Search

During the operation of deep-sea pipelines, the accumulation and deposition of hydrates are important reasons for pipeline blockage. The current main measure to solve the hydrate plugging problem is the addition of low-dose inhibitors (LDHIs), but it is not yet known whether the precipitation of wax crystals will affect their effectiveness. Therefore, in this study, the hydrate cohesive force within the wax-free/wax-containing system was directly measured by using a micromechanical force device (MMF) and the reasons for the change in cohesive force were analyzed from a morphological point of view. The results showed that glycine was effective in reducing the cohesion between hydrate particles in both wax-free/wax-containing systems and still exerted the effect of antiagglomeration agent (AA) at very low concentrations (as low as 0.10 wt %). Moreover, the optimum concentration of glycine was 0.50 wt %. At this concentration, the cohesive force decreased from 8.54 to 7.07 mN/m in the wax-free system, a decrease of about 17.2%, while the cohesive force decreased from 5.94 to 2.15 mN/m in the wax-containing system, a decrease of about 63.8%. By observation of the morphology of the hydrate particles, the presence of glycine was found to reduce the volume of the liquid bridge by changing the surface roughness and wettability of the particles, thereby reducing the cohesive force. And when wax was contained in the system, the wax further reduced the wettability by adsorbing on the surface of the hydrate particles. However, under certain AA conditions, the increase in wax concentration (from 0.1 to 0.3 wt %) resulted in the free water inside the hydrate being more likely to form liquid bridges with the surrounding particles, thus weakening the effect of AA. This work analyzes the effect on cohesive force in the simultaneous presence of LDHIs and wax from a morphological point of view, which is beneficial in providing more insights into securing safe hydrate flow management.

CH4–CO2replacement technology has broad application prospects in reducing CO2emission and developing natural gas hydrate (NGH) resources. It is of great significance to study the mechanism of CH4–CO2replacement. In this paper, the effect of H2O on CH4–CO2displacement behavior is studied by molecular dynamics (MD) simulation and quantum mechanics calculation. The interactions between the host and guest in cages of CH4hydrate are calculated using the symmetry-adapted perturbation theory method. The contribution of physical components of binding energy can be determined. The result indicates that the electrostatic interaction of H2O–H2O and H2O–gas is a key factor of the CH4–CO2replacement mechanism. Additionally, the microconfigurations and microstructure properties are analyzed by MD simulation in the systems containing a gas layer (CO2or CH4) and a CH4hydrate layer. The results showed that the movement and the arrangement of H2O molecules influence the hydrate structure due to the interaction of H2O–gas during the replacement process. The molecular simulation suggests that the change of electrostatic interaction with H2O molecules could improve the CH4–CO2replacement efficiency, which can be favorable for the investigation of CH4replacement technology in NGH with CO2injection.