Constructing Three-Phase Envelopes Using a Trust-Region-Based Algorithm

Abstract

Summary We develop a new trust-region (TR)-based algorithm to construct complete three-phase envelopes for reservoir fluid mixtures. The new algorithm is developed based on a basic algorithm for two-phase envelope constructions (Xu and Li 2023). A state-of-the-art TR method with a realistic exact subproblem solver is implemented in the algorithm, and an integrated strategy is adopted to construct complete phase envelopes with two-phase and three-phase branches. We test the performance of the TR-based algorithm by constructing multiphase envelopes for a total of 15 fluid mixtures that include hydrocarbons-CO2, hydrocarbons-asphaltene, and hydrocarbons-water mixtures. Comparison against the conventional Newton-based algorithm indicates that the TR-based algorithm leads to a much higher computational efficiency and an enhanced robustness.