3-D SEISMIC IMAGING AND INTERPRETATION OF BRUSHY CANYON SLOPE AND BASIN THIN-BED RESERVOIRS, NORTHWEST DELAWARE BASIN

A study was done at Nash Draw field, Eddy County, New Mexico, to demon strate how engineering, drilling, geologic, geophysical, and petrophys ical technologies should be integrated to improve oil recovery from Br ushy Canyon reservoirs at depths of approximately 6600 ft (2000 m) on the northwest slope of the Delaware basin. These thin-bed reservoirs w ere deposited in a slope-basin environment by a mechanism debated by r esearchers, a common model being turbidite deposition. In this paper, we describe how state-of-the-art 3-D seismic data were acquired, inter preted, integrated with other reservoir data, and then used to improve the siting of in-field wells and to provide facies parameters for res ervoir simulation across this complex depositional system. The 3-D sei smic field program was an onshore subsalt imaging effort because the O choan Rustler/Salado, a high-velocity salt/anhydrite section, extended from the surface to a depth of approximately 3000 ft (900 m) across t he entire study area. The primary imaging targets were heterogeneous s iltstone and fine-grained sandstone successions approximately 100 ft ( 30 m) thick and comprised of complex assemblages of thin lobe-like dep osits having individual thicknesses of 3 to 6 ft (1 to 2 m). The seism ic acquisition was complicated further by (1) the presence of active p otash mines around and beneath the 3-D grid that were being worked at depths of 500 to 600 ft (150 to 180 m), (2) shallow salt lakes, and (3 ) numerous archeological sites. We show that by careful presurvey wave testing and attention to detail during data processing, thin-bed rese rvoirs in this portion of the Delaware basin can be imaged with a sign al bandwidth of 10 to 100 Hz and that siltstone/sandstone successions 100 ft (30 m) thick in the basal Brushy Canyon interval can be individ ually detected and interpreted. Further, we show that amplitude attrib utes extracted from these 3-D data are valuable indicators of the amou nt of net pay and porosity-feet in the major reservoir successions and of the variations in the fluid transmissivity observed in production wells across the held, Relationships between seismic reflection amplit ude and reservoir properties determined at the initial calibration wel ls have been used to site and drill two production wells, The first we ll found excellent reservoir conditions; the second well was slightly mispositioned relative to the targeted reflection-amplitude trend and penetrated reservoir facies typical of that at other producing wells. Relationships between seismic reflection amplitude and critical petrop hysical properties of the thin-bed reservoirs have also allowed a seis mic-driven simulation of reservoir performance to be initiated.