Pore-Scale Modeling for Interphase Mass Transfer during the VAPEX Process
Creators: Yu, Haisheng
Publisher: name: University of Alberta Library
Year: 2024

<p>Solvent injection processes offer a promising alternative to steam-based techniques for heavy oil recovery. Multiple mass transfer mechanisms, including interphase mass transfer, diffusion, and convection, would affect the process efficiency and recovery performance. Understanding the mass transfer processes in solvent-based heavy oil recovery processes is fundamental to accurately modeling the solvent/heavy oil interfacial dynamics and designing efficient solvent recovery methods. The pore-scale modeling approaches offer a potential for handling the interface mass transfer in detail and provide some fundamental understanding of macro-scale modeling. However, the traditional interphase methods (e.g., continuous species transfer method) suffer numerical instability issues, especially for convection-dominated cases (Péclet number or Pe &gt; 1).<br>
In this thesis, a robust simulation framework based on the level-set method is proposed first to simulate the injection of a vaporized solvent (i.e., propane) into a bitumen-oil system. A pore-scale two-phase multi-component flow simulation is constructed. The solution of the Navier-Stokes equation is coupled with the level-set formulation to track the fluid/fluid interface; a concentration jump is applied to simulate the mass transfer across the gas-liquid interface. The model is validated against several bulk fluid systems where analytical solutions can be derived. The model is tested using a more complex pore-scale system; a macro-scale mass transfer coefficient is estimated based on the linear mass transfer model. For the convection-dominated cases, an artificial diffusion coefficient term was introduced into the interphase mass transfer equation to reduce the numerical stability. <br>
To overcome the issues of numerical instability issues for the traditional interphase mass methods, a conservative LS-C-CST formulation was developed. The new model (LS-C-CST) is suitable for a wider range of Péclet numbers. Compared with the standard LS-CST method, the LS-C-CST method accurately captures the interfacial concentration discontinuity for convection-dominated and significantly reduces the numerical instabilities. This new formulation was validated with a model where the analytical solution exists and compared with the standard CST method. Therefore, the proposed LS-C-CST method can achieve a good accuracy in capturing the interfacial concentration discontinuity for convection-dominated regime. Additionally, the proposed LS-C-CST method is further employed to simulate the interphase mass transfer mechanisms of the VAPEX process. The main mechanisms were captured through simulation studies, including the capillary effect, snap-off mechanisms, and gravity effects. Numerical simulation of the vapor extraction (VAPEX) process with uniform pore structure was studied to reproduce experimental observations. The influence of interfacial mass transfer was explored. Collectively, these contributions provide some insight into the solvent-assisted recovery methods for heavy oil and bitumen production in the future research. </p>