Shear-wave velocity estimation for calciferous sandy shale formation.

It has been found that the Xu–White method for shear-wave velocity estimation of the clay-sand model cannot yield accurate enough results for calciferous sandy shale formation. This work proposes a revised Xu–White model account for the effect of the volume of limestone in a clastic rock formation on the shear-wave velocity estimation. Based on detailed analysis of the effect of limestone volume, porosity, water saturation and pore aspect ratio on the shear-wave velocity estimation, an inversion scheme by means of the formation components analysis method is applied to obtain a better estimation of physical rock parameters, thereafter estimating the shear-wave velocity of calciferous sandy shale formation. Thus, the procedure of shear-wave velocity estimation for calciferous sandy shale formation includes calculation of physical rock parameters by the formation components analysis method as the first step, then varying the pore aspect ratio of sand, shale and lime for revising elastic parameters of dry rock continuously and, finally, estimating shear-wave velocity under constraint of the actual measured compressional-wave velocity. This method has been applied to estimate the shear-wave velocity of a calciferous sandy shale formation in Dongji Sag by means of analysis of real well logging data. The trial results suggest that the proposed model and scheme much improved the estimation accuracy of shear-wave velocity for calciferous sandy shale formations; thus, better results for reservoir and fluid prediction using pre-stack seismic data in a well-developed limestone zone can be achieved. [ABSTRACT FROM AUTHOR]