800 170692007200

Calculated %Ro vs. Measured Modeled maturity compared with measured %Ro Considerable scatter, although best fit shows 1:1 relationship, indicating that not consistently overunderestimating or underestimating maturity

Smackover Maturity Present-day 95 Ma Present-day

Hydrocarbon Generation & Expulsion Smackover: oil-prone Type II kerogen TOC data updip wells only Extrapolated downdip Ran models with range TOC Hydrocarbon generation and expulsion models require initial TOC content TOC data from Smackover limited to updip well penetrations. TOC values extrapolated downdip beneath reach of well penetrations using a general relationship between depositional water depth and TOC content

WATER-WET LITHOLOGIES 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 Relative perm for oil-water system in water-wet lithologies. Curves are shifted clockwise with decreasing absolute permeability (K) and increasing irreducible water saturation (Swirr). At oil saturation of 20% (example critical threshold saturation for expulsion from source rock), relative perm to oil greater than relative perm to water and oil will flow. However, no relative perm data available for oil source rocks, due to low perm and high Swirr. 0.1 WATER INCREASINGLY MOBILE Ex: saturation threshold = 0.20 0.01 0.7 0.4 0.0 OIL SATURATION Pepper (1991)

Oil Expulsion Volumetrics Source rock TOC and Saturation Threshold major variables impacting hydrocarbon volumes Maximum estimate of TOC values using water depth/TOC function For a set of given TOC values, saturation threshold major impact on oil volumetrics, followed by heat flow 109 bbls oil

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

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

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

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 M.a.

Generation-Expulsion 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

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%