Development of novel natural gas hydrate inhibitor and the synergistic inhibition mechanism with NaCl: Experiments and molecular dynamics simulation

Abstract

Drilling fluid systems with exceptional performance serve as a foundation for commercial hydrate extraction. However, most hydrate reservoirs are located at relatively deep water depths and have shallow burial depths. As a result, there are high demands on the density of a hydrate drilling fluid system. Thus, the traditional hydrate drilling fluid system no longer meet the drilling needs in deep water shallow hydrate reservoirs. In this paper, a copolymer SYZ-2 was synthesized based on N-Vinyl-ε-caprolactam and N, N-dimethyl acrylamide. The effects of SYZ-2 and its NaCl system on methane hydrate were first tested by a constant rate cooling method, and the inhibition mechanisms of the system on hydrate nucleation and formation were investigated by molecular simulations. Meanwhile, the formulation and properties of a low-density hydrate drilling fluid system (1.06 g/cm3) based on SYZ-2 were also described in detail. The experimental results show that the hydrate formation temperature with the influence of SYZ-2 decreases from 10.6 °C to 2.7 °C, which can even be significantly reduced to −3.1 °C in the presence of 7 % NaCl. The molecular dynamic simulation results show that SYZ-2 inhibits the nucleation of hydrates by decreasing the solubility of methane molecules, primarily by promoting the agglomeration of methane molecules. Additionally, SYZ-2 can also adsorb to the surface of hydrates and prevent the hydrate cage structure from capturing methane molecules. In contrast, NaCl inhibits hydrates formation by restricting the movement of water molecules. These results provide valuable insights into a better understanding of the gas hydrate inhibition mechanisms, the rational development of high-performance hydrate inhibitors for drilling fluids, as well as the construction of drilling fluid systems.