Kinetic inhibition of gas hydrates for efficient development of sour gas reservoirs

• Polyquaternium-based KHIs (PQ-7 & PQ-10) were developed for challenging sour gas reservoirs. • PQ-7 was exceptionally effective, even at low concentrations, making it highly efficient and cost-effective. • Both inhibitors exhibited low foaming, a critical property for easy chemical recovery and operational safety. • The inhibitors create "hydrate-free zones" by sterically blocking the assembly of hydrate cages around their molecules. Sour gas fields present substantial flow assurance challenges, particularly the rapid formation of gas hydrates that can obstruct pipelines, cause equipment failures, and lead to severe operational losses. The problem is especially critical for sour systems, where H₂S hydrates form more readily and remain stable under milder conditions than their methane counterparts. This study investigated two polyquaternium-based KHIs (PQ-7 and PQ-10), designed to enhance hydrate inhibition in sour gas systems through synergistic physicochemical and molecular mechanisms. In the uninhibited system, hydrate formation initiated rapidly with an induction time of 4.1 h and ΔT of 3.8 °C. PQ-7 demonstrated superior performance even at low dosages: at 1000–5000 ppm, it achieved induction times of 23–24 h and ΔT values exceeding 17 °C. PQ-10 exhibited concentration-dependent inhibition, with significant improvement only at higher dosages (>2500 ppm), where its ΔT reached 16.9 °C. Foaming analyses confirmed that both PQs exhibit low and transient foamability—an operationally desirable trait for offshore and subsea systems where excessive foaming complicates chemical recovery and separation processes. Complementary molecular dynamics (MD) simulations provided atomistic insights into the inhibition mechanisms. PQ-containing systems delayed nucleation onset to approximately 40 ns and exhibited significantly slower hydrate cage accumulation, lower F 4 structural order parameters, and attenuated energy transitions. Spatial mapping of water mobility revealed that PQ molecules created “hydrate-free zones” characterized by disordered, highly mobile water, confirming localized disruption of hydrogen-bond networks and steric hindrance near inhibitor molecules. These findings demonstrate that PQ-based KHIs impede both nucleation and growth stages of hydrate formation by modulating interfacial water structuring rather than altering bulk thermodynamics. This work establishes PQ-7 and PQ-10 as promising low-dosage, low-foaming KHIs for sour gas systems. By addressing the challenges posed by H₂S-rich environments, this research contributes to the safe and efficient development of increasingly critical sour gas resources.