The Rise of interfering solvent chambers: solvent analog model of SAGD
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AbstractA new concept of modelling the Steam-Assisted Gravity Drainage (SAGD) process was developed. This concept utilizes the analogy between the heat and mass transfer to model interfering steam fingers rising through a cold reservoir. The solvent in this process behaves similarly to the steam in Steam-Assisted Gravity Drainage and the diluted bitumen to the heated bitumen. Mass transfer by diffusion in this Solvent Analog Model is the analog of heat transfer by conduction in the SAGD process. This novel experimental technique enables one to study at room temperature the mechanism of bitumen recovery under a wide range of permeabilities in a vertical Hele Shaw cell. It is also suitable as a physical model of more complex situations, in particular those involving varying permeability across the cell or impermeable horizontal or slanted barriers. The technique utilizes a well-defined and reproducible solvent-bitumen system and avoids the complexities inherent in the use of high temperatures and pressures. It also allows easy visualization of flow patterns created by natural convection effects. The experimental work led to the observation that a boundary layer, delimited by two shock fronts, is formed around a rising solvent finger. It is the first time that this phenomenon has been described and studied n miscible flooding. Several theoretical approaches were taken to predict the bitumen drainage rate from basic material properties, such as diffusivity, viscosity and density. In the first approach, a Simple Countercurrent Flow set an absolute limit for the magnitude of the drainage rate. In the next three approaches, Concentration Gradient Models were developed that assumed a linear, an exponential and a linear step function concentration profile across the boundary layer. Finally, a comprehensive Solvent Chamber Theory was developed that predicts not only the drainage rate but also the solvent concentration at both fronts, the shape of the solvent fingers, the width of the boundary layer, the average (constant) solvent diffusivity and the concentration average solvent diffusivity. A comparison between experimental and theoretically predicted values show, in general, a degree of agreement which is encouraging.
Bibliography: p. 202-204.