The experimental studies carried out to evaluate oil recovery processes let optimum strategies be determined and necessary actions be taken before initiating a new project. Numerical simulators can, sometimes, perform same tasks in a much more economical and faster way, with many alternatives. Some of the complexity of oil recovery process, such as SAGD(Steam Assisted Gravity Drainage), can be resolved by carrying out experimental and numerical evaluations together.
In this study, numerical simulation of the SAGD process is performed. The CMG "STARS" ™ thermal simulator was used to simulate the data from the present dual-well SAGD experiment. The simulation uses a two-component (water and heavy oil) black oil, three-phase (water, heavy oil and steam) and three-dimensional numerical model. The results from the history-matched numerical simulation are found to be in reasonable agreement with those of the experiment for oil production rate, cumulative oil production, steam chamber and temperature contours in the model.
Effects of varying several physical conditions, such as steam injection pressure, vertical separation between injection and production wells, and model thickness, on the performance of the SAGD process were investigated in both the experimental and numerical studies. Varying physical conditions are noted to have similar effects both on the experimental and numerical results.
Effectiveness of the numerical simulator was also investigated by varying rock and fluid properties, such as oil viscosity, permeability, porosity and amount of heat loss from the model to the surroundings. The numerical results are in good agreement with the expectations in accordance of the input data in the simulator.
The theory of the steam-assisted gravity drainage (SAGD) process was developed by Butler (1991) and is illustrated in Figure 1. It is being applied in several field pilots and has promise as a method for achieving a higher ultimate recovery (more than 50 % of OOIP).
The SAGD process may be considered a special form of steam drive. Two horizontal wells are used. As steam is injected continuously through the upper well near base of the formation, the heated oil and the condensed steam at the interface of the steam chamber flow, by gravity down to the lower production well below the injection well. As the liquids are removed, the space left in the pores is filled with steam. A rising steam chamber growing upwards and sideways is formed with a broken fingering pattern at the upper interface. The oil remains hot as it is drained. The pressure within the steam chamber remains essentially constant. The pressure difference between the injection and the production well is very small. To prevent the excessive and premature steam breakthrough to the production well, a liquid leg is maintained between the two wells. The drainage from the production well is controlled by adjusting the bottom hole temperature and pressure so that the fluid in and around the production well remains in liquid form. The effect is similar to that of steam trapping.
Many experimental and numerical studies related to the SAGD process have been carried out on the different aspects of the process.
