H.W. Swan (Phillips Alaska, Inc.)
Seismic amplitude variation with offset (AVO) is a particularly leveraging technique in North Slope oil and gas exploration, where the reservoir presence and quality are the greatest risks. However, the arctic environment also introduces unique data quality problems, which must be overcome before AVO can be measured quantitatively. This talk focuses a method which normalizes and corrects seismic time, phase and amplitude variations with offset. These variations are caused by ice lakes, permafrost variations and other subsurface geology. The method first applies an ensemble automatic gain control, which corrects the time-varying amplitudes of individual gathers as a whole, but preserves their AVO. Raw AVO intercept and gradient traces are then computed and destretched to remove offset-dependent tuning. The intercepts and gradients are cross-correlated to estimate the background reflectivity. Corrections are then made to the gradients to force them to conform to an area-wide background standard. Seismic events which deviate significantly from the background are by definition “anomalies,” and can be further classified according to their location in the intercept-gradient plane. This classification helps to determine reservoir quality and fluid type. Product indicators classify AVO anomalies in a phase-independent manner. Results from producing fields will be shown.
AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.