High-resolution crosswell imaging of a West Texas carbonate reservoir; Part 4, Reflection imaging

Reliable crosswell reflection imaging is a challenging task, even after the data have been wavefield-separated in the time domain. Residual, strong coherent noise is still present in the data. Stacking is complicated by the wide range of reflection incidence angles available for imaging. With wavelengths of a few feet, small misalignments as a result of velocity or geometric errors produce destructive interference and degrade the quality of the stacked image. We present an imaging sequence that addressed these complications and allowed us to produce high-quality stacked images for both P- and S-waves from a large-volume crosswell data set. A very good tie was achieved at both wells. Heterogeneities imaged from well to well included very thin beds [less than 5 ft (1.5 m) thick] within the reservoir, pinchouts, and a major angular unconformity--the Grayburg/San Andres--that could not be observed reliably with any other technique (log correlation, surface seismic imaging, or tomography). In fact, the produced crosswell reflection images exhibit dramatically higher resolution and continuity than the P-wave traveltime tomogram.