Transcript Slide 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 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 S2: kerogen Tmax S1: existing hydrocarbons S3 S3: CO2 from spent kerogen HI (Hydrogen Index) = (S2/TOC).100 OI (Oxygen Index) = (S3/TOC).100 PI (Production Index = S1/(S1+S2) S2: kerogen Tmax: 400-430o 435-450o >450o S1: existing hydrocarbons immature oil zone overmature S3: CO from spent S Values as mg/gm3of sample: kerogen 2 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 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 Delaware Basin Maverick Basin Delaware/Rio Grande field area Delaware/Rio Grande Aulacogen EF outcrops Aulacogen Maverick Basin Eagle Ford 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 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 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)