Multiphase flow modeling and energy extraction performance for supercritical geothermal systems

Abstract

Beyond the critical point of 373.946 °C and 22.064 MPa, water presents in the supercritical state, which is of great potential for geothermal resource development. In this work, an improved EoS (Equation of State) module is developed for simulation in supercritical geothermal systems based on the structure of the TOUGH2 program. Compared to previous studies, this new module provides a more elaborate description of the multiphase flow behavior. A novel method is proposed, which is more accessible and physically reasonable for the flow between sub- and supercritical conditions. Moreover, the effect of pressure and temperature on relative permeability and capillary pressure is considered, which makes it smooth and continuous around the critical point.A 1-D vertical column model demonstrates the multiphase flow and phase transition behavior during the upward flow of supercritical fluid. Then it is applied to the reservoir condition found by well IDDP-2, Iceland, for qualitatively assessing optimal conditions for the supercritical geothermal exploitation. Results indicate that temperature around 400 °C may be more favorable; excessive temperatures likely cause an early thermal breakthrough. This code development provides a platform for further studies and in-depth investigation of the potential supercritical geothermal development.