Chronostratigraphic Framework for the Wilcox Formation (Upper Paleocene–Lower Eocene) in the Deep-Water Gulf of Mexico: Biostratigraphy, Sequences, and Depositional Systems
Larry Zarra, 2007. "Chronostratigraphic Framework for the Wilcox Formation (Upper Paleocene–Lower Eocene) in the Deep-Water Gulf of Mexico: Biostratigraphy, Sequences, and Depositional Systems", The Paleogene of the Gulf of Mexico and Caribbean Basins: Processes, Events and Petroleum Systems, Lorcan Kennan, James Pindell, Norman C. Rosen
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The Wilcox Formation (upper Paleocene–lower Eocene) is a world-class hydrocarbon resource in the Gulf of Mexico. Since the late 1920’s, the onshore Wilcox trend has produced primarily gas from fluvial, deltaic, and shallow marine sandstone reservoirs from southwest Louisiana to south Texas and northeast Mexico. Total estimated ultimate recoverable reserves (EUR) from the onshore trend exceed 30 trillion cubic feet (TCF) of natural gas, or 5 billion barrels of oil equivalent (BBOE), most of which has already been produced. Recent exploration in the offshore Gulf of Mexico has documented a deep-water Wilcox turbidite trend containing significant hydrocarbon resources. Since 2001, exploration and appraisal drilling has discovered nearly 2.5 billion barrels of potentially producible oil reserves in the deep-water Wilcox trend.
Chronostratigraphic analysis is the key to correlating accurately the established onshore Wilcox trend to the new deep-water Wilcox trend. Stratigraphy for the onshore Wilcox is documented in numerous publications, but there are differences in ages assigned to various lithostratigraphic components of the section. A new onshore chronostratigraphic model based on integrated paleontologic data from downdip wells is presented to clarify the ages of Wilcox sequences in the Texas subsurface. This onshore model is consistent with the new chronostratigraphic framework developed for the deep-water Wilcox.
The primary focus of this paper is a detailed description of a new deep-water Wilcox chronostratigraphic framework. Five chronostratigraphic units are recognized. In ascending order, they are; Wilcox 4, Wilcox 3, Wilcox 2, Wilcox 1B, and Wilcox 1A. These units represent early lowstand turbidite deposits of single third-order sequences or groups of third-order sequences. Each unit is defined by relevant biostratigraphic control, sequences and systems tracts, depositional systems, and sedimentary processes.
On the basin floor, early lowstand sandy turbidite sequences are characterized as channelized fan systems or distributary fan systems. Sand-poor intervals on the basin floor are in bypass zones or are condensed. The lower slope is mudstone dominated by turbidite channels and discrete ponded fans. Sedimentary processes are interpreted from approximately 3,000 feet of conventional core, which is used to calibrate interpretation of depositional systems.
Since the initial deep-water Wilcox well at Baha prospect in 2001, more than 20 wildcat wells have penetrated Wilcox turbidites, resulting in a 65 to70 percent discovery rate. With continued exploration and appraisal success in the last six years, the Wilcox has become an increasingly important trend in the deep-water Gulf of Mexico.