基于NMR的低渗岩体硅溶胶吸渗注浆试验研究

Experimental study of silica-sol imbibition grouting in low-permeability rockmasses based on NMR

为研究纳米硅溶胶对含泥质低渗岩体的吸渗注浆机制,采用2种低渗人造岩芯开展了硅溶胶的无压自吸渗试验,并基于低场核磁共振(NMR)系统测试了低渗岩芯吸浆过程中微观渗流特征,从微观尺度揭示了吸渗过程中孔隙填充及封闭规律。结合岩芯孔径分布和硅溶胶凝胶生长规律分析了硅溶胶对低渗岩体的可注性,并讨论了硅溶胶的吸渗注浆机制和工程应用前景。结果表明:硅溶胶对低渗岩芯吸渗能力突出,亲和力为去离子水的92.2%。硅溶胶的吸渗曲线呈指数三阶段分布特征,其中0.1 mD岩芯吸渗过程主要受微孔控制,20 mD样品吸渗先后受中孔和微孔控制。岩体纳微孔隙特征和硅溶胶凝胶生长对硅溶胶吸渗注浆可注性影响显著,且可注性与毛细管力共同影响吸渗结果。硅溶胶吸渗注浆能够满足低渗岩体纳微尺度孔隙-裂缝封闭的工程需求。

To study the mechanism of silica sol imbibition grouting for mud-bearing low-permeability rock,imbibition tests were carried out on two low-permeability artificial cores.The microscopic seepage characteristics during the imbibition grouting process of the low-permeability cores were tested based on the low-field nuclear magnetic resonance(NMR)system,which revealed the pore filling and closure patterns from the microscopic scale.The injectability of silica sol to low-permeability rock was analyzed in combination with core pore size distribution and silica sol-gel growth law,and the mechanism of silica sol imbibition grouting and engineering application prospects were discussed.The results show that silica sol has an outstanding ability to absorb and infiltrate low permeability cores,with an affinity of 92.2%of that of deionized water.The absorption curve of silica sol is characterized by exponential three-stage distribution,in which the absorption process of 0.1 mD core is mainly controlled by micropores while the absorption of 20 mD core is successively controlled by mesopores and micropores.The characteristics of nano-pores and the growth of silica-sol gel have significant effects on the injectability of silicasol imbibition,and the injectability and capillary force jointly affect the results of absorption.Silica sol imbibition grouting can meet the engineering requirements of nano-scale pore-fracture sealing in the low-permeability rock mass.