液态CO_(2)-高温蒸汽循环冲击煤体三维CT裂隙重构及劣化机理

Reconstruction and degradation mechanism of three-dimensional CT cracks in coal under the cycle impact of liquid CO_(2) high-temperature steam

为解决液态CO_(2)冻结煤层孔隙冰融化时间冗长问题,提出液态CO_(2)-高温蒸汽冷热循环冲击煤层增透技术。本文借助三维CT扫描测试技术,分析冷热循环冲击过程无烟煤三维孔隙结构参数及劣化机理。研究结果表明:(1)液态CO_(2)-高温蒸汽冷热循环冲击煤体三维孔隙不断延伸,逐渐形成贯通裂隙,三维孔隙数量、表面积、体积及切片最大面孔率均与冷热循环冲击次数指数相关;(2)根据霍多特孔隙分类法,结合等效直径计算公式,发现冷热循环冲击前期渗流孔体积比例增加,三维孔隙劣化表现为裂隙贯通,冷热循环冲击后期吸附孔体积比例增加,三维孔隙劣化表现为煤体内部产生大量新生孔隙。进一步分析得:(1)液态CO_(2)-高温蒸汽冷热循环冲击煤体渗流孔半径分形维数增加,孔隙分形特征增强,表面粗糙度提高,热储集性能降低;(2)孔隙半径分型模型中lg r随冷热循环冲击次数增加而增加,表明孔径劣化扩张明显;(3)基于冷热循环冲击煤体孔隙力学损伤特征,归纳液态CO_(2)-高温蒸汽冷热循环冲击煤体三维孔隙损伤模型;(4)利用投影法得到切片损伤率,定义液态CO_(2)-高温蒸汽冷热循环冲击煤体三维孔隙损伤量。当冷热循环冲击12次时,三维孔隙损伤量为48.55。

To solve the problem of long melting time of pore ice in coal seams frozen by liquid CO_(2),a technology of cold and hot cycling impact on coal seam for penetration enhancement was proposed using liquid CO_(2)high-temperature steam.This paper used the CT scanning testing technology to analyze the three-dimensional pore structure parameters and degradation mechanism of anthracite under cold and hot cycling impact.The research results indicated that:①the three-dimensional pores of the coal under the cold and hot cycle impact of liquid CO_(2)high-temperature steam continued to extend,gradually forming through cracks.The number,surface area,volume,and maximum slice porosity of the three-dimensional pores were all related to the index of cold and hot cycle impact times;②According to the Hodott pore classification method and the equivalent diameter calculation formula,it was found that in the early stage of cold and hot cycling impact,the proportion of seepage pore volume increased,and the three-dimensional pore degradation manifested as crack penetration.In the later stage of cold and hot cycling impact,the proportion of adsorption pore volume increased,and the three-dimensional pore degradation manifested as the generation of large number of new pores inside the coal.Further analysis shows that:①the Fractal dimension of seepage pore radius of coal body impacted by liquid CO_(2)high temperature steam cold and hot cycle increased,the fractal characteristics of pores increased,the surface roughness increased,and the thermal storage performance decreased;②The lg r in the pore radius classification model increased with the increase of the number of cold and hot cyclic impacts,indicating a significant expansion of pore size degradation;③Based on the characteristics of pore mechanical damage in coal under cold and hot cycling impact,a three-dimensional pore damage model of coal under liquid CO_(2)high-temperature steam cold and hot cycling impact was summarized;④The projection method was used to obtain the slice damage rate and define the three-dimensional pore damage amount of coal under the cold and hot cycle impact of liquid CO_(2)high-temperature water vapor.When subjected to 12 cycles of cold and hot impact,the three-dimensional pore damage was 48.55.