The Study On Relationship Between Wax And Hydrate Formation In Subsea Multiphase Pipeline

In subsea multiphase pipeline,both wax and hydrate may form due to the high pressure and the low temperature.It can block the pipelines and lead to serious security problems.So far,there are a lot of scholars have carried out extensive research on wax and hydrate,but most of all is to separate the two studies,does not take into account the interaction between the two.Although the nature of wax and hydrate is very different,but the generated from one side will change the composition of the fluid,affect the thermodynamic behavior of the other side.This work analyses the relationship between wax and hydrate formation from the perspective of thermodynamics.It mainly through the way that a solid phase generated causes the change of system consisting to analyze the influence of the party to generate condition.This work did selection and optimization on the basis of the proposed thermal models of wax and hydrate.And programming the wax and hydrate phase equilibrium calculation by Visual C++6.0.Using compiled programs to simulate wax or hydrate phase equilibrium independently for a lot of systems.The program predicted values are compared with the experimental data and software PVTsim's calculated values.The results show that the wax model can predict the wax phase equilibrium well,and better than software PVTsim's prediction.Hydrate model predicted values are very close to experimental data,and it shows good prediction effect.Combine the thermodynamic models of wax and hydrate with the flash calculation of wax and hydrate.This work studied the effect of wax formation on hydrate precipitation and the influence of hydrate precipitation on wax formation.The results show that the effect of wax formation on hydrate precipitation depends mainly on two aspects: the decrease of the molecular weight increase the liquid hydrocarbon's inhibition effect for hydrate;the increase of the light component content promotes the hydrate precipitation.When the wax precipitation amount is big enough,the influence of the light component content plays a decisive role;wax formation will promote hydrate precipitation and increase the hydrate formation temperature.The influence of wax formation on hydrate precipitation is significant or not,depends on how many the amount of wax crystal precipitation,the greater the formation of wax,the greater the effect on hydrate formation.On the other hand,hydrate precipitation could promote wax formation,increase the wax formation temperature under the same pressure.The effect of hydrate precipitation on wax formation depends mainly on system's water content and light component content.The more the water content and light component content,the greater the effect of hydrate precipitation on wax formation.Compared the systems we studied in this work,it shows that the effect of hydrate precipitation on wax formation is more notable than the effect of wax formation on hydrate precipitation.In addition,this work presents the principle of an integrated wax-hydrate prediction program.To system which hydrate and wax may coexist,considering the mutual influence between the two.