Stress-strain response and seismic signature analysis of phyllite reservoir rocks from Blue Mountain geothermal field

Geothermal energy is the earth heat that can be extracted from different resources such as deep rock reservoirs and hot water in the earth’s crust. A geothermal system involves injecting the fluid through the injection well and extracting the heated fluid from the deep geothermal reservoir. This clean and sustainable energy is used for electricity production. Geothermal energy plants might apply the hydraulic stimulation techniques to overcome the production decline issues by enhancing the permeability and fracture network connectivity of the reservoir. This type of geothermal system is called enhanced geothermal system (EGS). Geomechanical characterization of reservoir rock provides valuable information that can be used to optimize the hydraulic stimulation program. The current research aims to characterize the elastic, plastic, time-dependent, and failure behavior of the phyllite rock, extracted from Blue Mountain geothermal field, through a series of mechanical experiments including multi-stage elastic, cyclic, creep, and multi-stage failure tests. Furthermore, seismic signatures were collected at different loading stage to investigate the pressure dependency of the dynamic moduli and the changes of the time-frequency map. In addition, the experimental program was performed on both horizontally and vertically drilled phyllite sub-cores to evaluate the effects of anisotropy. According to the results, the discrepancy between the elastic moduli of the two specimens under different stress conditions reinforces the anisotropy hypothesis. Also, compared to the horizontally drilled specimen, the vertically drilled one indicated a higher degree of non-linearity during loading/unloading