Abstract:  The key to solving the problem of borehole instability is to reduce the density of the water-based drilling fluid to change the collapse stress. In this paper, the stress-strain rule,the mechanical properties of rock before and after immersion,and the deformation and destruction of rocks before and after soaking for 24 h by different treatment agents and systems are studied by a triaxial rock strength tester RTR-1000, to select and otpmize the drilling fluid system and treatment agents. The experimental results show to enhance the plugging and inhibition of the drilling fluid system can effectively reduce the collapse stress of shale formation. The addition of inorganic salt KCl and organic potassium formate in the drilling fluid can enhance the strength of shale. The residual strength of the rock is increased and the compressive strength is increased by the cloud point effects of the softening particles and the polymeric alcohol in the lugging agent. Through experiments and theoretical studies, the factors and laws affecting shale strength by the drilling fluid treatment agents areobtained, which provide theoretical and data support for the optimization of drilling fluid treatment agents such as plugging agents and inhibitors in anti-sloughing drilling fluid systems. At the same time, it will provide new ideas and methods for reducing the collapse pressure of shale formations, maintaining wellbore stability, increasing the ROP and downhole safety.

Key words:  , collapse stress, compressive strength, drilling fluid treatment agent, wellbore stability

摘要：  解决井壁失稳问题的核心是降低水基钻井液密度，进而改变坍塌应力大小。通过三轴岩石强度测试 仪RTR-1000，研究经不同处理剂及体系浸24ｈ后所表现出的应力—应变规律及浸泡前后岩石力学性能、岩石 变形和破坏规律，从而对钻井液处理剂及体系进行筛选和优化研究。实验结果表明，增强钻井液体系的封堵和抑 制能力可以有效降低地层页岩的坍塌应力。在钻井液中加入无机盐 ＫＣｌ和有机盐甲酸钾可以增强页岩的强度；通 过封堵剂中软化粒子以及聚合醇的浊点效应使岩石的残余强度增大，抗压强度增大。通过实验和理论研究，得到 钻井液处理剂影响页岩强度的因素和规律，从而为防塌钻井液体系封堵剂和抑制剂等钻井液处理剂的优选提供理 论和数据支持。同时为降低页岩地层坍塌压力，保持井壁稳定、提高机械钻速和为井下安全工作提供新的思路和 方法。

关键词:  坍塌应力, 抗压强度, 钻井液处理剂, 井壁稳定