--> Influence of Tectonic Setting on Borehole-Scale Deformation Around the Margins of the Permian Basin (Texas, USA)

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Influence of Tectonic Setting on Borehole-Scale Deformation Around the Margins of the Permian Basin (Texas, USA)

Abstract

Surface exposures of lithologically varied Permian strata around the margins of the Permian Basin in west Texas reveal a broad spectrum of bore-hole scale deformation styles that reflect their tectonic histories. These observations apply to both conventional (limestone and sandstone) reservoirs and unconventional (fine-grained mudrock) reservoir facies of the Permian Basin. The Eastern Shelf margin of the Permian Basin has outcrops of relatively undeformed rocks that provide constraints on the “background” fracture orientations in the subsurface. Small scale deformation tends to be dominated by extension fractures (joints and veins) in two, and locally three, sets of near vertical fractures. Deformation observed in outcrops at the western edge of the Basin includes extensional structures (normal faults and extension fractures) associated with the Basin and Range Province and Rio Grande rift deformation that overprint contractional deformation (contractional folds, thrust faults, tectonic stylolites) associated with the Laramide orogeny. The foothills of the Guadalupe Mountains expose a wide range of rock types that contain deformation features (faults, folds, and veins) developed by overprinting of these tectonic events. Along the southwestern margin of the Permian Basin, associated with the Marathon uplift, Permian strata in the Glass Mountains contain deformation features (thrust and strike-slip faults, tectonic stylolites, and veins) produced by both Late Paleozoic (Ouachita) and Late Mesozoic (Laramide) contractional deformations, and later Basin and Range extensional features (normal faults, extension fractures). Collectively, these exposures reveal structural styles and mechanical stratigraphy that vary with tectonic context around the margins of the Permian Basin. This spatial variability includes not only differences in meso-structural assemblages, but also captures a systematic 30 degree rotation of dominant strike trends around the basin. These results are directly relevant to predicting the distribution and style of sub-surface, small-scale deformation features that influence the permeability architecture and the potential for induced hydraulic fracturing of hydrocarbon reservoirs throughout the Permian Basin.