| Abstract |
The overall goal of this study was to investigate how fracture aperture anisotropy can impact flow and heat transport, and to demonstrate ways Enhanced Geothermal Systems can be harnessed to optimize thermal performance. To achieve the goal of this study, a systematic fracture characterization approach was used, and numerical simulation models were used to study the physical processes that govern the interaction between the fluid and the rock during heat extraction from Enhanced Geothermal Systems. It was demonstrated in this study that the flow-wetted surface area had a direct and significant contribution to the amount of heat extracted. For the lab-scale fractures, the Joint Roughness Coefficient (JRC) confirmed geometric anisotropy of the fracture aperture and was seen to have a direct correlation with the flow contact area. The lower the difference in JRC values between the perpendicular and parallel flow configurations, the more flow contact area is expected in the perpendicular flow direction, which will lead to more heat extracted from the rock. From the variogram model parameters, it was deduced that high geometric anisotropy results in high differences in thermal drawdown. The thermal performance appeared to be better in the perpendicular flow configuration with a ratio of 70:30 for the lab-scale fractures. For the field-scale fractures, it was seen that most of the synthetically generated fracture aperture distributions with a geometric anisotropy ratio of 2 had Hurst exponents of fracture surface aperture variability found in nature. For all the fracture aperture distributions analyzed for the field scale, the perpendicular flow configuration resulted in better thermal performance than the parallel flow configuration with a ratio of 64:36. Furthermore, for the geometric anisotropy ratio of 2, the ratio was 70:30. The results of this study suggest that placing an injector well in the direction perpendicular to shear or slip of an enhanced geothermal system may result in favorable thermal performance over a parallel flow configuration. |