1. The Eagle Ford Shale Outcrop Studies Related to the Oil and Gas Potential of a Major Unconventional Reservoir.
Brian E. Lock
University of Louisiana, Lafayette
Prepared for LGS meeting, September 21, 2011
Lauren Peschier and Nick Whitcomb (UL graduate students) contributed to the study

2. Outline Resource Plays and the Eagle Ford
Stratigraphy and Sedimentology of the Outcrops
Application of the Outcrops to Understanding the Eagle Ford Resource Play

3. Keys to a Successful Resource Play
Original organic richness and generation potential
Kerogen type (from Rock-Eval analysis)
TOC values (determine TOCo?)
Maturation (includes primary and secondary cracking) Ro
Tmax (from Rock-Eval analysis)
TTI

4. S3: CO2 from spent kerogen
S2: kerogen
Tmax
S1: existing
hydrocarbons S3
S3: CO2 from spent kerogen

5. S3: CO2 from spent kerogen
HI (Hydrogen Index) = (S2/TOC).100
OI (Oxygen Index) = (S3/TOC).100
PI (Production Index = S1/(S1+S2)
Tmax: o immature
o oil zone
>450o overmature
S2: kerogen
S1: existing
hydrocarbons S3
S3: CO2 from spent kerogen
Values as mg/gm of sample:
if S1 >1 mg/g = oil show
if S2 > 5 mg/g = good source rock

6. Keys to a Successful Resource Play (continued)
Retention of oil/gas in the resource reservoir
Gas adsorption and free oil and gas, vs. primary migration
Porosity
Increases with maturation and hydrocarbon generation
Brittleness
Mineral composition (from X-Ray Diffraction analysis)
Quartz
Carbonates
Clays
Open natural fractures (not cemented) or hydraulically fractured during stimulation
(note – reservoir quality lower in areas of greater open fractures)
Jarvie et al., AAPG Bulletin, 2007

7. REGIONAL STRATIGRAPHY
resource shales
REGIONAL STRATIGRAPHY
Eagle Ford and Austin considered
a single reservoir unit

8. Maverick Basin Eagle Ford has different tectonic, thermal and
Notes:
Maverick Basin Eagle Ford has different tectonic, thermal and
diagenetic history from the Reef Trend Eagle Ford, and is thick
and over-pressured. Thermally mature rocks have been uplifted.
Delaware
Basin
Delaware
Basin
Lower Cretaceous reef trend
Rio Grande Embayment
Maverick
Basin
Edwards reef
Delaware/Rio Grande
Aulacogen
Delaware/Rio Grande
Aulacogen
field area
EF outcrops
Sligo reef
Maverick Basin
Eagle Ford
Lower Cretaceous
Reef Trend Eagle Ford

9. The field study area – Eagle Ford outcrops
Outcrop D
Outcrop G
Lozier Canyon
Outcrop Q
The field study area – Eagle Ford outcrops

10. (“facies A” of BP workers). unstable slope deposits;
Lower member
(“facies A” of BP workers).
unstable slope deposits;
slump folds
debris flows
turbidite
traction deposits - ? contourites
Lowstand Systems Tract
Not present in the subsurface

12. debris flow
debris flow

13. Ash/turbidite marker bed extends from Comstock to Lozier Canyon (about 40 miles)
clast
debris flow
ash/turbidite
New LGS
Vice-President
Buda Formation

14. Sources of authigenic kaolinite (and silica)?
numerous ash beds throughout the Eagle Ford are composed almost entirely of kaolinite (possible source of diagenetic silica)
ash bed in
lower member

15. kaolinite
dolomite
Authigenic dolomite and kaolinite filling vug in lower member. Note: dolomite
(and de-dolomite) rhombs are almost universally present in Cretaceous carbonates in
southwest Texas.

16. The productive interval (lower Eagle Ford
in the subsurface)

17. Middle member (productive interval) in outcrop
Road cut G-1
upper beds of middle member (more calcareous)
limestone
“shale” (marlstone)
limestone
Middle member (productive interval) in outcrop

19. lowest chalky limestone
Road cut G-2
lowest chalky limestone
upper member
middle member

20. Lozier Canyon – bluffs expose full Eagle Ford section

21. Lozier Canyon section Austin Chalk upper member middle member
Lower member (obscured)
Buda Limestone

22. Lozier Canyon middle member:
rock is fresh because of stream
undercutting the bluff.

23. Note: most of the outcrop is weathered (oxidized iron).
2,000 ft long outcrop in same stratigraphic interval shows lateral consistency.
Road cut Q
upper beds, middle member
lower beds,
middle member
Note: most of the outcrop is weathered (oxidized iron).

24. grey patina (result of last 30 years since road-cut was made)
black color
of fresh
rock
grey patina (result of last 30 years
since road-cut was made)
Note laminae that pinch out – evidence for bottom currents (hyperpycnal flow)