Numerical study on the disturbance law between rock fractures in the coupling process of high voltage electric pulse- 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,裂缝的最大缝宽和起裂压力均增大,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,起裂压力和最大缝宽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,三条裂缝的应力阴影区比两条裂缝的影响范围更广。研究结果旨在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: The purpose of this study is to investigate the disturbance law between rock fractures during the coupling process of high-voltage electric pulse-hydraulic fracturing. Based on elasticity, fracture mechanics, damage mechanics, the discharge process of high-voltage pulse discharge under water pressure (3 MPa) was numerically simulated by using extended finite element method, and the cracks in rock mass were analyzed. The results show that under a discharge voltage of 5 kV, the maximum crack width of high-voltage electric pulse-hydraulic fracturing is increased by 35% compared to traditional hydraulic fracturing. With the increase of discharge voltage, the maximum crack width and crack initiation pressure of cracks increase, which improves the interference ability between cracks. In addition, the interference between cracks in rock mass is also related to the principal stress difference, injection rate and the number of cracks. Specifically, under the same voltage, the faster the injection rate, the longer the crack length, the more obvious the stress shadow effect, and the stronger the disturbance between cracks; Under the same injection rate, the larger the principal stress difference, the more obvious the directionality of the crack extending towards the maximum principal stress. The initiation pressure and maximum crack width both decrease with the increase of the principal stress difference. Multiple crack branches can expand and cross each other at the same time, and the stress shadow area of three cracks is wider than that of two cracks. The research results aim to provide a theoretical basis and research method for the research of underwater high-voltage electric pulse fracturing and coal seam permeability enhancement technology, and lay a certain foundation for artificial control of cracks in practical projects.
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