Abstract:

Shale hydration constitutes a critical mechanism governing wellbore instability during deep oil and gas drilling, yet its spatiotemporal evolution remains challenging to characterize with conventional monitoring techniques. This study introduces distributed optical fiber strain sensing based on optical frequency domain reflectometry (OFDR) to establish a continuous dynamic monitoring methodology for hydration-induced strain in shale. Laboratory-scale physical simulation experiments are conducted to quantitatively characterize the directional evolution of hydration strain. Results reveal that shale hydration-induced swelling exhibits distinct stage-dependent behavior: a rapid initial swelling rate followed by gradual stabilization, with inhibitive solutions significantly reducing both the magnitude and rate of swelling. Bedding inclination exerts a dominant control on hydration swelling, as preferential water migration along bedding planes causes the swelling strain perpendicular to bedding to prevail. A quantitative relationship between moisture content and hydration-induced strain is established by integrating fiber optic strain measurements with water uptake monitoring, revealing a logarithmic growth pattern that asymptotically approaches saturation. Furthermore, scanning electron microscopy observations demonstrate that hydration not only induces clay mineral swelling but also promotes the dissolution and detachment of minerals such as dolomite and potassium feldspar, facilitating the development of fractures and dissolution pores. These findings provide robust experimental evidence and technical support for elucidating hydration-induced wellbore instability mechanisms and optimizing engineering strategies for wellbore stability control.

Key words: shale hydration, distributed optical fiber strain sensing, optical frequency domain reflectometry, hydration-induced swelling, anisotropy, wellbore stability

摘要：

泥页岩水化作用是深层油气钻探中诱发井壁失稳的关键因素，准确表征其力学响应的时空演化规律对于厘清失稳机理具有重要意义。传统点式与间断式监测手段难以连续刻画水化膨胀过程中的非均匀、各向异性应变场。为此，本文引入基于光频域反射原理的分布式光纤应变感测技术，构建了泥页岩水化应变连续动态监测实验方法，并通过室内物理模拟实验定量揭示了不同方向水化应变的演化特征。实验结果表明，泥页岩水化膨胀具有显著阶段性，初期膨胀速率较高，随后逐渐趋于稳定；抑制性溶液可有效降低膨胀幅值与演化速率。层理倾角对水化膨胀行为具有显著控制作用，水分沿层理面优先渗透致使垂直于层理方向的膨胀应变占主导地位。联合光纤应变与吸水质量监测所建立的含水率-水化应变定量关系表明，含水率随时间呈对数增长并趋于饱和。微观分析进一步揭示，水化作用不仅引起黏土矿物膨胀，还伴随白云石、钾长石等矿物的溶解与颗粒脱落，促进了裂缝与溶蚀孔隙的发育。上述结果为阐明水化致井壁失稳机理及优化井壁稳定性调控方法提供了可靠的实验依据与技术支撑。

关键词: 泥页岩水化, 分布式光纤应变感测, 光频域反射, 水化膨胀, 各向异性, 井壁稳定