不耦合系数对CO_(2)相变致裂影响数值模拟及研究

Numerical simulation and experimental study on the effect of uncoupling coefficient on CO_(2) phase change cracking

为了提高液态CO_(2)相变致裂的增透效果,探究孔径尺寸对致裂效果的影响,采用LS-DYNA软件对“不耦合装药”结构下CO_(2)致裂效果进行数值模拟,分别得到了不同径向不耦合系数下的损伤分布云图、孔壁压力时程曲线、峰值速度分布图,采用“Logistic”函数对损伤分布进行描述。研究表明,随着不耦合系数的增大,压碎区范围先快速减小后缓慢减小,裂隙区呈先增大后减小的变化趋势,在K=1.46时破坏区范围最大,此时为最优不耦合系数;当K=1.60时,压碎区与裂隙区的过渡特征变得不再明显,破坏区主要由均匀的裂隙区构成;不耦合致裂结构能改变爆生气体应力波加载方式,降低应力波峰值、延长应力波作用时间,从而能有效降低CO_(2)相变致裂的振动效应,径向不耦合系数K=1.60相较K=1.07,振动强度降低2.48倍。现场试验表明:采用K=1.46致裂结构产生较小的压碎区,裂隙扩展区较K=1.07更大,裂纹发育更长,瓦斯体积分数与瓦斯纯流量较致裂前增加了4.28倍、4.89倍,相较K=1.07瓦斯抽采效果更佳。该研究结果可为CO_(2)相变致裂效果提供理论支撑。

In order to improve the antireflection effect of liquid CO_(2) phase change cracking and explore the influence of pore size on the cracking effect,the CO_(2) cracking effect under the"uncoupled charge"structure is numerically simulated by LS-DYNA software,and the damage distribution cloud map,hole wall pressure time history curve and peak velocity distribution diagram under different radial uncoupling coefficients are obtained respectively.The damage distribution is described by“logistic”function;The results show that with the increase of decoupling coefficient,the range of crushing zone first decreases rapidly and then decreases slowly,and the fracture zone first increases and then decreases.When K=1.46,the range of failure zone reaches the maximum,which is the optimal decoupling coefficient;When K=1.60,the transition characteristics between crushing zone and fracture zone become no longer obvious,and the failure zone is mainly composed of uniform fracture zone;The uncoupled crack structure can change the loading mode of stress wave of explosive gas,reduce the peak value of stress wave and prolong the action time of stress wave.Uncoupled cracking can effectively reduce the damage effect of seismic wave.Compared with K=1.07,the vibration intensity of cracked structure K=1.60 is reduced by 2.48 times.The field test shows that the fracture structure with K=1.46 produces a smaller crushing area,the fracture expansion area is larger than that with K=1.07,and the crack development is longer.The gas volume fraction and pure gas flow are increased by 4.28 times and 4.89 times compared with that before fracture,which is better than that with K=1.07.The results of this study can provide theoretical support for the effect of CO_(2) phase change cracking.