Vapour extraction (Vapex) has recently emerged as a cost effective and environmentally friendly recovery technique for the huge resources of heavy oils and bitumen available in Canada, USA, and Venezuela. The current version of Vapex relies on injection of light hydrocarbon gases for reducing the oil viscosity. The economic viability of this process is very sensitive to the cost of injected gases in relation to the selling price of the produced oil. One attractive option for reducing the cost of injected gases appears to be the use of CO2 as a major component of the injected solvent. This modification will utilize mixtures of CO2 and propane as the solvent instead of the currently popular mixtures of methane and propane. Since CO2 is significantly more soluble in heavy oils than methane, it is likely that such mixtures will provide greater reduction in viscosity compared to equivalent mixtures of methane and propane.
In this work methane-propane & CO2-propane were investigated as solvents for Vapex process for in situ recovery of heavy oil and bitumen. Twelve laboratory experiments were performed with 2 types of oil (4500 m.Pa.s & 18600 m.Pa.s at 21 °C). These tests were performed in a partially scaled physical model at different operating pressures (200 to 600 psia) and were designed to compare the performance of methane based solvents with that of CO2 based solvents. 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.
With the decline of the conventional oil reserves, a major thrust of oil industries throughout the word is on the exploitation of heavy oil and bitumen reserves. The magnitude of these resources worldwide is about six trillion barrels of oil in place, six times the total conventional reserves1, and may be the future source of energy. The majority of these resources are located in Venezuela, Canada and the United States2. In most cases, conventional recovery methods cannot be implemented in heavy oil and bitumen reservoirs due to the high viscosity, and lowdegree API gravities5 of the oil. This high viscosity rules out the primary production and even in lower viscosity reservoirs the primary recovery is less than 10% of the original oil in place (OOIP) 3,4. The viscosity of heavy oil and bitumen are strong functions of temperature and decrease drastically with increase in temperature. Therefore, thermal processes are the logical first option for such oils. With these processes namely, cyclic steam stimulation (CSS), in-situ combustion (ISC), steam-assisted gravity drainage (SAGD), etc., the viscosity is reduced by heating the reservoir.
Steam Assisted Gravity Drainage (SAGD) 6,7process has gained tremendous popularity in the industry for its usefulness in producing high viscosity heavy oil and bitumen. In this process the heat is injected into the reservoir by injecting steam through a horizontal well; steam condenses at the oil interface and heats the oil. Consequently the viscosity is lowered and the hot oil drains down under the influence of gravity into another horizontal well located near the bottom of the formation.
