SHEAR‐WAVE VELOCITY ESTIMATION IN POROUS ROCKS: THEORETICAL FORMULATION, PRELIMINARY VERIFICATION AND APPLICATIONS¹

A bstract Shear‐wave velocity logs are useful for various seismic interpretation applications, including bright spot analyses, amplitude‐versus‐offset analyses and multicomponent seismic interpretations. Measured shear‐wave velocity logs are, however, often unavailable. We developed a general method to predict shear‐wave velocity in porous rocks. If reliable compressional‐wave velocity, lithology, porosity and water saturation data are available, the precision and accuracy of shear‐wave velocity prediction are 9% and 3%, respectively. The success of our method depends on: (1) robust relationships between compressional‐ and shear‐wave velocities for water‐saturated, pure, porous lithologies; (2) nearly linear mixing laws for solid rock constituents; (3) first‐order applicability of the Biot–Gassmann theory to real rocks. We verified these concepts with laboratory measurements and full waveform sonic logs. Shear‐wave velocities estimated by our method can improve formation evaluation. Our method has been successfully tested with data from several locations.