화학공학소재연구정보센터
Transport in Porous Media, Vol.108, No.2, 437-480, 2015
Pore-Scale Performance Evaluation and Mechanistic Studies of the Solvent-Aided SAGD (SA-SAGD) Process Using Visualization Experiments
The pore-level recovery mechanisms of the SA-SAGD process were recently studied for the first time in the literature in Porous Media Lab at the University of Waterloo using glass-etched micromodels. The experiments were conducted at controlled environmental conditions of an inverted-bell vacuum chamber to reduce the excessive heat loss to the surroundings. Different chemical additives (n-pentane and n-hexane) were added to steam prior to injecting into the models. An integrated data acquisition and control system was used to control, monitor and adjust the environmental vacuum pressure as well as to monitor and record local temperatures along the model's height and width. The pore-scale events were videotaped, and the captured snapshots were analysed thoroughly using image processing techniques. The pore-scale visualizations revealed that gravity drainage process takes place in the mobilized region, formed ahead of the pore-scale oil-vapour mixture interface in which all the flowing fluid phases are present. The interplay between gravity and capillary forces results in the drainage of the mobile oil with a reduced viscosity due to combined pore-level heat and mass transfer. Heat transfer at the pore level is believed to take place by conduction as well as convection. The solvent content of injected vapour mixture diffuses into the oil phase and hence reduces its viscosity following dilution as a result of molecular diffusion as well as convective mass transfer. Asphaltene precipitation was observed when the condensed solvent reached the bitumen interface. The average horizontal advancement velocity of the pore-scale SA-SAGD interface was measured and then correlated with operating temperature, macroscopic and pore-scale properties of porous media and bitumen properties within the range of experimental conditions. Quantitative analysis of the experimental results revealed that is a more effective steam additive compared with at similar operating conditions. Greater solvent content of the injecting vapour accelerates the pore-scale recovery by increasing the pore-scale interface advancement velocity. When all the other experimental variables were remained unchanged, smaller in situ oil viscosity values resulted in superior pore-scale production performance of the SA-SAGD process. The pore-level sweep rate was also found to be a function of the pore-scale dimensional characteristics of the porous media including pore-to-pore distance, pore body width, pore throat width and diffusion distance.