Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
American Association of Petroleum Geologists Annual Meeting, Dallas, April 18-21, 2004
Using Seismic Geomorphology to Characterize Depositional Systems in Oligocene Growth-Faulted Intraslope Subbasins, Offshore South Texas
Hongliu Zeng, Frank Brown, Robert G Loucks, Ramon H Trevino, Ursula Hammes, and Randy Remington
Three-dimensional seismic data of growth-faulted intraslope subbasins were stratal sliced to produce sequential images of lowstand systems tracts following inferred geologic-time surfaces. Stratal-slicing techniques were applied to Oligocene strata in the Corpus Christi region of South Texas. The study was focused on application of seismic geomorphology for analyzing lowstand systems for potential hydrocarbon reservoirs.
Previous well log and seismic studies revealed seven third-order sequences. Each third-order lowstand systems tract essentially fills one intraslope subbasin. Sediment supplied by entrenched rivers overloaded lowstand depocenters, initiated gravity faulting, mobilized mud, and produced a new subbasin. The seismic representation of this unique syndepositional process is a series of diachronous reflection wedges separated by growth faults. Seismic data are difficult to interpret in vertical sectional views because of the poor continuity of seismic events, which is compounded by structural distortion.
Guided by sequence-stratigraphic-based correlations across intraslope subbasins in two 3-D seismic surveys, we conducted stratal slicing in three of the intraslope subbasins separated by two major strike-fault trends covering a 160-mi2 area. Along the depositional axis of intraslope subbasins, amplitude stratal slices show dip-oriented, mostly straight, incised valleys on the shelf (updip footwall blocks) and distributaries and deltaic lobes in the below-shelf-edge lowstand prograding-wedge complex (downdip hanging-wall blocks). Between depositional axes, strike-oriented barrier complexes dominate. A series of stratal-slice movies illustrate how incised valleys loaded lowstand depocenters and created younger intraslope subbasins seaward in multiple-cycle deposition. Stratal slices outline areas of potential lowstand reservoir sands.