FRACTURE CHARACTERIZATION FROM NEAR-OFFSET VSP INVERSION

A global optimization method incorporating a ray-tracing scheme is use d to invert observations of shear-wave splitting from two near-offset VSPs recorded at the Conoco Borehole Test Facility, Kay County, Oklaho ma. Inversion results suggest that the seismic anisotropy is due to a non-vertical fracture system. This interpretation is constrained by th e VSP acquisition geometry for which two sources are employed along ne ar diametrically opposite azimuths about the well heads. A correlation is noted between the time-delay variations between the fast and slow split shear waves and the sandstone formations.