The signature of shear-wave splitting: Theory and observations on heavy oil data

Abstract

The use of shear-wave splitting analysis as a tool for fracture analysis is well established. In this article, we discuss the analysis of shear-wave splitting in a relatively new context—shallow heavy oil plays where we believe stress is the dominant cause of the shear-wave splitting, rather than macroscale fracturing. There is clear laboratory evidence in the literature for shear-wave splitting caused by differential stress, which we believe supports this viewpoint. We are particularly interested in the use of shear-wave splitting technology for monitoring reservoir stress changes which correlate with thermal production for heavy oil reservoirs. This article also takes a fresh look at some well-established characteristics of split shear waves as they appear in wide-azimuth multicomponent data, and in particular the relative merits of the radial and transverse amplitude signatures. We describe a recently developed method, which combines both radial and transverse analysis to improve the effective azimuthal coverage. This approach is beneficial when the survey has been coarsely acquired, as we demonstrate on a heavy oil example. The article concludes with a case study at Kerrobert, a reservoir in the Canadian heavy oil region where thermal recovery methods are in use, and where shear-wave splitting is being utilized to help characterize the resulting stress changes in the reservoir.