--> Application of Geochemistry to Exploration in the Austin Chalk, First Shot Field Area, Gonzales County, Texas, by J. D. Edman; #90986 (1994).

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Abstract: Application of Geochemistry to Exploration in the Austin Chalk, First Shot Field Area, Gonzales County, Texas

Janell D. Edman

Geochemical data were used to help evaluate the exploration potential of the Austin Chalk in the First Shot field area, Gonzales County, Texas. This evaluation included both source rock and oil-source/oil-oil correlation analyses. Specifically, total organic carbon, Rock-Eval pyrolysis, pyrolysis-gas chromatography and visual kerogen/vitrinite reflectance analyses were performed on core samples of Austin Chalk marls and on core and cuttings samples of the underlying Eagle Ford Shale to assess source potential in these units. In addition, sterane and terpane biomarkers were used to further identify the source for oils produced in the area.

Results of these analyses demonstrate that in the First Shot field area the thin Austin Chalk marls are typically organic lean with at best minimal source capacity. Instead, of the 17 oils analyzed, 13 are sourced solely out of the Eagle Ford and the other four are mixtures of Austin and Eagle Ford liquids. Recognition of the Eagle Ford as the dominant source has significant implications for exploration in the First Shot field area. Previously most drilling had targeted the thick, fairly clean chalk of the Austin "C" zone. However, identification of source beneath the Austin opens up exploration possibilities in the deeper Austin "D" zone as well as in the Eagle Ford itself. This is particularly true of "D" and Eagle Ford intervals that have been extensively fractured. In some instanc s, the potential for deeper production might alter drilling economics and make certain areas more attractive.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994