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 modelled a 30-metre-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 steam-oil ratios much lower than those observed for steam assisted gravity drainage (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. Introduction 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. Because of 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 the injector and the producer. The heat also serves to speed the diffusion of solvent into the oil. The combination of heated wellbores and VAPEX is known as the thermal solvent process.

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VAPEX and related processes for the 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 the electrically heated well/ethane reflux experiment. The experiments provided a database which can be used for economic comparison of process options, and for developing numerical simulations for field predictions. Introduction 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(1) has been considered as a means of mobilizing heavy oil or bitumen. Figure 1 illustrates the concept of the VAPEX process. Heating 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 the solvent into the oil. Heat may be injected by injecting steam, or by injecting heated Solvent(2). The wellbore may be heated by means of an electrical heater or a steam or glycol loop. Heat vapourizes 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 vapourized solvent is driven out of the oil by the heat as it enters the near wellbore region or the production well. The vapourized solvent will return to the vapour chamber, where it will mobilize additional oil. The result is a Thermal Solvent Reflux process(3). The process concept is illustrated in Figure 2. FIGURE 1: VAPEX process (Available In Full Paper) FIGURE 2: The thermal solvent process (Available In Full Paper)

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In 1998, Butler and Mokrys proposed a "Closed-Loop Extraction Method for the Recovery of Heavy Oils and Bitumens Underlain by Aquifers." The process has potential application to many Alberta and Saskatchewan heavy oil reservoirs. The objective of our work was to produce an experimental evaluation of solvent-assisted process options for bottom water reservoirs. The current work is entirely experimental, and provides data that may be used to back up a numerical simulation effort. The experimental series modelled a bottom water process in order to determine its feasibility for a field-scale oil recovery scheme. A series of five experiments were run in an acrylic visual model. Pujol and Boberg's scaling criteria(1) were used to produce a lab model scaling a field process by a geometric ratio of 100:1, and compressing field time by a ratio of 10,000:1. The model simulated a slice of a 30 m thick reservoir with a 10 m thick bottom water zone, containing a pair of horizontal wells at the oil-water interface, offset by 25 m. For field prediction, experimental results were scaled up to represent a 30 m thick reservoir (20 m thick oil zone) with 500 m horizontal wells. The experimental rates were negatively impacted by continuous low permeability layers and by oil with an initial gas content. The lower effective diffusion rates required that the surface area exposed to solvents be increased in order to achieve commercial oil recovery rates. The Bottom Water Process described in this report offers the opportunity to do just that, as the large surface area of the oil water interface between the wells will provide contact for solvent by injecting gas at the interface. Given an appropriate well spacing, high production rates should be possible. Introduction The Alberta Research Council (ARC) has done several years of investigative work into solvent-assisted heavy oil recovery processes(2, 3). The present report describes a particular contribution to solvent-assisted oil recovery technology; a comparative scaled physical model study of bottom water process options. The results of this work showed scaled field rates of 25.3 m3/d and a live oil scaled rate of 16.5 m3/d, both at 25 m offset well spacing. Mechanisms of the Bottom Water VAPEX Process The Bottom Water VAPEX Process, illustrated in Figure 1, is a recovery process depending on the interplay of several mechanisms for its success. The solubility of the gas in the oil is controlled by the k-values of the oil/solvent system. Diffusion, hydrodynamic dispersion, and swelling also play a role in the movement of gas into the reservoir oil. The oil flow is enabled by viscosity reduction due to the dissolution of solvent in the oil. Oil-solvent contact is further augmented by capillary pressure moving some oil into the vapour chamber zone, as was observed in Experiment #2. Heterogeneity of the reservoir sand further increased the surface produced by capillary action, but excessive layering can hinder the movement of oil, as was shown by Experiment #3.