Study on Steam and Microemulsion Alternate Injection for Enhanced Productivity in Heavy Oil Fields

Steam injection is widely used as an enhanced oil recovery method for heavy oil fields; however, its efficiency normally decreases in late injection stages. Recent studies have suggested that steam and chemicals together have a potential to increase oil recovery. Despite the use of microemulsion alone has been previously made as a chemical enhanced oil recovery technique, steam and microemulsion alternated injection has not been reported yet. Thus, the present study evaluates this recovery method as an innovative way to optimize heavy oil recovery in sandstone reservoirs. Three microemulsions were produced using Ultranex NP100 (surfactant), n-butanol (cosurfactant), kerosene (oil phase), and synthetic produced water (aqueous phase), by varying surfactant concentrations. The viscosity, stability, surface tension, and interfacial tension of these systems were analyzed and assessed. Berea sandstone was used to represent sandstone reservoirs, in which the effect of microemulsions on rock wettability was measured. Using a coreflooding system, rock plugs were initially saturated with heavy oil (degrees API 17.1; from Northeast Brazil). Nine enhanced oil recovery tests were performed using steam and microemulsion alternated injection. In the tests, the injection bank order and the surfactant concentration were evaluated. The results showed that the alternated injection of steam and microemulsion achieved recovery factors between 42.79 and 51.23%, which is higher than that by steam injection alone (33.63%). It was observed that oil recovery using steam injection followed by microemulsion showed a better performance due to a higher effectiveness of displacement mechanisms. Steam reduces oil viscosity, while microemulsions decrease interfacial tensions and alter the sandstone wettability. Additionally, oil recovery increases together with the surfactant concentration due to a higher micelle number. Therefore, this study proves that steam and microemulsion alternated injection is a novel and effective method for enhanced heavy oil recovery in sandstone reservoirs.