Failure modes of shales and their implications for natural and man-made fracture assemblages

Abstract

Shale is one of the most common rock types, with a rich and complex variety of failure structures in the Earth’s continental crust. In this paper, a synopsis of these structures including joints, pressure-solution seams and cleavages, faults, and shear bands is presented. First, two main categories, sharp and diffuse structures, each of which has subclasses based on its displacement discontinuity type including shear, compaction, and dilation are defined. Then, natural field examples are provided for each class as well as complex structural assemblages that include more than one type of failure-mode structures. Finally, the significances of these assemblages in terms of how older structures may influence later natural and man-made fractures and how they may interact in terms of fluid and gas flow are briefly discussed.