Three-phase equilibrium in a GPU-based compositional reservoir simulator
摘要
Reservoir simulation typically considers the aqueous phase as inert, i.e., water is not in thermodynamic equilibrium with other components; specific applications nevertheless require accounting for mass exchange between aqueous and hydrocarbon phases. Søreide and Whitson Equation of State (EoS) was recently implemented in a mass variables-based reservoir simulator and applied to models where only vapor and aqueous phases are present at reservoir conditions (Panfili et al. Computational geosciences, pp 1–14, 2023). We here describe the extension of said implementation to support component partitioning across the three reservoir phases. With the mass variables formulation, phase equilibrium calculations are needed in each cell at each Newton’s iteration. The equilibration algorithm adopted in this work consists in starting with a negative flash and an initial guess containing three phases. This approach is computationally heavier than one where additional phases are progressively introduced as needed based on stability testing, but is simpler to implement while representing an acceptable fraction of the overall simulation time in practical cases. Realistic application cases where hydrocarbon-water mass exchange plays an important role in the physics of the recovery/storage process, such as estimation of the impact of water vaporization on the final recovery in high-pressure/high-temperature gas condensate fields, CO