AVO Attributes from P-SV Data for Shale Characterization

Seismic attributes based on amplitude variations with offset (AVO) have been widely applied for characterization of gas saturation and lithology in exploration for and development of hydrocarbon resources. These AVO attributes consist of A (intercept) and B (slope, or gradient) of observed reflection amplitudes vs. sin**2 i, of the incidence angle. Similar A and B coefficients for P-SV reflections, in terms of sin i and sin**3 i, have been discussed in the literature for isotropic materials, and descriptions of anisotropic materials might fit this scheme as well. We show a modified pair of A-B attributes, with some convenient assumptions, that are derived from AVO analysis of mode-converted P-SV data and applied to interpretations of shale reservoirs. Testing on calculations for properties consistent with Bakken, Woodford and Eagleford Shales, and a model simulating a multi-layered Woodford interval, confirm that such attributes are sensitive to weak anisotropy parameters epsilon and delta. We found that variations in epsilon and delta are isolated in the presence of variations in Vp and density of ± 5% and Vp/Vs of ± 2.5% Results lead us to propose a test the stability of the extraction of these attributes from real P-SV data.