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天然气偏差系数是气田和凝析气田开发中一项非常重要的基础数据，主要用于油气藏储量计算等油气藏工程、采气工程和地面工程中，近年来天然气偏差系数的测试越来越受到重视，但目前我国还没有建立天然气偏差系数的测定标准。针对干气、湿气和凝析气的特点，利用高压物性PVT分析仪，分别给出了干气、湿气和 凝析气偏差系数的实验测定方法，对于凝析气还考虑了露点压力以上和露点压力以下偏差系数实验测定方法的差别，同时给出了实验步骤。采用该方法对我国几个气田和凝析气田的天然气偏差系数进行了实验测试，并与四种常用计算方法的预测结果进行了比较，结果表明该测试方法用于干气较准确，误差在1％以内，用于凝析气误差较大，在7．02％以内，平均相对误差1．61％－1．98%，最大相对误差6．67％－7．02％，最小相对误差－0．04％－0．2％。这说明该方法是行之有效的。

Measurement of Gas Deviation Factor

??Gas deviation factor is a very important basic datum in both gas field development and condensate field development and it is mainly used for reservoir reserve estimation,reservoir engineering,gas production engineering and surface construction engineering.The measurement of gas deviation factor has been highly thought of more and more in recent years,its measuring standard,however,has not been established yet in China at present.In the paper,in light of the characteristics of dry gas,wet gas and condensate gas,the laboratorial measurement methods of deviation factors of these gases by use of PVT analyzer are given out respectively;and the difference between the laboratorial measurement methods of the condensate gas deviation factors at over and under dewpoint pressures is considered and their laboratorial procedures are given out meantime.The deviation factors of natural gas collected from several gas fields and condensate gas fields in China were measured by use of the methods mentioned above.Through comparing the results with those predicted by four commonly adopted methods,it is shown that the measuring method used for dry gas is more accurate with errors of 1% and the one for condensate gas is of large errors of 7.02%,average relative errors being 1.61%??1.98% ,maximum relative errors 6.67%??7.02% and minimum relative errors -0.04%??0.2%,which indicates that these methods are effective.