On-shelf lower Miocene Oakville sediment-dispersal patterns within a three-dimensional sequence-stratigraphic architectural framework and implications for deep-water reservoirs in the central coastal area of Texas

Abstract

Through integrating three-dimensional seismic and wireline-log pattern data, we found that the sequence-stratigraphic architecture of the lower Miocene Oakville Formation along the central part of the Texas Gulf Coast reveals four third-order sequences: the lower two containing lowstand (LST), transgressive (TST), and highstand systems tracts (HST); and the upper two appearing to contain only TST and HST. These sequences average 1.2 m.y. in duration. The lowstand incised valley fill sandstones are massive, as thick as 420 ft (73 m) on wireline logs. Seismic stratal slices demonstrate that the incised valleys are dip oriented and more than 20 mi (32 km) wide. Strata (reflections) within the incised valleys onlap the sides of the valley. The third-order TST comprise backstepping high-frequency sequences. Seismic stratal slices and wireline-log patterns within the TST suggest deltaic sediment dispersal patterns that appear reworked. Third-order HST comprise aggradational to progradational high-frequency sequences, and seismic stratal slices and wireline-log patterns indicate a variety of depositional environments that we interpreted as deltaic, shoreface, coastal plain, and interdistributary. The HST is significantly truncated by the overlying sequence boundary. Sandstone-rich incised-valley fills suggest that large amounts of sediment may have been transported through these channels and may have supplied lowstand deposits and associated reservoirs seaward of the previous shelf edge.