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At Big Sky, Montana, in 1992, the SEG/EAEG Joint Research Committee held the summer workshop, “How useful is amplitude-versus-offset (AVO) analysis?” From the worldwide exploration examples shown during this six-day conference, the answer could clearly be stated that AVO was an integral part of recognizing and high-grading prospects and well locations.

During the Big Sky Conference, Revoir et al. (1992) and Russell et al. (1992) presented evaluations of AVO through seismic processing, modeling, and inversion utilizing the same data set from a Pliocene-trend gas field in the Gulf of Mexico. The field is located offshore in a fault basin bounded by major growth faults, and is near several salt and shale diapirs. The structure is broken up into several reservoirs by small (50–150-ft) (15-50-m) faults (Fig. 7.A.1). A 2-D amplitude analysis was performed from a 3-D seismic data sail line. A directional well that was parallel to the 2-D line provided borehole control.

The expanded sedimentary section consists of regressive sequences of deep marine deposits (including slope fans) overlain by shallower deltaic deposits (shelf, delta front and lower delta-plain deposits). The major productive sands are between 5000 and 12,000 ft (1500 and 3700 m) in depth and range in thickness from 20 to 180 ft (6 to 50 m) (Fig. 7.A.2). The high amplitudes in the figure characterize the major sand pays. In addition, flat spots and phase reversals were dominant HCI’s for recognizing the gas/water contacts. Overall, the amplitude anomalies from the three productive sands showed excellent fit to structure.

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