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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.

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Presentation on theme: "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."— Presentation transcript:

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

2 Outline Resource Plays and the Eagle Ford Stratigraphy and Sedimentology of the Outcrops Application of the Outcrops to Understanding the Eagle Ford Resource Play

3 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

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

5 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

6 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

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

8 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

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

10 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

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12 debris flow

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

14 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

15 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

16 The productive interval (lower Eagle Ford in the subsurface)

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

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

20 Lozier Canyon – bluffs expose full Eagle Ford section

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

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

23 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

24 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)

25 Parasequences in highway outcrop, middle member

26 Parasequences in a core gamma ray log, from a Petrohawk well. 10 ft

27 carbonate factory hyperpycnal flow marine snow flocculation, pelletization sea level fluctuation hundreds of feet few feet clay CaCO 3 depth terrigenous clay and silt, suspended carbonate mud shoaling parasequence 1 parasequence 2 mfs Is the limestone the base or the top of the parasequence? water Deep water sedimentation and parasequences What controls limestone/shale alternations? Eustasy? Climate? Tectonics? or periodic gravity flows from unstable platform margin? deep water traction currents (meteorological? geostrophic?) limestone – brittle marl (“shale”) - ductile Includes possible hypopycnal flow

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

29 Core photos from Petrohawk core with permission Graded bed – white dots are planktic forams Inoceramid fragments Note evidence of current action

30 copepod fecal pellet

31 Evaluating the Eagle Ford outcrops Original organic richness and generation potential – Kerogen type Rock-Eval analyses Oil prone

32 Evaluating the Eagle Ford outcrops Original organic richness and generation potential – TOC values (determine TOC o ?) Blue: data from BP study (Donovan et al., 2011). Red: from UL study

33 Maturity TTI – estimate of time/temperature burial history. Not currently available R o – vitrinite reflectance - microscopy Evolution on Van Krevelen plot (Kerogen Transformation Ratio – KTR) – from Rock Eval T max – from Rock Eval Production Index – from Rock Eval

34 Van Krevelen Diagram modified Van Krevelen Diagram Kerogen Transformation

35 Evaluating the Eagle Ford Outcrops Maturation Close to, but not yet in oil window T max from Lozier Canyon samples (UL). No R o or TTI data available

36 Vitrinite Reflectance (R o ) data Performed by USGS (Mark Pawlewicz) via Russ Dubiel, on US Hwy 90 samples. Essentially no vitrinite, only solid bitumen (two generations? – R o values around 0.6 and a second bitumen from external source with higher R o )

37 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 –

38 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

39 Core photos from Petrohawk core with permission

40 Evaluating the Eagle Ford outcrops Porosity – Increases with maturation and hydrocarbon generation

41 EM images, following Argon milling: Barry Wawak, Core Labs Note quantities of organic material (om), but R o data unsatisfactory

42 Evaluating the Eagle Ford outcrops Brittleness – Mineral composition Quartz Carbonates Clays UL samples from Hwy 90, analyzed by Core Lab (Barry Wawak)

43 Our data from Lozier Canyon

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45 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)


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