The experiments and numerical simulations described in this paper were performed to determine the effectiveness of the Thermal Solvent Reflux and Thermal Solvent Hybrid processes and to determine the key parameters involved in these two processes. It was also intended to improve the capability of modelling these processes.
SAGD is the current technology of choice for Athabasca reservoirs. It is commercially proven, delivers high oil rates and high ultimate recoveries. However, it is energy intensive. In addition, steam injection may be limited by the fact that some reservoirs are water-sensitive, by lack of water, or by regulatory issues.
VAPEX does not have the energy and water problems associated with SAGD.
However, it is inherently slower than SAGD. One solution to the above difficulties is to combine processes, by heating the horizontal wellbores. The heat serves to initiate communication between the injector and producer. In addition, it may increase the rate of diffusion of the solvent into the oil. Heat may be applied by electric heaters, by a closed steam or glycol loop, or by direct injection of steam. In the first three of four experiments described in this report, the wells were electrically heated. In the fourth experiment, steam was co-injected with the solvent.
Two experiments showed tests using Hillmond oil showed that similar results were obtained whether heating was obtained by electrically heating the wells (Thermal Solvent Reflux process) or by direct steam injection (Thermal Solvent-Hybrid process).-For these two experiments, the oil rate and recovery were similar. Numerical simulations were used to history match the experiments and effective diffusivity values were estimated.
The technical objective of the Thermal Solvent Reflux experiments was to develop a solvent-assisted process for recovery of heavy oil from thick, cold reservoirs such as Cold Lake and Athabasca. The Thermal Solvent process concept (Figure 1) is:
Inject solvent and produce oil through horizontal wells
Heat the injection and production wells to re-boil the solvent in situ (solvent reflux)
In-situ recycle of solvent
The advantages of the thermal solvent process are:
Requires less heat than SAGD
Lower energy cost.
Less steam plant emissions, possible CO2 credits.
Smaller solvent recycle plant on surface
Smaller injection facility needed.
Lower capital and operating cost.
Does not inject water into the reservoir
Suitable for reactive reservoirs
No treatment of boiler feed water required
Minimal water disposal.
Minimal oil/water separation facilities required
Heat will speed mass transfer over cold VAPEX.
Heat assists in startup of long wells
The Thermal Solvent Hybrid process delivers heat through co-injected steam, (Figure 2). The numerical component of the study involved history matching the experiments and determining the effect of oil phase total dispersion coefficient (includes effect of diffusion) on oil and gas production.
It is well known that diffusion and dispersion play an important role in the VAPEX process1-4,6,7. Oil rate is primarily dependent on diffusion/dispersion of the solvent into the oil and on the gravity drainage of the oil-solvent mixture.