In order to restore the normal development of nitrogen drilling technology, it is significant to gain a deep and comprehensive insight into the bottom-hole rock failure mechanism induced by gas-induced fracture. In this paper, the mechanism of bottom-hole rock failure induced by gas-induced fracture was analyzed by means of conventional analysis method of wellbore instability. The research suggests when the bottom-hole is gradually approaching the gas-induced fracture, the difference between circumferential stress and radial stress of the crack face gradually increases. The increasing shear stress caused by the difference between principal stresses leads to the compression-shear failure; then, the failure mode evolved from single-shear failure mode to combined mode of shear and tensile failure with the failure zone extending. If the wellbore is connected with the fracture, then the high-pressure gas in fracture carrying plenty of debris is injected into the wellbore, releasing lots of energy. The mechanism analysis of bottom-hole rock failure can explain the abnormal behaviors of logging data in well QL1 located in Baimamiao structural belt, Dayi County, Sichuan Province. The results not only provide a theoretical basis for the prevention and control of bottom-hole rock failure, but also provide a new perspective for studying the dynamic instability of deep rock in the field of petroleum engineering.

为了恢复氮气钻井技术的正常发展，深入了解气致裂缝引起的井底岩石破坏机理具有重要意义。本文采用常规的井筒失稳分析方法，对由气致裂缝引起的井底岩石破坏机理进行了分析。研究表明，当井底逐渐接近气致裂缝时，裂缝面的周向应力和径向应力之差逐渐增大。由主应力之间的差异引起的剪切应力增加导致压缩剪切破坏。然后，破坏模式从单剪切破坏模式演变为剪切破坏和拉伸破坏的组合模式，并扩展了破坏区域。如果井眼与裂缝相连，则裂缝中携带大量碎屑的高压气体会被注入井眼，释放出大量能量。井底岩石破裂的机理分析可以解释四川大邑县白麻庙构造带QL1井测井资料的异常行为。研究结果不仅为预防和控制井底岩石破裂提供了理论依据，而且为研究石油工程领域深部岩体的动态失稳提供了新的视角。井底岩石破裂的机理分析可以解释四川大邑县白麻庙构造带QL1井测井资料的异常行为。研究结果不仅为预防和控制井底岩石破裂提供了理论依据，而且为研究石油工程领域深部岩体的动态失稳提供了新的视角。井底岩石破裂的机理分析可以解释四川大邑县白麻庙构造带QL1井测井资料的异常行为。研究结果不仅为预防和控制井底岩石破裂提供了理论依据，而且为研究石油工程领域深部岩体的动态失稳提供了新的视角。