Insight into the Interfacial Behavior of Surfactants and Asphaltenes: Molecular Dynamics Simulation Study

Heavy oil and bitumen drive the leading energy supply in Canada. Several techniques, including in situ thermal methods and mining, have been applied to the recovery of these unconventional resources. Nowadays, to improve the efficiency of in situ thermal methods, coinjection of steam and different types of additives, including chemicals, solvents, and noncondensable gases, is being investigated. Adding these additives to steam can reduce the required amount of steam and, as a result, lowers carbon dioxide emissions; meanwhile, the oil production can be improved. Different interaction mechanisms contribute to oil recovery in each type of additives. In this paper, we focused on the investigation of mechanisms using surfactant additives. One of the primary behaviors that needs to be fully understood is the interfacial behavior of surfactant molecules and asphaltene molecules, the key component of heavy oil and bitumen. Four different types of surfactants, including anionic, cationic, nonanionic, and amphoteric, were employed to study the interaction parameters between asphaltene and surfactant molecules. Two different asphaltene molecules with the archipelago and island architectures were extracted from oil sands from the Athabasca oil field in Alberta, Canada. All thermodynamic conditions were chosen based on the operational steam-assisted gravity drainage (SAGD) conditions. For the sake of comparison, different molecular analyses, including the radial distribution functions (RDFs), interfacial thickness, solubility parameter, and hydrogen bond numbers, were used. According to the results of this study, the anionic surfactant has a good interaction with asphaltenes, and it can lessen the aggregation of asphaltenes. The outcomes of this paper provide useful information to have a deeper understanding on how a surfactant interacts with asphaltene under the thermodynamic conditions of a surfactant-steam coinjection process.