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## The effect of thermal stress on injection-induced seismicity

Victor Vescu, Kyungjae Im, & Jean-Philippe Avouac

Submitted September 10, 2023, SCEC Contribution #13217, 2023 SCEC Annual Meeting Poster #140

A better understanding of the mechanisms driving injection-induced seismicity requires an accurate model of the stress changes resulting from the injection. We, therefore, consider how deep fluid injection changes the state of subsurface stress in two ways: poroelastic stressing, caused by increased pore fluid pressure, and thermoelastic stressing, caused by an overall cooling and contraction of the medium surrounding the injection. Considering both the inside and outside of the volume in which the cooler-than-ambient fluid is pumped, we estimate the resulting thermal stress changes and the effect on the seismicity rate based on Dieterich’s semi-analytical model [Dieterich, 1994]. To this end, we numerically simulate a spherical fluid injection at a temperature lower than the reservoir. The reservoir is assumed to be a fluid-saturated, slightly compressible isotropic medium. Under spherical geometry, we use the mass conservation equation and volumetric flow rate based on Darcy’s law to calculate the mass of advected fluid away from the well and the increase in pore fluid pressure. The heat balance equations determine the temperature evolution of the ambient elastic medium. We use Eshelby’s formulation for poro-thermo-elastic coupled stress change caused by pressure change and cooling. We analyze the temporal evolution of the stress field surrounding the injection point under the increasing influence of thermal effects. We also show how the injection rate and other reservoir parameters (e.g., permeability and thermal conductivity) influence the resulting stress field and seismicity rate. The simulation result can be used as an input in a discrete fault network model to investigate the induced seismicity further. The study will allow us to quantify the role of thermal stress in driving seismicity and faulting during fluid injections. It is particularly relevant to geothermal applications (EGS and conventional) and CO2 storage.

Key Words
thermo-poroelastic stressing, induced seismicity

Citation
Vescu, V., Im, K., & Avouac, J. (2023, 09). The effect of thermal stress on injection-induced seismicity. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)