Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
Bureau Seminar, Friday, September 30, 2005
Mapping sandstone distribution in high-frequency sequences using seismic sedimentology in Corpus Christi Bay, Texas
A seismic sedimentologic study was performed to map fourth- and fifth-order systems tracts for potential hydrocarbon reservoirs in Oligocene (Frio) strata in Corpus Christi Bay, South Texas. Guided by third-order sequence-stratigraphic correlations, we prepared stratal slices from a 3-D seismic volume to reveal high-resolution (10-m levels) sediment dispersal patterns and depositional history in a relative geologic-time domain. On average, 1,200 m sediments were deposited in the third-order lowstand expansion cycle, and at least 16 higher order sequences (fourth- and fifth-order sequences) were recognized. Three types of depositional systems were identified in the Frio stratigraphic section: (1) Off-shelf lowstand slope fans are best characterized by submarine channel/levee systems inside and outside the incised submarine channels and by fan-shaped sand-body geometry. (2) Lowstand prograding deltaic systems are composed of strike-oriented and lobate deltaic sand bodies deposited inside and outside the incised submarine channels. (3) Highstand and transgressive systems are represented by strike-oriented, broad barrier/lagoon on-shelf systems. Higher order sequence development is controlled by the interaction of relative sea-level change, sediment supply, and gravity tectonics. Multistory submarine channels are located above shale ridges and on present domal areas. Sand dispersal patterns are controlled primarily by accommodation resulting from rollover topography associated with growth faulting. Between the boundary fault and the hingeline atop rollover structures, strike-oriented sand bodies dominate; within submarine channel/incised valley and beyond the hingeline to the distal basin, dip-oriented sandstone bodies prevail. Sandstone thickness can be predicted by integrating wireline-log measurements and seismic amplitude patterns.