With the advent of horizontal drilling and hydraulic fracturing in the Midcontinent, USA, fields once thought to be exhausted are now experiencing renewed exploitation. However, traditional Midcontinent seismic analysis techniques no longer provide satisfactory reservoir characterization for these unconventional plays; new seismic analysis methods are needed to properly characterize these radically innovative play concepts. Time processing and filtering is applied to a raw 3D seismic data set from Osage County, Oklahoma, paying careful attention to velocity analysis, residual statics, and coherent noise filtering. The use of a robust prestack structure-oriented filter and spectral whitening greatly enhances the results. After prestack time migrating the data using a Kirchhoff algorithm, new velocities are picked. A final normal moveout correction is applied using the new velocities, followed by a final prestack structure-oriented filter and spectral whitening. Simultaneous prestack inversion uses the reprocessed and time-migrated seismic data as input, along with a well from within the bounds of the survey. With offsets out to 3048 m and a target depth of approximately 880 m, we can invert for density in addition to P-and Simpedance. Prestack inversion attributes are sensitive to lithology and porosity while surface seismic attributes such as coherence and curvature are sensitive to lateral changes in waveform and structure. We use these attributes in conjunction with interpreted horizontal image logs to identify zones of high porosity and high fracture density.
The Barnett Shale is one of the first and most fully developed shale gas plays in North America. In this play, the knowledge of natural and induced fracture orientation and intensity is of great importance in the choice of drilling direction and completion program. In this study, the organic-rich Barnett Shale reservoir has been extensively hydro-fractured by high pressure to simulate production prior to the acquisition of the 3D seismic survey. The objective is to recognize gas-or water-charged induced damaged rock and to identify any bypassed pay. We migrate our seismic data using a new binning approach that sorts the data by azimuth as it is imaged in the subsurface. The motivation for this binning method is to better image lineaments as indicated by the most-positive principal curvature. We find a preferential image when structural lineaments lie perpendicular to the illumination direction. We also measure the impedance as a function of azimuth in an effort to determine the present day stress field and induced fractures in the Barnett Shale. Since velocity is anisotropic in the presence of anisotropic stress fields and/or the presence of natural or induced fractures, Pwave impedance, which is the product of density and velocity, is also anisotropic. The resultant image of the azimuth of maximum impedance and degree of impedance anisotropy correlates well with the k 1 most positive principal curvature.
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