P‐wave azimuthal variations in attenuation, amplitude, and velocity in 3D field data: Implications for mapping horizontal permeability anisotropy

Abstract

3D P-wave data processed as limited-azimuth volumes through pre-stack time migration document an area in which the east-west (EW) travelpaths have greatly diminished amplitudes, while the north-south (NS) travelpaths display high-amplitude mappable reflection events. If the effective horizontal permeability is significantly different by azimuth, at the reservoir scale (the inter-well scale and the seismic wavelength scale), then azimuthal variation in the attenuation should be examined in addition to the azimuthal variation in velocity and AVO. The more attenuated azimuth is predicted by Akbar et al. (1994) to be perpendicular to the aligned flow conduits, that is, in the slow velocity direction, while Gelinsky and Shapiro (1996) predict the fracture-parallel azimuth to be more attenuated for P-waves. Other attenuation mechanisms than the squirt flow mechanism (Akbar et al., 1994) do exist and may control the seismic response. For such cases, our ability to extract information about horizontal permeability anisotropy will decrease. To calculate the attenuation using P-wave reflection seismic data is often a daunting task however, to calculate an azimuthal variation in the apparent attenuation may be more tractable (personal communication, Leon Thomsen, 1997).