岩心气测渗透率的不确定度评定

Evaluation of Uncertainty of Core Gas Permeability Measurement

为实现气体法测量岩心渗透率不确定度的评定,进而优化实验流程、提高实验精度,基于达西定律开展室内实验,建立数学模型,确定气测渗透率过程中不确定度来源。考虑气体流量校正及测量参数之间的相关性,逐层分析,依据不确定度传播律计算合成相对不确定度。计算结果表明:4个测试点下气测渗透率合成相对标准不确定度的平均值为0.016。对合成相对不确定度贡献最大的是流量测量及校正,其次是测量总重复性与进口压力的测量,由大气压力测量、气体黏度、长度、直径引入的不确定度可以忽略。压差越小,最终测定结果的不确定度越大,考虑在允许范围内尽可能地增大压差,以降低气测渗透率的不确定度。

In order to evaluate the uncertainty of core permeability measured by gas method,optimize the experimental process and im⁃prove the experimental accuracy,laboratory experiments are carried out based on Darcy's law,and mathematical model is established to determine the sources of uncertainty in the process of gas permeability measurement.Considering the correction of gas flow-rate and the correlation measurement parameters,the composite relative uncertainty is calculated according to the propagation law of uncertain⁃ty.The result shows that the average relative standard uncertainty of four test points is 0.016.The biggest contribution to the composite relative uncertainty is the measurement and correction of gas flow-rate,followed by the measurement of total repeatability and inlet pressure.The uncertainty introduced by the measurement of atmospheric pressure,gas viscosity,length and diameter can be ignored.The smaller the pressure difference,the greater the uncertainty of the final measurement results.Therefore,the pressure difference should be increased as much as possible to reduce the uncertainty of gas permeability.