Oil phase viscosity behaviour in Expanding-Solvent Steam-Assisted Gravity Drainage

In the Expanding-Solvent Steam-Assisted Gravity Drainage (ES-SAGD) process, solvent added to injected steam mixes with the oil at the edge of the depletion chamber to help reduce the viscosity of the oil phase below that which would result with steam alone. In this gravity drainage process, the key to heavy oil and bitumen production is the mobility of the oil phase which is controlled largely by the viscosity of the oil phase. In ES-SAGD, injected solvent can be used to substitute for steam and thus yield a more environmentally friendly recovery technology because the amount of flue gases emitted is lowered because less steam is required. It is not completely clear at what values the pressure and temperature of the depletion chamber should be maintained at to yield optimum production of oil and solvent. The higher the pressure, the higher the corresponding saturation temperature and the lower the viscosity of the oil phase. Also, the higher the pressure, the higher the solubility of solvent in the oil phase and the lower the viscosity of the oil phase. However, the higher the pressure, the higher the corresponding saturation temperature, and depending on the relative roles of pressure and temperature, the solubility of the solvent can be higher or lower. This means that there is a complex relationship between the operating pressure and its corresponding saturation temperature, the solubility of solvent, and the viscosity of the oil phase. In this research, the steam and solvent injection strategy is examined by viewing process trajectories on the pressure versus temperature diagram. After the process is visualized on these phase diagrams, the operating strategy required to maximize oil production and minimize the cumulative steam-to-oil ratio becomes clearer.