Robust AVO Processing for Arctic Exploration
By
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.