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Fault and Fracture Systems Related to Reactivation of Pre-Existing Structural Elements, Devil's River Uplift and Maverick Basin, Texas

Abstract

Pre-existing structural elements can have profound effects on fracture and fault development in younger strata, especially in areas that undergo significant changes in tectonic setting due to reactivation along older structures. This may effect reservoir permeability, yet remain difficult to detect in subsurface data. Given this challenge in mind, we investigated the influence of two styles of pre-existing structures—Paleozoic thrust belts and Triassic rift faults in the Devil's River Uplift and Maverick Basin—on the development of faults and fractures in Cretaceous strata. Fault and fracture data were quantified and characterized in both the outcrop and within a 3D seismic volume. Furthermore, we investigate the role of mechanical stratigraphy on fault and fracture style in both localities. The Pecos River Canyon exposes over 60 continuous miles of Albian-age carbonate platform which directly overlies the Paleozoic Ouachitan fold-thrust belt with associated EW and SE-NW trending structures. At the surface, faults expressed in two predominant orientations (N38E and N70E) are clustered in zones above the subsurface structures. The faults form at predictable angles if the pre-existing structural fabrics are reactivated during left lateral oblique slip. Detailed investigation of the fracture development related to these faults was conducted in a dry side canyon along the Pecos River. Photographs acquired by an unmanned aerial vehicle of a 1.6 km long canyon pavement enabled detailed fracture mapping. Mechanical facies were identified and mapped in outcrop to highlight fracture intensity variations between the different facies as well as in proximity to faults. 3D seismic and semblance volumes in the Maverick Basin reveal linear discontinuities, interpreted as low offset faults, within the Cretaceous Glen Rose through Austin Chalk succession. The faults are concentrated within strata above Triassic-age rift faults and exhibit vertical terminations against five identified mechanical boundaries. A key observation common to both the outcrop and subsurface systems is the intensity of deformation increases over pre-existing structures yet no direct connection is evident (e.g. fault from older feature to mapped zones). This has important implications for petroleum basins where reactivation is likely to occur and anomalous fracture intensities develop.