The Vapor Extraction process (Vapex) is one of the few options for the recovery of huge resources available in the form of highly viscous heavy oil and bitumen. Vaporized hydrocarbon solvents are used to reduce the bitumen viscosity, which then moves towards the production well by gravity drainage. IOR processes such as Vapex, have been difficult to study in the laboratory in any sort of quantitative way. The reason for this is that much of the information needed to get estimates of the mass transfer process is contained in the concentration gradients around the edge of the vapor chamber. Conventional 2D visual models provide information only about the position of the vapor chamber and its advance. The use of Magnetic Resonance Imaging (MRI) as a tool to observe the movement of the vapor chamber not only includes its position but also gives useful information about the concentration gradients along the leading edge. Not only are the gradients measured, but the information is inherently 2D and, as such, with an appropriate mathematical model, a parametric description of the magnitude of the mass transfer can be defined in both the horizontal and vertical directions. The use of phenomenological mathematical models in image analysis to describe the concentration gradient in functional terms allows the investigator to extract a great deal of parametric information from each experiment. This information includes enough spatial resolution to confirm that the movement of a point on the vapor chamber wall occurs in steps while at the same time, the width of the dispersion zone (where gas has diffused into the oil) increases before each step. These results have been obtained from a sand pack model saturated with Athabasca bitumen and propane as the solvent gas. An analysis of two of these experiments (one dry sand and the other water saturated sand) has provided enough quantitative information to give solid support to the standard two step model of the Vapex process. The gas must first diffuse into the bitumen for some time to reduce the viscosity of the oil/gas mixture sufficiently so that in the second step the gravitational forces can overcome the capillary forces and allow the oil to drain down the vapor chamber wall. Additional information about the relative effect of connate water supports the observations that the process is faster when connate water is present. The role of asphaltene precipitation was observed but not quantified. Introduction Recent advances in image analysis developed at the Petroleum Recovery Institute(PRI), have provided us with a set of tools, which allow us to extract a great deal of detailed information from suitable experiments. The general type of tool used, is the phenomenological mathematical model applied to 1D data sets, selected from multiple time dependent images. The solution of these models by nonlinear least squares allows us to extract parametric information about the process in a form which can be transferred into models with a stronger set of physical definitions, such as Fick's law of molecular diffusion.

Mass transport of solvent into heavy oil during Vapex was studied using techniques of Magnetic Resonance Imaging (MRI) and visual glass micro-models aided by advanced image analyses. Whereas experiments involving MRI images of sand-pack provided detailed description of vapour chamber propagation and phenomena such as asphaltene deposition, diffusion and dilution of heavy oil occurring in the transition zone (on scale of several centimetres), micro-models revealed phenomena at pore level. These included episodic nature of de-saturation within transition region leading to mobilization and entrapment of heavy oil in the vapour chamber. It was seen that bulk of diluted/de-asphalted oil drains via sides of the vapour chamber. Episodes of capillary de-saturation within the transition zone cause not only a relatively long residence time of solvent into diluted oil within the reservoir but also provide large surface area for expediting such transport. Consequently, solvent content in the diluted oil within the transition zone could exceed the amount needed for onset of de-asphalting. De-asphalting also seems to be promoted by the presence of connate water. The diluted and de-asphalted oil, in turn, drains near the edge of the vapour chamber as continuous oil column or, within the transition region as discontinuous oil ganglia. With continued solvent transport, oil viscosity as well as, interfacial tension between diluted oil and vapour decrease. As a result, occasionally, interfacial forces holding up diluted oil ganglia are reduced below the prevailing hydrostatic head and episodes of de-saturation are initiated. These episodes may culminate in mobilized oil ganglia coalescing with other ganglia, or with continuous oil column to the production well. Alternately, upon encountering finer sized pores, they could break-up and some oil may again get held up. Propagation of vapour chamber and oil rates during Vapex, therefore, depends upon properties of diluted and de-asphalted oil within the transition region (between the vapour chamber and oil region unaffected by solvent transport). This paper presents evidence for these mechanistic insights and discusses practical implications to operation and design of Vapex projects. Introduction In the Vapex (Vapour Extraction) operations for heavy oil recovery, a condensable solvent (e.g. propane or CO2) is injected into the reservoir via a horizontal injector and mobilized oil is drained via a horizontal producer placed directly underneath it1,2. The solvent is chosen such that it is close to its dew point under reservoir conditions and resulting solvent-oil mixture in vicinity of the vapour chamber, has significantly lower viscosity as compared to the native oil. The main driving mechanism is gravity to help drain the oil thus mobilized (having reduced viscosity) as shown in Figure 1. The main motivation for this work was to investigate role of different factors on oil rates during Vapex operations. Specifically, it was to obtain further understanding of process mechanisms and to identify optimal operating and design factors, including solvent selection.

