Background
Permian Basin oil and gas production in the past decade has primarily focused on the Wolfcamp Shale in the Delaware and Midland Basins. Success of this play is influenced by pre-existing natural deformation and the ability of hydraulic fracturing to induce new faults and fractures in the rock. The Marfa Basin is a third sub-basin associated with the Permian Basin. Recent work by U.S. Geological Survey researchers showed that the Wolfcampian strata exposed in the Chinati Mountains area of the Marfa Basin represent >5,000 feet of deep-water deposits. In particular, the Alta Formation is similar in rock type and depositional environment to the Wolfcamp Shale being exploited in the Permian Basin, making it potentially the best outcrop analog for the Wolfcamp reservoir, and providing the opportunity to expand Phase 3 of SwRI’s Permian Basin Consortium.
Approach
The objectives of this project were to (i) collect geologic field data from outcrops of Wolfcampian strata in the Chinati Mountains, (ii) generate detailed datasets for structural geologic characterization of deformation fabrics at select sites, and (iii) document and evaluate deformation of basinal deposits in the Marfa Basin. Initial effort focused on gaining access to outcrops of Wolfcampian strata in the Marfa Basin, and reconnaissance field work to visit as many outcrop exposures as possible, document locations, and record geological observations. For outcrops of particular interest, additional structural geologic data were recorded, including orientations (strike and dip) of bedding and documentation of deformation features (e.g., faults, extension fractures, vein mineral fill). Drone photogrammetry was used to (i) generate high-resolution digital elevation models of key outcrop areas to serve as base maps, and (ii) construct virtual outcrops of high value outcrop exposures including outcrop areas that are not safely accessible. Fracture, fault, and bedding data were analyzed to explore local versus regional deformation patterns. Bedding measurements along with mapped outcrop patterns were used to generate a geologic cross section of the Alta Formation type section.
Accomplishments
The project was technically successful, accomplishing all of the project objectives. We secured access to two private ranches with key Wolfcampian Alta Formation exposures, and collected observations and data from 110 locations in the Chinati Mountains area of the Marfa Basin, including fault, fracture, and bedding orientation measurements. The project team identified a variety of deformation features including soft-sedimentary slump folds, igneous dikes, normal faults, thrust faults, and abundant extension fractures. Observed extension fracture sets within Alta Formation include up to four bed-perpendicular extension fracture sets in sandstone and some shale beds recording the deformation history of the basin. From drone photogrammetry, we generated detailed digital elevation models of two key Alta Formation outcrop areas – one of which was previously unmapped – and made virtual outcrop models of six outcrops. Our detailed cross section through the Alta Formation type section provides the basis for constraining formation thickness in detail and context for structural data. Finally, this project successfully enabled us to expand the scope of the Permian Basin Consortium.