Estimating rock porosity and fluid saturation using only seismic velocities

Abstract

Evaluation of the fluid content in deep earth reservoirs or of fluid contaminants in shallow earth environments has required the use of geophysical imaging methods such as seismic reflection prospecting. The processing of these seismic data has involved meticulous care in determining the changes in reflected seismic amplitude as the point of observation for the received signals at the earth's surface is moved away from the seismic source (Ostrander, 1984). The now commonly used method called AVO (for Amplitude Versus Offset) is based on theories of fluid-saturated and partially saturated rocks that have been available since the 1950's. Here we present a new synthesis of the same physical concepts that uses some of the same data as AVO (compressional wave velocities) together with some different data (shear wave velocities) in a scheme that is much simpler to understand and apply, yet yields the desired information about porosity and fluid saturation. The method is designed especially for near surface applications and for use with crosswell and VSP data, but it can also be applied to reflection seismic data assuming that reliable interval velocities are available. Since the new method does not require hard-to-obtain wave amplitude information, it can be used for a wider range of seismic source-receiver configurations, including crosswell seismic transmission tomography (well-to-well), vertical seismic profiling (well-to-surface), as well as seismic reflection profiling (surface-to-surface), since reflection data can be used but are not a necessity.

On the propagation of a disturbance in a heterogeneous, deformable, porous medium saturated with two fluid phases

“…The capillary pressure function given above (see equation 73) was used in our modeling. These observations have been used in studies involving elastic wave propagation in a partially saturated porous medium (Tuncay and Corapcioglu, 1996;Berryman et al, 2002).…”

Estimation of rock physics properties from seismic attributes — Part 1: Strategy and sensitivity analysis

“…Berryman et al (2002) estimate the porosity and water saturation from the propagation velocities V P and V S measured under laboratory conditions for several rocks. Tang and Cheng (1996) fix all other constitutive poroelastic parameters and deduce the permeability from Stoneley waves.…”

Estimates and Rigorous Bounds on Pore-fluid Enhanced Shear Modulus in Poroelastic Media with Hard and Soft Anisotropy

“…Berryman and Wang (2001) show that deviations from Gassmann's results sufficient to produce shear modulus dependence on fluid mechanical properties require the presence of anisotropy on the microscale, thereby explicitly violating the microhomogeneous and microisotropy conditions implicit in Gassmann's original derivation. Berryman et al (2002a) go further and make use of differential effective medium analysis to show explicitly how the undrained, overall isotropic shear modulus can depend on fluid trapped in penny-shaped cracks. Meanwhile, laboratory results [see Berryman et al (2002b)] show conclusively that the shear modulus does depend on fluid mechanical properties for low-porosity, low-permeability rocks, and high-frequency laboratory experiments (f > 500 kHz).…”