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South Tisdale Gas Field, Sacramento Basin, California: Discovery by Use of Seismic Amplitude Variation with Offset Analysis

Frank E. Weagant, Robert H. Sterling

The South Tisdale gas field is located on the eastern flank of the central Sacramento basin of California. The field was discovered in June 1986 by Nahama and Weagant Energy Company using seismic data concentrating on analysis of amplitude variation with offset in conjunction with subsurface data. The producing intervals, the Upper Cretaceous Forbes sands and the "G" zone Guinda sands, were deposited as fine-grained turbidite sands bounded by shales. Seismic bright spots observed in the Forbes interval can be caused by several materials, ranging from bentonites to gas sands. Amplitude-with-offset analysis was employed to high grade the bright spots to locate the "gas response" signature. The discovery well was drilled between two dry holes, 2,000 ft apart, where an amplit de-with-offset seismic anomaly developed in the lower Forbes interval. All subsequent development wells have been drilled on such anomalies, resulting in four successful wells and one in progress as of this writing. Synthetic seismograms were made from each well to integrate the subsurface data into the seismic data. Additional proprietary seismic lines have been acquired and reviewed, revealing more anomalies to be tested. The amplitude-with-offset analysis, integrated with subsurface data, has resulted in a significant gas discovery.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.