How to select the right solvent for solvent-aided steam injection processes

Solvent-steam processes gained popularity in recent years in the extraction of high-asphaltenes-content heavy hydrocarbons. However, while solvent selection is key for the success of these processes, the criteria for solvent selection are still not fully established. In this study, three asphaltenes insoluble (propane, n-hexane, carbon dioxide) and one asphaltenes soluble (toluene) solvents were tested on solvent-aided steam processes to extract a bitumen sample from Alberta, Canada. Both steam flooding and SAGD performances were analyzed. The impact of clay presence was investigated by conducting experiments with and without the addition of clays, consisting of an illite-kaolinite mixture. The results of this study suggest that the produced oil samples from steam injection processes are in the form of water-in-oil emulsions. It has been observed that the amount of asphaltenes in produced oil determines the amount of water trapped in the form of emulsions. Co-injection of solvent with steam decreases the interfacial film between water and asphaltenes. However, asphaltenes insoluble solvents were found to be more effective to eliminate the forces at the oil-water interface. Presence of clays also reduced the water content of emulsions. The results of this study suggest that carbon dioxide, which is a non-hydrocarbon asphaltenes-insoluble solvent, yields the greatest quality oil with the lowest amount of water and clay in produced oil and provides high oil recovery. Hence, it is recommended to use asphaltenes-insoluble, non-hydrocarbon solvents for the extraction of low API gravity, high viscosity, and high asphaltenes content reservoirs.