1. 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

2. 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

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. 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

6. 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

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

9. 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

10. 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

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
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)

12. Lithology (Upper Glen Rose)

13. 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

14. 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

15. 2 Jackson Miocene Oligocene Wilcox Austin Hosston Midway Mooringsport
Wash/Fred
Cotton Valley
Glen Rose
Sligo
Tuscaloosa
Smackover

16. 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

17. 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

18. 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

19. 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

20. Thermal History: Paleoheat Flow
Constant vs. rift model
b = 2.0
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

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

22. Thermal History Late K Igneous Event SABINE UPLIFT Trend B Trend A
MONROE UPLIFT
Thermal History
Late K Igneous Event
SABINE UPLIFT
Surface %Ro (expected)
Trend A
Trend B
50 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
Maturity modeled as kinetic reaction, dependent on time and temperature
Used LLNL kinetic parameters and equations for Type II marine kerogen

30. Thermal History: Paleoheat Flow
Thermal maturity constrained by %Ro
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

32. 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

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

34. 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

35. 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)

36. 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

37. 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

38. Gas Generation and Expulsion
Secondary gas
Primary 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. 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.

41. 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

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%