Permian Basin Regional Burial and Exhumation History: Implications for Source Rock Distribution, Maturity and Charge Access

Abstract

The subsidence history of the greater Permian Basin takes place in the larger context of related subsidence in regional basins including the Marathon-Oachita foreland, Gulf of Mexico basin, and Sevier-Laramide foreland. We apply a regional basin model that links the Delaware and Midland Sub-basins with the surrounding basins in Texas and New Mexico, which reveals the complex tectonic history of the region. Using constraints from the regional context to establish new burial histories, we demonstrate significant burial during the Cretaceous through Eocene. This result is consistent with fission-track, and vitrinite reflectance, as well as expected depositional trends associated with the Cretaceous Interior Seaway and Cretaceous Gulf of Mexico.

Reconstruction of major regional unconformities, invoking significant erosion in the Jurassic and the Oligo-Miocene, has significant implications for the petroleum systems of the Delaware and Sub-Midland basins.

1) Basin differentiation during the Pennylvanian-Permian allowed different Organofacies to develop on shelves (clay-poor Organofacies A) vs. basins (clay-rich Organofacies B)

2) In parts of both the Delaware Sub-Basin and the Midland Sub-Basin, maximum burial took place during the Cretaceous through Eocene, following Jurassic uplift and erosion around the basin margins.

3) Maximum burial took place prior to the Jurassic erosion event beneath the Paleozoic foreland wedges bounding the Permian Basin, including the Marathon-Oachita foreland.However, our model suggests that maximum standard thermal stress (STS) was not reached in many areas until Cretaceous-Paleogene reburial.Source rock maturity resulting from this modeled STS is higher than would result from pre-Jurassic burial alone, changing both the expected timing and fluid properties associated with hydrocarbon generation and expulsion.

4) Reservoir fluid properties such as GOR and viscosity, important for development of both conventional and unconventional targets, are also likely impacted by the greater depths of maximum burial and increased thermal stress due to the addition of significant Cretaceous-Paleogene overburden, removed by later erosion.

5) High overpressures, such as those observed in Pennsylvanian-Wolfcampian age reservoirs, are more easily explained by recent deep burial than by the presence of exceptionally low permeability seals, which would be required to maintain overpressure since the early Mesozoic.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018