A Mini-Review of the Solvent Steam Co-Injection Process: Solvent Selection Criterion and Phase Behavior

A large amount of high temperature steam has been injected to produce per unit volume of heavy oil in thermal recovery processes since the 1950s. Solvent steam coinjection processes (e.g., expanding solvent-SAGD (ES-SAGD), solvent aided process (SAP), the liquid addition to steam for enhancing recovery (LASER), and steam alternating solvent process (SAS)) have the potential to reduce the injection amount of steam, energy consumption, and greenhouse gas emissions, improve petroleum quality intrinsically, and boost production. Recently, the solvent steam coinjection process has attracted attention, and hence it has progressed in both laboratory and field applications as an alternative or an assisting way for thermal methods for more than 40 years. However, research results are scattered in many publications and are not readily available for most petroleum engineers. Hence, our purpose is to present a review of current knowledge and available data, and to delineate the steam solvent coinjection process, and to fill the void for key issues when compared with existing review publications. Before discussing the possibility of future applications in targeted oilfields, attention should be focused on answering the critical question of solvent selection criteria, which is always neglected in previous review work. Moreover, phase behavior of the solvent/heavy-oil/water system was reviewed to support solvent selection criteria above. Lastly, economics feasibility, challenges, and perspectives were discussed in the view of field applications. This critical review will help identify the next challenges and opportunities in the solvent assisting thermal technique for enhancing the production of heavy oil and bitumen.