Recovery Factors in High-Pressure Air Injection Projects Revisited

High-pressure air injection (HPAT) is in increased-oil-recovery (IOR) process in which compressed air is injected into I deep light-oil reservoir with the expectation that. the oxygen ill the injected ail will react with a fraction of the reservoir oil at ail elevated temperature to produce carbon dioxide. The resulting flue-gas mixture provides the main mobilizing force to the oil downstream of the reaction region, sweeping it toward production wells. The combustion zone itself may provide a critical part of the sweep mechanism. In 1994, Fassihi et al. (1997) proposed a method for estimating recovery factors of light-oil air-injection projects, on the basis of the performance of two successful HPAI projects. Their suggested method relies oil the extrapolation of the field gas/oil ratio (GOR) up to an economic limit. In other words, it treats HPAI as ill immiscible gasflood and neglects any potential Oil that Could be recovered by the combustion front. The truth is that, although early production during,in HPAI process is mostly caused by repressurization and gasflood effects, once I pore volume of air has been injected, the combustion front becomes the main driving mechanism. Moreover, one of the unique features of air injection is the self-correcting nature of the combustion zone, which promotes good volumetric sweep of the reservoir. This paper presents laboratory and field evidence of the presence of a thermal front during HPAI operations, and its beneficial impact oil oil recovery. Ail analysis of the three HPAI protects in Buffalo field, which are the oldest HPAI projects Currently in operation, shows that only a small fraction of the reservoir has been burned and, if time allows and the projects Eire managed appropriately, burning Of more reservoir volumes Could result. ill much higher oil recoveries than predicted by the gasflood approach.