Abstract: Crosswell Seismic Imaging at the McElroy CO[2] Pilot

LANGAN, ROBERT T., JERRY M. HARRIS, SPYROS K. LAZARATOS, ZHIJING WANG, and KARLA A. TUCKER

We have imaged both fluid pressure changes and CO[2]-saturation effects in a Grayburg Formation carbonate reservoir in the McElroy oil field in west Texas using time-lapse, high resolution crosswell seismology. These images have a vertical resolution on the order of 10 to 15 ft (3 to 5 m). We use pre-CO[2] data collected during a water flood to compute baseline images, and then we monitor changes in the reservoir due to CO[2] displacing the oil-water mix by collecting data during the CO[2] flood. We obtain two types of interwell images from the crosswell data, P- and S-wave velocity images ("tomograms"), and P-wave reflection images with frequencies exceeding 1000 Hz. In combination these images are very powerful tools for determining reservoir architecture and observing flow patterns within the reservoir.

Near an injector, the bulk of flow (as defined by the velocity changes) is confined to a 40 ft (12 m) thick interval within the upper half of the 100 ft (30 m) thick reservoir. The flow travels along relatively flat-lying strata (as defined by both the reflection images and the velocity changes) for about 300 ft (90 m), appears to "jump" upwards to a 20 ft (6 m) thick interval at the top of the reservoir, and continues horizontally to a producing well. There are disruptions in the reflection events at the "jump" that may be an indication of a fracture that is allowing vertical communication between flow units. The time-lapse changes in the reflection amplitudes clearly support this interpretation.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California