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

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

S3: CO2 from spent kerogen HI (Hydrogen Index) = (S2/TOC).100 OI (Oxygen Index) = (S3/TOC).100 PI (Production Index = S1/(S1+S2) Tmax: 400-430o immature 435-450o 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

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

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

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

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

(“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

debris flow 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)

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

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

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.

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).

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)