Multiphase mass and heat transfer in fractured high-enthalpy geothermal systems

Multiphase mass and heat transfer are ubiquitous in the subsurface within manifold applications. The presence of fractures magnifies the uncertainty of the heat transfer process, which will significantly impact the dynamic transport process. However, accurate modeling methodologies for thermal high-enthalpy multiphase flow within fractured reservoirs are quite limited. In this work, the geothermal multiphase flow in the high-resolution fractured reservoir is numerically investigated. The discrete-fracture model is utilized to describe the fractured system with discretization of optimized resolution. A synthetic fracture model is selected to run on different levels of discretization with different initial thermodynamic conditions. A set of comprehensive analysis is conducted to compare the convergence and computational efficiency of simulation results. The numerical scheme is implemented within the Delft Advanced Research Terra Simulator (DARTS), which can provide fast and robust simulation to energy applications in the subsurface. Based on the converged numerical solution, a thermal Peclet number is defined to characterize the interplay between thermal convection and conduction. Different heat transfer stages are recognized on the Peclet curve in conjunction with production regimes in synthetic fractured reservoir. Afterward, a realistic fracture network, sketched and scaled up from a digital map of a realistic outcrop, is utilized to perform sensitivity analysis on the key parameters influencing the heat and mass transfer. The thermal propagation and Peclet number are found to be sensitive to flow rate and thermal parameters. The findings provide insights for the multiphase mass and heat transport in the fractured high-enthalpy geothermal reservoirs, which can be taken as guidance for the practical geothermal developments with uncertainties.