Vapex and related processes for recovery of heavy oil and bitumen have potential application to oils containing some methane in solution. A set of experiments has been completed to evaluate the potential for Thermal Vapex operations in heavy oils containing significant dissolved methane content. Three experiments were run to evaluate a Vapex process operating in a reservoir in which the oil had significant initial methane saturation. The first experiment tested a 3-component mixture (C1-C2-C3) that was used in an earlier non-thermal dead oil Vapex test. The second experiment used horizontally offset wells and 100% ethane as the working solvent. The production well was heated to reflux the solvent in situ. The third experiment also used horizontally offset wells and 100% ethane plus steam. The steam was injected into the production well, to reflux the solvent. Results indicated that the live oil inhibited solvent absorption and hence production rates, but that a properly designed solvent system could produce oil at reasonable rates. Oil production from the steam-heated well/ethane experiment was similar to that from electrically heated well/ethane reflux experiment. The experiments provided a database used for economic comparison of process options, and for developing numerical simulations for field predictions.
Some heavy oil reservoirs cannot be produced by cold production. They may be immobile at reservoir temperature, or they may have some initial oil mobility and some reservoir drive energy, but the sand strength precludes the production of sand or wormholes. These reservoirs may be dead oil, as in the case of Athabasca bitumen, or they may have some dissolved gas, as in the case of Cold Lake reservoirs. The Vapex process (Reference 1) has been considered as a means of mobilizing heavy oil or bitumen. Figure 1 illustrates the concept of the Vapex process.
Heating of a horizontal wellbore is a possible means of mobilizing these oils. Heat will reduce viscosity sufficiently to produce a large increase in oil rate. Heat also serves to initiate communication between an injection well and the producer, enabling solvent injection. Heat may also serve to speed the diffusion of solvent into the oil.
Heat may be injected by injecting steam, or by injecting heated solvent. Reference 2 refers to an application where direct injection of heated solvent vapour is used.
The wellbore may be heated by means of an electrical heater or a steam or glycol loop. Heat vaporizes the injected solvent. Solvent vapour moves to the oil interface at the edge of the vapour chamber and dissolves in the oil. The diluted oil is reduced in viscosity and flows down the edge of the vapour chamber to the production well. The vaporized solvent is driven out of the oil by the heat as it enters the near wellbore region or the production well. The vaporized solvent will return to the vapour chamber, where it will mobilize additional oil. The result is a Thermal Solvent Reflux process (Reference 3). The process concept is illustrated in Figure 2.
