The SPWLA Permian Basin Chapter

Technical Lunch and Learn
  Tuesday, March 28, 2023 at 11:30 - 1:00 PM CST
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“Mapping post-Permian rocks from the Marfa Basin into the Delaware Basin: a synthesis using geological maps, cross sections, and sample logs from wells”
By: Ben Johnson

Abstract: 

In 2018, the U.S. Geological Survey (USGS) estimated that Pennsylvanian to Permian rocks in the Delaware Basin of West Texas and southeastern New Mexico contain a mean undiscovered resource of 46.3 billion barrels of oil and 281 trillion cubic feet of natural gas, making it the largest continuous oil and gas resource assessed in the onshore U.S. (Gaswirth et al., 2018; USGS Fact Sheet 2018–3073). A major source of uncertainty in the resource numbers is the burial and uplift history of key source rock intervals identified in the deep Delaware Basin. Petroleum system modeling studies have estimated that post-Permian burial ranges from 2,000 to greater than 8,000 ft, with maximum burial occurring during the Paleocene (ca. 56 Ma). Burial was then followed by uplift and erosion during Laramide contraction and Basin and Range extension. Much of the post-Permian section in the Delaware Basin, however, is now missing, and it remains poorly mapped because wireline log coverage in shallow sections is sparse.
In this study, we digitized more than 200 sample logs and integrated them with surface geological maps and regional cross sections to constrain thicknesses of the post-Permian section across the basin. The sample logs, which were originally compiled by the Permian Basin Sample Laboratory in Midland, TX using wellbore cuttings, are useful in regional mapping because they typically record the lithology from the surface to the deepest stratigraphic intervals in the basin. Our mapping shows that the preserved post-Permian section across the Delaware Basin can be subdivided into three, unconformity bound, sedimentary packages, which include: 1) Upper Triassic units of the undivided Dockum Group, 2) Lower Cretaceous (upper Aptian) units of the Trinity, Fredericksburg, and Washita Groups, and 3) Pleistocene and younger unconsolidated alluvial sediments at the surface (includes the informal Pecos Valley alluvium). Collectively, these sedimentary packages have been shown to not exceed 2,000 ft in their present-day thickness across the Delaware Basin.
The Marfa Basin, which is located to the southwest of the Delaware Basin and Diablo Platform, records a similar Pennsylvanian to Permian history to that of the Delaware Basin. Preliminary Rock-Eval pyrolysis and vitrinite reflectance data from outcrop samples suggest that Permian-aged source rocks in the Marfa Basin reached the oil window during their burial history. The post-Permian history of the Marfa Basin, however, is quite different from that of the Delaware Basin. No Triassic units are mapped in outcrop belts or in the subsurface of the Marfa Basin. The preserved Lower Cretaceous section in the Marfa Basin can be partially correlated to rocks in the Delaware Basin, but older units of the Trinity Group, including the Yucca, Presidio, and Bluff Mesa Formations, are only mapped in the Marfa Basin. The Cretaceous rocks of the Marfa Basin are also significantly thicker than that of the Delaware Basin, reaching thicknesses of greater than 3,000 ft in the western part of the basin, which was involved in the Late Jurassic to Early Cretaceous opening of the Chihuahua Trough. Upper Cretaceous rocks are sparse in the Marfa Basin because they were eroded during the eruption and deposition of the Eocene to Miocene Trans-Pecos Volcanic Field, which includes greater than 5,000 ft of volcanic and volcaniclastic rocks. In contrast, no volcanic rocks are preserved in the Delaware Basin. Finally,
the Marfa Basin was subjected to Basin and Range extension and the formation of the Presidio Bolson, a large asymmetric graben along the U.S.–Mexico border that includes greater than 3,000 ft of Miocene to Holocene sedimentary fill. Although the collective thickness of the post-Permian section in the Marfa Basin is much greater than that of the Delaware Basin, its distribution is not spatially uniform due to the polyphase tectonic history of the basin. From our regional mapping, we infer that the Marfa Basin was subjected to greater amounts of post-Permian uplift and erosion than in the Delaware Basin.

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