Miocene Lowstand Deep-Water Sand Plays, Offshore Texas

Dennis W. Cratsley, Taylor E. Blood

The Minerals Management Service, United States Department of the Interior, in support of the 1995 National Oil and Gas Resource Assessment, is identifying conceptual plays to assess potential oil and gas resources on the Gulf of Mexico Outer Continental Shelf. Sequence stratigraphic analysis is used to synthesize a depositional model for reservoir-quality sands in several undrilled deep-water sand plays in the Miocene section of offshore Texas.

The model suggests that favorable sand conditions occur downdip from several Miocene-age shelf deltas in lowstand turbidite sands -- potential exploration targets downdip of production from the more commonly played deltaic sands. Finding potential reservoir sands depends, in part, on locating the geologic settings in which deep-water sands are likely to have formed and on recognizing the seismic character of lowstand deep-water sand deposits -- the "basin-floor fan" and "slope-fan" lowstand systems tract components of Vail.

Paleo-environmental maps reconstruct the inferred lowstand shelf edge(s) and fluvial distributary channel/canyon system(s). Deep-water sands fill-in bathymetric lows and conform to preexisting seafloor topography and basin structure -- frequently as multiple "stacked" sand bodies.

Sequence stratigraphic analyses define and map lowstand systems tracts, depositional systems, and their associated lithofacies in the Miocene section. Lowstand systems tracts are defined on seismic records and isochron thickness is calculated and mapped to outline exploration targets in isopach "thicks." Sand-prone deposits are delineated by "seismic facies analysis" interpreting seismic reflector character. Facies maps outline areas of highest potential.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995