Polymeric Kinetic Hydrate Inhibitors in NaCl Brine–Sediment Media: Hydrate Performance, Rheological Structuring, and Interfacial Responses

Gas hydrate plugging remains a persistent flow-assurance challenge in offshore oil and gas operations. PVP, pectin, CMCS, and PASP were compared at 0.1–0.5 wt% in pure water, 3.5 wt% NaCl brine, pure water–sediment, and brine–sediment media using hydrate kinetics, Raman spectroscopy, CST, SEM/EDS, zeta potential, viscosity screening, and quantitative rheology. At 0.5 wt% and 3 °C, all sediment-containing formulations were shear-thinning. CSS ramps revealed continuous stress-dependent flow consistent with progressive yielding, while oscillatory measurements indicated weak elastic-dominant responses for polymer-containing suspensions. Pectin gave the highest storage modulus and the strongest salinity-induced increase in oscillatory flow-point stress (approximately 0.092 to 0.178 Pa), whereas PASP retained the most favorable multimetric KHI response and the highest 500 s recovery in brine–sediment. PVP shifted from an oscillatory flow point above 0.209 Pa in pure water–sediment to approximately 0.156 Pa in brine–sediment. These results show that small-deformation stiffness, steady yielding, oscillatory flow transition, post-shear recovery, and KHI performance are distinct but partially coupled material responses. The combined evidence supports weak, deformable polymer–sediment structuring rather than a single rheological strength mechanism governing hydrate inhibition.