A set of experiments involving steam and steam-additive drives in Athabasca oil sands have been performed in a 45 cm diameter pressure vessel at reservoir conditions. These experiments formed part of the AOSTRA/Alberta Research Council Joint Research Program.
Three experiments are discussed in this paper. Injected fluids for the three experiments are steam, steam-CO2 and steam-N2. All three experiments are continuous injection experiments and involve no pressure draw-downs. These experiments are examined together with numerical simulations in order to demonstrate the capability of the numerical model to capture the significant physical processes.
Experimental results from the physical simulators suggest the possible existence of an optimum CO2 concentration in steam for bitumen recovery from oil sands. The results also indicate that the efficiency of the steam-additive process depends on injection strategies employed during the experiments.
The numerical model is used to predict the effect of a range of CO2 concentrations and communication path permeabilities on recovery curves. Results obtained from this study are of importance in understanding the recovery process and future design of steam-additive experiments.
The 45 cm experimental simulator is a cylindrically shaped pressure vessel, 45 cm in diameter and 25 cm in height. It is one of a series of Alberta Research Council physical simulators and one in which a very large body of experimental data was generated. A feature of the experiments discussed here is that they were characterized by high flow rates resulting in high energy injection rates and high heat loss.
Another important feature of most of the experiments carried out in this pressure vessel is that although the walls of the pressure vessel are cylindrical, the communication path used to provide a flow path from the injection well to the production well was rectangularly shaped. This caused a problem from a mathematical point of view in modelling experiments carried out in this pressure vessel. Radial coordinates were needed in order to accurately represent the mass in the active zone of the test bed. but the flow of fluids could not be well represented by any representation of the rectangular communication path with cylindrical coordinates.
After first discussing the overall characteristics of the experimental apparatus and the particular experiments under analysis, details of the numerical model are given. Then the simulation and analysis of the physical experiments is presented including a discussion of the discrepancies between the model and experiments. Finally, a sensitivity analysis is carried out on the effect of CO2 concentration in the injection stream, and the effect of communication path permeability.
Three systems are involved in the running of an experiment in the 45 cm diameter pressure vessel. First is the injection system which is capable of injecting steam, water, solvents or gases. The injection system connects to the pressure vessel by means of the injection well. The pressure vessel is the second system. Thirdly, the production well from the pressure vessel leads to a production system composed of a separator and a condenser for produced liquids and gases.