Study On The Influences Of Composite Inhibitor And Wall Water Film On Hydrate Formation In Pipeline

Hydrate risk management plays an important role in oil and gas production,transportation and processing.Adding chemicals is the main technical means of hydrate risk management.Traditional kinetic inhibitors with poor biodegradability will fail under high undercooling.Therefore,pectin which is the pure natural green kinetic inhibitor and ionic liquids with double-effect inhibition have great research potential.Pectin is a pure natural green kinetic inhibitor,and ionic liquid has double-effect inhibition.Therefore,they have great research potential as new kinetic inhibitors.However,there are a lack of systematic experimental verifications on the inhibition of pectin and ionic liquid in different systems.In addition,the researches on hydrate risk management mainly focus on the hydrate macroscopic formation and plugging characteristics,and there is still a lack of researches on the influence mechanism of water film in pipeline on hydrate formation.In view of the above problems,this paper selected the kinetic inhibitors with the best inhibition from three pectins and three ionic liquids,and combined them with PVCap to form a mixed inhibitor.The optimum ratios were studied in pure water system and oil-water system.Then the dynamic simulation of water film formation in fully visible rocking cell was carried out by numerical simulation,and the influence of water film thickness on hydrate formation was studied.The main research contents are as follows:Hydrate formation experiments with inhibitors were carried out in pure water system,and the inhibition of AC pectin,Tara gum and Guar gum were evaluated.It was found that AC pectin had the best inhibition performance in a certain concentration range and the induction time was more than twice that of PVCap at the same concentration.AC pectin can effectively delay the time for hydrate formation,but can’t reduce the final hydrate quantity.However,with the increase of AC pectin,the hydrate induction time decreased and the inhibition was failed.The composite inhibition properties of PVCap and AC pectin were studied.When the ratios of PVCap and AC pectin were 4:1 and 2:1,the performances of the composite inhibitors were the best,and there were almost no hydrates in 1000 min.The inhibition of[HMIM]Br,[HMIM]PF₆and[DMIM]PF₆ were evaluated.The[HMIM]Br can delay the nucleation time of hydrate and had the anti-agglomerant effect,which was the best on the effect of inhibition.When the ratios of PVCap and[HMIM]Br were 1:1 and 1:2,the effects of composite inhibitors were the best.Hydrate formation experiments with inhibitors were carried out in oil-water system,and the inhibitors were evaluated.PVCap was compounded with AC pectin and[HMIM]Br respectively.When the ratio of PVCap to AC pectin was 2:1 and the ratios of PVCap to[HMIM]Br were 2:1,1:1 and 1:2,the performance of the compounded inhibitors were the best,and the hydrates were not formed within 1000min.Under the high gas oil-water system,the above optimal ratio was verified.It was found that hydrates grew when the ratio of PVCap to[HMIM]Br was 1:2,but other ratios were still valid.In order to study the effect of water film on hydrate in pipeline,the VOF model and EWF model in Fluent were used to simulate the fully visible rocking cell dynamically at first.It was found that the water film often covered the pipe wall near the gas-liquid interface,and the water film was also thicker at this position.Through experimental verification,it was found that hydrates were often formed preferably at the coverage area of water film,indicating that the thickness and coverage of water film had an important impact on the initial formation of hydrate.Secondly,the formation of water film with different water content was simulated.It was found that with the increase of watercut,the coverage area of water film decreased,but the thickness of local water film first increased and then decreased.When the watercut was 60%,the local water film was the thickest and the distribution range was the largest.With the increase of watercut,the induction time of hydrate formation first decreased and then increased through experimental verification.When the watercuts were 50%and 60%,the induction times were the shortest and hydrates were formed fastest.Simulation and experiments showed that with the increase of local thick water film range,the hydrate was formed faster and the induction time was shorter.In addition,through simulation and experiments,it was found that with the increase of contact angle or the hydrophobicity of the wall surface,the coverage area of water film increased and thicker water film appeared,which caused the faster formation of hydrates.The wettability of pipe wall surface had an effect on the hydrate formation characteristics such as formation rate by affecting the coverage area and thickness of the water film.