Pore size characteristics of tectonic coal and its influence on gas bearing properties
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摘要: 煤孔隙对储层含气性具有重要影响，构造煤储层尤甚。采集淮南煤田潘一矿13号煤层中4种煤体结构的煤样进行低温液氮实验，运用最小二乘法原理并采用FHH分形模型，系统地分析了煤储层纳米级（1.7~20nm）孔隙结构特征及其与分形维数之间的关系。结果表明：煤体破坏程度增强致使BJH孔容和BET比表面积增大，过渡孔与微孔含量增加；构造煤中毛细凝聚开始发生在2~3 nm并随着相对压力的增大而逐渐增强；对气体吸附做主要贡献的是孔径为5nm的孔隙，糜棱煤中此类孔隙最多致使含气性最好；研究区内除原生结构煤外，其他煤储层纳米级孔隙分形维数均大于2.6，平均孔径与分形维数呈明显负相关且相关性系数在0.9以上，表明此类孔隙具有明显的分形特征，孔隙结构复杂程度较高。综合孔隙特征表明：构造煤中孔隙结构越复杂且5nm附近吸附孔隙含量越高，含气性越强。Abstract: The coal pores have an important effect on the gas bearing property of the reservoir, especially in the tectonic coal reservoir. The low temperature liquid nitrogen experiments were carried out in the coal samples with 4 kinds of coal structure, the coal samples were collected from the No. 13 coal seam of Panyi coal mine, Huainan coalfield. The characteristics of pore structure of coal reservoir at the nanoscale (1.7-20 nm) and its relationship with fractal dimension were systematically analyzed based on the least square method principle and the FHH fractal model. The results show that the increase of coal destruction increases the BJH pore volume and BET surface area, and the content of transitional pores and the micropore in mylonite. The capillary condensation in tectonic coal began to occur at 2-3 nm, gradually increased with the increase of relative pressure. The pores with size of 5 nm are the main contribution to gas adsorption, the better development of which leads to the best gas content of mylonitized coal. Besides the primary tectonic coal, the fractal dimension of nanoscale pores of the other coal reservoir in the study area is more than 2.6, and the average pore size is negatively correlated with the fractal dimension and the coefficient of correlation is above 0.9, which shows that the pore has obvious fractal characteristics and the complexity of pore structure is high. The comprehensive pore characteristics indicate that the more complex pore structure in tectonic coal and the higher the adsorption pore content with near 5 nm, the stronger the gas content.
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Keywords:
- coal structure /
- pore structure /
- fractal dimension /
- gas bearing property
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