Upper Paleocene-Lower Eocene 'Wilcox'-Sourced Petroleum Systems of the Gulf of Mexico Basin: A Re-Evaluation and Comparison with the Coeval Patala Formation-Sourced Petroleum System in the Upper Indus Basin, Pakistan

摘要

Wilcox Group, Gulf of Mexico The upper Paleocene-lower Eocene Wilcox Group of the Gulf Coast represents a complete non-marine to deep marine series of systems tracts ranging from coaly delta plain environments onshore Gulf Coast to a time-equivalent bathyal condensed section on the floor of the Gulf of Mexico. Source potential is present in each environment: terrigenous organic matter (OM) in paralic coals has waxy oil and gas expulsion potential; marine shelf and slope mudstones are dominated by marine OM with varying but generally minor contribution of terrigenous OM; the abyssal condensed section has totally marine OM. OM in these marine-dominated environments was subjected to varying degrees of oxidation and is variably oil and gas prone. Early source rock studies of the Wilcox Group (e.g., Sassen, 1990), identified relatively poor to modest source potential at scattered locations in Mississippi and Louisiana; and at unspecified stratigraphic positions in the group. Chinn McDade (1992) studied a lower Paleocene-Eocene dataset spanning along strike through southern Louisiana, and provided logs with a stratigraphic zonation within the Wilcox. In this near shore marine to paralic transitional paleogeographic position, the Wilcox Group sediments contain aquatic marine OM in clay-rich mudstones (organofacies B in the general OM scheme of Pepper and Corvi [1995], which is used here throughout and which was also illustrated in Pepper [2016]), with a variable contribution of terrigenous OM including waxy material (organofacies E). Chinn McDade's (1992) random and representative sampling of the entire Wilcox Group, similar to Sassen's (1990, resulted in a low average organic richness (C_(org)) of~1.5 wpc (weight percent of dry rock) with a low average hydrogen index (HI) of 150 wptC (weight parts per thousand relative to organic carbon). A smaller subset of samples has higher C_(org) and HI, presumably representing the subordinate part(s) of the whole formation with oil