Microscopic insights into synergism effect of different hydrate inhibitors on methane hydrate formation: Experiments and molecular dynamics simulations

Abstract

To reveal the synergism effect of hydrate inhibitors on the formation of methane hydrate was the key to developing new gas hydrate inhibitors and drilling and completion fluid systems. The characteristics of hydrate formation under thermodynamic inhibitors, kinetic inhibitors, and their compound systems were investigated by experiments and molecular simulations from macroscopic and microscopic points of view, respectively. The experimental results presented that a thermodynamic inhibitor was able to significantly reduce the hydrate formation temperature in combination with a kinetic inhibitor, where a compound system of 1% PVP and 5% CaCl2 was comparable to 9.76% CaCl2, or 10.84% NaCl, or 19.85% MEG for the formation of hydrate. The molecular simulation results showed that the thermodynamic inhibitors (NaCl) reduced the steric effects of the kinetic inhibitors (PVP) by limiting the motion of water molecules, which enhanced the effect of inhibitors on methane molecules and accelerated the aggregation of those to form nanobubbles. This study helps us to understand the mechanism of a synergism effect with different hydrate inhibitors on methane hydrate formation and is of applicable importance to develop new natural gas hydrate inhibitors and drilling and completion fluid systems.