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Articles |
Shell International Exploration and Production Inc., 3737 Bellaire Blvd, Houston, TX 77025 (e-mail: Scott.Wilkins{at}shell.com)
A geomechanical method is presented for the prediction of subseismic fracture intensity associated with faulting using a boundary element model conditioned from 3D seismic interpretation within the Green River Basin, Wyoming, USA. Seismic data indicate two major phases of deformation: (1) an early phase of approximately ESE-verging contraction accommodated along a NNE–SSW striking system of basement-involved reverse faults and associated drape folds; and (2) a later phase of transtension accommodated by ENE–WSW-trending normal faults that are preferentially located in the hanging wall, above the crest of the drape fold.
The models predict different spatial patterns of fracture intensity for each phase of deformation. For D1, enhanced probability for shear failure develops in the upper quadrant of the footwalls along the reverse faults (i.e. forelimb) and the greatest magnitudes occur adjacent to regions with the largest component of observable dip-slip displacement along the faults. During D2, enhanced probability for joint and fault formation occurs along-strike of the normal faults and in a general NE trend. Seismic velocity anisotropy data support the geomechanical predictions for both phases of deformation in that the location and azimuth of large anisotropies correlate with regions of predicted enhancement in joint and fault intensity.
