Wellbore instability and formation collapse are crucial issues in the process of well excavation in the oil industry under extreme salinity and high-temperature conditions. This study demonstrates that a salt-responsive zwitterionic polymer brush (NS-DAD) based on modified nanosilica as a fluid-loss additive utilizing the anti-polyelectrolyte effect in water-based drilling fluids (WDFs) to overcome the wellbore instability caused by the failure of polyelectrolytes at extreme salinity and high temperature. Additionally, a nonionic polymer brush (NS-D), an anionic polymer brush (NS-DA), and a cationic brush (NS-DD) were also prepared for comparison. Compared with NS-D, NS-DA, and NS-DD, NS-DAD exhibited the anti-polyelectrolyte phenomenon, in which the sodium chloride electrolyte shields the electrostatic interaction in the molecular chain of the polyzwitterion and the molecular structure changes from a collapsed sphere to a more open helix. Macroscopically, NS-DAD exhibited a higher viscosity than NS-D, NS-DA, and NS-DD in saturated salt-based mud (SSBM). A typical “star-net” structure was observed between NS-DAD and the bentonite layer. Energy-dispersive spectroscopy (EDS) analysis of filter cakes showed that NS-DAD could significantly reduce the content of chloride and sodium ions in the bentonite layer. Therefore, compared with NS-D/SSBM, NS-DA/SSBM, and NS-DD/SSBM, NS-DAD/SSBM had excellent rheological properties, thermal stability, less fluid-loss volume, and thinner filter cake under extreme salinity and high-temperature conditions. The fluid-loss additive can be used to reduce the fluid-loss volume of WDFs in harsh reservoir conditions of high temperature and high salinity.

中文翻译：

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基于改性二氧化硅纳米粒子的盐响应性两性离子聚合物刷，作为水性钻井液中的失水添加剂

在极端盐度和高温条件下，井筒的不稳定性和地层塌陷是石油工业中油井开挖过程中的关键问题。这项研究表明，基于改性纳米二氧化硅的盐响应性两性离子聚合物刷（NS-DAD）作为失水添加剂，利用了水基钻井液（WDFs）中的反聚电解质作用来克服由于故障引起的井筒不稳定性在极高盐度和高温下的电解质。此外，还准备了非离子聚合物刷（NS-D），阴离子聚合物刷（NS-DA）和阳离子刷（NS-DD）进行比较。与NS-D，NS-DA和NS-DD相比，NS-DAD表现出抗聚电解质现象，其中氯化钠电解质屏蔽了两性离子分子链中的静电相互作用，分子结构从塌陷的球体变为更开放的螺旋。宏观上，在饱和盐基泥浆（SSBM）中，NS-DAD的粘度高于NS-D，NS-DA和NS-DD。在NS-DAD和膨润土层之间观察到典型的“星网”结构。滤饼的能量色散光谱（EDS）分析表明，NS-DAD可以显着降低膨润土层中氯离子​​和钠离子的含量。因此，与NS-D / SSBM，NS-DA / SSBM和NS-DD / SSBM相比，NS-DAD / SSBM在极高盐度和高盐分下具有优异的流变性，热稳定性，较少的滤失量和更薄的滤饼。高温条件下。