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Digital Outcrop Model of the Eagle Ford Group, Lozier Canyon, Terrell County, West Texas

Abstract

The Eagle Ford Group is a prolific producer of unconventional oil and gas in south Texas. Operators typically target the Lower Member of the Lower Eagle Ford Formation to drill horizontal wells. The Upper Member of the Lower Eagle Ford Formation is generally avoided due to an abundance of bentonite beds infamous for obstructing hydraulic fractures. With laterals averaging nearly 1 mile in length, geologic variability can be significant. Thus, understanding the variability of reservoir thicknesses, facies distributions, and fractures, paired with petrophysical data, is valuable in characterizing unconventional reservoirs. Digital outcrop models (DOMs) using photogrammetry methods offer a unique tool to study variability of Eagle Ford Group strata in outcrops in Lozier Canyon located in Terrell County, Texas. Stratigraphic variability within the Eagle Ford Group has been well documented; however, lateral variability of Eagle Ford Group strata is minimally understood and is fundamental to developing this play. The objective of this study is to analyze the variability of Eagle Ford Group strata in outcrops at Lozier Canyon using DOMs. Complete vertical sections of the Eagle Ford Group are exposed along several cut banks spanning a canyon length of 7.1 miles north-to-south from U.S. Route 90 to the Rio Grande River. The project focuses on southern Lozier Canyon and incorporates data from northern Lozier Canyon and side tributary Antonio Creek. The dataset consists of measured sections and hand-held gamma-ray profiles, and integrates these data in the framework of reservoir-scale DOMs to develop an improved high-resolution model of variability. The results characterize lateral thickness variation of the Eagle Ford Group, and identify continuous and discontinuous limestone beds across the study area. Image and fracture analysis using DOMs gives insight to Eagle Ford Group variability, specifically the relationship between fractures, limestone beds, and shale. This understanding has direct application to the subsurface and could help to characterize unconventional reservoir architectures in Texas and around the world. Preliminary results indicate that the Eagle Ford Group thickens from northern Lozier Canyon to southern Lozier Canyon by approximately 20 feet. Limestone beds in the Lower Eagle Ford Formation become more discontinuous toward the Upper Eagle Ford Formation contact. Fracture height, terminations, and estimated orientation are discernible from DOMs.