| Gas hydrate formation may lead to the blockage of the pipelines and critical safety problems in deepwater oil & gas exploration and transportation.Hydrate agglomeration and deposition are considered to be the main reasons of the hydrate plugging.Many factors could affect the hydrate agglomeration and deposition and herein their mechanism remains unclear.Hydrate agglomerants and pipeline modification are the promising methods to prevent the formation of hydrate blockage.This paper aims to systematically investigate the mechanisms of hydrate agglomeration and deposition via numerical modeling,agglomerants evaluating and pipeline surface modification and obtain a preliminary hydrate mitigation method.In order to study the mechanisms of hydrate agglomeration,a micromechanical force(MMF)apparatus has been assembled to measure the interaction force between two hydrate particles in the presence of a liquid bridge.In addition to this,a numerical micromechanical force model,which is in good agreement with the measured data,has been developed to study the effects of the liquid bridge conversion(to hydrate),size of the water droplet and the water/cyclopentane interfacial tension on the hydrate-droplet-hydrate interaction force.It is found that the interaction force could be increased by increasing the liquid bridge volume,the hydrate conversion rate and water/oil IFT.Besides,a numerical force model considering the hydrate dissociation has also been developed.Based on this model,the effects of the volume of the liquid bridge,the dissociation degree and dissociation rate on the interaction forces are investigated.In this paper,based on the self-assembled MMF apparatus,the effects of the concentration of AA(Cocamidopropyl dimethylamine),hydrate dissociation on the hydrate-droplet-hydrate interaction force has been investigated.The macro properties of the AA in a condensate/brine/methane system with different water cuts(10%-100%)and salt concentrations at a constant high pressure are investigated via a sapphire rocking cell.It found that,at low water cut,the present of Na Cl could decrease the performance of AA;at high water cuts,Na Cl could increase the performance of AA.Considering the weak performance of the AA at low water cut(< 10%),a dual surfactants system containing AA and Span 80 has been developed.This combined anti-agglomerant system can improve the performance of AA.The synergy mechanisms between AA and Span 80 has also been investigated.In this paper,the adhesion forces of cyclopentane hydrate on different substrates are determined via a self-assembled mechanical force apparatus.The effects of annealing time,subcooling,substrate material and agglomaerants on the adhesion forces have been investigated.It is found that a higher adhesion force could be obtained by increasing the subcooling,the annealing time and the surface energy of the substrate.The agglomerants could decrease the adhesion force,the AA's performance is found to be the best.The observation of the process of the sequences of hydrate growth from water droplets submerged in cyclopentane on a substrate and the morphology of the hydrate at different subcoolings and AA concentrations have been realized via a self-assembled apparatus.The morphology of the hydrate could be significantly affected by the AA concentration and subcooling.Finally,a superhydrophobic coating with excellent water-repelling properties on the X90 pipeline steel has been prepared through electronic deposition,hydrothermal oxidation and surface modification.An observing apparatus has been assembled to record the formation and growth of hydrate on different substrates.A mechanical force apparatus has been modified to measure the adhesion force of hydrate on the superhydrophobic coating.A significant reduction in the adhesion force on the coating compared that on the bare X90 steel is observed. |
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