井壁稳定性对于油气勘探开发过程中的安全高效钻井至关重要。本文介绍了一种可以在水基钻井液钻井过程中强化井壁稳定性的疏水型纳米二氧化硅（HNS），采用线性膨胀实验、滚动回收率实验和抗压强度测试研究了其井壁强化性能，利用zeta 电位、粒径、接触角、表面张力等测试和扫描电子显微镜（SEM）观察分析了井壁强化机理。此外，利用接触角法计算了HNS处理前后页岩表面自由能的变化。实验结果表明，HNS在抑制页岩膨胀和分散方面表现出良好的性能，优于常用的页岩抑制剂KCl和聚胺。与水相比，HNS可使膨润土试样的线性膨胀高度降低20%，对强水化页岩的回收率提高11.53 倍。更重要的是，HNS可有效防止页岩强度的降低。机理研究表明，HNS良好的井壁强化性能可归因于三个方面：首先，带正电荷的HNS通过静电吸附中和部分黏土表面的负电荷，从而抑制渗透水化作用；其次，HNS在页岩表面吸附后可形成具有微纳米层次结构的“荷叶状”表面，显著增加页岩表面的水相接触角，大幅度降低了页岩表面自由能，从而抑制表面水化；再次，毛细作用的减弱和页岩孔隙的有效封堵减少了水的侵入，对井壁稳定有利。本文所述的方法对于抑制页岩的表面水化和渗透水化提供了一种新途径。

Wellbore stability is essential for safe and efficient drilling during oil and gas exploration and development. This paper introduces a hydrophobic nano-silica (HNS) for use in strengthening the wellbore wall when using a water-based drilling fluid (WBF). The wellbore strengthening performance was studied using the linear swelling test, hot-rolling recovery test, and compressive strength test. The mechanism of strengthening the wellbore wall was studied by means of experiments on the zeta potential, particle size, contact angle, and surface tension, and with the use of a scanning electron microscope (SEM). The surface free energy changes of the shale before and after HNS treatment were also calculated using the contact angle method. The experimental results showed that HNS exhibited a good performance in inhibiting shale swelling and dispersion. Compared with the use of water, the use of HNS resulted in a 20% smaller linear swelling height of the bentonite pellets and an 11.53 times higher recovery of water-sensitive shale—a performance that exceeds those of the commonly used shale inhibitors KCl and polyamines. More importantly, the addition of HNS was effective in preventing a decrease in shale strength. According to the mechanism study, the good wellbore-strengthening performance of HNS can be attributed to three aspects. First, the positively charged HNS balances parts of the negative charges of clay by means of electrostatic adsorption, thus inhibiting osmotic hydration. Second, HNS fabricates a lotus-leaf-like surface with a micro-nano hierarchical structure on shale after adsorption, which significantly increases the water contact angle of the shale surface and considerably reduces the surface free energy, thereby inhibiting surface hydration. Third, the decrease in capillary action and the effective plugging of the shale pores reduce the invasion of water and promote wellbore stability. The approach described herein may provide an avenue for inhibiting both the surface hydration and the osmotic hydration of shale.