电脉冲水力压裂煤体机理及裂缝效果评价

为了研究高压电脉冲水压致裂煤体的机理和作用,在高压电脉冲水压致裂理论的基础上进行了3 MPa静水压力、不同放电电压条件下煤样的压裂试验。通过压力传感器记录了煤样孔底脉冲水压力的变化情况,然后利用超声波探伤仪和CT扫描技术进行了试验前后煤样宏、微观裂纹的分布、发育情况的观测。结果显示:水中高压脉冲放电产生的峰值压力远大于3 MPa静水压力,最大峰值压力能达到27 MPa(9 k V电压);通过超声波检测发现在钻孔周围一定范围内有新生宏观裂纹产生,越靠近中心钻孔位置,首波声时差越大,新生裂纹数量越多、裂纹宽度越大;CT扫描结果也证明在钻孔周围存在着长短不一,宽度不等,形态各异的新生微观裂纹。试验结果表明,高压电脉冲水压压裂煤体技术可行,致裂效果良好。

Evaluation on mechanism of electric-pulse hydraulic fracturing of coal mass and its cracking effect

In order to study the high-voltage pulse hydraulic fracturing effect on coal mass，the coal sample fracturing experiments under the conditions of 3 MPa hydrostatic pressure and different discharge voltages are carried out on the basis of the high-voltage pulse hydraulic fracturing theory. The change of the pulsed water pressure at the bottom of the coal sample hole is recorded through pressure sensor，and then the distributions of the both the macro and the micro cracks of coal samples before and after the experiments are observed with ultrasonic flaw detector and CT scanning technique. The result shows that the peak pressure generated from the high voltage discharge in water is far larger than the 3 MPa hydrostatic pressure and its maximum peak pressure can reach to 27 MPa( 9 kV) . Through the ultrasonic flaw detection，it is found out that some newly generated cracks are there around the drilling hole to a certain extent，for which the more close to the center of the drilling hole the newly generated cracks are and the more large the acoustic time difference of the first wave is，the number of them are to be more and their widths are to be more large; while the result from CT scanning demonstrates that the newly generated cracks with different lengths，widths and patterns are there around drilling hole as well. The experiments indicate that the technology of high-voltage pulse hydraulic fracturing of coal mass is feasible with a better fracturing effect.