The wellbore stability in shale gas reservoir is the key factor for safe drilling and effective development of shale gas. However, the instability mechanism remains unclear in shale gas wells. In this work, the wellbore instability mechanism was studied by conducting experimental and field case studies in Longmaxi shale. A high-pH condition strengthened clay mineral hydration by increasing the absolute ζ-potential of the shale clay minerals. Alkali-soluble minerals (clay minerals, quartz, feldspar, etc.) were eroded greatly in a high-pH fluid, resulting in a large number of dissolution pores and weakening the microstructure of the shale. The high-pH fluid further reduced the difficulty of shale frictional sliding by lubricating the shale surface and weakening the asperity strength of the surface. Adjusting the pH value of drilling fluids and plugging lost circulation channels became key jobs to maintain the wellbore stability in shale gas wells. This study provides theoretical guidance for drilling fluid optimization used in shale gas wells.

中文翻译：

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页岩气井中高pH流体-页岩反应与裂缝表面滑动耦合引起的井筒失稳：实验和现场研究

页岩气储层的井筒稳定性是安全钻探和有效开发页岩气的关键因素。但是，页岩气井的失稳机理仍不清楚。在这项工作中，通过在Longmaxi页岩中进行实验和现场案例研究，研究了井筒失稳机理。高pH条件通过增加页岩粘土矿物的绝对ζ电位来增强粘土矿物的水合作用。碱溶性矿物（粘土矿物，石英，长石等）在高pH值的流体中被严重侵蚀，从而导致大量的溶蚀孔隙并削弱了页岩的微观结构。高pH值的流体通过润滑页岩表面并减弱表面的粗糙强度，进一步降低了页岩摩擦滑动的难度。调节钻井液的pH值和堵塞循环流失通道成为保持页岩气井井眼稳定性的关键工作。该研究为页岩气井中钻井液的优化提供了理论指导。