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Quantitative Outcrop Characterization of Incised Valley Fill Combining UAV-Based Photogrammetry and Traditional Geologic Field Methods

Abstract

A scalable, readily repeatable methodology for quantitative outcrop characterization has been developed combining Unmanned Aerial Vehicle (UAV) based photogrammetry with more typical field-based outcrop characterization techniques. The utility of this methodology is demonstrated in extracting high-resolution dimensional data from estuarine incised valley fill deposits exposed in the Cretaceous John Henry Member of the Straight Cliffs Formation in southern Utah, USA. While the use of photogrammetry to produce 3D outcrop models is not new to the geosciences, the increased availability of UAVs has improved our ability to efficiently collect high-resolution outcrop imagery necessary to develop these models. Spatially oriented outcrop models facilitate quantitative outcrop characterization from the bedding- to petroleum system-scale. Transgressive estuarine incised valley fills possess significant potential as hydrocarbon reservoirs in the subsurface, though the dynamic nature of tidal systems make them especially heterogeneous. The complex architectures expressed from the geobody- to reservoir-scale introduce substantial uncertainty to reservoir volume and performance prediction. Quantitative outcrop analog characterization provides dimensional data for geobodies and key surfaces required to improve subsurface reservoir predictions. A 3D outcrop model was produced using Structure from Motion (SfM) to combine overlapping aerial imagery and GPS data collected in the field. Decimeter-scale stratigraphic sections were then draped over the outcrop model, serving as the primary control points for an iterative process of 3D geologic interpretation (definition of geobodies and identification of key bounding surfaces). Dimensional data was extracted to quantify the thickness, aerial extent, stacking, and internal architecture of a laterally accreting mid-estuarine bar and multiple tidal channels. The thickness and lateral extent of key bounding surfaces were also measured. This data has been added to a dimensional database for paralic systems created as part of an ongoing research effort and will be used to inform future performance prediction simulations. Based on the internal architecture and stacking of geobodies within the incised valley fill we expect significant connectivity between channels and bars, where they overlap, and with the underlying sand-rich shoreface deposits. Internal shale drapes form the greatest potential for reservoir compartmentalization.