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Unmanned Aerial Vehicles (UAVs) and Digital Outcrop Models of Carbonate Reservoir Analogs

Abstract

Digital outcrop models have evolved in the past three decades and have allowed geoscientists to interrogate critical geospatial relationships with high levels of accuracy and provide insight into subsurface reservoirs. The introduction of commercial unmanned aerial vehicles (UAVs) provides a unique opportunity for additional improved digital outcrop model development, especially when coupled with photogrammetry which allows for 3D point cloud development from overlapping photographs. UAVs are relatively inexpensive and when used in combination with differential GPS, can be used to develop accurate and informative outcrop models. The western coast of West Caicos, BWI is an extraordinary 6 km long exposure both in terms of preserving depositional facies and displaying extensive early fracture development in Pleistocene carbonate strata. UAVs and real-time kinematic GPS were used to generate an integrated map and 3D model of fractures within a framework of depositional facies. Preliminary results from this study have demonstrated a critical link between facies and fracture style, intensity and orientation. Early formed fractures occur in both the margin parallel and perpendicular direction and the longest features develop in grainstone facies. In addition, fracture systems play a fundamental role in the orientation of easily identified spur and groove systems preserved in the outcrop exposure. Lewis Canyon along the Lower Pecos River Canyon of southwest Texas contains fault-related fractures within variable facies along a 3 km long canyon exposure. UAVs were used to develop high-resolution photos and 3D models which allowed for the interrogation of the fracture style, orientation, length and intensity within different facies that occur near several small faults (offset ranging from 10 cm to 4 m) within a 1.6 km stretch of the canyon floor. Key observations include the development of highly fractured horizons near faults and a change in orientation from orthogonal fracture orientations to linear near faults with increased offset. UAV application to the digital outcrop model is revolutionary in the ability to acquire previously unattainable high-resolution photographs in an economic and safe environment. Coupled with differential GPS and photogrammetry, UAV acquired photos can be used to develop accurate 3D models for improved outcrop characterization.