AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
USGS Assessment of Undiscovered Oil and Gas Resources in the Lower Cretaceous Greater Glen Rose Carbonate Shelf and Reef Interval, U.S. Onshore Lands and State Waters of the Gulf of Mexico
(1) Eastern Energy Resources Science Center, U.S. Geological Survey, Reston, VA.
The U.S. Geological Survey (USGS), following a geology-based assessment methodology, has recently updated estimates of the technically recoverable undiscovered oil and gas resources that are expected to be found in Jurassic-to-Tertiary-aged sediments underlying the U.S. Gulf of Mexico Coastal Plain and State waters. For purposes of USGS assessments, an Upper Jurassic-Cretaceous-Tertiary total composite petroleum system (TPS) was defined for the Gulf of Mexico Basin by the USGS Gulf Coast assessment team in 2007. Geologic, geochemical, and petrophysical framework studies define the petroleum systems and assessment units (AUs) in the Gulf Coast region. As part of this assessment effort, the Greater Glen Rose Carbonate Shelf and Reef Gas and Oil AU was defined. The primary source-rock interval for the AU is probably the Upper Jurasssic Smackover Formation. The AU consists of Lower Cretaceous late Aptian to early Albian carbonate and evaporite rocks that comprise the Glen Rose, Rodessa, Ferry Lake Anhydrite, Rusk, Mooringsport, and equivalent formations. The AU extends from south Texas to the East Texas Basin, southwestern Arkansas, northern Louisiana, and southwestern and southern Mississippi. In Texas and Louisiana, the downdip boundary of the AU is determined by a line that extends 10 miles (16.1 km) downdip of the Lower Cretaceous shelf margin to include potential reef-talus reservoirs. The updip AU boundary is defined either by basin-margin fault zones or a facies change into siliciclastic-dominated sediments. The rocks within the AU were deposited in back-reef lagoon, patch reef, reef, and fore-reef environments. Isopach and structure maps were created to better define the interval.
Current petroleum production is primarily from fractured carbonate and reef trends in northeastern Texas, northern Louisiana and southeastern Mississippi. New exploration efforts in the Maverick Basin of south Texas have shown that 3-D seismic and horizontal drilling can greatly improve exploitation efforts in the isolated patch reef trends that dominate the interval. Assessment results are expected to be released in late 2011, with detailed geologic reports released at a later date.