岩心渗透率的计算方法与适用范围

Core permeability calculation methods and application scopes

由于低渗透和高渗透储层都存在不同程度的非线性渗流特征,而且渗透率越趋向于两个极端,非线性就越严重,由此造成渗透率计算结果偏差较大。为此,对于易发生非达西渗流的储层,通过引入克氏方程,可校正计算低渗透岩心的非达西渗透率;通过推导气体的非达西二项式渗流方程,可得到计算高速非达西渗透率的新方法。结合400块岩心的渗透率测试实验结果,明确了不同渗透率计算方法的适用范围：储层渗透率小于1 mD时,滑脱效应对气体渗流产生的影响较大,应进行克氏渗透率校正计算;渗透率大于10 mD时,气体高速非达西渗流特征明显,应采用高速非达西渗透率的计算方法;渗透率介于1~10 mD之间时,需要同时考虑两种渗流规律的影响而采用复合计算。对比分析计算结果后认为,常规计算获得的表观渗透率与考虑储层实际状况得到的渗透率相差较大,相对误差一般都在20%以上或更高。因此,岩心渗透率计算方法的选取应根据实验测试的表观渗透率而定,其计算结果才能更加真实地反映储层的渗流能力和开发动态。

Since both low-permeability and high permeability reservoirs have various degrees of nonlinearity, and the more the per meability approaches the two extremes, the severer the nonlinearity, so the resulted error will bc larger. Therefore, for the rescr voirs prone to non-Darcy flow, the Kirschner equation is used to correct the non Darcy permeability of low permeability core sam pies; a new method for calculating high-speed non-Darcy permeability was obtained by deducing the non-Darcy binomial flow equa tion of gas. According to the permeability of 400 core specimens tested by experiments, the application scope of different permcabili ty calculation methods was clarified： when the reservoir permeability is less than 1 roD, the slip effect has stronger influence on the gas flow, so Kirschner permeability correction should be used; when the permeability is more than 10 mD, gas has obvious high speed non-Darcy flow, so the calculation method for high speed non Darcy flow should be adopted; when the permeability is between 1 mD and 10 mD, two kinds of flow patterns should be considered, so the combined calculation metthod should be used. Comparison of calculation resul, ts shows that the apparent permeability ca!.culated hy conventional methods usually has big discrepancy from the actual permeability considering the reservoir conditions with a relative error being generally over 20% or more. Therefore, the calcu lation method of core permeability should be selected according to the apparent permeability measured by experiments, and only the results by the selected method can better reflect reservoir percolation ability and development performance.