Application of shear wave estimation based on Poisson's ratio model in Block T of the eastern margin of the Pre-Caspian Basin

Zhang Yiqiong; Sun Lianju; Wang Zhen; Ji Zhifeng; Sheng Shanbo; Jiang Ren; Lin Yaping

doi:10.19987/j.dzkxjz.2024-110

Abstract：The inversion of pre-stack wave impedance is closely related to the parameters such as incident angle,P-wave velocity,S-wave velocity,and density.Compared to post-stack inversion,the inclusion of both P-to S-wave velocities allows for the derivation of more comprehensive elastic parameters.This enhances the ability to differentiate lithology and hydrocarbon-bearing formations,providing a more accurate foundation for drilling decisions.Shear-wave velocity data are particularly critical for pre-stack impedance inversion.However,in the T block,only one set of S-wave logging data is available,and its reliability is uncertain due to factors such as mud invasion.As a result,accurately estimating shear-wave velocity especially its hydrocarbon-sensitive variations are a crucial step in elastic parameter inversion for pre-stack analysis.Given the characteristics of the main target formations,KT-Ⅰ and KT-Ⅱ,in the T block,porous carbonate reservoirs with strong heterogeneity,this study proposes a shear-wave velocity estimation method based on an empirical Poisson's ratio model.This approach effectively enhances the sensitivity of pre-stack seismic attributes to hydrocarbons.Through test processing,parameters of the Poisson's ratio-based estimation model were selected to the geological conditions of the T Block.A reservoir-sensitive threshold for the vP/vS ratio was identified as 1.8.Based on the vP/vS parameters of KT-ⅡG formation,the thickness of effective reservoir is predicted.The predicted thickness is more than 85％consistent with well verification,which provides a strong support for exploration and evaluation of well location deployment.