基于损伤理论的硬脆性泥页岩井壁稳定分析

Borehole Stability Analysis of Hard Brittle Shale Based on Damage Theory

硬脆性泥页岩地层的失稳破坏机理是非常规油气开发工作者的重点研究对象之一。从硬脆性泥页岩微裂缝的角度出发,将微裂缝视为硬脆性泥页岩的损伤,通过随机函数确定微裂缝的分布,将损伤力学和断裂力学相结合建立了硬脆性泥页岩的损伤本构模型。利用FLAC3D软件将硬脆性泥页岩的损伤破坏模型应用到井壁稳定分析中,并通过计算结果分析了钻井液、微裂缝形态等在硬脆性泥页岩破坏中占有的比重。计算结果显示,硬脆性泥页岩对钻井液的敏感度以及硬脆性泥页岩微裂缝的发育程度对井壁稳定影响最大,硬脆性泥页岩微裂缝的方向对井壁稳定影响很小。因此,钻井液的封堵性和密度是确保硬脆性泥页岩稳定的重要手段,控制钻井方向对维持硬脆性泥页岩稳定的作用有限。

The failure mechanism of the hard brittle shale formation is the key research object to ensure the safety development of unconventional oil and gas.From the perspective of microcracks in hard brittle shale,the microcracks was regarded as damage,the distribution of microcracks was determined by random function,and the damage constitutive model of hard brittle shale was established by combining damage mechanics and fracture mechanics.FLAC3D software was used in borehole stability analysis with damage model of hard brittle shale.The role of drilling fluid and microcracks morphology in the failure of hard brittle shale was analyzed.The results show that the sensitivity of hard brittle shale to drilling fluid and the development degree of microcracks in hard brittle shale have great impact on the stability of borehole,while the direction of microcracks in hard brittle shale has little impact on the stability of borehole.The plugging and density of drilling fluid is an important means to ensure the stability of hard brittle shale,and the control of drilling direction has limited effect on maintaining the stability of hard brittle shale.