Mechanics of Foamy Oil during Methane-Based Cyclic Solvent Injection Process for Enhanced Heavy Oil Recovery: A Comprehensive Review

Foamy oil flow is a commonly encountered drive mechanism in the primary production (depletion of naturally methane-saturated heavy oil) and secondary stage (cyclic gas-mostly methane-injection after primary production). In the former, among other important parameters, pressure depletion rate has been reported to be the most crucial parameter to control the process. In the latter, type and amount of the gas (also described as "solvent") and application conditions such as soaking time durations and depletion rates are critical. The cornerstone of the foamy oil behavior relies on its stability, which depends on parameters such as oil viscosity, temperature, dissolved gas ratio, pressure decline rate, and dissolved gas (solvent) composition. Although the process has been investigated and analyzed for different parameters in the literature, the optimal conditions for an efficient process (mainly foamy oil stability) has not been thoroughly understood, especially for the secondary recovery conditions (cyclic solvent injection, CSI). In this paper, internal and external gas drive mechanisms for foamy oil performance are reviewed in detail. The optimal conditions of the applications were compiled and listed for different primary production and secondary recovery stages. Combination of methane with other gases as a CSI practice was also discussed to accelerate the process and reduce cost in an effort to improve efficiency. It is reported that combining methane injection with air as a secondary recovery method can save up to 51% of solvent gas.