Davis, Drew Edward (2017-05). Digital Outcrop Models of the Eagle Ford Group in Lozier Canyon, Terrell County, Texas. Master's Thesis.
The Eagle Ford group was a prolific producer of unconventional oil and gas in south Texas during the last decade. Operators typically target the Lower Eagle Ford formation to drill horizontal wells with lateral lengths averaging nearly 1 mi (1.61 km). Geologic variability can be significant at these distances, thus an understanding of lateral variability of reservoir thicknesses, facies distributions, and fractures paired with geochemical and petrophysical data is valuable in characterizing unconventional reservoirs.
High-resolution digital outcrop models (DOMs) using photogrammetry techniques provide a unique tool to study variability of Eagle Ford group strata in outcrops in Lozier Canyon in Terrell County, West Texas. Stratigraphic variability within the Eagle Ford group is well documented; however, lateral variability of Eagle Ford strata is minimally understood and is fundamental to developing this productive unconventional play. This project focuses on world-class outcrops that expose complete vertical sections of the Eagle Ford group. The study area covers a north-to-south straight line distance of 6.2 mi (10 km) allowing analysis at reservoir-scale.
The average gross stratigraphic thickness of the Eagle Ford group increases by approximately 27.8 ft (8.47 m), a 13.59% increase, from the Scott Ranch site in north Lozier Canyon to south Lozier Canyon. Each Eagle Ford facies increases in thickness from north-to-south Lozier Canyon with Facies C exhibiting the largest percent change in thickness at 20.18%. Skeletal packstone-grainstone bedforms in Facies B are less laterally continuous up-section from the base of the Sub-facies B2 - B3 contact into the mud-dominated uppermost Facies B (B5). A characterization of fractures traced in 2-D orthomosaics is related to bedding features in Facies B and Facies C. Fractures are generally shorter (vertically and laterally), more closely spaced, and have higher intensities in Facies B than in Facies C at each respective study site. Furthermore, our findings indicate that, as apparent fracture spacing decreases, apparent fracture dip increases. This inverse relationship between apparent fracture spacing and apparent fracture dip is related to outcrop strike and used to estimate the orientation of dominant fracture sets in Lozier Canyon.
This study highlights the practicality of using unmanned aerial vehicles (UAVs) and photogrammetry techniques to study vast areas of largely inaccessible outcrop. DOMs were interpreted and imported into Schlumberger's Petrel 2014 and will be used to construct improved reservoir models of the Eagle Ford group in future studies. These models may have application in helping to predict subsurface reservoir variability in the Eagle Ford group and may be valuable for improving our understanding of other unconventional carbonate mudstone reservoirs, such as the Haynesville and Utica shales.