Comprehensive Study of Synergistic-Dual-Functional Mechanism of Kinetic and Thermodynamic Inhibitors in a Hydrate Drilling Fluid System

Pipeline blockage and drilling problems caused by the deposition of natural gas hydrate are difficulties in the process of oil and gas production. Adding chemical inhibitors to drilling fluid is one of the main methods to prevent hydrate regeneration in wellbore. In recent years, kinetic inhibitors with low doses and high inhibition performance have been widely and deeply studied. In this paper, based on the improved wellbore hydrate deposits and an inhibition and decomposition simulation experimental device, and based on the evaluation and analysis of the synergistic effect between the three commonly used kinetic inhibitors of polyvinylpyrrolidone, glycine, and pectin and the thermodynamic inhibitors of salts, a high-efficiency hydrate inhibition drilling fluid system was developed. The results show that (1) Compared with the pure water system, the kinetic inhibitor can inhibit the deposition of hydrate in the reactor by prolonging the induction time of hydrate deposits, adsorbing on the hydrate surface, or destroying the stability of hydrate. (2) Due to the differences in the mechanism of inhibiting hydrate deposits among different kinetic inhibitors, the optimal dosage of the three kinds of kinetic inhibitors is different, which is 1.0 wt % PVP, 1.0 wt % Gly, and 0.1 wt % pectin, respectively. Only when Gly and PVP are combined with NaCl and KCl can the synergistic inhibition effect be obvious. (3) The inhibition effect of the drilling fluid system with an inhibitor on hydrate deposits was evaluated, and the efficient inhibition drilling fluid systems "Base mud +0.5 wt % pectin" or "Base mud +0.5 wt % PVP+5 wt % KCl" suitable for hydrate production in marine environment were selected. The results of this study provide a reference for solving the stability and safety problems in the process of hydrate drilling.