Comprehensive review on stability and demulsification of unconventional heavy oil-water emulsions

Unconventional petroleum ores have been considered to be an important part of petroleum resources and an important alternative source of chemicals and energy supply. Extremely stable heavy oil–water emulsions frequently encountered in the separation of unconventional petroleum ores. This emulsions considerably increase operation and production costs and cause technical challenges (i.e., fouling and corrosion). Chemical demulsification as a primary method has been extensively applied to destabilize the highly stable emulsions. Demulsifiers play the key role in breaking this emulsions, and understanding the stability mechanisms of heavy oil–water emulsions is the premise of developing effective demulsifiers. This critical review systematically reviews stabilization mechanisms of the heavy oil–water emulsions, including presence of interfacially active substance (e.g., asphaltenes, resins, naphthenic acids, crystalline paraffin, and amphiphilic solids), and their considerable effects on properties of oil–water interface. According to the stability mechanisms, the basic principle and influence factors of chemical demulsification, evaluation and types of demulsifiers, and application of different demulsifiers in breaking heavy oil–water emulsions have been discussed comprehensively. Additionally, the present challenges and future engineering considerations have been touched to provide potential insights and theoretical fundamentals for developing novel demulsification materials in this important heavy oil–water emulsions field.