Disturbance law between rock fractures in the coupling process of high-voltage electric pulse and hydraulic fracturing
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摘要:
为了研究高压电脉冲-水力压裂岩体缝间扰动及裂缝扩展规律，以弹性力学、断裂力学、损伤力学为基础，采用扩展有限元法对高压电脉冲在水压（3 MPa）下的放电过程进行了数值计算，并对岩体裂缝进行了分析。结果表明：在5 kV放电电压下，高压电脉冲-水力压裂较传统水力压裂的最大裂缝宽度提高了35%，且随着放电电压增大，裂缝的最大裂缝宽度和起裂压力均增大，缝间干扰能力增强。此外，岩体中缝间干扰还与主应力差、注入速率、裂缝数量有关。具体而言，在相同的电压下，注入速率越快，裂缝长度越长，应力阴影效果越明显，缝间扰动越强；在注入速率相同的情况下，主应力差越大，裂缝朝最大主应力延伸的方向性越明显，起裂压力和最大裂缝宽度均随着主应力差的增大而减小；多个裂缝分支可以同时扩展并相互交叉，3条裂缝的应力阴影区比2条裂缝的影响区范围更广。研究结果可以为水下高压电脉冲压裂和煤层增透技术的研究提供理论依据和研究方法，并且为实际工程人为控制裂缝奠定一定基础。
Abstract:Objective This study aims to investigate the interaction between rock fractures during the high-voltage electric pulse and hydraulic fracturing coupling process.
Methods Based on elasticity, fracture mechanics, and damage mechanics, the high-voltage electric pulse discharge process under a water pressure of 3 MPa was numerically simulated using the extended finite element method to analyze rock mass fractures.
Results The results showed that under a discharge voltage of 5 kV, the maximum crack width in high-voltage electric pulse-hydraulic fracturing is 35% greater than that of traditional hydraulic fracturing. With the increasing discharge voltage, both the maximum crack width and crack initiation pressure increased, and the interference between fractures was enhanced. Additionally, the interference between crack in rock mass is also correlated to the principal stress difference, injection rate, and fracture number. Specifically, under the same voltage, higher injection rates result in longer crack lengths, a more prominent stress shadow effect, and stronger fracture interference. At the same injection rate, the greater the difference in principal stress, the more pronounced the directionality of crack extension towards the maximum principal stress. Both the initiation pressure and maximum crack width decrease with the increase of principal stress difference. Multiple crack branches can simultaneously expand and intersect, with the stress shadow area of three fractures being broader than that of two.
Conclusion These findings provide theoretical support and a research framework for the study of underwater high-voltage electric pulse fracturing and coal seam permeability technology, laying a foundation for artificial crack control in practical applications.
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图 2 激波超压时程曲线
AC段. 正压区；CD段. 负压区；AB段. 升压区；BC段. 降压区；Pm. 峰值压力；Tt. AB段对应的波前时间；Td. BC段对应的下降时间；Tw. 正负压转换作用时间；P0. 静水压力；P. 压力；t. 时间
Figure 2. Shock overpressure time history curve
图 6 裂缝扩展路径模拟结果对比（a. 本研究；b. 文献[11]）
Figure 6. Comparison of the simulation results of the crack growth path
图 8 3 MPa（a）和3 MPa+5 kV（b）压裂效果图
Figure 8. 3 MPa (a) and 3 MPa+5 kV (b) fracturing effect diagrams
图 9 不同电压下的最大裂缝宽度与起裂压力
Figure 9. Maximum joint width and cracking pressure at different voltages
图 10 不同电压下的高压电脉冲水力压裂裂缝扩展图
Figure 10. High-voltage electric pulse hydraulic fracturing fracture growth diagram at different voltages
图 11 不同电压下的初始起裂压力（a）和最大裂缝宽度（b）
Figure 11. Burst pressure (a) and maximum seam width (b) at different voltages
图 12 不同主应力差下的最大裂缝宽度与起裂压力
Figure 12. Maximum joint width and cracking pressure under different principal stress differences
图 13 不同主应力差的裂缝扩展图
Figure 13. Crack propagation diagrams in the case of different principal stress differences
图 14 不同注入速率的裂缝应力扩展云图
Figure 14. Crack stress propagation curves at different injection rates
图 15 不同裂缝数量的裂缝扩展图
Figure 15. Crack propagation diagram in the case of different numbers of cracks
图 16 不同裂缝数量下的最大裂缝宽度和起裂压力
Figure 16. Maximum crack width and initiation pressure with different numbers of fractures
表 1 岩样物理学参数[24]
Table 1. Physical parameters of the rock samples
参数 抗拉强度/MPa 杨氏模量/GPa 泊松比 渗透系数/（m·d−1） 液体黏度/（Pa·s） 数值 2.59 8.402 0.23 0.001 0.001 
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表 2 方案设计
Table 2. Scheme design
组别 编号 三轴围压MPa 注入速率/（m3·s−1） 水压/MPa 电压/kV 裂缝数量 与最大主应力夹角/（°） $ {\sigma }_{{\mathrm{h}}} $ $ {\sigma }_{{\mathrm{H}}} $ $ {\sigma }_{\mathrm{z}} $ A 1 4 5 4 0.5 3 5 3 20，45，75 2 4 6 4 0.5 3 5 3 20，45，75 3 4 7 4 0.5 3 5 3 20，45，75 4 4 9 4 0.5 3 5 3 20，45，75 B 5 4 6 4 0.5 3 2 3 20，45，75 6 4 6 4 0.5 3 3 3 20，45，75 7 4 6 4 0.5 3 4 3 20，45，75 8 4 6 4 0.5 3 5 3 20，45，75 9 4 6 4 0.5 3 6 3 20，45，75 C 10 4 6 4 0.25 3 5 3 20，45，75 11 4 6 4 0.5 3 5 3 20，45，75 12 4 6 4 0.75 3 5 3 20，45，75 D 13 4 6 4 0.5 3 5 1 75 14 4 6 4 0.5 3 5 2 45，75 15 4 6 4 0.5 3 5 3 20，45，75
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