关键词: 生产初期, 压降法, 动储量, 固定压力计, 水驱气藏

Abstract: According to existing references,in the early development stage,water-drive gas reservoir has similar pressure drop characteristics with constant volume gas reservoir,therefore the dynamic reserves of gas reservoir can be obtained by linear relationship pressure drop extrapolation methods. However,the applicable range of gas recovery degree and the calculated dynamic reserve error have not been evaluated. Based on material balance equation and unsteady state aquifer model,the variation of reserve error with gas recovery degree under different aquifer multiplier and water permeability was calculated by iteration algorithm method. The results show that, taking dynamic reserve error less than 10% as criterion,the gas recovery range suitable for the early reserves calculated by linear relationship in water drive gas reservoirs is very narrow,generally less than 5%. Taking waterdrive gas reservoir in Xihu Sag of East China Sea as an example,the differences between the conventionally used method of pressure monitoring and the method of real-time pressure monitoring in obtaining early dynamic reserves by linear relationship were compared. Because of the long-time interval of pressure monitoring,the former method is liable to lead to misjudgment of the linear part of p/Z vs cumulative production in the initial production stage and the deviation in the evaluation of dynamic reserves. The latter method can accurately determine the starting time of the water influx so as to use straight-line extrapolation method to calculate dynamic reserves of water-drive gas reservoirs. The research result has significantly guidance for correct evaluation of dynamic reserves of water-drive gas reservoir in the early development stage.

Key words: early stage of development, pressure drop method, dynamic reserve, fixed downhole pressure gauge, water-drive gas reservoir