Changes

The Upper Cretaceous Eagle Ford Shale is the source of Austin Chalk-produced oils (Grabowski, 1995) along a trend running from central northeastern Texas to south Texas counties bordering Mexico (no. 24 in Appendix immediately following this chapter, Figure 1, shale resource systems in North America). The Eagle Ford Shale averages about 3.7 to 4.5% TOC, with an original HI of about 414 mg HC/g TOC (Grabowski, 1995), although immature roadcuts in Val Verde County, Texas, have HI values more than 600 mg/g.<ref>D. M. Jarvie, unpublished data</ref> Grabowski (1995) also estimates oil yields to be about 0.0515 m3/m3 (400 bbl/ac-ft), with values as high as 0.1547 m3/m3 (1200 bbl/ac-ft). EOG Resources currently estimates the Eagle Ford Shale play as having 1.43 times 108 m3 (900 million BOE) in their lease areas alone.<ref name=EOGResources2010 />

The Upper Cretaceous Eagle Ford Shale is the source of Austin Chalk-produced oils (Grabowski, 1995) along a trend running from central northeastern Texas to south Texas counties bordering Mexico (no. 24 in Appendix immediately following this chapter, Figure 1, shale resource systems in North America). The Eagle Ford Shale averages about 3.7 to 4.5% TOC, with an original HI of about 414 mg HC/g TOC (Grabowski, 1995), although immature roadcuts in Val Verde County, Texas, have HI values more than 600 mg/g.<ref>D. M. Jarvie, unpublished data</ref> Grabowski (1995) also estimates oil yields to be about 0.0515 m3/m3 (400 bbl/ac-ft), with values as high as 0.1547 m3/m3 (1200 bbl/ac-ft). EOG Resources currently estimates the Eagle Ford Shale play as having 1.43 times 108 m3 (900 million BOE) in their lease areas alone.<ref name=EOGResources2010 />

A geochemical database of Eagle Ford Shale demonstrates that many samples show oil crossover<ref name=Jrv2007>Jarvie, D. M., 2007, [http://wwgeochem.com/references/Jarvie-HGSMudstone2007.pdf Organic geochemical constraints on mudstone productivity]: HGS Applied Geoscience Conference (AGC) on Mudstones, October 1–2, 2007, Houston, Texas.</ref> ([[:M97Ch1.2FG10.jpg|Figure 10]]). A geochemical log of the Champlin Petroleum Co. 1-Mixon well in De Witt County, Texas, illustrates what is commonly seen in wells along the Austin Chalk trend (Figure 11). This mudstone shale-gas/shale-oil resource system contains about 60% carbonate content on average. Thus, the Eagle Ford may be more aptly described as a calcareous shale or argillaceous lime mudstone (J. A. Breyer, 2010, personal communication). The lean TOC interval from 2475 to 2510 m (8120–8235 ft) is the Austin Chalk, which shows intermittent oil crossover. The Austin Chalk is productive along this trend, and such productive zones are readily identifiable by the oil crossover effect. The Eagle Ford Shale is present below 2511.5 m (8240 ft), and the TOC increases to a high of just less than 6.00%, with carbonate contents remaining very high. Intermittent, but consistent, oil crossover occurs in various intervals of this well, for example, 2523.7 to 2542.0 m (8280–8340 ft) and especially 2546.6 to 2572.5 m (8355–8440 ft). This geochemical log is typical of almost all wells along this trend that are in the oil or early wet gas window.

A geochemical database of Eagle Ford Shale demonstrates that many samples show oil crossover<ref name=Jrv2007>Jarvie, D. M., 2007, [http://wwgeochem.com/references/Jarvie-HGSMudstone2007.pdf Organic geochemical constraints on mudstone productivity]: HGS Applied Geoscience Conference (AGC) on Mudstones, October 1–2, 2007, Houston, Texas.</ref> ([[:File:M97Ch1.2FG10.jpg|Figure 10]]). A geochemical log of the Champlin Petroleum Co. 1-Mixon well in De Witt County, Texas, illustrates what is commonly seen in wells along the Austin Chalk trend (Figure 11). This mudstone shale-gas/shale-oil resource system contains about 60% carbonate content on average. Thus, the Eagle Ford may be more aptly described as a calcareous shale or argillaceous lime mudstone (J. A. Breyer, 2010, personal communication). The lean TOC interval from 2475 to 2510 m (8120–8235 ft) is the Austin Chalk, which shows intermittent oil crossover. The Austin Chalk is productive along this trend, and such productive zones are readily identifiable by the oil crossover effect. The Eagle Ford Shale is present below 2511.5 m (8240 ft), and the TOC increases to a high of just less than 6.00%, with carbonate contents remaining very high. Intermittent, but consistent, oil crossover occurs in various intervals of this well, for example, 2523.7 to 2542.0 m (8280–8340 ft) and especially 2546.6 to 2572.5 m (8355–8440 ft). This geochemical log is typical of almost all wells along this trend that are in the oil or early wet gas window.

Some oil carryover into the remaining generation potential (Rock-Eval S2 peak) likely occurs but not sufficient to affect Tmax to any substantial amount. The Tmax values range from 440 to 450degC (824 to 842degF) (or sim0.75 to 0.95% Roe), placing the Eagle Ford Shale in this well in the peak oil-generation window.

Some oil carryover into the remaining generation potential (Rock-Eval S2 peak) likely occurs but not sufficient to affect Tmax to any substantial amount. The Tmax values range from 440 to 450degC (824 to 842degF) (or sim0.75 to 0.95% Roe), placing the Eagle Ford Shale in this well in the peak oil-generation window.