地层条件下气体的偏差系数是用来计算气藏储量的关键数据，通常使用图版法、经验公式法和实验法进行确定。但由于深层超高压凝析气藏地层温度高、压力高，常用的图版法等方法是否适用，缺乏实测资料的佐证。高温高压实验研究表明，超高压下的气体偏差系数和临界压力均远高于低压气藏，超出Standing―Katz图版范围，常规的方法不适用；高压条件下的气体偏差系数与压力呈直线关系，可由较低压力下的实验结果直线外推得出超高压下的偏差系数，不仅降低了对实验设备的要求，且简化了实验过程

Gaseous Z-factor is key data that is used to calculate the reserves of gas reservoir, we can generally make certain Z-factor by Z-factor charts, experience methods and experimentation. However,because deep layer and ultrahigh pressure gas reservoir has high temperature and high pressure, we are devoid of proof of practical measurement whether these conventional methods are applicable. Experiment of high temperature and high pressure show Z-factor and critical pressure are greatly excessive lowpressured gas reservoirs under ultrahigh pressure condition, which has gone beyond applicable scope of Z- factor charts, so conventional methods are usually inapplicable; Z-factor and pressure has good linearity relation under high temperature and high pressure condition, therefore, it is feasible for Z-factor of ultrahigh pressure gas reservoir to apply experiment result and linearity relation to extrapolate the original stratum pressure condition, which will greatly reduce the request of experiment equipment, and predigest the process of experiment.