Huge wave attenuation in partially saturated fractured reservoirs

Abstract

A conceptually simple superposition model is presented for dispersion and attenuation of compressional waves in fractured porous rocks that are saturated by a mixture of liquid and gas. These two different types of heterogeneities are described by four parameters: The fracture spacing (fracture density) and fracture weakness characterizing the fractured medium; the correlation length and degree of saturation characterizing the fluid patches that are embedded between the fractures. All four controlling parameters have a clear physical meaning and can be potentially constrained if there is additional information like well-log data. This model is employed to explain the relatively strong P-wave velocity dispersion found for a limestone reservoir. The mechanism of wave-induced flow may well explain large P-wave dispersion and attenuation in heterogeneous porous media.