A novel POD reduced-order model based on EDFM for steady-state and transient heat transfer in fractured geothermal reservoir

A new proper orthogonal decomposition reduced-order model (POD-ROM) for fluid flow and heat transfer processes in a fractured geothermal reservoir is proposed. First, the primary governing equations are established based on the embedded discrete fracture model. Second, the POD-ROM is developed by projecting the discrete matrix equations instead of the primary governing equations onto the low-dimensional space spanned by the pressure and temperature basis functions. Compared with the typical POD modeling method, the new model reduction technique can easily deal with mass and energy transfer between the matrix and fractures, thus ensuring the mass and energy conservation of the whole system in the projection process. The new model does not require complex mathematical deduction and is easy to implement in practical applications. The accuracy and robustness of the model were carefully studied for three complex heat transfer cases. Calculation results indicated that the computational efficiency can be improved by at least 10–15 times while high reconstruction and prediction accuracy is maintained.