SUBSURFACE MAPPING OF A DOWNDIP VICKSBURG GROUP OIL AND GAS ASSESSMENT UNIT, TEXAS AND LOUISIANA GULF COAST ONSHORE AND STATE WATERS
Vicksburg Group strata defined as ‘downdip’ along the TX Gulf Coast are delineated by the downdip extent of maximum normal fault expansion as observed in interpretation of three regional 2-D seismic surveys in southern TX. This coincides with the uppermost Vicksburg paleo-shelf edge, but does not incorporate some slope reservoirs in the lower Vicksburg landward of the downdip extent of faulting. At the time of Vicksburg deposition the major clastic sediment supply to the coast was from the Rio Grande Embayment in south TX. Lack of major sediment supply to LA during Vicksburg time abated the formation of extensive normal faulting at the shelf edge. Therefore, the ‘downdip’ Vicksburg Group in LA was defined by changes in stratal thickness and depositional character from well log interpretation, indicating transition from outer shelf to upper slope environments. The transition is also evident in structural and stratigraphic architecture observed in north-south 2-D seismic surveys for the LA Gulf Coast. Based on this subsurface mapping, the assessment unit encloses that volume of rock that contains Vicksburg Group sediments between the Upper Vicksburg paleo-shelf margin extending from the Mexican-USA border in south Texas to southeast Louisiana and seaward from that margin to the Federal-State waters boundary.