Solvent Gas Uptake of CO2 and Propane in Heavy Oil for Enhanced Oil Recovery

Abstract

Abstract Cold heavy oil production utilizes the energy inherent in the reservoir for primary oil production and has been applied with commercial success in the area surrounding Lloydminster. The primary cold production of heavy oil can be expected to produce about 5-10% of initial oil in place before the process becomes uneconomical. Solvent gas injection processes can be utilized for the recovery of remaining heavy oil from post-primary reservoirs. The processes involve the injection of solvents or solvent mixtures into an oil reservoir, dissolution of the solvents or solvent mixtures into the oil and production of the solvent-oil mixture. Mixing of the injected solvents with oil in the reservoir is governed by molecular diffusion, mechanical dispersion and non-equilibrium solvent dissolution/exsolution. A key aspect of exsolution for solvent gas-based heavy oil recovery processes is its stimulation of foamy oil behaviour. Maximizing the solvent gas uptake during the dissolution process is vital for attaining foamy oil behaviour during the exsolution process. A suite of experiments is presented where CO2, propane and a CO2-propane mixture are injected into both dead and live heavy oil sandpacks at a constant pressure and temperature. The solvent uptake rate was monitored with time. Numerical simulation of selected experiments is also presented. Interestingly, propane showed a slower solvent uptake rate with live oil than with dead oil in the sandpack, whereas CO2 showed a faster rate. The CO2-propane mixture indicated little rate change between live and dead oil experiments. CT experiments further concluded that propane sorbs faster into dead oil. This indicates that methane interferes with propane sorption into the oil in live oil cases. The numerical study found that a non-equilibrium treatment is necessary in simulating solvent dissolution behaviour. This study will help in the design of solvent gas-based heavy oil recovery processes such as VAPEX, Thermal Solvent, Hybrid Solvent, ES-SAGD, and Cyclic Solvent Injection (CSI). It provides insight into the concentration of injected solvent with distance into the oil, and the time required for adequate solvent injection and soaking. The volume of solvent gas uptake plays a key role in foamy oil behavour during exsolution, and a solid understanding of the solvent gas uptake by heavy oil can help in optimizing oil recovery from sustained foamy oil drive in the reservoir.