Generation of pickering emulsions by activating natural asphaltenes as nano materials: An experimental analysis for cost-effective heavy-oil recovery

Abstract

Enhancing oil recovery through emulsification is possible during both cold and hot production in the heavy oil process. Emulsion stability is the key issue controlling the success of this process; conventionally, surfactants were used to facilitate emulsification and improve emulsion stability, increasing the cost remarkably. This study promotes an alternative way to generate stable -Pickering- emulsions without using expensive surfactants, a method that will reduce the operational costs and thus favor the field application step of emulsification in heavy-oil recovery. Throughout the paper, we explored answers to the following questions: (1) What conditions (asphaltene content) allow asphaltenes to stabilize W/O emulsions? (2) What are optimal aqueous conditions (pH, salinity) for stable emulsions? (3) Can such emulsions stabilized by asphaltenes be formed in-situ in a porous medium and thus improve recovery? These questions were answered through glass vial tests under controlled experimental conditions and sandpack flooding experiments. Emulsion stability was evaluated through glass vial tests, and the emulsion structure and type were determined using an optical microscope. Furthermore, sand-pack flooding experiments were performed using the formulation which favored the formation of stable emulsions. The glass vial tests showed that the optimal asphaltene concentration was 0.5 wt% to stabilize water-in-oil (W/O) emulsions. And the emulsion stability improved with water pH. The optimal salinity of 1 wt% led to the most stable W/O emulsions. The sandpack flood experiments showed that highest oil recovery was achieved when the emulsions with an intermediate stability instead of the most emulsion stability were formed in-situ in the sandpacks, such as at pH = 10 condition. Finally, recommendations were made for choosing the optimal formulation to help improve heavy-oil recovery.