ABSTRACT

Geochemical fingerprinting of many upper Gulf slope oils indicates an origin from deeply buried Mesozoic carbonate source rocks. Substantial vertical migration (>6 km; 19,680 ft) along salt and fault migration conduits must be invoked to explain the emplacement of Mesozoic-sourced oils in shallow Miocene to Pleistocene reservoirs. Gulf slope seeps provide evidence of oil and gas charge in a rapidly subsiding salt basin, where oil and gas migration is a geologically recent or ongoing event. Sea-floor oil and gas seeps, gas hydrates, chemosynthetic communities, authigenic carbonate derived from hydrocarbon oxidation, and natural oil slicks are diagnostic indicators of charge. There is a regional association between seeps and the upper Gulf slope oil province offshore Louisiana and Texas. There is also a subregional relationship between seeps and the localized charge systems that give rise to individual oil accumulations. Key case histories include Marquette Field, Jolliet Field, and the GC 228 discovery in northwest Green Canyon, as well as the Cooper and Auger discoveries in northeast Garden Banks.