Experimental and Numerical Investigation of EGS Shear Stimulation

Abstract

This paper presents the results of an experimental program along with numerical modeling to study shear stimulation of fractures in response to cold water injection. Laboratory-based experimental and numerical analysis results are used to provide a physics-based understanding of shear stimulation phenomena (hydroshearing) and its evolution during stimulation. In order to study hydroshearing in the laboratory, a test system has been configured to (1) simulate reasonable downhole EGS environmental conditions, (2) flow cool water along fractures in hot and stressed fractured rock, (3) from (2) promote slip, (4) model the experiments in a tractable manner such that insight may be obtained of slip mechanisms. Thermo-poroelastic finite element analysis of a fractured rock injection experiment has been carried out to explore the role of pore pressure, cooling and coupled processes on fracture deformation and slip. Good agreement between modeling and experimental observations is achieved. Simulation results illustrate that pore pressure and cooling cause the fracture system to deform resulting in permeability modifications. Fracture permeability evolution with stress variations in the sample is also observed in these experiments. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2015-9072 A