Publications

Experimental and numerical investigation of hydro-thermally induced shear stimulation

Bauer, Stephen J.; Huang, K.; Chen, Q.; Ghassemi, A.; Barrow, P.

The objective of this research is to produce laboratory-based experimental and numerical analysis that will provide a physics-based understanding of shear stimulation phenomena (hydroshearing) and its evolution during stimulation. Water is flowed along fractures in hot and stressed fractured rock, to promote slip. The controlled laboratory experiments potentially provide a high resolution/high quality data resource for evaluation of many analysis methods developed by to assess EGS "behavior" during this stimulation process. Segments of the experimental program provide data sets for model input parameters, i.e., material properties, and other segments of the experimental program represent small scale physical models of an EGS system, which may be modeled. The project is a study of the response of a fracture in hot, water-saturated fractured rock to shear stress which is experiencing fluid flow. Under this condition, the fracture experiences a combination of potential pore pressure changes and fracture surface cooling, resulting in slip along the fracture. As such, the work provides a means to assess the role of "hydroshearing" on permeability enhancement in reservoir stimulation. Using the laboratory experiments and modeling, including pore pressure, thermal stress, fracture shear deformation, and fluid flow, insight into the role of fracture slip on permeability enhancement-"hydro-shear" is obtained. This paper presents the results of an experimental program along with numerical modeling to study shear stimulation of fractures in response to cool water injection into hot stressed rock with simulated fractures. 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 numerical modeling and experimental observations is achieved. Simulation results illustrate that pore pressure and cooling cause the fracture system to deform (slip) resulting in permeability modifications. Fracture permeability evolution with stress variations in the sample is also observed in these experiments.