Abstract

This paper proposes a new and robust formulation for numerical compositional simulation which has an implicit equation for the oil-phase pressure and water saturation, a linearised explicit equation for the hydrocarbon saturation, and explicit equation for the overall explicit composition for each hydrocarbon components that satisfy thermodynamic equilibrium. The phase equilibrium and the physical property calculations are carried out by using Equations of State. Interfacial tension effects are also considered in order to simulate miscibility behaviour and the dynamic nature of the relative permeability. A new two-dimensional relative permeability algorithm is included which handles lumped hydrocarbon phase as well as individual phase flows.

The codified formulation has been tested to simulate the behaviour of volatile oil and gas condensate reservoir realisations under straight depletion and gas cycling both cylindrical and Cartesian co-ordinates. Some SPE test cases taken from the literature are included in the numerical experiments for validation.

It is demonstrated in this present paper that the results are compared favourably with analytical techniques and other publised numerical results. They also confirm that the proposed codified formulation is unconditionally stable and it is as stable as fully compositional model yet the computational cost reduction was substantial.