Treatment of water-in-oil emulsions produced by thermal oil recovery techniques: Review of methods and challenges

•Nearly 100 studies reviewed of treating emulsions of water-in-heavy oil.•Chemical, microwave, and ultrasound strategies reported to treat emulsions.•Future opportunities for demulsification techniques are discussed. Thermal oil recovery techniques allow the commercial production of heavy and extra-heavy crude oil. However, these same techniques generate emulsions during the production and transportation of the crude oils. The high stability and viscosity of these water-in-oil emulsions represent a challenge to this sector of the oil industry. This paper reviews recent strategies focused on the demulsification of water in heavy oil/bitumen emulsions. It then discusses future opportunities for demulsification techniques and the prospects of other methods to improve separation performance. Opportunities to improve demulsification exist if certain forms of energy input are combined with particular classes of chemicals, such as thermal energy with polymers, surfactants, and mechanical energy with ionic liquids and solvents.