Partially miscible VAPEX displacement of a moderately viscous oil

The vapor extraction (VAPEX) process is studied here for a moderately viscous oil (78 cP) both experimentally and numerically. A scaled model representing one symmetric half of a VAPEX pattern has been constructed. The effect of well spacing, solvent composition and injection rate on recovery has been studied. Injecting a partially miscible solvent ethane (C2) at 200 psi (much below the MMP at 77 °F) in the VAPEX mode recovers a substantial amount of oil (up to 40% PV in 2 PVI). Gravity and diffusional mixing aid this process. As the vertical distance between the injector and producer increases, the oil recovery increases. Reducing the solvent injection rate from 50 cm3/h to 5 cm3/h improves oil recovery for C2 injection. Slower rate provides more time for mixing. A higher level of mixing and a lower viscous-to-gravity force ratio improve oil recovery. Partially miscible solvent (C2) recovers slightly more oil than immiscible gas (N2 and C1). Injecting a totally miscible solvent (C3 and C6) improves oil recovery over partially miscible and immiscible gases.

Research Highlights
► Injecting a partially miscible solvent in the vapex mode recovers a lot of oil.
► As the vertical distance between wells increases, oil recovery increases.
► Reducing the solvent injection rate improves oil recovery for C2 injection.
► As the miscibility of the gas increases, oil recovery increases.