Turning gas hydrate nucleation with oxygen-containing groups on size-selected graphene oxide flakes

Gas hydrate is a promising alternative for gas capture and storage due to its high gas storage capacity achieved with only structured water molecules.Nucleation is the critical controlling step in gas hydrate formation.Adding an alien solid surface is an effective approach to regulate gas hydrate nucleation.However,how the solid surface compositions control the gas hydrate nucleation remains unclear.Benefiting from the fact that the surface compositions of graphene oxide(GO)can be finely tuned,we report the effect of functional groups of size-selected GO flakes on methane hydrate nucleation.The carbonyl and carboxyl of GO flakes showed a more prominent promotion for methane hydrate nucleation than the hydroxyl of GO flakes.Surface energy,zeta potential,Raman spectra,and molecular dynamics simulation analysis were used to reveal the regulation mechanism of the functional groups of size-selected GO flakes on methane hydrate nucleation.The GO flakes with abundant carbonyl and carboxyl exhibited higher charge density than those enriched in hydroxyl.The negatively charged GO flakes can induce water molecules to form an ordered hydrogen-bonded arrangement via charge-dipole interactions.Therefore,the water molecules surrounding the carboxyl and carbonyl showed a more ordered hydrogen-bonded structure than those around the hydroxyl of GO flakes.The ordered water arrangement,similar to methane hydrate cages,significantly accelerated methane hydrate nucleation.Our study shows how the surface chemistry of solids control gas hydrate nucleation and sheds light on the design of effective heterogeneous nucleators for gas hydrate.

Simulation of the effect of hydrate adhesion properties on flow safety in solid fluidization exploitation

During the solid fluidization exploitation of marine natural gas hydrates,the hydrate particles and cuttings produced via excavation and crushing are transported by the drilling mud.The potential flow safety issues arising during the transport process,such as the blockage of pipelines and equipment,have attracted considerable attention.This study aims to investigate the impact of hydrate adhesion features,including agglomeration,cohesion,and deposition,on the flow transport processes in solid fluidization exploitation and to provide a reference for the design and application of multiphase hydrate slurry transport in solid fluidization exploitation.We established a numerical simulation model that considers the hydrate adhesion properties using the coupled computational fluid dynamics and discrete element method(CFD-DEM)for the multiphase mixed transport in solid fluidization exploitation.An appropriate model to simulate the adhesion force of the hydrate particles and the corresponding parameter values were obtained.The conclusions obtained are as follows.Under the same operating conditions,a stationary bed is more likely to form in the transport process due to the hydrate adhesion forces;adhesion forces can increase the critical deposition velocity of the mixture of hydrate particles and cuttings.Hydrate adhesion lowers the height of the solid-phase moving bed,while the agglomeration and cohesion of particles can intensify the aggregation and deposition of hydrate debris and cuttings at the bottom of the pipe.These particles tend to form a deposit bed rather than a moving bed,which reduces the effective flow area of the pipeline and increases the risk of blockage.

A large-scale experimental simulator for natural gas hydrate recovery and its experimental applications

To facilitate the recovery of natural gas hydrate(NGH)deposits in the South China Sea,we have designed and developed the world's largest publicly reported experimental simulator for NGH recovery.This system can also be used to perform CO_(2) capture and sequestration experiments and to simulate NGH recovery using CH_(4)/CO_(2) replacement.This system was used to prepare a shallow gas and hydrate reservoir,to simulate NGH recovery via depressurization with a horizontal well.A set of experimental procedures and data analysis methods were prepared for this system.By analyzing the measurements taken by each probe,we determined the temperature,pressure,and acoustic parameter trends that accompany NGH recovery.The results demonstrate that the temperature fields,pressure fields,acoustic characteristics,and electrical impedances of an NGH recovery experiment can be precisely monitored in real time using the aforementioned experimental system.Furthermore,fluid production rates can be calculated at a high level of precision.It was concluded that(1)the optimal production pressure differential ranges from 0.8 to 1.0 MPa,and the wellbore will clog if the pressure differential reaches 1.2 MPa;and(2)during NGH decomposition,strong heterogeneities will arise in the surrounding temperature and pressure fields,which will affect the shallow gas stratum.