Freeze-Thaw Damage Characteristics of Anhydrite Rock Pore Structures Based on Nuclear Magnetic Resonance Technology
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摘要:
为研究寒区遭受冻融作用的石膏质岩石的细观和微观孔隙结构损伤特性,以硬石膏岩为研究对象,基于核磁共振试验,获得硬石膏岩在冻融循环作用下的孔隙度、孔径和孔喉分布特征;结合分形理论,推导岩石孔径和孔喉分形维数的计算式,探讨冻融循环作用对硬石膏岩孔隙结构分形维数的影响规律;建立不同孔隙结构及孔隙分形维数与孔隙度之间的关系,并指出对孔隙度影响程度较大的孔隙结构类型. 结果表明:冻融循环作用下,硬石膏岩的孔径呈“三峰”型分布,随着冻融次数增加,硬石膏岩微孔(孔径
r ≤ 0.100 μm)、PT-Ⅰ (r ∈(0~0.100] μm)孔喉、孔隙分形维数($ {{D}}_{\text{P}} $)和孔喉分形维数($ {{D}}_{\text{PT}} $)呈指数型递减,而中孔(r ∈[0.100~1.000) μm)、大孔(r ≥1.0 μm)、PT-Ⅱ (r ∈(0.100~4.000] μm)孔喉和孔隙度则呈指数型递增,规模较大的孔隙、规模较小的孔喉以及孔喉分形维数对硬石膏岩孔隙度的影响程度较大.Abstract:In order to study the damage characteristics of meso and micro pore structures of gypsum rock subjected to freeze-thaw cycles in cold regions, anhydrite rock was taken as the research object, and the porosity, pore size, and pore throat distribution characteristics of anhydrite rock were obtained based on nuclear magnetic resonance (NMR) experiments. According to fractal theory, the calculation formulas of the fractal dimension of pore size and pore throat of rock were derived, and the influence of freeze-thaw cycles on the fractal dimension of pore structures of anhydrite rock was discussed. The relationship among different pore structures, fractal dimensions of pores, and porosity was established, and the pore structure types that had a greater impact on porosity were revealed. The results show that the pore size of anhydrite rock under freeze-thaw cycles presents a “three-peak” distribution. With the increase in freeze-thaw cycles, the micropore (
r ≤ 0.1 μm), PT-Ⅰ (r ∈[0–0.1) μm) of pore throat, fractal dimension of pore (D P), and fractal dimension of pore throat (D PT) decrease exponentially. While, the mesopores (r ∈[0.1–1) μm), macropores (r ≥ 1 μm), PT-Ⅱ(r ∈(0.1–4] μm) of pore throats, and porosity increase exponentially. It can be concluded that larger pores, as well as smaller pore throats and fractal dimension of pore throats, have a greater influence on the porosity of anhydrite rock.-
Key words:
- nuclear magnetic resonance /
- anhydrite rock /
- pore structure /
- freeze-thaw cycle /
- damage characteristic
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表 1 不同冻融循环次数下硬石膏岩孔隙度
Table 1. Porosity of anhydrite under different freeze-thaw cycles
% 试样编号 N=0 N=30次 N=60次 N=90次 N=120次 N1 0.64 0.78 0.91 1.03 1.12 N2 0.73 0.79 0.93 1.06 1.15 N3 0.70 0.81 0.92 0.98 表 2 不同类型孔隙对应的曲线面积
Table 2. Curve area for different types of pores
试样
编号孔隙
类型N=0 N=30次 N=60次 N=90次 N=120次 N1 微孔 0.17 0.11 0.14 0.1 0.06 中孔 0.94 1.51 1.67 2.12 1.61 大孔 17.38 19.86 21.28 25.08 37.77 N2 微孔 0.14 0.12 0.11 0.09 0.06 中孔 0.86 0.99 1.18 1.41 1.54 大孔 12.79 17.26 20.15 24.63 33.34 N3 微孔 0.12 0.09 0.08 0.05 中孔 1.21 1.5 1.67 2.22 大孔 13.96 19.11 20.18 24.06 表 3 冻融循环作用下硬石膏岩不同类型孔喉占比
Table 3. Proportion of different types of pore throats for anhydrite rock under freeze-thaw cycles
% 试样编号 孔喉类型 N=0 N=30次 N=60次 N=90次 N=120次 N1 PT-Ⅰ 41.39 20.64 19.27 17.86 14.12 PT-Ⅱ 42.41 44.61 56.77 64.77 61.03 PT-Ⅲ 16.08 34.75 23.96 17.37 24.85 N2 PT-Ⅰ 43.14 36.64 28.83 18.62 16.58 PT-Ⅱ 31.37 42.14 45.65 55.07 59.90 PT-Ⅲ 25.50 21.22 25.52 26.30 23.31 N3 PT-Ⅰ 33.14 18.19 19.15 15.24 PT-Ⅱ 49.37 59.68 65.63 69.26 PT-Ⅲ 17.50 22.13 15.22 15.50 -
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