| As oil and gas development moves toward deep water region,the blockage of hydrates in subsea multiphase pipelines has become one of the biggest challenges for oil and gas transportation.Hydraflow helps to realize the safe transportation of oil and gas in long-distance pipelines.The key of Hydraflow is the research and development of high-performance anti-agglomerants(AAs).In this dissertation,high performance and low dosage AAs were developed through screening,evaluation and compounding.In order to efficiently screen additives and classify their AA performance,the rocking cell apparatus was designed and built,which can simulate the deepwater subsea oil and gas pipelines,and a method to classify the AA performance was established.A large number of additives based on surfactants and polymers were screened,and the one with best AA performance were evaluated in high-pressure autoclave under different concentrations,pressures and watercuts.In order to develop high performance and low dosage AAs,a synergist was added for compounding,the effect of the mixtures was studied,and the concentration of AA and synergist were optimized.In this paper,17 cationic surfactants,6 nonionic surfactants,12 zwitterionic surfactants,21 polymers,and 10 other types of additives were screened.The results showed that zwitterionic surfactants may have more potential in preventing hydrate from agglomerating.Among all additives,nonionic surfactant AA-7 has the best AA performance,which can keep the slider moving in the whole reactor when the hydrate volume fraction up to 18.76%.At 30% watercut,AA-7 shows good AA performance.When hydrate volume fraction<10%,concentration of AA-7 has no effect on its AA performance,while the AA performance is enhanced with the increase of AA-7 concentration when hydrate volume fraction of hydrate≥10%.However,AA-7 does not completely prevent the gas hydrate from aggregating.It was also found that AA-7 has kinetic inhibiting effect and can significantly delay the formation of hydrate,0.75 wt.% AA-7 can delay the formation of hydrate by 3.1 h.The performance of AA-7 under different pressures has no obvious regularity.At 60% watercut,AA-7 also shows good AA performance,which is enhanced with the increase of AA-7 concentration.The optimum concentration of AA-7 is 2wt.%,and loose and porous powder-like morphology of hydrate can be observed at this concentration.In 60%watercut system,AA-7 still has strong kinetic inhibiting effect,and 0.5wt.% AA-7 can delay the hydrate formation by 9.1 h.The effect of pressure on performance of AA-7 was investigated,and it was found that pressure has no significant effect on AA performance of AA-7 when hydrate volume fraction <35%,when hydrate volume fraction ≥35%,AA performance of AA-7 weakens with the increase of initial pressure.The effect of watercuts on the AA performance of AA-7 was investigated.The results showed that the system with 40% watercut has the highest risk of hydrate blockage in the range of 10%-50% watercuts.At 40% watercut,the highest relative current value is close to16 in the presence of 0.5wt.% AA-7.The AA performance of the mixture of AA-7 and synergist SY-1 was studied,and the mass ratio of AA-7 and SY-1 was optimized.The results showed that synergist SY-1 has no or poor AA performance,but SY-1 can significantly enhance the AA performance of AA-7 at different mass ratios,and the relative current is less than 2.75 during the hydrate formation,indicating that AA-7 and SY-1 have excellent synergistic inhibition effect.The optimum mass ratio of AA-7 to SY-1 is 5:1 with 0.5wt.% AA-7,which can maintain the relative current within 1.4,and its AA performance is better than 2wt.% AA-7. |
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