Abstract: The whole cyclic gas injection and partial pressure maintenance processes are used for development of Yaha23 gas condensate reservoir firstly in China.In order to take full advantage of the natural energy maintain the reasonable recirculation ratio and maximize the economic benefits,it is very important to estimate the efficient aquifer size and drive energy.In this paper with material balance equation,the mathematic model is set up to calculate the gas in place and the efficient aquifer size of Yaha23 gas condensate reservoir.The change of drive index during production is also calculated the result provides significant guidance for the dynamic analysis and followingup production of Yaha23 gas condensate reservoir.

Key words: Yaha23 gas condensate field, water influx rate, material balance equation, drive index