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

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.