干热岩流动换热多尺度有限容积法

Efficient and reliable numerical simulation technology is crucial to deeply understanding the flow and heat transfer process in hot dry rock reservoirs and formulate reasonable development plans. However, the traditional high-fidelity finite volume method is time-consuming when it is used to solve complex flow and heat transfer of fractured reservoirs. To this end, this paper puts forward an integrated thermal-hydraulic multi-scale finite volume solution method based on the embedded discrete fracture model. And its solution process is mainly as follows. First, obtain the pressure and temperature basis functions in the coarse grid support area of matrix and fractures through Jacobian iteration. These basis functions can not only reflect the heterogeneity of matrix in the fine-scale area, but also can represent fracture distribution characteristics. Second, construct a transient coarse grid discrete system by using pressure and temperature basis functions and pre-defined coarse scale operators. And third, adopt the strategy of two-step iterative multi-scale solution to successively dissipate the surplus multi-scale error in the coarse and fine scales, so as to achieve the required solution accuracy. Then, the calculation accuracy and efficiency of the multi-scale finite volume method were verified based on two examples of fractured geothermal reservoir exploitation. And the following research results were obtained. First, the solution accuracy of pressure and temperature fields by the multi-scale finite volume method decreases slightly with the increase of simulation time. The calculation accuracy can be increased by increasing the number of multi-scale cycles, but if the number of cycles is too large, the multi-scale acceleration effect will be spoiled. Second, when the number of multi-scale cycles is in the range of 50-100, the relative deviation of two norms between the multi-scale solution and the fine-scale solution is 10^-3-10^-4. In conclusion, compared with the traditional finite volume method, the multi-scale finite volume method can increase the calculation efficiency by 4-5 times while ensuring the calculation accuracy.