Evaluation of Engineered Geothermal Systems as a Heat Source for Oil Sands Production in Northern Alberta

摘要

This paper evaluates the application of geothermal energy by numerically modeling the heat extraction that would result from the injection of cold water into an artificially fractured hot dry rock (HDR). The HDR that would be utilized in Alberta is expected to be granite with a network of pre-existing natural fractures. However, to ensure a continued flow of injected water from the reservoir to the production wells, creation of additional fractures is required. Thus, the properties of these fractures are of prime importance to the efficiency of geothermal energy production. The fracture networks for the simulations were created using a numerical code and were converted into a grid format to be used in a commercial thermal simulator. A new approach to embed a complex fracture system into the numerical model was applied. Various properties of the fractures such as aperture, length, and spacing were changed and their absolute and relative effects on energy production were quantified and the results are presented in this paper. This modeling technique was also verified by comparison with the conventional dual porosity model and by performing a history match with real field data obtained from literature. The applicability of this approach to provide heat for oil sands extraction was investigated using the volumes of water currently needed in northern Alberta. Based on these constraints, numerical simulations were run to evaluate the optimum well spacing that would be required using a three-well configuration. In this simulation, the fracture parameters (density and aperture) were kept fixed assuming that they are not affected by cold water injection. The results of this study suggest that geothermal energy has a potential to be a sustainable form of thermal energy for oil sands extraction in northern Alberta.