Stratigraphic Analysis of 3D and 2D Seismic Data to Delineate Porous Carbonate Debris Flows in Permian Strata Along the Northwestern and Eastern Margins of the Midland Basin

Jory A. Pacht, Larry Brooks, Frank Messa

Porous carbonate debris flows are very important plays in both Wolfcamp and Leonard strata along the northwestern and eastern margins 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 are very common in all carbonate slope and base of slope environments, however, many exhibit a 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 porous debris flows are too thin to exhibit discrete reflections. 3D seismic data are used to define subtle changes in amplitude and frequency which suggest presence of porous strata. Along the northwest shelf, porous debris flows are 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, are delineated on a subregional basis using 2D data, they can be interpreted throughout a local 3D dataset. Amplitude maps are constructed and used o delineate dim spots located on the basin floor and time structure maps are made to help show associated updip slump scars.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995