Owing to the harsh downhole environments, poor dispersion of silica at high salinity and high temperature can severely restrict its application as the nano-plugging agent in shale gas exploitation. The objective of this study is to improve salt tolerance and thermal stability of silica. Herein, silica was successfully functionalized with an anionic polymer (p SPMA) by SI-ATRP (surface-initiated atom transfer radical polymerization), named SiO₂-g-SPMA. The grafted pSPMA brushes on silica provided sufficient electrostatic repulsion and steric repulsion for stabilizing silica in a harsh environment. The modified silica (SiO₂-g-SPMA) had excellent colloidal stability at salinities up to 5.43 M NaCl (saturated brine) and standard API brine (8 wt% NaCl + 2 wt% CaCl₂) for 30 days at room temperature. Simultaneously, the SiO₂-g-SPMA was stable at 170 °C for 24 h as well as stable in weakly alkali environment. Furthermore, the plugging performance of SiO₂-g-SPMA in water-based drilling fluids for low permeate reservoir reached to 78.25% when adding a small amount of 0.5 wt% SiO₂-g-SPMA, which effectively hindered the water invasion into formation and protected the reservoir.

Purpose: The purpose of this paper is to adopt both the fragments of imidazole and thiosemicarbazide as reaction centers, to synthesize a water-soluble corrosion inhibitor named as thiosemicarbazide-imidazole derivative (TH-IM). Design/methodology/approach: This paper presents potentiodynamic polarization tests, electrochemical impedance spectroscopy tests and morphology study of metal surface by scanning electron microscope and thermodynamic study. Findings: In the aggressive condition of CO₂ saturated Wt. NaCl solution at 333 K for 72 h with 400 ppm inhibitor dosage, the efficiency of inhibition increases approximately 98 per cent through the method of weight loss. Originality/value: This paper finds a new corrosion inhibitor about TH-IM which has a good solubility in water.