Abstract To achieve potent inhibition, reduced environmental impacts and excellent compatibility between drilling fluid and shale inhibitors, an eco-friendly amphoteric inhibitor based on carboxymethyl chitosan (CMCS) was synthesized. The molecular structure of CMCS was characterized by potentiometric titration, Fourier transform infrared spectroscopy and nuclear magnetic resonance, and the carboxymethyl substitution degree was revealed to be approximately 0.94. The inhibition performance was evaluated through linear swelling and hot-rolling dispersion tests, and the results were compared with those obtained with low-molecular-weight cationic polyether diamine, high-molecular-weight non-ionic polysaccharide encapsulator, and potassium chloride. The interaction between clay particles and CMCS molecules was investigated by X-ray diffraction, scanning electron microscopy, surface wettability, particle size distribution, zeta potential and surface tension tests. The results showed that CMCS with a specific amphoteric molecular structure exhibited a different inhibition behaviour compared with conventional inhibitors, more effectively prevented clay hydration and swelling and inhibited shale disintegration at both 77 °C and 150 °C. CMCS could absorb onto the clay surface via electrostatic force and hydrogen bonding, and an encapsulation film was formed through intermolecular interactions to immobilize outer free water molecules and to provide hydrophobic characteristics. CMCS intercalates into clay lattice, expels inner water and reduces the interlayer space. Additionally, CMCS reduces the surface tension of the bulk solution and hinders fluid invasion. Furthermore, CMCS was compatible with bentonite dispersion and improved the rheological and filtration properties at a suitable concentration.

中文翻译：

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水基钻井液中环保型两性页岩抑制剂羧甲基壳聚糖的合成及抑制机制评价

摘要 为实现有效抑制、减少环境影响以及钻井液与页岩抑制剂的良好相容性，合成了一种基于羧甲基壳聚糖的环保型两性抑制剂（CMCS）。通过电位滴定、傅里叶变换红外光谱和核磁共振对CMCS的分子结构进行表征，发现羧甲基取代度约为0.94。通过线性溶胀和热轧分散试验评价缓蚀性能，并将结果与​​低分子量阳离子聚醚二胺、高分子量非离子多糖包封剂和氯化钾的结果进行比较。通过 X 射线衍射研究了粘土颗粒与 CMCS 分子之间的相互作用，扫描电子显微镜、表面润湿性、粒度分布、zeta 电位和表面张力测试。结果表明，具有特定两性分子结构的CMCS与常规抑制剂相比表现出不同的抑制行为，在77℃和150℃下均能更有效地阻止粘土水化和膨胀，抑制页岩崩解。CMCS 可以通过静电力和氢键吸附到粘土表面，并通过分子间相互作用形成包封膜以固定外部游离水分子并提供疏水特性。CMCS 嵌入粘土晶格中，排出内部水分并减少层间空间。此外，CMCS 降低了本体溶液的表面张力并阻碍了流体侵入。此外，