Computational Framework for EGS Fracture Stimulation

Abstract

We are interested in simulating the shear strain damage that can be induced in an in situ poroperm medium stressed by overpressurization of a wellbore fluid such as might be conducted in interest of flow stimulation of an inter-wellbore EGS heat exchange volume. Our strain-damage simulation is performed in a 2D section of a fracture-heterogeneous poroperm medium characterized by (i) a normally-distributed fracture-density population organized into percolation pathways induced by spatial correlations at all scale lengths (consistent with generic well-log spatial fluctuation systematics), and (ii) long-tailed (‘lognormal’) permeability distributions ? associated with percolation pathways related to porosity distributions ? through the relation ? = ?0 exp(?(?-?0)), ? = ratio of standard deviations of log? and ? distributions (consistent with clastic reservoir well-core poroperm fluctuation systematics). The pressurized wellbore fluid creates shear strains in the fracture heterogeneous poroperm medium, putatively generating grain-scale fracture damage additional to the existing grain-scale fracture damage in the medium. Fluidpressure- induced grain-scale fracture damage can be seen as creating new fluid flow pathways (and higher overall permeability) via newly created grain-scale fracture-connectivity. This leads to greater fluid throughput in the EGS heat-exchange volume equivalent to incrementing the value of the fracture-connectivity parameter ?. Our computation proceeds through a fully coupled finite element analysis of the thermal, hydraulic, and mechanical (THM) energy scheme.