Abstract In oil and gas production, natural fracture (NF) activation and the seismicities induced by hydraulic fracturing can cause unpredictable damage and even catastrophic consequences to reservoirs, which seriously threatens the safety of construction personnel and equipment. In this paper, the seismicities induced by hydraulic fracturing in naturally fractured reservoirs were investigated based on the moment tensor. Firstly, an algorithm for evaluating seismicities was generated using an independently developed subroutine. Then, a systematic simulation was implemented to explore the characteristics of seismic events (SEs) produced by the interaction of hydraulic fractures (HFs) and natural fractures. Finally, a sensitivity analysis was performed to examine the effects of the stress difference, approaching angle (θ), and friction coefficient on seismicities under different working conditions. The results show that there are four modes of interaction between hydraulic fractures and natural fractures. In the Type II mode, an NF can combine with other NFs to form fracture networks, however SEs produced in this mode are the most dangerous. In the Type IV mode, SEs are fewer and smaller in magnitude compared to those in the Type II mode. Additionally, in the Type IV mode, HFs can also cross NFs and thus become interconnected with other NFs. When θ ≤ 30°, the stress difference becomes the main factor controlling the seismicities. Meanwhile, when 45°≤θ ≤ 60°, the stress difference and the approaching angle jointly affect the interaction modes. The NF friction coefficient also plays a role in SEs at this stage, however its effect is not prominent. When θ ≥ 75°, the modes produced by the HF–NF interactions belong to Type IV or are in a transition to Type IV.

中文翻译：

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基于矩张量的天然裂缝性油藏水力压裂诱发地震活动研究

摘要 在油气生产中，天然裂缝活化和水力压裂诱发的地震活动会对油藏造成不可预测的破坏甚至灾难性后果，严重威胁施工人员和设备的安全。本文基于矩张量研究了天然裂缝性油藏水力压裂诱发的地震活动。首先，使用独立开发的子程序生成用于评估地震活动的算法。然后，实施系统模拟以探索由水力压裂 (HF) 和天然裂缝相互作用产生的地震事件 (SE) 的特征。最后，进行敏感性分析以检查应力差异、接近角 (θ)、和摩擦系数对不同工作条件下地震活动的影响。结果表明，水力裂缝和天然裂缝之间存在四种相互作用模式。在 Type II 模式下，一个 NF 可以与其他 NF 结合形成裂缝网络，但是这种模式下产生的 SE 是最危险的。在 Type IV 模式中，与 Type II 模式中的 SE 相比，SE 在数量级上越来越少。此外，在 Type IV 模式下，HF 也可以跨越 NF，从而与其他 NF 互连。当θ≤30°时，应力差成为控制地震活动的主要因素。同时，当45°≤θ≤60°时，应力差和接近角共同影响相互作用模式。NF 摩擦系数在此阶段也对 SE 起作用，但其影响并不突出。当θ≥75°时，