Shear-wave amplitude variation with offset (AVO) analysis can be used to map changes in density, shear-wave velocity, and fracturing at reservoir scale by allowing the influence of each factor to be separately extracted from the observed seismic response. Weighted least-squares inversion of the anisotropic reflection coefficients was implemented to find the shear-wave splitting coefficient and velocity-contrast parameters. A time-lapse nine-component, 4-D seismic survey acquired over Vacuum field in Lea County, New Mexico, was used to test our methodology of shear-wave AVO analysis and to compare the results with well production and azimuthal P-wave AVO analysis.
Weighted least-squares shear-wave AVO stacks of the splitting parameter were found to be excellent predictors of well fluid-production performance, implying a strong link between seismically inferred fracturing and reservoir-scale permeability of the San Andres dolomites at Vacuum field. Analysis of the shear-wave velocity contrast indicated the presence of a second set of open fractures to the south of a carbon dioxide injector well where a 4-D anomaly associated with injection had been observed.