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Seismic Imaging of Producing Trend of Marathon Thrust Belt, Terrell County, Texas

Allen J. Bertagne, J. L. Pennachioni, Tim C. Leising

Exploration in the Marathon thrust belt has resulted in the discovery of three fields producing from fractured Caballos novaculite of Devonian age. The relatively shallow depth of production makes Caballos anticlines attractive targets. However, seismic data in the area are generally very poor due largely to high-amplitude coherent surface noise generated within Edwards Group limestones (Lower Cretaceous) during shooting.

In January 1986, a Vibroseis test line was shot southeast of McKay Creek field (Terrell County) with the objective of recording useable data from the thrusted section. Extensive field tests were conducted before selecting final acquisition parameters. The Wide Line Profiling (TM) technique was used to acquire three parallel lines spaced 220 ft apart. The lines were recorded and processed separately and later were stacked together to generate a "superstack" of 120 fold. The superstack shows coherent events in the shallow (thrusted) section and relatively continuous events in the deeper (subthrust) section. The productive anticlinal trend in the vicinity of McKay Creek field was found to have a distinctive seismic expression.

To facilitate seismic interpretation, a geologic field study was made of McKay Creek. The field is interpreted to consist of a (Woods Hollow) shale-cored Caballos anticline overridden by a shallower thrust that "carries" Caballos. The seismic data are interpreted to exhibit a similar structural style.

The test line appears to have successfully imaged the producing trend of the Marathon thrust belt, suggesting that it will be possible to explore this play seismically in the future.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.