Speaker
Description
Predicting what permeability enhancements are feasible in a geothermal system (EGS) and the potential seismic activity they may trigger is challenging. Geomechanical simulations are computationally expensive because they require a discretized fracture network with a relevant level of complexity and a quantification of frictional sliding and tensile opening of individual fractures therein. Yet, computations of the fracture aperture distribution are essential, because they are decisive for predictive simulations of coupled flow and transport in EGS.
Here, we model this deformation assuming that the rock matrix is homogeneous with linear elastic behavior and that the slip profile of failing isolated fractures is elliptic with a linear relationship between maximum slip and induced stress. We employ such simplified single-fracture slip solutions as basis functions to predict displacement fields. Overall stresses are obtained by mapping the basis functions to the fracture ensemble of interest. This stress field combines far-field- and all slip-induced stresses, constraining the maximum slip and tensile opening along each fracture while considering local force balance constraints.
We illustrate the method for single-, parallel-, and intersecting fractures, as well as fracture networks. Importantly, our approach dramatically reduces the number of degrees of freedom as compared to an element-based mechanics simulation of the same model. It also permits the calculation of displacement and stress fields via superposition of precalculated basis functions. This opens the door to coupled mechanics, flow and transport in realistic EGS.
| Country | Switzerland |
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