ABSTRACT:

The understanding of geothermal fields requires coupling between heat flow through fractures and induced seismicity. In this context, we develop a semi-analytical approach for estimating (1) thermo-poro-elastic stresses in a fractured geothermal system, and (2) seismicity rates based on the model of Dieterich (1994). Cold water is injected at constant rate into a single fracture surrounded by hot impermeable layers. Heat flow is dominated by advection and conduction respectively inside and outside the fracture. Poro- and thermo-elastic stresses are estimated separately following the nucleus-of-strain concept; and for any potential fault around the single fracture the induced Coulomb stress rates are resolved. For this particular scenario, the thermal stresses are dominant. We show that thermal-stressing rates can induce an increase in the rate of seismicity of more than hundredfold at distance up to 200m from the single fracture. Our fast forward model is suitable for data assimilation, and by predicting the spatio-temporal evolution of the locations of increase/decrease of seismicity rate one might optimize geothermal systems while keeping seismicity at a relatively low magnitude.

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