Steam Assisted gravity drainage (SAGD) is demonstrated as a proven technology to unlock heavy oil and bitumen in Canadian reservoirs. One of the long-term concerns with the SAGD process is high energy intensity and related environmental impacts. The addition of suitable hydrocarbon solvents to steam has long been regarded as the simplest and most effective method to increase SAGD performance. Higher oil recovery, accelerated oil production rate, reduced steam to oil ratio and generally more favorable economics is expected from the addition of potential hydrocarbon additives to steam. This paper summarizes experimental results of addition of potential solvents to steam in SAGD process. N-Hexane and n-heptane were co-injected with the steam and the experimental results were compared with pure steam injection. In addition, pure heated n-hexane was injected in one experiment to assess the performance of solvent-based processes. Experiments were conducted using a scaled two-dimensional physical model. Peace River Bitumen samples were used to conduct the experiments at 80 psia. Experimental results were analyzed to determine the key variables involved in Solvent Assisted SAGD (SA-SAGD) processes. Solvent choice is not solely dependent on mobility improvement capability but also reservoir properties and operational conditions. Co-injection of suitable solvents with the steam led to accelerated oil production rate, higher oil recovery and lower energy to oil ratio. Solvent requirement for pure heated n-hexane injection was considerably high. The vaporized solvent chamber expansion was slow due to low heat content of the solvent and heat losses.

Steam assisted gravity drainage (SAGD) is demonstrated as a proven technology to unlock heavy oil and bitumen in Canadian reservoirs. One of the long-term concerns with the SAGD process is high energy intensity and related environmental impacts. Addition of potential alkane solvents to steam in processes such as ES-SAGD can reduce the high use of energy and green-house emissions in SAGD. However, the principal challenge is the high cost of the solvents. As a result, the economic viability of solvent assisted processes highly depends on the original reservoir and fluid properties and the operating strategy used to co-inject the solvents.The main objective of this study is to compare the simulation results of addition of potential solvents to steam in two different types of reservoirs, cold lake and Athabasca. Propane, Butane, Pentane, Hexanes and Heptanes with different proportions from 1%-20% by weight have been co-injected with the steam. The simulations carried out in absence and presence of initial solution gas to find out the effect of solution gas on performance of SAGD and solvent assisted SAGD processes. Simulation results show that initial solution gas reduces the oil recovery especially in Athabasca reservoir. A varying thickness non-condensable gas layer impedes heat transfer from the condensing steam to bitumen zone. Hydrocarbon additives create a high oil phase mobility zone resulting in production acceleration. Solvents heavier than butane are considered suitable candidates for Athabasca type and butane gave better results in Cold Lake type reservoir under operating conditions of this study. In addition, a detailed study is carried out on the properties of different phases such as phase mobility, saturation and viscosity at the steamsolvent-oil interface to have a better understanding of the effect of presence hydrocarbon additives in the steam chamber.

Steam-Assisted Gravity Drainage (SAGD) is the preferred in-situ technology to recover heavy oil and bitumen from Canadian reservoirs. It is commercially proven, delivers high oil rates and high ultimate recoveries. Given the large energy requirement and the volume of emitted greenhouse gases from SAGD process, there is a strong motivation to develop enhanced oil recovery processes with lower energy and emission intensities. Addition of potential alkane solvents to steam in processes such as ES-SAGD can reduce the high use of energy and green-house emissions in SAGD. Potential hydrocarbon additives provide an additional means to raise oil phase mobility beyond that achieved by heat. Numerous simulation studies are published on the effect of hydrocarbon additives on SAGD process but few experimental results exist in public domain. Often, Conflicting results exist both in simulation studies and even field tests. In addition, numerical simulations are unable to fully capture the mechanism of hybrid steam solvent processes. This paper summarizes experimental results of addition of potential solvents to steam in SAGD process. N-hexane was selected as the preferred additive to be co-injected with the steam and the experimental result are compared with pure steam injection process. Experiments were conducted using a scaled two dimensional cylindrical model. Peace River Bitumen samples were used to conduct the experiments at 80 psia. Experimental results were analyzed to determine the key parameters involved in solvent assisted SAGD processes. Experimental results confirmed the effectiveness of hydrocarbon additives to enhance SAGD process. Co-injection of potential solvents led to accelerated oil production rate, higher oil recovery and lower energy to oil ratio.

