升温-降温全过程北山花岗岩渗透试验研究

Experimental study on permeability of Beishan granite during whole process of temperature-rise and temperature-drop

花岗岩是高放废物地质处置库的主要围岩体。为认识温度改变对北山花岗岩渗透特性的影响,采用多功能岩石低渗测试系统,以氮气为渗透介质,测试了北山花岗岩升温-降温全过程中渗透率(分别加热至120℃、140℃和160℃)。试验结果表明,升温-降温全过程北山花岗岩渗透率在0.055~0.1 mD范围内,在升温阶段,渗透率随温度的升高呈现降低的趋势;在降温过程的高温阶段,渗透率随温度的降低持续降低;温度降至60℃水平时渗透率出现回升趋势,但不能恢复至初始渗透率;通过核磁共振对比试验前后试样孔隙特征发现,温度渗流处理后北山花岗岩孔隙结构出现了不可逆改变,大孔段孔径分布曲线峰值对应的孔径大小及孔隙量均出现显著降低,温度对花岗岩孔隙表现明显的不可逆愈合作用,导致北山花岗岩渗透率降低。研究成果对花岗岩体内高放废物地质处置工程具有重要意义。

As granite is one of the main surrounding rock masses for building high-level radioactive waste geological disposal repository,the permeability of Beishan granite during the whole process of temperature-rise and temperature-drop(the samples are heated to 120℃,140℃and 160℃respectively)is tested by taking nitrogen as permeation medium with multi-functional rock low-permeability test system,so as to understand the influence from temperature change on the permeability of Beishan granite.The experimental result shows that the permeability of Beishan granite is within the range of 0.055~0.1 mD during the whole process of temperature-rise and temperature-drop.During the stage of temperature-rise,the permeability exhibits a decreasing trend with rise of temperature,while the permeability continuously decreases with drop of temperature during the high temperature stage of the temperature-drop process.When temperature drops to the level of 60℃,a rebounding trend of the permeability occurs,but the initial permeability cannot be recovered.The pore characteristics of the samples before and after the test are compared by means of NMR,it is found out that the irreversible change of the pore structure of Beishan granite occurs after the heating treatment of seepage flow,while both the pore size and the pore volume corresponding to the peak value of the pore size distribution curve in the large-pore section are significantly decreased and the temperature has an obvious irreversible healing effect on the pore of granite,which leads to the decrease of the permeability of Beishan granite.The study result has an important significance for the project of high-level radioactive waste geological disposal repository to be built in the rock mass of granite.