Integration of regional gravity modeling, subsidence analysis, and source rock maturity data to understand the tectonic and hydrocarbon evolution of the Permian Basin, West Texas

Abstract

The Permian Basin of West Texas and southeast New Mexico is currently the most prolific oil-producing basin in the United States. This region experienced deformation and extreme rates of subsidence (up to 500 m/my), especially during the Late Paleozoic. To investigate the larger scale crustal geometry of the Permian Basin, its tectonic evolution, and the distribution of its most productive late Paleozoic source rocks, we have created regional 2D and 3D gravity models that incorporate density and lithologic controls from wireline logs, published seismic refractions, and regional cross sections. These gravity models better define a regional northeast-trending gravity low called the Abilene gravity minimum (AGM) that underlies the northern Permian Basin. We infer this feature to be underlain by a low-density assemblage of Precambrian granitic and metasedimentary rocks. Structural inversion from the gravity model shows that the top of the lower crust and the Moho is presently depressed beneath the AGM. Subsidence analysis defines five tectonic phases from Cambrian to recent with maximum subsidence during the main, late Paleozoic deformational phase resulting in deposition of sediments up to 2.4 km thick. We have determined that the geobody under the AGM acted as a zone of preferential weakness in a “broken foreland basin” setting that accommodated regional shortening related to the Marathon orogeny and to other coeval orogenies along the Sonoran margin and Nevadan margin. Our new regional map of the top basement defines the limits of deep basinal areas that may host the most productive and thermally mature, late Paleozoic source rock kitchens — some of which are localized in depocenters controlled in part by syncollisional, left-lateral strike-slip faults that align with the edges of the AGM. Our results show a deeper basement ranging from 5.5 to 6.2 km in the Delaware basin that predicts a broader zone of source rock thermal maturity.