A Novel Analytical Model for Steam Chamber Rise in Steam- Assisted Gravity Drainage

Fluid flow and heat transfer during steam chamber rise (ramp up) in the steam-assisted gravity-drainage (SAGD) process is very complex. The majority of existing analytical models fail to capture the physics of this stage and their estimations of oil production and steam/oil ratio (SOR) may be questionable. This paper presents a new analytical model to predict the advancing velocity of the steam chamber in the vertical direction, correlations of oil production rate and SOR, and the evolution of chamber profile during this stage using material/ energy conservation and gravity-drainage theory. The new analytical model was validated against field observations, laboratory measure-ments, and numerical simulations. Results showed that the new analytical model not only successfully predicted oil production rate and SOR with improved reliability and accuracy but also for the first time properly predicted the chamber profiles with time during the ramp up stage. Using this model, impacts of the key parameters were investigated. The investigation revealed that permeability anisotropy had a considerable impact on development of the chamber profile. Under the constant horizontal permeability condition, the smaller the ratio of vertical to horizontal permeability, the shorter and wider the chamber profile. A small subcool control strategy could boost oil production and steam chamber growth, which is consistent with experiments and field data. Investigation also found that increasing the distance be-tween injector and producer was beneficial for oil production. However, changing this distance may cause some operating/performance/ economic problems and so should be approached cautiously. This paper represents the first time that the evolution of chamber profiles in the ramp up stage was characterized mathematically. Useful guidance for operators on improving ramp up performance can be extracted directly from this model.