Phosphonated Inulin as an Eco-Friendly Thermally Stable Scale Inhibitor for the Oil and Gas Industry: Synthesis, Characterization, Efficacy, and Molecular Insights

The oil and gas industry grapples with mineral scale deposits during production, which hinder efficiency and damage equipment. The need for eco-friendly scale inhibitors for high-pressure, high-temperature (HPHT) applications has risen due to offshore regulations. This study investigates phosphonated Inulin (PIn), a modified biopolymer, as an eco-friendly scale inhibitor against calcite, gypsum, and Barite in harsh environments. Inulin, a natural polysaccharide, was functionalized with phosphonate groups, achieving a degree of substitution (DS) of 48.78%. Characterization through NMR and FTIR spectroscopy confirmed the successful modification. The scale inhibition effectiveness of PIn was tested in high-pressure dynamic tube-blocking tests at 100 °C and 80 bar compared to commercial carboxymethyl inulin (CMI). PIn effectively inhibited calcite and gypsum at 5 ppm under dynamic conditions and showed excellent thermal stability after 7 days at 130 °C, along with compatibility with high calcium ion concentrations, though it had minimal impact on barite scale. Molecular simulations offered insights into the morphology of the functionalized polysaccharides with GFN2-xTB MD simulations indicating a transition to a more compact structure. DFT analysis revealed that hydrogen bonds from phosphonate groups are stronger than those from hydroxyl or carboxylic groups, explaining PIn’s higher thermal stability compared to CMI.