The Eagle Ford Shale Outcrop Studies Related to

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

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

S 2: kerogen Tmax S 1: existing hydrocarbons S 3: CO 2 from spent kerogen

HI (Hydrogen Index) = (S 2/TOC). 100 OI (Oxygen Index) = (S 3/TOC). 100 PI (Production Index = S 1/(S 1+S 2) S 2: kerogen Tmax: 400 -430 o 435 -450 o >450 o S 1: existing hydrocarbons immature oil zone overmature S 3: CO from spent S Values as mg/gm 3 of sample: kerogen 2 if S 1 >1 mg/g = oil show if S 2 > 5 mg/g = good source rock

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 REGIONAL STRATIGRAPHY Eagle Ford and Austin considered a single reservoir unit

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 o Ri Gr de an o ce a t re Em ba r we en ym Maverick Basin t Delaware/Rio Grande field area Delaware/Rio Grande Aulacogen EF outcrops Aulacogen Maverick Basin Eagle Ford rds Edwa reef r us en r t f d ee C Lo ef o re Slig Lower Cretaceous Reef Trend Eagle Ford

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

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

debris flow

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

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

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.

The productive interval (lower Eagle Ford in the subsurface)

Road cut G-1 ous) r (more calcare e b m e m le d id per beds of m up limestone) “shale” (marl limestone Middle member (productive interval) in outcrop

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

Lozier Canyon – bluffs expose full Eagle Ford section

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

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

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).

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