For researching crack initiation condition and water injection pressure needed, this paper built up a mechanics model of crack tip based on crisp fracture theory of compound crack.

为研究初始裂缝尖端起裂的条件和所需注水压力，依据断裂力学的复合型裂纹的脆性断裂理论，建立了裂缝尖端力学模型，给出了计算方法。

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The result indicates that the initiation fracture pressure can be obviously reduced by raising the perforation diameter and depth;

计算结果发现，增加射孔直径、深度可以显著降低起裂压力；

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