Computer Modelling Group Ltd.

Alkaline/Surfactant/Polymer (ASP) is an important chemical EOR process that involves the generation of in-situ soap through the reaction of the acid component in the oil with the alkali, in conjunction with intra-aqueous reactions, mineral dissolution and precipitation, micro-emulsion behavior and salinity gradient. The mechanistic simulation of ASP is very complex and has been carried out with specialized chemical flood simulators. Current trends in EOR processes show an interest in hybrid methods where chemical flooding is combined with other EOR methods such as low salinity waterflood, foam and gas/CO2 injection. Thus, it is beneficial to develop such capabilities in an Equation-of-State (EOS) compositional simulator for screening and combining different EOR processes.

This paper presents a framework for mechanistic modeling of the ASP process within an EOS compositional simulator. A new approach for modeling the Winsor Type I, II and III micro-emulsion phase behavior is introduced based on laboratory solubility data. In the Type III system, the emulsion is distributed judiciously between the oil and water phase without the introduction of a third liquid phase. The optimal salinity variation with the soap/(soap + synthetic surfactant) mole fraction is modeled. This feature allows the design of salinity gradient, an essential requirement for a successful ASP flood. The above physics are coupled with comprehensive geochemistry calculations (intra-aqueous reactions and mineral precipitation/dissolution reactions) and three-phase oil/gas/water flash calculations with an equation of state and Henry's law. The whole system of associated equations is solved simultaneously with the flow and energy equations using Newton's method, making the simulator one of the most robust and comprehensive simulators for EOR methods.

The simulator is validated with ASP core flood experiments. The optimization of the ASP process for a typical field is illustrated and discussed with regard to alkali, synthetic surfactant and polymer injection with decreasing salinity.