A new waterflooding process, toe-to-heel waterflooding (TTHW), was developed, based partly on a recently developed thermal TTH displacement process, TTH air injection (THAI). TTHW is a novel oil-recovery process that uses a horizontal producer (HP) and a vertical injector (VI). The HP has its horizontal leg located at the top of formation, while its toe is close to the VI, which is perforated at the lower part of the formation.TTHW realizes a gravity-stable displacement, in which the water/oil mobility ratio becomes less important and its detrimental effect on sweep efficiency is diminished; the injected water always breaks through at the toe, after which water cut gradually increases.A systematic investigation of the TTHW process in a Hele-Shaw laboratory model mimicking a simulated porous medium showed that the process substantially improved the vertical sweep efficiency as compared to conventional waterflooding. Following these semiquantitative tests, a more comprehensive 3D-model testing was undertaken to investigate the overall sweep efficiency of the process. The 3D model consists of a metal box filled with glass beads and saturated with oil at connate-water saturation. Oil was displaced with high-salinity brine, either in a TTH configuration or in a conventional array, using only vertical wells.A staggered line drive was used by injecting water in two vertical wells located at one side of the box and producing oil by using either an HP with its toe close to the injection line or a vertical producer located at the HP's heel position.Several TTHW tests were carried out at different injection rates. For a given injection rate, the TTHW results were compared to those of conventional-waterflooding tests. For the same amount of water injected, the ultimate oil recovery increased by a factor of up to 2, as compared to that for conventional waterflooding.All in all, the results of these investigations show that the novel TTHW process is sound and can be optimized further.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA new waterflooding process, Toe-To-Heel Waterflooding (TTHW) was developed, partly based on recently developed thermal toe-to-heel displacement processes: THAI and CAPRI. TTHW is a novel oil recovery process utilizing a horizontal producer (HP) and a vertical injector (VI). The HP has its horizontal leg located at the top of formation, while its toe is close to the VI, which is perforated at the lower part of the formation.TTHW realizes a gravity stable displacement, where water/oil mobility ratio becomes less important, and its detrimental effect on sweep efficiency is diminished. The main advantage of TTHW process is that the water always breaks-through at the toe, following which water cut gradually increases.A systematic investigation of the TTHW process in a Hele Shaw laboratory model mimicking a simulated porous medium showed that the process substantially improved the vertical sweep efficiency as compared to conventional waterflooding. Following these semi-quantitative tests, a more comprehensive 3-D model testing was undertaken in order to investigate the overall sweep efficiency of the process. The 3-D model consists of a metal box filled with glass beads and saturated with oil at connate water saturation; the thickness of "oil layer" is 16 cm and the length is 42 cm. Oil was displaced with a high salinity brine, either in a toe-to-heel configuration, or in a conventional array, using only vertical wells.A staggered line drive was used, by injecting water in two vertical wells located at one side of box and producing oil through either a horizontal producer with its toe close to injection line, or by using a vertical producer located at the horizontal producer's heel position. Several TTHW tests were carried out at different injection rates. For a given injection rate, the TTHW results were compared to those of conventional waterflooding tests. For the same amount of water injected, the ultimate oil recovery increased by a factor of up to two, as compared to that for conventional waterflooding. Numerical simulation models successfully matched the observed performance in the laboratory.All in all, the results of laboratory investigations and numerical simulations show that the novel TTHW process is sound, and can be further optimized.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSingle Well Steam Assisted Gravity Drainage (SW-SAGD) process was evaluated by closely examining performance of field projects in the public domain, physical modeling and numerical simulation.It was seen that in order to be economically acceptable, field implementation emphasizes the "Single Well (SW) aspects" (near well bore heating), as opposed to the "SAGD aspects" (creation of a large steam chamber).The reported steam-oil ratio of about one for SW-SAGD field projects includes contributions due to primary production. Obviously, the performance will be attractive where the primary production is strong. Presence of mobile water or gas in the vicinity of a target location will have a negative effect on performance.The economic performance can be stronger than that for primary and cyclic steam stimulation but perhaps not as strong as for a dual well steam assisted gravity drainage. Therefore targets should typically have a continuous pay thickness of 10 to 15 m. Potential improvements can be obtained from optimizing well bore configurations by way of reducing steam by-pass and extending the effective well length utilized for production during the process. Other optimizing ideas involve the use of gases as steam additives and injection-production rate scheduling.The process is essentially a variation of cyclical steam stimulation (CSS) rather than of SAGD. Using certain elements of the SW-SAGD process, one should be able to profitably modify the cyclic steam stimulation (CSS) process while using horizontal wells.