Numerical investigations of key aspects influencing CO2 foam performance in fractured carbonate system using CO2 soluble surfactants

Abstract

Experimental studies have showed that CO2 soluble surfactants were more effective than aqueous soluble surfactant as supercritical CO2 foaming agent in fractured carbonate cores, in terms of higher foam strengths and oil recoveries. This paper aims to reveal the potential causes responsible to those superiorities and probe the impacts of key aspects during this complex process. Variable surfactants are examined to investigate the presence of optimal partition coefficient. The impact of surfactant structure on critical foaming concentration is also studied. Effect of reservoir pressure is investigated through stepwise independent manipulations attempting to decouple its influences on miscibility between CO2/oil, free gas phase availability and surfactant partition coefficient between CO2/brine. Effect of injection foam quality (gas volumetric fraction) is probed at constant liquid injection rate. It is found that the optimal partition coefficient for selected system is affected by multiple practical conditions including injection periods and surfactant structure relevant model parameters, but not determined by absolute coefficient values. The results of increasing system pressure and injection foam quality are combination of multiple aspects, including miscibility between CO2/Oil, local pressure drop, foam apparent viscosity, among of CO2 injection, gaseous CO2 available for surfactant delivery, and interplay between faster surfactant propagation and reduced local pressure gradient (“spreading” effect). The contribution of promoted or suppressed spreading effect could depend on magnitude of individual partition coefficient. The findings here reveal the complex interactions of multiple key aspects affecting CO2 soluble surfactant foams performance and promote the understandings to apply this novel technology in fractured systems.