| Abstract |
The purpose of this study is to evaluate the effect of permeability heterogeneity in a hydraulic fracture of an Enhanced Geothermal System (EGS). The thermo-hydraulic behavior of the EGS will be investigated under different types of heterogeneity distributions of the hydraulic fracture permeability, as a function of space and time compared to a homogeneous HF permeability. Also, when an EGS is operating (injection/production) the geomechanical stress regime in the reservoir tries to go back to its original state. Subsequently, it applies a significant stress in the vicinity of the hydraulic fracture, trying to close the fracture aperture. This may lead to restriction of flow, which may affect the EGS performance. In this study, this will be replicated by gradually decreasing the permeability of the hydraulic fracture as a function of time as injection/production is underway. The EGS system that we investigate involves an injector and a producer, a hydraulic fracture (HF) and the rock subdomain. Because of the low permeability of the rock matrix, majority of flow is expected to occur in the HF, with fluid and heat exchanges between the HF and the rock matrix. All relevant metrics will be monitored, either globally on a reservoir scale basis or locally at areas of interest (production well). This numerical simulation study is conducted with the TOUGH+RealGasBrine V1.5 code, with high-resolution 3-D Cartesian grids. The cooling front propagation (in the HF and into the rock matrix), optimal production rates, and produced heat flow (MW¬th) are the main criterion for the thermo-hydraulic evaluation of the performance of the EGS. ‘ The results showed a significant effect of these changes on the overall performance of the EGS. The exact heterogeneity distribution of the HF permeability/conductivity will play a big role on the injected fluid trajectory, thus the cooling front propagation rate. Pressure builds up concerns may become an issue at some point as well given the permeability distribution, especially if low permeability “damaged†zones are present. This is also the case when simulating the closure of the HF aperture by decreasing the HF permeability incrementally as a function of time. |