The Eagle Ford Shale Outcrop Studies Related to the Oil and

Gas Potential of a Major Unconventional Reservoir.

Brian E. LockUniversity of Louisiana, LafayettePrepared for LGS meeting, September 21, 2011

Lauren Peschier and Nick Whitcomb (UL graduate students) contributed to the study

Outline

• Resource Plays and the Eagle Ford

• Stratigraphy and Sedimentology of the Outcrops

• Application of the Outcrops to Understanding the Eagle Ford Resource Play

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

S1: existing hydrocarbons

S2: kerogen

S3: CO2 from spent kerogen

S3

Tmax

S1: existing hydrocarbons

S2: kerogen

S3: CO2 from spent kerogen

S3Values as mg/gm of sample: if S1 >1 mg/g = oil show if S2 > 5 mg/g = good source rock

HI (Hydrogen Index) = (S2/TOC).100OI (Oxygen Index) = (S3/TOC).100PI (Production Index = S1/(S1+S2)

Tmax: 400-430o immature435-450o oil zone>450o overmature

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

resource shales

REGIONALSTRATIGRAPHYEagle Ford and Austin considered

a single reservoir unit

MaverickBasinDelaware/Rio Grande

Aulacogen

Lower Cretaceous reef tr

end

Edwards reef

Sligo reef

Delaware Basin

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.

Maverick BasinEagle Ford

Lower CretaceousReef Trend Eagle Ford

Delaware Basin

Delaware/Rio GrandeAulacogen

Rio Grande Embayment

field areaEF outcrops

Lozier Canyon

The field study area – Eagle Ford outcrops

Outcrop Q

Outcrop G

Outcrop D

Not present in the subsurface

Lower member(“facies A” of BP workers).

unstable slope deposits;slump foldsdebris flows

turbiditetraction deposits - ? contourites

Lowstand Systems Tract

debris flow

debris flow

Ash/turbidite marker bed extends from Comstock to Lozier Canyon (about 40 miles)

Buda Formation

ash/turbidite

debris flowclast

New LGSVice-President

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 inlower member

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.

kaolinite

dolomite

The productive interval (lower Eagle Fordin the subsurface)

limestone“shale” (marlstone)

limestone

upper beds of middle member (more calcareous)

Road cut G-1

Middle member (productive interval) in outcrop

upper membermiddle member

lowest chalky limestone

Road cut G-2

Lozier Canyon – bluffs expose full Eagle Ford section

Lozier Canyon section

Austin Chalk

middle member

upper member

Lower member (obscured)

Buda Limestone

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

lower beds,middle member

upper beds, middle member

2,000 ft long outcrop in same stratigraphic interval shows lateral consistency.

Note: most of the outcrop is weathered (oxidized iron).

Road cut Q

grey patina (result of last 30 yearssince road-cut was made)

black colorof fresh

rock

Note laminae that pinch out – evidence for bottom currents (hyperpycnal flow)

Parasequences in highway outcrop, middle member

Parasequences in a core gamma raylog, from a Petrohawk well.

10 ft

carbonate factoryhyperpycnal flow

marine snow

flocculation, pelletizationsea level fluctuation

hundredsof feet

few feet

clayCaCO3

depth

terrigenous clay and silt, suspended carbonate mud

shoaling

parasequence 1 parasequence 1

parasequence 2 parasequence 2

mfsmfs

Is the limestone the base or the top of the parasequence?

water

Deep water sedimentation and parasequencesWhat controls limestone/shale alternations? Eustasy? Climate? Tectonics?

or periodic gravity flows from unstable platform margin?

deep water traction currents(meteorological? geostrophic?)

limestone – brittlemarl (“shale”) - ductile

Includes possible hypopycnal flow

Smaller scale cycles – result of climate/sea level variations or individual hyperpycnal flows?

Core photos from Petrohawk core with permission

Graded bed – white dots are planktic forams

Inoceramid fragments

Note evidence of current action

copepod

fecal pellet

Evaluating the Eagle Ford outcrops• Original organic richness and generation

potential– Kerogen type

• Rock-Eval analyses Oil prone

Evaluating the Eagle Ford outcrops• Original organic richness and generation

potential– TOC values (determine TOCo?)

Blue: data from BP study (Donovan et al., 2011). Red: from UL study

Maturity

• TTI – estimate of time/temperature burial history. Not currently available

• Ro – vitrinite reflectance - microscopy

• Evolution on Van Krevelen plot (Kerogen Transformation Ratio – KTR) – from Rock Eval

• Tmax – from Rock Eval

• Production Index – from Rock Eval

Van Krevelen Diagram

modifiedVan Krevelen Diagram

Kerogen Transformation

Evaluating the Eagle Ford Outcrops• Maturation Close to, but not yet in oil window

Tmax fromLozier Canyonsamples (UL).

No Ro or TTIdata

available

Vitrinite Reflectance (Ro) data

• Performed by USGS (Mark Pawlewicz) via Russ Dubiel, on US Hwy 90 samples.

• Essentially no vitrinite, only solid bitumen (two generations? – Ro values around 0.6 and a second bitumen from external source with higher Ro)

Evaluating the Eagle Ford outcrops

• Retention of oil/gas in the resource reservoir– Gas adsorption and free oil and gas

• Oil types in the First Shot Field (Austin Chalk)(Corbet 2010) and general sourcing of other Cretaceous reservoirs from Eagle Ford demonstrates migration from the Eagle Ford

–

Natural fractures

• Indicate brittleness (good!)• May have already permitted hydrocarbon

primary migration out of the reservoir (not so good!). – Experience in the Barnett Shale indicates that

areas that are most highly fractured are less productive

• Distinguish open fractures from calcite filled fractures

Core photos from Petrohawk core with permission

Evaluating the Eagle Ford outcrops

• Porosity– Increases with maturation and hydrocarbon

generation

EM images, following Argon milling: Barry Wawak, Core Labs

Note quantities of organic material (om), but Ro data unsatisfactory

Evaluating the Eagle Ford outcrops

• Brittleness – Mineral composition

• Quartz• Carbonates• Clays

UL samples from Hwy 90, analyzed by Core Lab (Barry Wawak)

Our data from Lozier Canyon

THANKS!• The following ran samples for me or paid to have them run:

– Barry Wawak, Core Labs– Russ Dubiel, USGS– Bruce Hart, ConocoPhillips

• The following supported my graduate students (Lauren Peschier, Nick Whitcomb) with grants:– GCAGS, GCSSEPM, STGS

• The following helped in the field:– Dr. Vicky Hover, Ashley Fife, Natasha Jeansonne, Rob Glaser, Aaron

Summerfield

• Dr. Art Donovan (BP) provided access to the Lozier Canyon outcrops• Mr. Billy Foster allowed us to access his land (Old Hiway road cut)