刚性约束环境下蓬莱镇组泥岩水化膨胀特征

泥岩水化膨胀是影响井壁稳定性的重要因素，目前对距离井壁一定深度处于刚性约束条件下的泥岩水化膨胀特征尚无研究。文章通过模拟刚性约束环境，研究压力、离子类型以及矿化度对蓬莱镇组泥岩水化膨胀特征的影响规律，以此为现场生产以及室内实验提供指导。实验结果表明，随着压力增大，泥岩水化膨胀应力增加，而轴向应变以及密度差则减小，即刚性约束条件下泥岩吸收少量流体后将发生明显水化，且较小的水化膨胀应变将引起较大的水化膨胀应力。同时，钾盐对刚性约束条件下的泥岩水化具有明显抑制作用，且抑制剂矿化度越高，抑制泥岩水化能力越强。为此建议，在实际钻井工况条件下，泥岩层段位置越深，越要注意防止泥岩水化，在钻井液安全密度窗口之内，尽量使用高矿化度以及高化合价抑制性盐类。在地面实验测试泥岩水化膨胀时，应添加一个应力释放所引起的附加值，以避免实验结果偏于保守。

The hydration swelling characteristics of Penglaizhen mudstone

The hydration expansion of mudstone is an important factor affecting the wellbore stability, but there are few studies on the mudstone hydration characteristics under the rigid constraints condition and a certain distance from the borehole wall. In this paper, we have researched how pressures and ion types and salinities affect on the Penglaizhen mudstone hydration features under the rigid bound environment. The results show that mudstone hydration swelling stress increases, but the axial strains and the density differences reduce as the pressure increases. That is to say, the mudstones absorb a small amount of fluid can cause a significant hydration and the smaller hydration expansion strain can also lead to a large hydration expansion stress as the pressure increases. Sylvites have a significant inhibitory effect on mudstone hydrations, the higher concentration of inhibitor, the better the inhibitory effect is. It is recommended that the deeper mudstone formation is, the more we should pay attention to prevent mudstone hydration. Making use of the high concentration and high valence inhibitory salts prevents mudstone hydration when drilling fluids density window is safe. The mudstone hydration expansion tests should add an additional value, which is caused by a stress release, to avoid experimental results are somewhat conservative.