Steam-Assisted Gravity Drainage (SAGD) is the main commercial technology used for in-situ recovery of Canadian heavy oil and Bitumen. It is commercially proven and delivers high oil rates and high ultimate recoveries. One of the long-term concerns with the SAGD process is high energy intensity and related environmental impacts. Hybrid processes have been developed to take partial advantage of steam and solvent processes while introducing a more efficient and more economically viable recovery methods. Several processes such as Propane-SAGD, Expanding Solvent-SAGD (ES-SAGD), Solvent-Aided Process (SAP), Liquid Addition to Steam to Enhance Recovery (LASER) and Steam-Alternating-Solvent (SAS) were proposed; some of them currently under pilot test. Hybrid steam-solvent processes aim to accelerate oil production rate with lower cost than SAGD and also increase the ultimate oil recovery. Despite remarkable amount of laboratory and computational studies on these processes, there was no extensive critical review of the knowledge obtained for more than a decade. The current level of understanding of the hybrid processes and knowledge around the fundamental physics and mechanisms involved are not fully satisfactory. We believe that a critical review of the status of the hybrid processes will fill the gap by shedding the light on the deficiencies and the limitations of the process, further development areas, and new research topics. Analytical, numerical simulations, laboratory modeling efforts along with pilot test results are summarized. In addition, the main technical challenges of different aspects of hybrid steam-solvent processes are analyzed at different levels. In this paper, special attention is given to a) The effect of reservoir and operational parameters, b) solvent injection strategies, c) The inconsistency between laboratory, simulation and field results and d) problems faced in numerical modeling (capturing the physics of heat and mass transfer). It is believed that a good compilation of the records produced over one decade will constitute a useful reference for the industry and academics. Analytical, simulation, laboratory studies and reported field data strongly support hybrid steamsolvent processes. However, the results are mixed at different level levels and there exists some inconsistencies. The cost of the solvent retained in the reservoir is the major concern and the economics of selected hybrid steam-solvent process for a specific reservoir has to be verified using available tools. The main challenges are verifying effective mixing of the solvent with the in-situ bitumen, managing the solvent placement and distribution in the reservoir, reliably determining the incremental benefit of solvent-addition and ensuring economic solvent recovery.

Vapor extraction (VAPEX) process is solvent analogue of SAGD process in which low molecular weight solvent are used to reduce the viscosity of heavy oil and bitumen. This process may be a good candidate to be applied in problematic reservoirs in which thermal methods are not efficient due to severe heat losses. Asphaltene precipitation as a result of compositional alteration of solvent/bitumen has substantial effects on performance of VAPEX. In this process if operating pressure is very close to dew point pressure, asphaltene precipitation occurs. In-situ deasphalting of heavy oil and bitumen reduces the viscosity of the produced oil and creates the oil that is more easily refined, but the main concern is whether this advantage can outweigh reduced permeability and plugging of formation caused by adsorption and precipitation of asphaltenes. In current work experiments have been conducted in low permeability sandpacks in both dry and non-dry systems to assess the performance of Vapex process when asphaltene precipitation occurs. Experiments are carried out in a 2D visual cell using highly asphaltenic heavy oil from one of Iranian reservoirs (Kuh-e-Mond) and propane as a solvent. The results show that performance of Vapex process increases when asphaltene precipitation occurs provided that optimal pressure has been designed to prevent extensive asphaltene deposition and subsequent plugging of porous media. It has been observed that adsorption of asphaltenes has considerably decreased in non-dry systems. Movement of precipitated asphaltene and less adsorption in non-dry experiments results in a more stable and efficient Vapex process while in dry experiments higher adsorption of asphaltenes resulted in plugging of low permeability porous medium. Introduction Concurrent with increase in oil demand, there is marked decline in conventional oil production. Huge heavy oil and bitumen resources are increasingly recognized as a strategic resource and potential contributor to worldwide energy security. Thermal processes like SAGD and CSS have increased tremendously worldwide reserves especially in Canada and probably SAGD could be considered as one of the most effective EOR techniques applied in petroleum industry. But, thermal processes cannot be applied in cases with severe heat losses like thin formations and heavy oil in deep reservoirs and offshore. Solvent-based methods like VAPEX process may be a suitable option for the recovery of heavy oil in problematic cases. The Vapour extraction is basically an analogue of the steam assisted gravity drainage (SAGD) process. In VAPEX process, vaporized solvents are used instead of high temperature steam and the oil viscosity is lowered by in-situ dilution instead of heating. A vaporized light hydrocarbon or a mixture of solvents, such as propane or butane, is injected through a horizontal well into the formation containing the viscous oil or bitumen (Butler & Mokrys 1991, Das 1997). It has been experimentally shown that the optimum solvent injection condition is near solvent dew point where the vapour phase has the maximum solubility and diffusivity in the heavy liquid phase (Butler & Mokrys, 1993).Carrying out experiments with pure solvents in these conditions leads to asphaltene precipitation as a result of high solvent concentration in boundary layer (Das & Butler 1998). Asphaltene flocculation and deposition during natural depletion and/or miscible gas injection in enhanced oil recovery (EOR) processes is a common problem in oilfields throughout the world. Changes in some environmental parameters, such as pressure and composition (addition of solvent or dispersant injection), can change the stable condition of an oil mixture to another condition where the mixture will be unstable and heavy organics, such as asphaltenes or waxes, flocculate and deposit (Mofidi & Edalat, 2006).