The Kevin Dome [Formula: see text] storage project, located in northern Montana, attempted to characterize the Duperow Formation as a potential long-term storage zone for injected [Formula: see text]. A multicomponent (9C) seismic survey was acquired for the Big Sky Carbon Sequestration Partnership over a portion of the Kevin Dome using P- and S-wave sources. Prestack migrated PP, PS, SH, and SV data sets were generated. We then applied several stratigraphic inversion workflows using one or several kinds of seismic wavefield at the same time resulting in joint inversions of each data set. The aim of our study is to demonstrate the benefits of doing quadri-joint inversion of PP-, PS-, SH-, and SV-wavefields for the recovery of the elastic earth parameters, especially the S-wave impedance and density. These are crucial parameters because they can help determine lithology and porefill in the reservoir characterization workflow. Because the inversion workflow always uses the original seismic data recorded in its own time domain, it is necessary to compute registration laws between PP-PS-, PP-SH-, and PP-SV-wavefields using a time shift computation procedure (warping) based on inverted S-wave impedances from inversion of a single wavefield. This generated a significant improvement over methods that rely on attempting to match trace waveforms that may have a different phase, frequency content, and polarity. Finally, we wanted to investigate the reliability of the quadri-joint inversion results in the Bakken/Banff Formations, which have less lateral geologic variation than the underlying Duperow target. This interval shares many of the geophysical characterization challenges common to shale reservoirs in other North American basins. We computed geomechanical parameters, such as Poisson’s ratio and Young’s modulus, which are a proxy for brittleness. Comparison of these results with independent laboratory measurements in the Bakken interval demonstrates the superiority of the quadri-joint inversion method to the traditional inversion using P-wave data only.
Shear-wave amplitude variation with offset (AVO) analysis can be used to map changes in density, shearwave 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 timelapse 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.
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