Abstract: Stratigraphic Analysis of 3D and 2D Seismic Data to Delineate Porous Carbonate Debris Flows--Northwestern Midland Basin, West Texas

Jory A. Pacht, Larry Brooks, Frank Messa

Porous carbonate debris flows are very important plays in Permian strata along the northwestern margin of the Midland Basin. Delineation of these strata, however, is difficult and detailed stratigraphic analysis of both 2D and 3D seismic data is important in reducing risk. Debris flows occur in all carbonate slope and base of slope environments; however, many exhibit muddy matrix and low permeability. Porous debris flows are best developed during lowstand time. When sea-level falls to a point at or below the shelf margin, sand to boulder-sized clasts created by reef-front erosion are funneled through slope gullies onto the base of the slope.

Large debris flows exhibit well-defined mounds which downlap onto the sequence boundary. Many of these flows, however, are nonporous, and some productive debris flows were too thin to exhibit discrete reflections. 3D seismic data were used to define subtle changes in amplitude and frequency which suggest presence of porous strata. Along the northwest shelf, porous debris flows were distinguished by areas of lower amplitude (dim spots) and lower frequency than surrounding strata. These areas are commonly developed immediately downdip of major slump scars. Once sequence boundaries and, where present, mounded reflections which downlap on top of them, were delineated on a subregional basis using 2D data, they were interpreted in detail using a much smaller 3D dataset. Amplitude maps were used to delineate dim spots located on the basin floor. Time structure maps were made to help show associated updip slump scars, and isochron maps were made to delineate specific debris flows.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela