AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Geochemical Evaluation of Eagle Ford Group Source Rocks and Oils from the First Shot Field, Texas: Implications and Applications for Appraisal of Eagle Ford Resource Plays
(1) Geochemical Consultant, Denver, CO.
(2) U. S. Geological Survey, Lakewood, CO.
Total organic carbon, Rock-Eval pyrolysis, and vitrinite reflectance analyses performed on Eagle Ford Group core and cuttings samples from the First Shot field area, Texas demonstrate these samples have sufficient quantity, quality, and maturity of organic matter to have generated oil. Furthermore, gas chromatography and biomarker analyses performed on Eagle Ford Group oils and source rock extracts as well as weight percent sulfur analyses on the oils indicate the source rock facies for most of the oils are fairly similar. Specifically, these Eagle Ford source rock facies vary in lithology from shales to marls, contain elevated levels of sulfur at lower thermal maturities, and were deposited in a marine environment under anoxic conditions. It is these First Shot Eagle Ford source facies that have generated the oils in the First Shot field. That is, most of the First Shot oils appear to have been generated locally and have not migrated into the area from long distances. However, in contrast to the generally similar source rock facies and organic matter, Eagle Ford thermal maturity varies from the early oil window to the late oil window in the study area, and these maturity variations have had a pronounced effect on both the source rock and oil characteristics. Overall, this study suggests there may be more local variations in Eagle Ford thermal maturity than have previously been recognized. Such local variations can impact Eagle Ford economics and whether the Eagle Ford will produce mostly oil or condensate and wet gas.