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摘要
Extensive physical modeling of vapor extraction (VAPEX) has been studied in the past two decades, yet the theoretical modeling of VAPEX has not gained much progress. The major VAPEX mechanisms, i.e., oil viscosity reduction through solvent dissolution and gravity drainage, occur mainly in a thin solvent heavy oil transition zone. Therefore, modeling of the transition zone is the key to model the VAPEX process. Current analytical models are based on some potentially unreliable assumptions for the transition zone, such as steady-state mass transfer and constant boundary moving velocity. Numerical models cannot fully capture the physical features because the gridblock is usually much larger than the transition-zone thickness. This paper develops a new mathematical model for the VAPEX transition zone that is simplified as a piecewise linear profile and updated step by step. In each step, first, a solvent concentration distribution is calculated by using Fick's second law. Then the oil drainage velocity is computed by using Darcy's law. Finally, the momentary boundary moving velocity is estimated by using a mass balance equation. The VAPEX model is not only able to describe the evolution of the solvent chamber, but also characterize the dynamic oil properties across the transition zone. Compared with numerical simulation, this new model shows more sensitivity to the diffusion coefficient.
- 出版日期2014
