The need for improved models to simulate chemical enhanced oil recovery (CEOR) methods involving either free gas or solution gas has increased in recent years as it has become more common to inject surfactants to recover live oils using surfactant-polymer or alkaline-surfactant-polymer flooding, or to inject gas with the surfactant solution (low-tension gas flooding or foam). A four-phase flow and transport formulation is needed to accurately model these EOR methods. New experimental data are now available to help in the development and validation of such models. In particular, the effect of pressure and solution gas on microemulsion phase behavior is now much better understood because of new and much more systematic experimental data. New low-tension gas or alkali surfactant foam experiments have also recently been published.
In this paper, we present a four-phase flow formulation implemented in the numerical reservoir simulator UTCHEM, a compositional model developed specifically to simulate both lab-scale and field-scale chemical EOR. UTCHEM includes a third-order TVD finite-difference method to improve numerical accuracy of the extremely non-linear chemical processes. A black-oil model for oil/water/gas is coupled with the surfactant/oil/water (microemulsion) phase behavior model through a new formulation. The new formulation includes water, oil, gas, surfactant, polymer and electrolyte components in the aqueous, oleic, microemulsion and gas phases. The PVT properties are calculated for each phase using this model. The impact of pressure and solution gas on the optimum salinity and interfacial tension will be discussed.
The four-phase flow simulator has been used to model low tension gas flooding taking into account process mechanisms. The results aid in the understanding and interpretation of four-phase flow chemical EOR processes. The simulator can be used to evaluate chemical EOR methods involving solution gas and/or free gas, to scale up lab experiments to the field and to optimize chemical EOR process design for field tests among other applications. The need for a reliable mechanistic simulator has greatly increased due to more field applications of chemical EOR with gas and the expected further increase of this type of EOR.