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Molecular d@sion of gases in oil plqys a role in several heavy oil recovery processes. In solution gas drive, the gas diffusion coefficient has a direct impact on the amount of gas that is released and the level of supersaturation that exists during pressure depletion.Kijt21 In the Vapex process, molecular d$%sion controls the rate at which the solvent vapour is absorbed by the oil. Molecular dif/usion is also important in supercrtticaljluid extraction of heavy oils and in recovery of residual oil by miscible displacement.Unfortunately experimental data on gas difision coefficient in heavy oils are relatively scarce due to the tedious nature of diffisivi@ measurements, The main objective of this work was to develop a simple experimental technique for measuring gas diffusion coefficients in heavy oils.Diffusion coeficients of carbon dioxide and methane were measured by measuring the rate of gas absorption in a high-pressure windowed cell. The d@usion equation, coupled with the gas material balance equation, was used to history match the gas absorption data using the diffusion coefficient as an adjustable parameter. The diffusion coefficients calculated by this history match technique are compared with the reported values of diffusion coeflcients in similar systems.

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Interest in the vapor-extraction (Vapex) process for heavy-oil and bitumen recovery has grown considerably as a viable and environmentally friendly alternative to the currently used thermal methods. The potential for the success of the Vapex process is even more attractive in some scenarios that preclude the thermal methods. The presence of an overlying gas cap and/or bottomwater aquifer, thin pay zones, low thermal conductivity, high water saturation, and unacceptable heat losses to overburden and underburden formations are some of the limitations with the thermal techniques, which potentially can be overcome by Vapex implementation. However, predicted low production rates by previous researchers for field application of the Vapex technique remain a serious barrier to commercial applications of the process. The scaleup methods that have been used by previous workers for translating the laboratory results to field predictions were based primarily on the reservoir transmissibility. An analytical model developed by Butler and Mokrys 1 showed that the oil rate should be proportional to the square root of reservoir transmissibility. The effect of convective dispersion between solvent and virgin heavy oil in porous media was ignored in developing this model.The main objective of this work is to develop an improved scaleup method for the Vapex process using physical-model experiments carried out in models of different sizes. In this paper, we report the results of a new series of experiments that extend the previously reported results of Karmaker and Maini 2 to a significantly wider range of model heights. These new experiments used a new design of slice-type physical models that places the sandpack in the annulus formed by two cylindrical pipes. Combining the new results with the previous data of Karmaker and Maini, 2 we show that the transmissibility-based scaling-up method seriously underpredicts the results at larger scales. This observation suggests that much higher rates can be expected in the field implementation of the Vapex process.A new correlation also has been proposed for scaling up the experimental data to the real field cases. It indicates the height dependency of the convective-dispersion contribution, which can be the dominant mass-transfer mechanism for the process, to be a higher order than previously postulated. Experimental results from this work show that the stabilized rate is a function of drainage height to the power of 1.1 to 1.3, instead of the square-root functionality of the Butler and Mokrys 1 model.

A modified pressure decay method has been designed and tested for more reliable measurements of molecular diffusion coefficients of gases into liquids. Unlike the conventional pressure decay method, the experimental setup has been designed such that the interface pressure and consequently the dissolved gas concentration at the interface are kept constant. This is accomplished by continuously injecting the required amount of gas into the gas cap from a secondary supply cell to maintain the pressure constant at the gas−liquid interface. The pressure decay is measured in the supply cell. The advantage of the new technique is that, assuming the diffusion coefficient to be constant, a simple analysis allows determination of the equilibrium concentration and diffusion coefficient.

Vapour extraction (VAPEX) is a potentially economic process for the recovery of heavy oil and bitumen in Canadian reservoirs, as all of the injected solvent is effectively delivered to the zone of interest. In addition, the process has the potential to sequester greenhouse gases, and is capable of in situ upgrading of heavy oil. The research described in this paper was undertaken to identify the main processes governing the interfacial mass transfer of solvent into bitumen. A number of experiments were carried out in a Hele-Shaw cell, and the results were incorporated into a predictive model. Good agreement between theory and experiment was found when dispersion effects were incorporated into a mass transfer model of the process at identical values of Peclet number. Introduction Vapour extraction (VAPEX) is an alternative method for recovery of heavy oil and bitumen. This technique, which involves a solvent-leaching gravity drainage mechanism, reduces the viscosity of heavy oil by dissolution of a vapourized solvent into the bitumen. VAPEX has recently received a lot of attention from industry, as a promising means for recovery of heavy oil deposits in Canada. The primary drive for this interest is the potential economic attractiveness of the process in comparison to other heavy oil recovery techniques. Unlike steam injection, which is associated with significant heat losses to the media surrounding the wellbore and reservoir, all of the injected solvent by VAPEX is effectively delivered to the zone of interest. This process also appears to provide an alternative method for potential sequestration of greenhouse gases, particularly in regions at close proximity to power plants of northern Alberta. Moreover, experimental work has proved that VAPEX is capable of in situ upgrading of the heavy oil, due to the stripping phenomenon associated with scavenging the lighter end hydrocarbons by the flowing solvent(1). Therefore the costs associated with treatment and processing of produced oil by VAPEX is considerably less than that for other heavy oil production schemes. The prime objective of this paper is to identify the main processes governing the interfacial mass transfer of solvent into bitumen and incorporate those mechanisms into a reliable, predictive model. The estimated recovery rates for laboratory experiments in a Hele-Shaw cell appears to be well within the range of drainage rates predicted by molecular diffusion-based models(1). However, subsequent experiments in sand-packed porous media resulted in drainage rates, considerably higher than predicted values from analytical models(1, 3-5). Earlier researchers had suggested several different factors that might potentially enhance the mass transfer of solvent into the bitumen in the VAPEX process(5). However, no systematic investigation was carried out to understand and/or verify the viability of either of their proposed enhancement mechanisms. In order to have a better understanding of the dispersion and diffusion mechanisms of mass transfer for VAPEX, we began our experiments in a Hele-Shaw cell. Further experiments will be conducted in porous media, once the questions surrounding the process in a Hele-Shaw cell are addressed.