Enhanced oil recovery techniques for heavy oil and oilsands reservoirs after steam injection

The in-situ steam-based technology is still the main exploitation method for heavy oil and oilsands resources all over the world. But currently most of the steam-based processes (e.g., cyclic steam stimulation (CSS), steam flooding and steam assisted gravity drainage (SAGD)) in heavy oilfields have entered into an exhaustion stage. Considering long-lasting steam-rock interactions, how to further enhance the heavy oil and bitumen recovery in the post steam injection era is currently challenging. In this paper, we present a comprehensive and critical review of the enhanced oil recovery (EOR) processes in the post steam injection era in both experimental and field cases. Specifically, the paper presents an overview on the recovery mechanisms and field performance of thermal EOR processes by reservoir lithology (sandstone and carbonate formations) and offshore versus onshore oilfields. Typical processes include an in-situ combustion process, a thermal-solvent process, a thermal-NCG (non-condensable gas, e.g., N2, flue gas and air) process, and a thermal-chemical (e.g., polymer, surfactant, gel and foam) process. Some other processes and new processes are also presented in this work. This review shows that offshore heavy oilfields will be the future exploitation focus. Moreover, currently several steam-based projects and thermal-NCG projects have been operated in Emeraude Field in Congo and Bohai Bay in China. A growing trend is also found for an in-situ combustion process and a solvent assisted process in both offshore and onshore heavy oilfields, such as EOR projects in North America, North Sea, Bohai Bay and Xinjiang. The multicomponent thermal fluids injection process in offshore and the thermal-CO2 and thermal-chemical (surfactant and foam) processes in onshore heavy oil reservoirs are some of the opportunities identified for the next decade based on preliminary evaluations and proposed or ongoing pilot projects. Furthermore, the new processes of an electrical method, in-situ upgrading (e.g., ionic liquids, addition of catalyst and steam-nanoparticles) and novel wellbore configurations have also gained some attention. We point out that there are some newly proposed recovery techniques that are still limited to a laboratory scale study, with the need for further investigations. In such a time of low oil prices, cost optimization will be the top priority for all the oil companies in the world. This critical review will help them identify the next challenges and opportunities in the EOR potential of heavy oil and bitumen production in the post steam injection era.