压汞法测定页岩孔隙特征的影响因素分析

Study on Influencing Factors in Determining Pore Characteristics of Shale by Mercury Intrusion

压汞法是目前测定岩石内部孔隙特征的常用方法,但测试结果受样品尺寸、测量范围等多种因素的影响。本文以页岩为主要研究对象,采用压汞法等测试手段分析了不同的样品尺寸、接触角等条件下的孔隙特征。结果表明:1孔隙率与所选的孔径范围有关,在7.1 nm^100μm孔径范围内测量孔隙率的准确性更高;样品制备时可能产生人为裂隙导致孔隙率的测量误差较大。2在一定孔径范围内,与人工合成样品相比,页岩的平均孔径、孔隙率、比孔容等特征值受样品尺寸影响更大。页岩样品尺寸的减小,不仅能增加小孔隙间的连通性,而且可以降低较大裂隙的影响。3接触角从130°增加到150°,平均孔径变大约35%。因此应在准确测量接触角的情况下采用小尺寸样品进行测试,同时进一步完善并统一压汞法测量页岩孔隙特征的实验规范,以提高测试结果的准确性和可比性。

Mercury intrusion is a common method for the determination of pore characteristics of shale, but the measurement results are affected by a number of factors, such as sample size and measuring range. The pore characteristics of shale and synthetic materials were analyzed under different contact angles, sample sizes and measuring ranges, all of which are reported in this paper. Porosity was related to the measuring range, and high precision results were acquired when the measuring range was between 7. 1 nm and 100 μm. The fractures produced during sample preparation may have increased the porosity. Compared with synthetic samples, the mean pore diameter, the porosity and the specific pore volume of the shale were strongly influenced by the sample size, within a certain measurement range. Reducing the sample size of shale, not only increased the connectivity between the small pores, but also reduced the impact of large fractures. The mean pore diameter increased by 35% when the contact angle increased from 130° to 150°. Therefore, in order to improve the accuracy and comparability of the results, the measurement should be performed using small sample sizes and exact contact angle. Meanwhile it is necessary to further perfect the test standard concerning the measurement of pore characteristics of shale by mercury intrusion.