A Unified Compositional Flow Model for Simulating Multiphase High-Enthalpy Geothermal Reservoirs

Abstract

Simulating high-enthalpy geothermal reservoirs poses significant challenges due to the complex interactions between multicomponent, multiphase geothermal fluids influenced by varying pressure, temperature, and other physical conditions. These complexities complicate the development of models that can efficiently quantify the impact of production strategies and other aspects relevant to the engineering of geothermal systems. In this work, we propose a unified compositional flow model for geothermal reservoir simulation, which integrates mass and energy conservation laws across predefined phases, advanced equations of state (EOS), and a comprehensive thermodynamic framework. This unified formulation maintains a persistent set of unknowns and equations, and efficiently manages phase transitions using complementarity conditions. This approach eliminates the need for manual phase switching, enhancing both numerical stability and computational efficiency. Our model captures essential phase behaviors and allows a general, thermodynamically consistent representation of fluid properties, crucial for the development and operation of geothermal reservoirs. Implemented within the open-source, Python-based framework PorePy, we verify our model through numerical experiments simulating various geothermal reservoir conditions. The results present valuable insights into phase transitions, heat transfer, and component transport and show strong agreement with key simulations from the commercial geothermal simulator CSMP++