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常规测试的渗透率与数值模拟及压后测试的渗透率比较明显偏低，主要原因是由于煤层割理中存在游离气，形成贾敏效应，因此采用常规测试解释方法解释单相注入测试压力降落分析不能求出正确的地层渗透率值，所求得的值小于地层的真实渗透率。根据EXDOS数值模拟软件模拟，当游离气饱和度为0.05%~0.15%时，计算出的渗透率比原来小了近60%~90%。本文在考虑游离气影响，存在贾敏效应的情况下运用渗流力学理论建立了注入压降测试分析的新数学模型，根据数值模拟软件模拟，计算出的渗透率接近实际的渗透率。应用新模型解释40多井次的结果与压后生产实践和地质评价结果分析，符合煤层的实际情况，解决了常规试井解释方法所计算的渗透率偏小的问题。

Study on Pressure-drop Well Test with Injection of Coal-bed Gas Well

The permeability measured by the conventional method is obviously lower than that by numeric simulation or after fracturing. The main reason is that there is some free gas in the cleat of coal seams，which produce Jiamin effect. So，the correct permeability can′t be derived with the conventional interpretation based on the pressure drop test by single phase injection. The value of the permeability calculated by the method is smaller than the real one. According to EXDOS software of numeric simulation，the calculated permeability is 60% ~ 90% smaller than the real one when the free gas saturation is 0.05%~0.15%. In the article，a new mathematical model is established for pressure drop test with injection by the percolation mechanics′ theory considering the influence of free gas and Jiamin effect. According to the results achieved from more than 40 wells with the new model，the production practice and the geological evaluation，it is found the results fit the real situation of the coal bed. The method solves the problem that the permeability calculated with the conventional interpretation method is smaller.