Rapid phase stability calculations in fluid flow simulation using simple discriminating functions

•Method allows for the rapid determination of mixtures' phase stability state.•Uses discriminating functions to provide “quick & safe” answers.•Can be combined to any conventional algorithm.•Ideal for problems where repeated phase behavior calculations are needed.•Great CPU time savings in compositional reservoir simulation runs.

This paper presents a new phase stability method that is applicable when repeated phase behavior calculations are needed as it is the case with multiphase fluid flow compositional simulation in upstream petroleum engineering. Two discriminating functions act as classifiers in such a way that a positive value of one of the two functions determines the stability state of the mixture. The two functions are generated off line, prior to the simulation, and their expressions are very simple so that they can be evaluated rapidly in a non-iterative way for every discretization block and at each timestep during the simulation. The CPU time required for phase stability calculations is dramatically reduced while still obtaining correct classification results corresponding to the global minimum of the system Gibbs energy function. The method can be applied to any chemical engineering problem where the class of several objects needs to be determined repeatedly and quickly.