A Geomechanics-Coupled Embedded Discrete Fracture Model and its Application in Geothermal Reservoir Simulation

Geomechanics plays an essential role in fluid/heat flow by affecting hydraulic parameters. This influence could be amplified when fractures exist in the system because fracture aperture is highly sensitive to stresses. Coupled fluid/heat flow and geomechanics model is considerably important in simulating thermal-hydrologic-mechanical process, such as geothermal reservoir development. At the same time, due to the rock matrix shrinkage or expansion, thermal stress exerted on fracture surface remolds the aperture significantly and should be incorporated in modeling heat related process. In this study, a coupled fluid/heat flow and geomechanics model, TOUGH2-THM, was developed based on the parallel framework of TOUGH2-CSM, with stress tensor components as primary variables. This modification is aiming on computing normal stresses on discrete fracture surface such that fracture related parameters can be fully coupled with geomechanical model. Embedded discrete fracture model was also improved to be compatible with the geomechanical coupling. Both of TOUGH2-THM and modified EDFM were validated for further application. A geothermal reservoir simulation is conducted by the newly developed model, demonstrating the capability of this program to perform coupled modeling. It is also concluded that geomechanics and especially temperature alteration induced stress could affect fluid/heat flow in fracture and rock matrix. Thus, production efficiency could be impacted as well. The thermal stress generated by temperature reduction could enhance the fracture permeability in orders of magnitude. Various scenarios of injection temperature were modeled and compared. It can be observed that geothermal reservoir development is negatively influenced by geomechanical (and thermal) effect on fractures. The coupled model is helpful to improve the simulation accuracy.