Abstract: Imaging Through a Badly Weathered Near-Surface: A Case History at Elk Hills

BAILEY, BILL, CGG, Houston, TX; JACK WEYER, CGG, Houston, TX; GUILLAUME CAMBOIS, CGG Calgary, Calgary, Alberta; JOEL SCOTT, Occidental of Elk Hills, Inc, Tupman, CA; NEVILLE MANDERSON, Occidental Bakersfield, Bakersfield, CA; MIKE FENTON, Occidental Bakersfield, Bakersfield, CA

Seismic exploration over the Elk Hills field, San Joaquin Valley, California has historically been unsuccessful. The lack of seismic response was blamed on a particularly complex weathered zone that corresponds to the outcropping of the Tulare Formation. The topography is so rough that conventional refraction static methods fail to provide a decent solution.

A 1998 acquisition test at Elk Hills has showed that the adverse near-surface conditions can be attributed to a badly weathered outcropping formation. The main problem associated with this weathered zone is the generation of large short- and long-wavelength static shifts. Rough topographies can be handled by applying elevation statics before refraction, but this is only valid if the weathered layer is uniform. To solve this problem, we developed an innovative static solution named Refraction from Floating Datum (RFD). This approach applies elevation corrections with respect to a floating datum, and then computes a refraction from this floating datum. As a result of this process, the Elk Hills exploration team was able to see a seismic image of the producing reservoirs for the first time. Petrophysical Properties and OOIP from a Predominantly Old E-log Suite, Huntington Beach Field, California.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California