A Four-Phase Flow Model to Simulate Chemical EOR with Gas

Abstract

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.

Simulation of Surfactant Oil Recovery Processes and the Role of Phase Behaviour Parameters

“…This is mainly due to what was exposed above: the salt component is present in the aqueous phase and travels faster than the oleous one, so that the salt content in the surfactant bank decreases rapidly, and thus it does the partition coefficient. However, the salt content increases the sweeping efficiency, which agrees with previous results [64][65][66]. This is shown in Figures 18 and 19, where the partition coefficient and the oil saturation are plotted.…”

“…A 3-fold increase in the salt content caused an oil recovery growth of 2-fold, due to the significant increase in the partition coefficient (Table 7). Therefore, it is advisable in oil recovery processes with surfactants the injection of low salt concentration brine in order to improve sweeping efficiency, which agrees the results reported by several authors [47,[64][65][66]71].…”

“…The first part of the analysis, and the one deemed as the most important in surfactant flooding, is the study of the influence of the phase behaviour parameters on the three-component system. This importance has already been discussed previously [33,41,42,44,52,[63][64][65][66][67][68], and it plays an important role in the recovery process, because it determines the fractions of chemical, oil and water in each of the phases. It is noteworthy that, while these parameters are dependent on the salt content present in porous media, in this section this dependence will not be considered since this component is not taken into account.…”

“…On this new simulator no distinctions are made between monoor divalent salt ions. The salt changes the phase behaviour in systems with surfactants [49,[64][65][66]70], so this is crucial to be taken into account during the simulation and laboratory or field experiments, in order to understand the actual behaviour of the system. The partition coefficient is affected by the latter according to Figure 3 [51].…”

Numerical simulation of foam flooding in porous media in the absence and presence of oleic phase

“…To be able to predict the effect of the concentration on the foam apparent viscosity, they extend the model such that five foam parameters vary with surfactant concentration. Lotfollahi et al (2015) presented a numerical model to simulate foam flooding in the presence of micro-emulsion phase. However, in this work no validation was given with respect to the experimental data.…”