Year: 2026
Type: article
Abstract: A new algorithm for phase equilibrium calculations in water-hydrocarbon mixtures is proposed, based on the free-water assumption, in which only the solubility of water in vapor and hydrocarbon-rich liquid phases is taken into account and solubility of hydrocarbon components in water is neglected (the aqueous phase is pure water). This assumption greatly simplifies the mathematical structure of the problem, reducing its dimension for an nc-component mixture from 2 × nc in a full three-phase flash to nc +1 in the free-water flash (FWF). However, all previous implementations of the FWF used successive substitution iterations (SSI). In this work, a second-order method is used for the first time in FWF calculations and the problem is formulated in a Gibbs free energy minimization framework. In an outer loop, equilibrium constants are updated using SSI in early iterations stages and then a switch is made to the Newton method, including the negative flash option. In the inner loop a Modified Rachford-Rice (MRR) equation is efficiently solved using convex transformations. The proposed method is tested for various water-hydrocarbon mixtures and proved its robustness and efficiency. An excellent agreement between results with FWF and full three-phase flash calculations is observed. The proposed method is very useful in compositional reservoir simulation of CO 2 storage and certain oil recovery methods, as well as in process simulation.
Author: Dan Vladimir Nichita
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,350
OpenAlex ID: W7221440615