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我国存在大量的水驱气藏,其压力及产量动态特征不同于气驱气藏,这已经被气藏开发的实践证实。目前对于水驱气藏气井产量递减分析理论与方法的研究,都是基于复合油藏中单相油流动时的产量递减分析理论与方法,没有涉及到水驱气藏中气井的产量递减分析问题。文章针对水驱气藏中气井的产量递减分析问题,在建立递减分析数学模型并采用拉普拉斯变换方法获得解的基础上,利用数值反演方法计算了气井产量递减分析的典型曲线,从理论上分析了气井产量递减主要受到内外区半径、气水传导系数比及气水流度比的影响,获得了产量递减的三个阶段,即第一阶段为压力波只在气区中传播的产量递减特征;第二段为压力波传播到气区边界时的产量递减特征;第三段为压力波传到水区的产量递减特征,同时用实例验证了该理论与方法的正确性。文章所研究的内容为水驱气藏气井的产量递减分析提供了理论基础。

Theory and Application of Production Decline Analysis for Gas Wells in Water-drive Gas Reservoirs

There are many water-drive gas reservoirs in China. Their characteristics of pressure and production performance are different with those of gas-drive gas reservoirs. It has been proved by the production practice of gas reservoirs. The present theory and method of production decline analysis for gas wells in water-drive gas reservoirs are based on the theory and method of production decline analysis for single phase oil flowing in composite oil reservoirs, which can' t cover the production decline analysis for gas wells in water-drive gas reservoirs. Aiming to the problem of production decline analysis for gas wells in water-drive gas reservoirs,the mathematical model of the decline analysis is developed and its solution is obtained with Laplace transformation. Then with numeral reversion method, the typical curves of production decline analysis for gas wells are derived. It is recognized theoretically the production decline of gas wells is affected mainly by the radius of inner/outer zones, the ratio of gas/water conducting coefficients,and the ratio of gas/water flowing rates. The production decline can be divided into 3 stages. In the first stage, the pressure waves are transmitted only in the gas zone. In the second stage,the pressure waves are transmitted to the boundary of the gas zone. In the third stage, the pressure waves are transmitted to the water zone. Real cases prove the theory and method is correct. The article provides the theoretical ground for the production decline analysis for gas wells in water-drive gas reservoirs.