Evaluation of CO₂ Based Vapex Process for the Recovery of Bitumen from Tar Sand Reservoirs

The vapour extraction (Vapex) process has recently gained considerable attention for its promising application for the recovery of heavy oil and bitumen reservoirs that are deemed unsuitable for thermal methods. In conventional Vapex process, a mixture of vaporized solvent (propane and/or butane) and a commercially available non-condensable gas (methane, natural gas) is injected into the reservoir to reduce the oil viscosity. Therefore, the cost of these injected gases per barrel of produced oil is critical for the economic viability of the process. With predicted increase in the gas prices, the process has lost some of its initial attraction.

For reducing the solvent cost, the injection of CO₂ as a non-condensable gas appears to be an attractive alternative. The advantage of this low cost alternative is that the solubility of CO₂ in heavy oils is significantly higher than that of methane. Consequently, the mixture of propane and CO₂ can provide greater reduction in oil viscosity compared to the equivalent mixture of propane and methane. In addition, this CO2 injection can play a significant role in sequestering CO₂ emissions. However, the CO₂-propane-heavy oil system shows complex phase behaviour, forming multiple liquid phases. Such multiple liquid phases can reduce the effectiveness of gravity drainage process by introducing complex relative permeability effects.

This paper presents an experimental study aimed at developing a new CO₂ based Vapex process for in situ recovery of bitumen from tar sand reservoirs. The experiments have been performed in a partially scaled physical model at different operating conditions. The main conclusion from this study is that the CO₂ based Vapex process is more cost effective and environmentally friendly than the conventional Vapex process.