On the Origin of Hydrocarbons in the Gulf of Mexico Basin–A Reappraisal

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Abstract
The origin of hydrocarbons in the Gulf of Mexico basin has been a subject of controversy for many years. One series of arguments invokes source rocks of average organic enrichment, pervasively distributed throughout the Cenozoic sequence and intimately associated with the reservoir system. Other arguments invoke organic-rich, discrete source rocks not in direct contact with the reservoirs, possibly in pre-Tertiary sequences drained by deep-rooted faults and piercement structures. Geochemical analyses of hundreds of crude oils, natural gases, and nonreservoir rocks from the Mesozoic and Cenozoic trends along the northern Gulf of Mexico basin and from DSDP sites indicate the general inadequacy of the Oligocene to Recent section to source significant oil accumulations. Furthermore, isotopic data indicate that much of the gas found in Neogene and Quaternary reservoirs is thermogenically derived from much greater depths where maturation is consistent with dry gas generation. Geochemical data from several Mesozoic and Paleogene units in the basin indicate the existence of excellent oil-prone source rocks. It is proposed that such units extend below Cenozoic producing trends and are drained by deep-rooted faults and piercement salt structures. Maturation history, structural style, and patterns of migration and remigration control the variable productivity along the various trends.