Simulation and Modeling of Pressure Difference on Steam Chamber and Production Performance

Abstract

Abstract Steam Assisted Gravity Drainage (SAGD) is the most effective thermal recovery method to exploit oil sand. The driving force of gravity is generally acknowledged as the most significant driving mechanism in SAGD process. However, an increasing number of field cases have proven that pressure difference may even play an important role in some cases. Therefore, the objectives of this paper are to simulate the effects of injector-producer pressure difference on steam chamber evolution and SAGD production performance. A series of 2D numerical simulations are conducted on the basis of MacKay River and Dover reservoir in West Canada to investigate the influence of pressure difference. Meanwhile, the effects of pressure difference on oil production rate, stable production time, steam chamber development were studied in detail. Moreover, by combining Darcy's law and heat conduction along with a mass balance in the reservoir, a modified mathematical model considering the effects of pressure difference is established to predict the SAGD production performance. Finally, the proposed model is validated by comparing calculated cumulative oil production and oil production rate with the simulation results. The results indicate that the oil production first increases rapidly and then slows down when a certain pressure difference is reached. The impacts of pressure difference are much greater at steam chamber rising stage than at steam chamber expansion stage. Therefore, in the field, at the beginning of the SAGD recovery, it is better to augment pressure difference, while at the steam expansion stage, a lower pressure difference is preferred, so that a smaller chance of steam breakthrough and a higher economic benefit will be achieved. Besides, it is found that steam chamber expansion angle is a function of pressure difference. Based on this phenomenon, a new mathematical model is established considering the modification of the expansion angle which Butler treated it as a constant. With the proposed model, production performance, such as cumulative oil production and oil production rate can be predicted. Steam chamber shape is redefined at the rising stage and it changes from fan-shape to hexagonal-shape, but not the single fan-shape defined by Butler. This shape-redefinition can clearly explain why the greatest oil production rate does not happen when steam chamber reaches the cap-rock. Literature surveys show few studies on how pressure difference influences steam chamber development and SAGD recovery. This paper provides a modified SAGD production model and also a totally new scope for SAGD EOR, which makes the pressure difference a new optimizable factor in field.