The Northern Gulf of Mexico Offshore Super Basin: Reservoirs, Source Rocks, Seals, Traps, and Successes
The northern Gulf of Mexico federal offshore area easily qualifies as a super basin, based upon estimated petroleum endowment over 100 BBOE and cumulative production of 60 BBOE. Like other super basins, it has multiple petroleum systems and stacked reservoirs. Examination of four key elements of these petroleum systems (reservoirs, source rocks (and maturation windows), seals, and traps yields important insights to the geologic processes that result in such an exceptional habitat for conventional hydrocarbons.
The bulk of hydrocarbon resources in federal offshore waters are in Cenozoic sandstone reservoirs such as the Paleogene Wilcox reservoir of deepwater subsalt areas. Overall, Cenozoic sandstone reservoirs in both suprasalt and subsalt fields yield the highest flow rates and cumulative production volumes. Notable is the recent addition of the deepwater Jurassic Norphlet sandstone play, the newest and second largest by UTRR. Overall Gulf of Mexico reservoirs are diverse, formed in paleoenvironments ranging from aeolian to deepwater.
Powering this super basin are three primary marine source rocks centered in the Oxfordian, Tithonian, and Ceno-Turonian stages. These source rock intervals often act as top seals, but other Neogene and Mesozoic shales and even carbonate mudstones are also important trap sealing elements, as proven by analytical work and downhole pressure measurements. The extensive salt distribution and relatively late Cenozoic burial delayed source rock maturation and migration until culmination of trap formation in many areas.
High rates of Cenozoic deposition on a mobile salt substrate also generated a myriad of salt tectonic structures ranging from simple diapiric closures and extensional fault traps to complex subsalt configurations such as salt-cored compressional anticlines, salt-cutoff traps, and bucket weld traps. Exploration success in the past 20 years is a direct result of improved seismic imaging around and below salt, as well as advances in drilling, completing, and producing wells and fields.
Bio – Presenter: John Snedden
John Snedden is a Senior Research Scientist at Institute for Geophysics, The University of Texas at Austin. He is director of the Gulf Basin Depositional Synthesis project, a consortium dedicated to research on the depositional history of the Gulf of Mexico. Prior to taking his current position, he worked in the oil industry for 25 years, exploring basins around the world. He and William Galloway are authors of the recent book, The Gulf of Mexico Sedimentary Basin: Depositional Evolution and Petroleum Applications (Cambridge University Press, 2019).
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