Some consideration about fluid substitution without shear wave velocity

Abstract

When S‐wave velocity is absent, approximate Gassmann equation using P‐wave modulus is recommended by Mavko (1995) to calculate the fluid saturation effects. Using both lab data and log data, our study shows that the approximate Gassmann equation might introduce significant error in fluid saturation effect prediction except for unconsolidated rocks. Using S‐wave velocity estimated by existing techniques, with same input parameters, the exact Gassmann equation should provide more reliable estimation of fluid saturation effect than that predicted by approximate Gassmann equation.