Numerical Modeling of Permeability Enhancement and Induced Seismicity During Egs Operation Using A Partially Bridging Multi-Stage Hydraulic Fracture Design

Enhanced geothermal systems (EGS) have emerged as an alternative energy supply that is both green and tackles climate change. Multi-stage hydraulic fractured horizontal well design is a promising design for economic EGS development. In our previous work, we proposed a partially bridging fracture pattern that forces water to flow through the stimulated reservoir volume (SRV) of an EGS, which improves heat extraction efficiency. However, the associated induced seismicity and secondary permeability enhancement in the SRV during production have not been investigated. In this work, we use a fully coupled thermal-hydraulic-mechanical (THM) model, developed in the reservoir simulator, FEHM, to evaluate the proposed EGS design. The model includes coupled reservoir and horizontal wellbore components that account for the thermo-poroelastic induced stress changes and permeability enhancement over a 20-year production period. A Mohr-Coulomb failure criterion, empirical fracture permeability, and rate-and-state friction laws are applied to describe the permeability evolution and induced microseismicity associated with the partially bridging fracture design. We use these to evaluate the style of permeability enhancement, relative contributions by thermoelastic and poroelastic effects, and the rate of triggered seismic events. Finally, the effect of several key parameters including injection and fracture design parameters on induced-seismicity evolution are investigated, which could provide guidance and protocols for mitigating seismicity during EGS operations.