Numerical simulation of foamy-oil flow in a cyclic solvent injection process

Cyclic solvent injection (CSI) has emerged as a promising and environment-friendly heavy oil production process. One of its main recovery mechanisms is foamy-oil flow. This study first experimentally observes the foamy-oil flow under reservoir conditions in a sand-packed CSI test, and then theoretically interpret the flow pattern through mathematical modeling. Finally, the oil recovery mechanisms of CSI are investigated. Results show that foamy oil flows in an intermittent instead of continuous manner during the production period. Multiple waves of foamy oil start from the transition zone and push oil toward the producer. This is well predicted by our newly developed theoretical model: the oil and gas productions increase stepwise during a production period. Besides, the foamy-oil flow occurred 2-4 times, which is because the position of equilibrium state in the transition zone keeps changing during the pressure drawdown process. Moreover, larger diffusivity, higher initial solvent con-tent, slower pressure depletion, and slower formation rate of free gas leads to more waves of foamy-oil flow and higher oil production. This study provides some meaningful insights into foamy-oil flow process, as well as cleaner recovery of heavy oil reserves through solvent-based technique.

Automated summary

Cyclic solvent injection (CSI) is a promising and environmentally friendly process for heavy oil production, utilizing foamy-oil flow as one of its main recovery mechanisms. This study experimentally observes and theoretically models the foamy-oil flow under reservoir conditions, and investigates the oil recovery mechanisms of CSI. The results show that foamy oil flows intermittently during the production period, with multiple waves starting from the transition zone. Factors such as diffusivity, initial solvent content, pressure depletion rate, and formation rate of free gas influence the occurrence of foamy-oil flow and the overall oil production.