Tensile Failure of Shales: Impacts of Layering and Natural Fractures

Abstract

AbstractShale formations present anisotropic characteristics in mechanical, acoustic, and flow properties due to their layering and pre-existing natural fractures. This anisotropic behavior can create a complex fracture network rather than the conventionally presumed planar fractures. Although incorporating anisotropic behavior is essential for optimizing the hydraulic fracturing design and analyzing the post-fracture data, there are limited studies addressing the anisotropic tensile behavior of organic-rich shale formations. The objective of this study is to explore the tensile strength and tensile fracture patterns in shales by conducting splitting tests on variety of shale formations.Core samples from the Eagle Ford shale in the oil window, its overlying Austin Chalk and the underlying Buda formation, Green River immature oil shale, Mancos shale, and Berea sandstone samples have been tested to investigate the effects of layering, natural fractures, total organic carbon (TOC), maturity and mineralogy on tensile behavior. Having different types of Green River shale, the impact of TOC on the tensile strength was obtained. The anisotropic tensile behavior of Mancos and Green River shales were studied systematically at various orientations between the applied force and the bedding direction providing key understanding on the fracture growth patterns at any direction. Finally, the tensile strength and fracture patterns for several Eagle Ford, Austin Chalk and Buda core samples with extensive natural fractures are discussed.