Use of Magnetic Resonance Imaging and Advanced Image Analysis as a Tool to Extract Mass Transfer Information from a 2D Physical Model of the Vapex Process

Abstract

Abstract 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.