Effects Of Petroleum Asphaltene And Water-in-Oil Emulsion On Methane Hydrate Formation

Hydrate plugging inside the subsea multiphase transportation pipelines has become the major flow assurance of petroleum industry.Prediction and prevention of hydrate plugging is generally limited due to the complexity of oil composition and flowing property,among which two crucial factors,petroleum asphaltene and emulsifiability,are still lack of systematic investigation.Accordingly,this study aims to gain insight into the influence of asphaltenes on hydrate formation,particularly when they are located in water,light oil solvent,metal surface,inhibitor solution and water-in-oil emulsion.We are also focused on the evolution of dynamic and rheological properties during hydrate formation in the water-in-light oil emulsions,under the influence of water fraction,degree of emulsification,light oil composition and silica sands.Firstly,a typical model asphaltene is selected to investigate the effect of its aggregation at different location of water on the evolution of methane hydrate.Simulation results demonstrates that asphaltene at gas-water interface promotes hydrate formation,while asphaltene in the bulk water phase inhibits hydrate formation.These are attributed to the enhanced methane solubility and adsorption of free methane,respectively,which agrees with the experimental results.Moreover,asphaltene promotes hydrate dissociation,due to the adsorption of released methane.Secondly,n-heptane and toluene are selected to represent saturates and aromatics,respectively,while three commercial hydrate dynamic inhibitor are also chosen.The effect of oil-water system near metal surface on methane hydrate formation and the inhibiting effect of inhibitors are both investigated,while the role of asphaltene are highlighted.Results demonstrate that rough metal surface is adverse for hydrate formation in oil-water mixture,because the groove will enrich oil components.Toluene shows a stronger inhibiting effect on hydrate formation than n-heptane,which is enhanced with the addition of asphaltene.The inhibiting effect of inhibitors are closely related to the applied oil circumstance,overall,PVP-K15 has the highest inhibiting effect,while Inhibex is not suitable in oil-water system.Thirdly,we study the methane hydrate formation mechanisms inside water-in-oil emulsion containing asphaltene.Simulation results reveal that the influence factors on hydrate formation are related to each other,such as water droplet size,light oil composition and asphaltene.Moreover,asphaltene inhibited hydrate formation in emulsion,because asphaltene shell near the surface of water droplet prevents the penetration of methane into water,and the formation of hydrogen bonds between asphaltene and water disturbs the growth of hydrate structure.Finally,n-heptane,decane and paraffin mineral oil are selected to represent light oil.The evolution of dynamic and rheological properties during hydrate formation in the water-in-light oil emulsion are integrally investigated,under the influence of water fraction,degree of emulsion,oil composition and silica sands.Results reveal that hydrate growth rate and yield stress of hydrate slurry increase with the increased water fraction and emulsifier concentration,which are attributed to the increased degree of emulsification and amount of water droplets,respectively.The higher viscosity and higher stability of the high-carbon mineral oil emulsion contribute to its low hydrate growth rate and yield stress.Silica sands promote hydrate nucleation by decreasing nucleation time,increasing nucleation temperature and eliminating the stochasticity.Silica sands have no effect on the shear shining properties of emulsion,but will lead to the occurrence of hysteresis.