Inga Berre: [WS] Mixed-Dimensional Compositional Models for Multiphase Flow with Phase Separation in Fractured…

Speaker
Inga Berre, University of Bergen

Abstract
Fractures play a crucial role in controlling flow and heat transfer in geothermal reservoirs, where highly coupled processes occur under high-enthalpy conditions. We present a mixed-dimensional modeling framework that explicitly represents fractures as lower-dimensional planar surfaces within a three-dimensional rock matrix. A persistent-variable compositional formulation is introduced, where fluid properties are computed from advanced thermodynamic models and equations of state. The persistent-variable formulation keeps the equations and variables consistent in every cell throughout the simulation, fixing the number of tentative phases independent of their physical presence, thus avoiding the variable substitutions during phase transitions that are necessary in traditional natural variable formulations. Using enthalpy as the primary variable, the model handles phase transitions and captures complex flow phenomena such as localized boiling and condensation. The governing partial differential equations are discretized using control volume methods and implemented within the PorePy software framework. The nonlinearities induced by phase transitions are handled by embedding a local solver for the thermodynamic subproblem within a global Newton scheme for the fully implicit formulation.