Inversion of Shear Wave Anisotropic Parameters in Strongly Anisotropic Formations

Abstract

Deepwater reservoirs use highly deviated wells to reduce cost and enhance hydrocarbon recovery. Due to the strong anisotropic nature of many of the marine sediments, anisotropic seismic imaging and interpretation can improve reservoir characterization. Sonic logs acquired in these wells are strongly dependent on well deviations. Cross-dipole sonic logging provides apparent shear wave anisotropy in deviated wells, which can be far from the truth. Although anisotropic parameters have been successfully obtained using data from wells of several deviations or using single well data based on weak anisotropy approximation, estimation of strong shear wave anisotropy from single well data remains a challenge. Using sensitivity analysis, we find Stoneley wave velocity has good sensitivity to qSV and SH wave velocities in deviated wells. We create a linear inversion scheme to estimate shear wave anisotropy using SH, SV, and Stoneley wave velocities logged in one well. We first apply the method to laboratory measurements from boreholes of various deviations relative to the symmetry axis of an anisotropic material. We then apply the method to a field data set acquired in a deviated well. We also compute the vertical and horizontal shear wave velocity logs in this well using the inverted elastic shear wave constants.