Study on time-dependent injectability evaluation of mudstone considering the self-healing effect

Abstract

The injectability of mudstone is a key parameter for grout modification and is affected by hydration. Inherent injectability is predominantly determined by pore size distribution nuances, encompassing both the critical pore size and the heterogeneity inherent within the pore structure. In this study, low-field nuclear magnetic resonance technology is employed to delineate the transverse relaxation time distribution curves amidst the hydration process of three distinct clay rocks, namely kaolinite, illite, and montmorillonite. The evolution characteristics of permeability are assessed, leveraging the Schlumberger-Doll research model. It is ascertained that a prolonged hydration reaction (98 days) engenders a self-healing effect pertinent to rock permeability. A comprehensive analysis unveils the impacts rendered by various types of clay minerals and distinct durations of hydration upon the characteristic distribution of rock pore sizes. The diffusion and seepage pores are distinguished based on a pore diameter boundary of 100 nm, and the time-varying characteristics of their heterogeneity are studied based on fractal theory. The research results show that for rocks without clay minerals, the injectability reaches and basically maintains 11% unchanged after being soaked for 9 days. For rocks containing kaolinite, the injectability reaches and basically maintains 3.4% unchanged after being soaked for 42 days. For rocks containing illite, the injectability reaches a maximum of 0.9% after being soaked for 56 days, then slowly decreases to 0.6%. For rocks containing montmorillonite, the injectability reaches and remains unchanged at 7.8% after being soaked for 28 days. Combined with the time-varying characteristics of the fractal dimension of seepage pores, the heterogeneity of seepage pores weakens, so the pore structure evolution caused by the hydration of clay minerals has a beneficial effect on the injectability of muddy rock masses.

Keywords

• mudstone
• injectability
• self-healing effect
• seepage pores
• fractal dimension