Lithology prediction and subsurface analysis using anisotropic inversion

Analysis of VTI anisotropy in Gabon demonstrates the ability to link the parameter η with subsurface information. The method is primarily useful in delineating sand-shale distribution. Calibrating η with shale properties also suggests the ability to map regional shale seal layers, and data indicate the possibility of noting shale alteration related to vertical hydrocarbon migration. The approach uses the inversion method developed by Alkhalifah for determining anisotropy from surface seismic based on analysis of nonhyperbolic moveout in cdp gathers. The output of the inversion is compared with lithology and subsurface properties at several well locations in Gabon to calibrate the anisotropic output, and the analysis is carried out at intersecting 2D lines shot with very different acquisition parameters and orientation to verify the robustness of the procedure. Application of the method provides yet another parameter that can be extracted from surface seismic data to aid in delineating reservoir and hydrocarbon distribution.