Several partially scaled laboratory model experiments were conducted to evaluate a hybrid solvent-steam process for recovery of heavy oil or bitumen. All experiments used Athabasca UTF bitumen, and modeled a 30 meter thick formation. The experiments were compared using a common set of economic assumptions. The experiments showed that a hybrid solvent-steam process could recover bitumen at steamoil ratios much lower than those observed for SAGD, and achieve reasonable ultimate oil recovery (60% IOIP). The economic analysis based on experiments indicated that a hybrid solvent-steam process could be more cost-effective than SAGD for a 30 m Athabasca formation.
Some heavy oil reservoirs are difficult to produce by cold production. The oil may be immobile at reservoir temperature, or there may be some initial oil mobility and some reservoir drive energy, but the sand strength precludes the production of wormholes. These reservoirs may contain dead oil, as in the case of Athabasca bitumen, or they may have some dissolved gas, as in the case of Cold Lake or Burnt Lake reservoirs.
SAGD is the main commercial technology used for in-situ recovery of these oils. Due to the increasing costs for energy (natural gas) and the increasing restrictions on fresh water usage, solvent-based processes (VAPEX, Thermal Solvent, Hybrid Solvent, N-Solv, Savex) have been proposed as alternative technologies for heavy oil and bitumen production. Most of these technologies utilize a pair of horizontal wells, similar to those used in SAGD, but use a gaseous solvent, typically propane, alone or in conjunction with steam, to recover the oil.
The VAPEX process may be augmented by adding heat. Heating of a horizontal wellbore will reduce bitumen viscosity sufficiently to produce a large increase in oil production rate. The heat also serves to initiate communication between theinjector and the producer. The heat also serves to speed the iffusion of solvent into the oil. The combination of heated wellbores and VAPEX is known as the Thermal Solvent process.
In the Hybrid Solvent Process, a pair of horizontal wells is used, but the injector wells co-inject steam and solvent. The heat vaporizes the injected solvent. Solvent vapour and steam move to the oil interface at the edge of the vapour chamber and condense. Solvent 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 flashed out of the oil as it enters the heated area near the production well. The vaporized solvent then returns to the vapour chamber, where it mobilizes additional oil. The description of the Thermal Solvent process is found in Ivory et al (Ref. 1) and in Frauenfeld et al (Ref. 2). The Hybrid Solvent process is described in Frauenfeld et al (ref. 3).
A series of experiments was performed to model recovery processes where steam and solvent injection was combined. Because of the low thermal mass of solvent, it is expedient to heat the solvent by co-injection with steam. The result is a Hybrid Solvent process (Figure 1).
