Test Study on the Suffusion Process of Sand-Rock Mixtures by NMR Systems

Abstract

Test results on the suffusion of sand-rock mixtures (SRMs) in one-dimensional laboratory seepage tests are reported with details regarding the experimental setup and procedures. The nuclear magnetic resonance (NMR) systems were successfully applied to track fine-particle migration through pores and detect the pore size distribution of SRMs during suffusion. This article discussed the changes of pore size distribution and fine-particle migration and its effect on the suffusion mechanism at 0, 15, 30, 60, 90, and 120 min under the critical hydraulic gradient. Then, the mesostructural changes of mixtures—such as pore distribution, curvature coefficient, and pore fractal dimension—were analyzed to reveal the suffusion mechanism, and an original suffusion evaluation model was proposed. The results showed that the pore connectivity and fine-particle migrations as two controlling factors for suffusion are an interactive process. Furthermore, the pore size range was narrowed and mostly concentrated in large pores with an increase of pore volume, resulting in fine-particle migration and structural deterioration. Moreover, the suffusion evaluation model was divided into four stages by the mesostructural parameters variation.