Formation mechanism and main controlling factors of rock's initial damaged zone under explosive impact effect
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摘要: 为揭示燃爆冲击作用下井周岩石破坏区的形成机制，并分析影响初始破坏区(破碎区和初始裂隙区)的主控因素，开展了两种岩样在不同加载速率下的冲击破坏实验, 分析了岩石冲击破坏模式及岩石对加载速率的响应, 借助基于Von Mise准则建立的岩石冲击破坏的破碎区和初始裂隙区计算模型可知：加载速率低于190 GPa/s时，可依据冲击峰值压力引导的应力分布确定破碎区和初始裂隙区作用范围；燃爆压裂在近井地带主要产生破碎区和裂隙区，破碎区直径为井眼直径的1~3倍，初始裂隙区直径为井眼直径的5~7倍；冲击载荷作用下，初始破坏区与加载速率、脆性指数呈正相关，且受脆性指数影响更显著。研究结果可提高对燃爆压裂过程中岩石的破坏模式及其主控因素的认识深度，为燃爆压裂冲击条件设计提供指导。Abstract: In this work, to find out the formation mechanism of rock's initial damaged zone under explosive impact effect and investigate the main factors contributing to the initial damaged zone (including the crushed zone and the initial fractured zone) around the oil well, we analyzed the impact failure mode of rock and its response to loading rates by conducting impact failure experiments at different loading rates on two rock samples. With the help of the computational model of the crushed and initial fractured zone based on Von Mise, it is feasible to determine the the size of the crushed zone and the initial fractured zone according to the stress distribution generated by the peak pressure, when the rock crushes at a given loading rate (less than 190 GPa/s). The crushed zone and and the fractured zone are generated mainly in parts of the rock close to the oil well where explosive fractures occur. The diameter of the crushed zone and that of the initial fractured zone is 1~3 and 5~7 times that of the oil-well, respectively. The initial damaged zone is in direct proportion to the brittleness and the loading rate under loading impact and is more strongly influenced by the index of brittleness. The present work deepens the current understanding of the damage mode and main contributing factors of explosive fracture and provides guidance for the design of impact condition involving explosive fracture.
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Key words:
- mechanics of explosion /
- brittleness /
- loading rate /
- explosive fracture /
- initial damaged zone /
- impact
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表 1 应变率分析结果
Table 1. Analytical results of strain rate
γ/(GPa·s-1) tp/ms Δm/g ΔV/mm3 $\dot{\varepsilon}$/s-1 岩样Ⅰ 岩样Ⅱ 岩样Ⅰ 岩样Ⅱ 岩样Ⅰ 岩样Ⅱ 76.4 0.85 19.95 22.37 8 243.2 9 683.0 43.1 50.7 85.4 0.83 20.64 22.64 8 528.2 9 800.3 45.7 52.5 108.3 0.83 21.37 23.42 8 829.4 10 140.6 47.3 54.3 120.8 0.84 21.75 23.99 8 987.7 10 385.7 47.6 55.0 142.9 0.82 22.41 24.42 9 259.2 10 571.2 50.2 57.3 160.8 0.80 22.80 24.68 9 420.8 10 682.7 52.4 59.4 180.1 0.76 23.34 25.54 9 643.2 11 057.3 56.4 64.7 191.3 0.76 23.99 26.17 9 913.1 11 328.1 58.0 66.3 204.6 0.75 24.17 26.66 9 986.2 11 539.8 59.2 68.4 212.7 0.75 24.61 27.20 10 168.5 11 774.9 60.3 69.8 
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表 2 破碎区半径实验值
Table 2. Experimental value of crushed zone radius
γ/(GPa·s-1) 76.4 85.4 108.3 120.8 142.9 160.8 180.1 191.3 204.6 212.7 Ry/mm 岩样Ⅰ 5.206 5.368 5.455 5.521 5.633 5.699 5.789 5.897 5.926 5.998 岩样Ⅱ 5.805 5.902 5.987 6.083 6.155 6.198 6.341 6.443 6.522 6.609
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表 3 破坏区半径理论计算值
Table 3. Theoretical value of crushed zone radius
γ/(GPa·s-1) pdf/MPa Ry/mm Rl/mm 岩样Ⅰ 岩样Ⅱ 岩样Ⅰ 岩样Ⅱ 岩样Ⅰ 岩样Ⅱ 76.4 72.29 69.62 4.963 5.306 16.58 17.80 85.4 73.01 70.34 4.968 5.314 16.68 17.89 108.3 75.34 72.67 4.972 5.326 16.89 18.12 120.8 77.01 74.34 4.989 5.346 17.03 18.29 142.9 80.88 78.21 5.016 5.385 17.37 18.66 160.8 85.13 82.46 5.049 5.429 17.72 19.06 180.1 91.24 88.57 5.089 5.476 18.23 19.64 191.3 95.71 93.04 5.125 5.522 18.57 20.03 204.6 102.13 99.46 5.179 5.586 19.04 20.56 212.7 106.73 104.06 5.216 5.631 19.37 20.94
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表 4 破碎区半径对比结果
Table 4. Comparison results of crushed zone radius
γ/(GPa·s-1) 76.4 85.4 108.3 120.8 142.9 160.8 180.1 191.3 204.6 212.7 δ/% 岩样Ⅰ 4.90 8.05 9.72 10.67 12.30 12.88 13.75 15.07 14.42 15.00 岩样Ⅱ 9.41 11.07 12.40 13.79 14.30 14.17 15.80 16.68 16.76 17.37
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