The Study on the Gas Override Phenomenon in Condensate Gas Reservoir

The cyclic gas injection technique is commonly used in the development of condensate gas reservoir. However, the override of injected gas induces severe gravity segregation in formation, greatly limits the application of this technique, and relevant studies are rarely found in literatures. This paper studied the phase behavior of the mixture composed of injected dry gas and condensate gas during the process of dry gas injection. The visual PVT cell exhibits a combination of dry gas - condensate gas - condensate oil for pressure fluctuate around dew pressure and a combination of dry gas - condensate gas for pressure above dew pressure. Considering the main influencing factors, a corresponding theoretical model is established to portray the formation and development of injected gas override in condensate gas reservoir. The case study indicates that the injected dry gas would surpass the original condensate gas and break through from the top of the reservoir. In addition, a transition zone is formed between the injected gas and condensate gas, and the transition zone would evolve over time.