Synthesis of poly(citric acid–aspartic acid) copolymer for efficient inhibition of shale hydration in water-based drilling fluids

Abstract

Poly (citric acid–aspartic acid) copolymer was synthesized and assessed as a shale hydration inhibitor. The formation of the biomass-based eco-friendly copolymer was verified using Fourier transform infrared spectroscopy, and the structure confirmed by 13C and 1H nuclear magnetic resonance. Thermal degradation of the copolymer was evaluated by thermogravimetric analysis, which suggested that the copolymer has outstanding stability. Characterization using scanning electron microscopy, equipped with an energy-dispersive X-ray spectrometer, was carried out to confirm the shale morphology before and after copolymer treatment. Shale recovery tests, immersion experiments, and anti-swelling measurements were performed to determine inhibitor performance in the drilling process. The copolymer showed the highest shale dispersion recovery compared to a commonly used inhibitor (potassium chloride) and water. The anti-swelling and immersion results indicated that the copolymer was strongly adsorbed over the clay's surface through hydrogen bonding and electrostatic interaction. Consequently, clay hydrophobicity could be increased by producing a hydrophobic film on its surface, which would decrease the number of hydrogen bonds between shale and water, hence reducing the quantity of water invasion.