Experimental study on pore fluid characteristics of fractured sandstone based on nuclear magnetic resonance technology

The groundwater seepage in the fractured rock mass affects the stability of the surrounding rock of the roadway. To understand the fluid seepage characteristics and the change law of the microscopic pore structure of the fractured rock mass under different loading conditions, the low-field nuclear magnetic resonance technology (LF-NMR) was used to conduct a visual experimental study. The T2 spectrum distribution curve tested by nuclear magnetic resonance indicated that the pore structure of the fractured sandstone sample had three peaks (namely micropores, mesopores, and macropores) with medium and large pores distributed from 0.63 μm to 100 μm. Quantitative analysis of nuclear magnetic resonance imaging signals during water flooding of fractured sandstones revealed the characteristics of fluid migration and distribution at different times and locations at different flow rates in the core. The height of the fractured core at 23 mm had small water content and low porosity. The water content at the position of 25–40 mm was higher, and the porosity was large. Under the effect of flow velocity, there were obvious differences in the state of fractured core displacement. That is, the greater the flow velocity, the shorter the water flooding time and the more concentrated the fluid sweep area. The dominant channel for seepage was formed quickly. The research results can provide a reference for preventing the erosion of roadway surrounding rock caused by groundwater fluid.