Abstract
Borehole-sealing solidified material plays a significant role in improving sealing quality and enhancing gas drainage performance. In this study, the MTS815 electro-hydraulic triaxial servo test system and MR-60 NMR test system were adopted to conduct triaxial compression control experiment on the coal sample material, concrete material, and new solidified sealing material, respectively. This paper aims to analyze the difference of support effects, porosity, and stress sensitivity between those materials. Experimental results show that under the same stress condition, the stiffness of traditional concrete solidified material is the largest, while the new solidified material is the second, and the coal sample material is the smallest. Compared with the traditional concrete solidified material, the new solidified sealing material has better strain-bearing capacity and volumetric expansion capacity under each confining pressure in the experiment. The axial strain and volume increment of new solidified material is higher than those of the traditional concrete solidified material at the peak stress. Meanwhile, the confining pressure has a certain hysteresis effect on the postpeak stress attenuation. Fracture has the strongest stress sensitivity in three pore types, and its T2 map relaxation area has a larger compression than adsorption pore and seepage pore under the same pressure. The relative content of seepage pore and fracture in the new solidified material is less than that of coal and concrete samples, and the stress sensitivity of the new solidified materials is weaker than that of coal and concrete materials, thence, new solidified material will have better performance in borehole sealing. Outcomes of this study could provide guidance on the selection of the most effective sealing materials for sealing-quality improvement.
Highlights
Coal is the main energy source in China, accounting for over 70% of the primary energy [1]
Some researchers have discussed the stress sensitivity and porosity under different stress state based on a series of experiments of coal and rock samples [26,27,28]; Li used the transverse relaxation time (T2) spectrum of nuclear magnetic resonance to conduct quantitative study of the compression characteristics of pore-fracture system [29]; Meng studied the differences of gas adsorption-diffusion and adsorption deformation of low and high rank coal and its permeability evolution in isothermal adsorption experiment and desorption-seepage testing system [30]; Wang revealed the characteristics of micropore, mesopores, and fractal dimensions of bituminous coal during the process of cyclic gas adsorption/desorption by combining N2 and CO2 adsorption experiments from microscopic aspect [31]
nuclear magnetic resonance (NMR) scanning experiments were performed on all samples before and a er the loading of experiments using the MR-60 NMR test system, the T2 spectra of all samples were obtained by experiment (Figures 5–7). e relative content of different types of pores in the sample can be obtained by calculating the peak relaxation area in the T2 spectrum [43]
Summary
Coal is the main energy source in China, accounting for over 70% of the primary energy [1]. Some researchers have discussed the stress sensitivity and porosity under different stress state based on a series of experiments of coal and rock samples [26,27,28]; Li used the transverse relaxation time (T2) spectrum of nuclear magnetic resonance to conduct quantitative study of the compression characteristics of pore-fracture system [29]; Meng studied the differences of gas adsorption-diffusion and adsorption deformation of low and high rank coal and its permeability evolution in isothermal adsorption experiment and desorption-seepage testing system [30]; Wang revealed the characteristics of micropore, mesopores, and fractal dimensions of bituminous coal during the process of cyclic gas adsorption/desorption by combining N2 and CO2 adsorption experiments from microscopic aspect [31]. It is considered that the achievements of the study will be one of the better guidance for advancement of borehole sealing process and improvement of drilling efficiency of gas drainage
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