3D Geologic Modeling and Fracture Interpretation of the Tensleep Sandstone, Alcova Anticline, Wyoming

Nathaniel J. Gilbertson, Geology & Geological Engineering, Colorado School of Mines, 1516 Illinois St, Golden, CO 80401, phone: 303.549.4626, [email protected] and Neil F. Hurley, Dept. of Geology & Geological Engineering, Colorado School of Mines, 1516 Illinois St, Golden, CO 80401.

Alcova Anticline is a Laramide-age structure on the southeast margin of the Wind River basin, central Wyoming.  The Pennsylvanian Tensleep Sandstone, a prolific oil-producing reservoir in the Rocky Mountains, occurs at the core of the exposed anticline.  The North Platte River cuts across the axis of the anticline, resulting in two near-vertical walls of Tensleep Sandstone, approximately 500 m wide, 100 m tall, and separated by 140 m.  High-resolution (1-2 cm) Lidar scans of the two walls were acquired to study the frequency and orientation of fractures in the structure.  The Lidar survey at Alcova was designed to collect sufficient data points to resolve fracture planes ≥1 m² in area.  Additionally, high-resolution photomosaics were draped over the data set.  The Lidar dataset has been processed using various decimation approaches.  Fracture planes have been detected using automated and handpicking approaches. One goal of the study is to populate a 3D geologic model with a fracture network, based on outcrop work.  The 3D geologic model, which is built from serial cross sections, is constrained by GPS measurements of key formation contacts in the study area.  Extracted fracture data from the Lidar dataset determine the parameters used to seed the fracture generating model.  A further goal of this study is to provide input into a reservoir model of Teapot Dome anticline, an analogous Tensleep reservoir and a proposed CO₂ sequestration site.