The depositional system for the Middle and Lower Wilcox in Houston Embayment, Northern Gulf of Mexico Basin
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The Paleocene-Eocene Wilcox formation has been a very oil and gas productive formation in the Gulf of Mexico. Recoveries are on the order of 40 to 500 million barrels of oil, but the potential exists to produce 3 to 15 billion barrels of oil. However, a number of technical and intellectual difficulties arise in economically producing the Wilcox Formation. Deep water Wilcox discoveries are located in low-permeability turbidite sandstones deposited in lower slope channels and basin floor fans in the Gulf of Mexico. The turbidite channels and fans are deep basin equivalents to the shelf delta systems located >250 miles updip, now below onshore Texas. It is important to understand the Paleocene-Eocene shelf depositional system dynamics as these are sediment feeders to the deep water turbidites and will provide a better understanding of the delivery system into the basin. This thesis focuses on the Middle and Lower Wilcox Formation specifically looking in the area of the Brazos and Colorado paleo-delta systems below the present day Texas coastal plain. The study areas represent shelf, shoreline and deltaic coastal deposits. The data used were well logs, such as gamma ray, spontaneous potential and resistivity. Using well log patterns the deposits have been broken down into six stratigraphic sequences on vertical logs, mapped, and analyzed. Signatures of log patterns also have been used to identify depositional systems from fluvial to coastal plain to the shelf in order to understand cycle stacking. The migration of the depocenters indicated a slight progradation, followed by retrogradation, followed by progradation caused by changes in accommodation and sediment supply. The analysis of the shelf and coastal depocenters suggest a possible complex link to the deep basin sediment transfer rather than a simple fluvial-delta-shelf-edge delta to deep water pathway.