HIGH-RESOLUTION, CROSS-WELL REFLECTION IMAGING - POTENTIAL AND TECHNICAL DIFFICULTIES

The case study presented in this paper demonstrates that reflections c an be found in high-frequency cross-well data. These reflections can b e enhanced by a processing sequence similar to the one applied to VSP data to produce very high-resolution images. Vertical resolution of th e order of 3-5 ft (1-1.5 m) for well distances of a few hundred feet i s potentially feasible. Although this study produced a good tie betwee n the cross-well reflection image and the sonic log, our research also illustrated some of the technical difficulties associated with cross- well reflection imaging. Specifically, we found that the signal-to-noi se ratio of the image decreases as the distance between the imaged ref lection points and the wells increases, and that aliased tube waves as well as shear and converted waves were the main components of the noi se. We also observed that interpretation of wide-angle reflections mig ht be misleading, since these events are significantly stretched, both horizontally and vertically, during imaging. Improvements are require d both in data acquisition (denser data collection, more fold, smaller angles of incidence) and processing/imaging (optimal use of fold) to make cross-well reflection imaging useful. Still, the quality of these preliminary results, produced from a single gather of aliased data, i ndicates the promise of the approach.