An Experimental Study of Steam-Assisted Gravity Drainage Using A Large-Scale Physical Model

This paper presents a large-scale experimental study of the compositional effect on produced bitumen properties in SAGD. The SAGD experiment used a sandpack in the cylindrical pressure vessel that was 1.22 m in length and 0.425 m in internal diameter. The pore volume of the sandpack was 58 L, and the porosity and permeability were 0.33 and 5.5 D, respectively. The sandpack was initially saturated with 93% bitumen and 7% deionized water. The SAGD experiment after preheating was operated mostly at a steam injection rate of 35 cm3/min (cold-water equivalent) at 3600 kPa (244°C). The produced fluids (gas, oil, and water) were analyzed; e.g., ten oil samples were analyzed in terms of carbon number distribution (CND), the asphaltene content, density, and viscosity to investigate the compositional change of the produced bitumen. After the experiment, the sandpack was excavated and samples were taken for analysis of solid, water, oil, asphaltene, and sulfur contents. Experimental data (e.g., propagation of a steam chamber and production of oil and water) were history-matched by using a numerical reservoir simulator. Results showed that the produced bitumen was lighter and contained 1 to 5 wt% less asphaltenes than the original bitumen. Also, the remaining oil inside the steam chamber contained 6 wt% more asphaltenes. As a result, the produced bitumen was 1 to 6 kg/m3 less dense than the original bitumen. In the actual operations, bitumen is diluted with condensate to reduce the oil viscosity for pipeline shipping. This reduction in bitumen density corresponds to a reduction of the diluent cost by 5-10%. The produced bitumen became less dense with increasing steam-chamber volume. The history-matched simulation indicated that the progressively decreasing density of the produced bitumen can be attributed to the vaporization of the relatively volatile components in the remaining oil, and condensation of those components near the chamber edge. The history-matching also indicated that varying flow regimes (counter-current and co-current flow of water and oil) affected the oil recovery during in the SAGD experiment.