Optimal Control of Vapor Extraction of Heavy Oil

Vapor extraction (Vapex) process is an emerging technology for viscous oil recovery that has gained much attention in the oil industry. However, the oil production rates in Vapex are too low to make it attractive for field implementation. Although several researchers have investigated several aspects of Vapex, there are few reported attempts to enhance oil production in Vapex. This research aims to enhance the same using solvent injection pressure versus time as a control function. For this purpose, the necessary conditions for maximum heavy oil production are derived based on a detailed mass transfer model of the Vapex experiment carried out in this work. These conditions are then used to develop an optimal control algorithm to determine the optimal solvent injection pressure polices to maximize oil production in Vapex. The optimal policies successfully generate 20–35% increase in experimental oil production with propane and butane as pure solvents, and heavy oil of 14,500 mPa·s viscosity in lab scale reservoirs of 25 and 45 cm heights, and 204 Darcy permeability. The accuracy of optimal control is experimentally validated. The results show that the experimental oil production values from the optimal policies are within ± 5% of those predicted by the optimal control algorithm.