To study crack propagation around the fracture hole in the coal body induced by high-pressure CO₂ gas produced by CO₂ phase transition fracturing, the mechanism of permeability enhancement of fractured coal induced by liquid CO₂ phase transition fracturing was studied from two aspects, the process of coal gas displacement by competitive adsorption and physical characteristics of fractured coal induced by phase transition. Crack propagation pattern in coal under different lateral coefficients was explored by using discrete-element numerical simulation software. Distribution characteristics of hoop stress of fractured coal were analyzed through theoretical calculation. The results show that: (1) Micro-cracks in damaged coal body generated during phase transition process are mainly crack_tension type, which are formed by the composite action of tension and compression. The crack propagation is the result of the continuous release of compressive stress from concentrated area to the surrounding units. Micro-cracks are radially distributed in a pattern of “flame”. (2) The main crack formed above the fracture hole grows in the direction of vertical minimum initial stress, and the main crack formed below the fracture hole develops in the direction of horizontal initial stress. As the lateral compression coefficient increases, the extension distance of the second crack will not change after reducing to a certain length. (3) As the distance from the fracture hole increases, the peak compression loaded at the monitoring point decays, and the loop stress in the cracked coal is distributed in a pattern of “peanut”. It provides practical methods and ideas for studying the macroscopic and microscopic development of cracks, as well as theoretical support for the on-site hole layout.

为了研究CO ₂相变压裂产生的高压CO ₂气体在煤体内裂隙周围的裂纹扩展，研究了液态CO ₂引起的裂隙煤渗透率提高的机理。从竞争吸附驱替煤气的过程和相变引起的裂化煤的物理特征两个方面研究了相变压裂。利用离散元数值模拟软件，研究了煤在不同横向系数下的裂纹扩展规律。通过理论计算，分析了压裂煤的环向应力分布特征。研究结果表明：（1）相变过程中产生的损伤煤体中的微裂纹主要为裂纹-张力型，是由拉伸和压缩的复合作用形成的。裂纹扩展是压缩应力从集中区域连续释放到周围单元的结果。微裂纹以“火焰”的形式径向分布。（2）在裂缝孔上方形成的主裂纹在垂直最小初始应力的方向上扩展，在裂缝孔下方形成的主裂纹在水平初始应力的方向上扩展。随着横向压缩系数的增加，第二裂纹的延伸距离在减小到一定长度后将不会改变。（3）随着距裂孔距离的增加，在监测点处的峰值压缩衰减，并且裂化煤中的回路应力以“花生”形分布。它为研究裂纹的宏观和微观发展提供了实用的方法和思想，并为现场孔的布置提供了理论支持。裂纹孔下方形成的主裂纹沿水平初始应力方向发展。随着横向压缩系数的增加，第二裂纹的延伸距离在减小到一定长度后将不会改变。（3）随着距裂孔距离的增加，在监测点处的峰值压缩衰减，并且裂化煤中的回路应力以“花生”形分布。它为研究裂纹的宏观和微观发展提供了实用的方法和思想，并为现场孔的布置提供了理论支持。裂纹孔下方形成的主裂纹沿水平初始应力方向发展。随着横向压缩系数的增加，第二裂纹的延伸距离在减小到一定长度后将不会改变。（3）随着距裂孔距离的增加，在监测点处的峰值压缩衰减，并且裂化煤中的回路应力以“花生”形分布。它为研究裂纹的宏观和微观发展提供了实用的方法和思想，并为现场孔的布置提供了理论支持。（3）随着距裂孔距离的增加，在监测点处的峰值压缩衰减，并且裂化煤中的回路应力以“花生”形分布。它为研究裂纹的宏观和微观发展提供了实用的方法和思想，并为现场孔的布置提供了理论支持。（3）随着距裂孔距离的增加，在监测点处的峰值压缩衰减，并且裂化煤中的回路应力以“花生”形分布。它为研究裂纹的宏观和微观发展提供了实用的方法和思想，并为现场孔的布置提供了理论支持。