Relationships Between Mechanical Properties and Fracturing Conductivity for the Eagle Ford Shale
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SummaryCreating propped-fracture conductivity that is sustainable at the closure stresses occurring during production is critical to the success of hydraulic-fracture treatments in unconventional reservoirs. In addition, knowledge of the expected fracture conductivity is important information to guide the design of fracturing treatments. This study presents the results of an extensive set of fracture-conductivity experiments conducted using Eagle Ford Shale outcrop samples, as well as supporting measurements of mineralogy and mechanical properties of the shale samples.The Eagle Ford Shale is subdivided into five different geological facies: A, B, C, D, and E (Donovan et al. 2012). Facies A lies just above the Buda Limestone, and is overlain by Facies B, which has the highest total organic content (TOC). Facies A and B are known as the Lower Eagle Ford, whereas Facies C, D, and E are the Upper Eagle Ford. Facies E underlies the Austin Chalk. Outcrop Eagle Ford Shale samples were collected over the entire vertical extent of a complete exposure of the Eagle Ford Shale in Antonio Creek and Lozier Canyon near Langtry, Texas. Unpropped and propped conductivities of fractured shale samples from all major subfacies of the Eagle Ford Formation were measured using a modified American Petroleum Institute (API) fracture-conductivity cell. Before the fracture-conductivity tests, the fracture surfaces were scanned with a laser profilometer, providing detailed maps of the fracture surfaces. With other samples from the same intervals, the mineralogy, Brinell hardness, Young's modulus, and Poisson's ratio were measured.The measured fracture conductivities were compared with the fracture surface roughness, elastic mechanical properties, Brinell hardness, and mineralogy of the samples. It was found that propped and unpropped conductivities declined exponentially with closure stress. Propped-fracture conductivity was found to primarily depend on proppant size and loading, with less effect of the rock properties. Conductivity was positively related to rock brittleness and inversely related to Poisson's ratio.
