为了探讨欠饱和煤层气藏临界解吸压力的物理意义,基于煤层气藏赋存状态,介绍了目前已有的传统临界解吸压力计算方法、液相吸附理论的计算方法以及矿场统计算法,讨论了在煤岩气相湿润前提下的“欠饱和”现象的来源。在修正的气相吸附基础上,解释了临界解吸压力与基质孔隙毛管压力的关系,得到了新的临界解吸压力计算方法。通过对比4种方法在误差分析、理论完备性以及可操作性的优缺点,认为提出的新计算方法理论较为完备、可操作性强、计算简便,并在实例计算中得出了合乎实际生产范围内的结果。由此可得到在煤岩气相润湿前提下,煤层气吸附平衡且临界解吸现象可解释为储层压力与毛管压力之间作用的结果,改进的气相吸附理论与临界解吸压力新计算方法值得进一步研究。

In order to investigate the physical meaning of critical desorption pressure in undersaturated CBM（coalbed methane） reservoirs, the traditional critical desorption pressure calculation method and the liquid phase adsorption theory commonly used in field are introduced based on the status of the reserves of CBM, and the origin of the “undersaturated” phenomenon under the premise of gas phase wet is discussed. On the basis of the modified gas phase adsorption, the relationship between the critical desorption pressure and the capillary pressure in matrix pores is explained, and a new calculation method of critical desorption pressure is obtained. By comparing the advantages and disadvantages of the four methods in error analysis, theoretical completeness and operability, it is considered that the new calculation method proposed is relatively complete in theory, has strong operability and is easy to calculate, and obtains a reasonable result in an example. It can be concluded that CBM adsorption equilibrium and critical desorption phenomenon can be interpreted as the result of the interaction between reservoir pressure and capillary pressure under the premise of coalbed gas phase wetting. The improved gas phase adsorption theory and the new calculation method of critical desorption pressure are worth the further study.