Three-dimensional petroleum systems modeling of the Mensa and Thunder Horse intraslope basins, northern deep-water Gulf of Mexico: A case study
van den Berg, A.A.
The petroleum systems of two adjacent Miocene intraslope minibasins in the northern deep-water Gulf of Mexico are modeled to investigate why one of them produces primarily gas but the other produces oil. Specifically, the Mensa field produces gas from a faulted four-way closure that overlies a turtle structure, whereas the adjacent Thunder Horse field produces from a turtle structure with four-way structural closure. To resolve this issue, a three-dimensional petroleum-system model was constructed, whose results indicate that the Lower Cretaceous source interval, comprising type II kerogen, matured significantly earlier in the Mensa basin; the oil window was reached between 11.4 and 9.0 Ma, and the thermogenic gaswindowwas reached between 6.2 and 0.0Ma. By contrast, within the Thunder Horse basin, the source interval reached the oil window by 10.75 to 9.4Ma and largely remains in the oilwindow. TheThunderHorse trap had formed by 13.05Ma, which was before the end of the oil window. The Mensa trap (9.0-8.2Ma) was not in placewhen the source rock passed though the oil window. The primary control on the timing ofmaturation and charge is related to the original thickness of allochthonous salt that created the accommodation for the thick Miocene deep-water sediments. Originally, the Mensa minibasin contained thicker Cretaceous allochthonous salt than the Thunder Horse minibasin. Consequently, as the salt was loaded with sediment and completely evacuated, the turtle structure (trap) formed earlierin Thunder Horse field than in Mensa. By contrast, the source rocks matured earlier in Mensa, prior to the deposition of reservoir sands and the formation of the trap. The results indicate that turtle structures with similar appearances can have subtle differences in the timing of their petroleum systems, which ultimately control whether the feature is charged and with what fluid. These features must be modeled carefully in evaluating their exploration potential. Copyright © 2017 The American Association of Petroleum Geologists. All rights reserved.
To reference this document use:
AG - Applied Geosciences
ELSS - Earth, Life and Social Sciences
Geological Survey Netherlands
Gulf of Mexico
American Association of Petroleum Geologists
AAPG Bulletin, 101 (7), 1173-1201