High-Resolution Sequence Stratigraphic Correlations of the Oligocene Frio Formation in South Texas

The Oligocene Frio Formation, totaling approximately 15,000 ft, is an important oil and gas reservoir in the South Texas Gulf Coast. More than 70 Tcf of gas and 8 Bbbl of oil have been produced from the Frio—mostly from Upper Frio sandstones and more recently from deeper, Lower Frio sandstones. Using system tract concepts, additional reserves are likely to be found in new downdip plays; therefore, an understanding of the regional sequence stratigraphy is necessary and critical.

Six third-order sequences have been recognized within the Frio depositional sequence. Each sequence consists of basin-floor and slope-fan deposits and a prograding wedge deposited off the shelf during a 3rd-order sea-level lowstand. Growth faults were active during lowstand sedimentation and ceased their influence with rising sea levels, when transgressive and highstand systems tracts shifted shelfward. The shifting of the depocenter in time in conjunction with fault activity created a strong volumetric partitioning between the slope and basin and the shelf. Because genetically similar but non-contemporaneous lowstand depositional systems successively filled each subbasin, this sequence-based approach proved to be very useful to unravel the complex stratigraphic architecture of the Frio subbasins.

This poster focuses on three subasins: Encinal (Corpus Christi), Red Fish and Mustang Island over a four-county area in the South Texas coastal area by integrating wireline-log, micropaleontologic, seismic, core, and reservoir data. We reconstructed individual systems tracts for each of the 6 sequences within the 3 sub-basins that will be displayed in cross-sections and isopach maps