液态CO2溶浸煤体孔裂隙演化特征的实验研究

文虎 刘名阳 樊世星 魏高明 刘荫 郝建池 程小蛟 王虎

摘 要：为研究煤层在液态CO2溶浸作用下煤体孔裂隙的演化特征，设计液态CO2溶浸实验系统，选取3种不同煤质的煤样，干燥后对其进行液态CO2溶浸實验，在一定压力温度下溶浸30 min，通过扫描电镜和核磁共振测试方法对溶浸前后的煤样进行观测，基于分形理论和T2谱分布方法定量地对煤体孔裂隙进行分析，分形理论分析得出：3种煤样分形维数均为增大趋势，且直线拟合系数均大于0.967;T2谱分布分析得出经液态CO2溶浸后，吸附孔T2谱面积增长率分别为15.9%，38.1%，29.1%;渗流孔增长率分别为11.9%，55.7%，61.1%;全孔T2谱面积分别增加24.7%，54.6%，56.1%.结合渗透率理论模型计算1/3焦煤、气煤和褐煤渗透率分别提高了

556%，13.79%和14.80%.液态CO2溶浸可有效促进煤体裂隙发育，有利于提高煤体的渗透性。关键词：液态CO2;溶浸;孔裂隙;扫描电镜;核磁共振;渗透率中图分类号：TD 712

文献标志码：A

文章编号：1672-9315（2020）06-0935-10

DOI：10.13800/j.cnki.xakjdxxb.2020.0601开放科学（资源服务）标识码（OSID）：

Experimental study on variations of pore-fissure in

coal-rock leached by liquid CO2

WEN Hu1，2，LIU Ming-yang1，2，FAN Shi-xing1，2，WEI Gao-ming1，2，

LIU Yin1，2，HAO Jian-chi1，2，CHENG Xiao-jiao1，2，WANG Hu1，2

（1.Key Laboratory of Western Mine Exploitation and Hazard Prevention，Ministry of Education，

Xian University of Science and Technology，Xian 710054，China;

2.College of Safety Science and Engineering，Xian University of Science and Technology，Xian 710054，China）

Abstract：In order to study the evolution characteristics of coal pore-fissure under the treatment of liquid CO2（L-CO2），the experimental system of liquid CO2leaching was designed.Three kinds of coal samples with different coal quality were selected，after drying the experiment was carried out at a certain pressure and temperature for 30 min treatment.The coal samples before and after liquid CO2 treatment were observed by means of scanning electron microscope and nuclear magnetic resonance.According to the analysis of fractal theory and T2 spectrum，the paper quantitatively analyzed the pore-fissure of coal body.The fractal theory analysis shows an increasing trend in the fractal dimension of three kinds of coal samples，and the linear fitting coefficient is greater than 0.967.T2 spectrum analysis indicates that the area growth rate of adsorption pore T2 spectrum are 15.9%，38.1% and 29.1%，and the seepage pore growth rate are 11.9%，55.7% and 61.1% respectively.The total pore T2 spectrum area grows by 24.7%，54.6% and 56.1% respectively.Calculation based on permeability theory model obtains the permeability of 1/3 coking coal，gas coal and lignite rise by 5.56%，13.79% and 14.80% separately.The relationship between permeability increment and coal rank after leaching indicates that the lignite is superior to gas coal，and the gas coal is superior to 1/3 coking coal，which is consistent with the analysis of effective porosity.The results of experiment show that the liquid CO2 leaching can effectively promote the development of coal fractures，possible to improve the permeability of coal.

Key words：liquid CO2;leaching;pore-fissure;scanning electron microscope;nuclear magnetic resonance;permeability

0 引 言

我國煤层气资源丰富，但具有渗透率低、瓦斯压力大及强吸附性的特点，致使瓦斯抽采效率低，瓦斯治理难度大[1-2]。如何提高煤层渗透率，疏通渗流通道，提高瓦斯抽采率一直是瓦斯抽采和灾害防治的研究重点[3]。国内外先后提出了多种提高煤层渗透性的技术方法，如爆破致裂、液态CO2相变致裂、水力压裂、超临界CO2改造煤层等，但现场应用效果仍不理想[4-9]。

近年来，液态CO2对煤体的内部孔隙特性及煤层渗透性的影响，国内学者也获得一些成果。文虎等开展了煤层注液态CO2压裂增透现场试验，研究煤层压裂过程裂隙扩展规律，得出煤层注液态CO2有效压裂半径范围及裂隙扩展形式及压裂孔周围煤体受到CO2作用产生裂隙发育初期扩展较快，延伸速度逐渐降低[10]。……