A parametric study of borehole influence in resolving seismic velocity in well-to-well tomograms

Abstract

The data collected in a well-to-well tomography experiment is inherently incomplete even when augmented by VSP data. The nature of the experiment suggests a geometric limitation to the resolution of any central structure. A parametric model has now been developed which examines the effect on reconstructed velocity due to the borehole size, transducer standoff, altered annulus, and the degree of velocity attenuation of the altered annulus, using a range of host velocities and hole separations. It was found that there are significant velocity variations caused by perturbations in borehole size. These errors are particularly significant for boreholes with large diameters and small transducer offsets. For an altered annulus, errors in both the dimensions and the degree of velocity alteration gave significant velocity variation in reconstructed velocity, particularly with large boreholes. In all cases it is observed that the variation and alteration in reconstructed velocities increased as hole separation is decreased.