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 TOC o ?) Maturation (includes primary and secondary cracking) – R o – T max (from Rock-Eval analysis) – TTI

S1: existing hydrocarbons S2: kerogen S3: CO 2 from spent kerogen S3S3 T max

S1: existing hydrocarbons S2: kerogen S3: CO 2 from spent kerogen S3S3 Values 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).100 OI (Oxygen Index) = (S3/TOC).100 PI (Production Index = S1/(S1+S2) Tmax: o immature o oil zone >450 o 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 REGIONAL STRATIGRAPHY Eagle Ford and Austin considered a single reservoir unit

Maverick Basin Delaware/Rio Grande Aulacogen Lower Cretaceous reef trend 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 Basin Eagle Ford Lower Cretaceous Reef Trend Eagle Ford Delaware Basin Delaware/Rio Grande Aulacogen Rio Grande Embayment field area EF 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 folds debris flows turbidite traction deposits - ? contourites Lowstand Systems Tract

debris flow

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

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

upper member middle 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 years since road-cut was made) black color of fresh rock Note laminae that pinch out – evidence for bottom currents (hyperpycnal flow)