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Anomalous reflection amplitudes from fractured reservoirs—Failure of AVOA?

University of Texas at Austin, USA

F. David Lane and Douglas J. Foster

ConocoPhillips, Houston, USA

Corresponding author: F.D.Lane{at}conocophillips.com

A fractured reservoir embedded in an isotropic background is equivalent to an anisotropic medium whose symmetry depends on fracture orientation. For this configuration, a variation of PP-reflection amplitude as a function of azimuth, at a given incidence angle is often observed. Here we report on an observation of unusual amplitude behavior for reflections from the top Cadotte and Falher formations in the Lynx Field, Western Canadian Sedimentary Basin, Alberta, Canada. Formation microscanner (FMS) images suggest considerable fracturing in the shallower Cadotte interval and resistivity measurements show fracturing in the Falher zone. Interestingly, reflection amplitudes from the Cadotte do not show the expected azimuthal variation consistent with a vertically fractured medium. Reflections from the deeper Falher interval, however, do exhibit large, unexpected azimuthal variation.