Theoretical model for roughness induced opening of cracks subjected to compression and shear loading

Abstract

The phenomenon of roughness induced opening or slip opening is well known in rock mechanics and relates to a crack (or rock joint) behaviour under compression and shear. It has been widely utilised in tight gas and coal bed methane industries to increase the permeability of geological reservoirs during hydraulic stimulations and has recently been extended to geothermal energy technologies for successful harnessing the thermal energy from hot rocks. However, this phenomenon is still poorly understood; and only several semi-empirical equations are currently available in the literature to predict values of the slip openings. In this paper new mechanical and mathematical models of the roughness induced opening are suggested. A computational approach based on the distributed dislocation technique was implemented to analyse various coupled effects. The focus of this paper is on stress analysis of a straight crack with rough faces located in an infinite impermeable body. The crack is subjected to remote normal and shear loading and a uniform fluid pressure applied inside the crack. The developed model can further be extended to investigate many other interesting and practically important problems such as analysis of fracture initiation in natural faults subjected to fluid pressure, residual opening after releasing the fluid pressure or permeability changes associated with hydraulic stimulations.