ATTENUATION AND DISPERSION OF COMPRESSIONAL WAVES IN FLUID-FILLED POROUS ROCKS WITH PARTIAL GAS SATURATION (WHITE MODEL) .2. RESULTS

In this investigation, Biot's (1962) theory for wave propagation in porous solids is applied to study the velocity and attenuation fo compressional seismic waves in partially gas-saturated porous rocks. The physical model, proposed by White (1975) is solved rigorously by using Biot's equations which describe the coupled solid-fluid motion of a porous medium in a systematic way. The quantitative results presented here are based on the theory described in Dutta and Ode (1979, see below). We removed several of White's questioned approximations and examined their effects on the quantitative results. We studied the variation of the attenuation coefficient with frequency, gas saturation, and size of gas inclusions in an otherwise brine-filled rock. Anomalously large absorption (as large as 8 dB/cycle) at the exploration seismic frequency band is predicted by this model for young, unconsolidated sandstones. For a given size of the gas pockets and their spacing, the attenuation coefficient (in d/B cycle) increases almost linearly with frequency f to a maximum value and then decreases approximately as 1/square root of f. A sizable velocity dispersion (of the order of 30%) is also predicted by this model. A low gas saturation (4-6%) is found to yield high absorption and dispersion.-Authors