考虑渗透率随压力变化的新煤层井压力衰减试井解释方法

AN INTERPRETATION METHOD OF PRESSURE ATTENUATION WELL TEST IN NEW COAL BED WELL IN CONSIDERATION OF THE CHANG IN PERMEABILITY WITH PRESSURE

煤基质的孔隙性对流体流动影响极小 ,试井所得渗透率反映的是割理系统的渗流能力。储层压力的变化引起有效应力改变 ,使得煤层裂隙张开度和渗透率发生变化 ,渗透率随储层压力下降而减小。文章针对压力衰减测试过程中 ,井筒附近储层压力变化影响煤层渗透率这一因素 ,应用Duhamel原理 ,导出了分析压力衰减测试数据的解释方法。该方法应用在新煤层甲烷井中 ,可以获得煤层原始渗透率、原始储层压力以及表皮因子 ,避免了用段塞流解释需要预先估计原始储层压力的困难。文中给出了山西煤层组甲烷气井的实测资料和解释结果。

The matrix pores in coal play a little role in fluid flow,therefore the permeability derived from well test is the reflection of the percolation flow capacity in cleat system.The change in reservoir pressure may cause that in effective stress,which makes the change in both open size and permeability of the fissures in coal bed,the permeability decreasing with the falling of the reservoir.In light of such a condition that the coal bed permeability was influenced by the change in the reservoir pressure near well bore in the process of pressure attenuation testing,an interpretation method of analyzing the pressure attenuation testing data is derived in the paper by use of the Duhamel principle.In new coal bed methane gas well,the primary permeability,primary reservoir pressure and skin factor may be obtained by use of the method,so as to aviod the difficulty in need of pre estimating primary reservoir pressure in slug flow interpretation.Finally,the measured data and interpreted results of the coal bed methane gas wells in Shanxi Province are proposed in the paper also.