Synthesis of modified natural polysaccharides for demulsification and corrosion inhibition

Oilfield chemicals play an important role in oilfield drilling, well completion, water injection, enhanced oil recovery, and gathering and transportation. The development of novel, environmentally friendly, multifunctional oilfield chemicals is an urgent research direction. In this study, two hyperbranched natural polysaccharides (AH and EH) were synthesized by modifying the biodegradable natural polysaccharide chitosan. AH and EH molecules contain a large number of polar groups, which interact with iron and adsorb on the iron surface, thus inhibiting corrosion. At the same time, the hyperbranched structure has a good bridging and aggregation effect on the dispersed phase in the emulsion, so as to achieve demulsification. In accordance with the strong fluorescence effect of crude oil, laser confocal microscopy was used instead of optical microscopy to observe the microscopic morphology of water-in-oil (W/O) emulsions. The demulsification tests indicate that the highest dehydration efficiencies of 86.24 % (AH) and 82.15 % (EH) were attained at a concentration of 500 mg L−1. The maximum corrosion inhibition efficiencies [90.24 % (AH) and 88.55 % (EH), at a concentration of 500 mg L−1] were calculated by weight loss experiments, micromorphology analysis, potentiodynamic polarization, and electrochemical impedance spectroscopy. Quantum chemical theory of the two natural polysaccharides was applied to further interrogate the molecular space structure. Laboratory test results indicate that the modified natural polysaccharides AH and EH exhibited good demulsification performance for W/O emulsions, and substantially inhibited the corrosion of carbon steel in brine. This study provides new ideas for developing natural polysaccharides as environmentally friendly, multifunctional oilfield chemicals.