Design Of Rocking Cell Experiment System For Natural Gas Hydrate And Experimental Study On Its Plugging Behaviors

Natural gas hydrate(NGH)is a kind of caged ice solid compound with non-stoichiometric properties and bound gas molecules.Because of its advantages of high energy density and low environmental pollution,it is regarded as the most promising new clean energy in the 21st century.However,as offshore oil and gas production moves to deep water,there may be a risk of hydrate plugging in the pipeline,which may lead to production interruption and even great economic losses and safety risks in serious cases.Therefore,the study on the plugging process and inhibition of hydrate in pipelines is of great significance to the development of deepwater oil and gas fields.In order to carry out the experimental study on the plugging characteristics of natural gas hydrate pipeline,an experimental system of Rocking Cell was designed and built in this thesis.The experimental system uses the all-visible pressure-resistant tube as the main body of the cell,and the designed pressure-resistant tube is 7 MPa.Precise angle and frequency swing can be realized through servo motor control.It can realize simulation of deep-water oil and gas transport pipeline operation in the process of hydrate formation and plugging.The temperatura and pressure changes in the cell are monitored by the temperature pressure sensor,and the phase equilibrium characteristics are obtained.In the real time,the system can observe the hydrate growth process by CCD camera,at the same time,the cell with inhibitor injection port,can carry out pipeline gas hydrate inhibitor evaluation experiment.The system of Rocking Cell provides the equipment foundation and experimental conditions for the establishment of hydrate plugging model and the evaluation of inhibitors.The debugging and reliability test of the Rocking Cell experimental system are carried out.The water conversion rate reaches the highest when the water content is about 60%.The evolution process of hydrate formation,agglomeration and deposition was observed by CCD camera,including initial crystallization,water film condensation,annular wall growth,deposition hardening,and the ice jam caused by the decomposition and heat absorption of hydrate due to the rapid depressurization.A series of comparative experiments with different swing angles and frequencies show that with the increase of swing angles and swing rates,the induction time will be shortened,but the reaction time will be prolonged without changing the final water conversion rate and the volume fraction of hydrate in liquid phase.The parameters of hydrate formation induction time t_a(t),water conversion rate WC(%)and volume fraction of hydrate in liquid phase?(%)were obtained under different hydrophilic and hydrophobic wall conditions.The effects of wetting characteristics on the growth and plugging of hydrate in pipelines were quantitatively analyzed.The results show that the hydrophilic interface has a hindrance effect on the growth rate of hydrate,but has no obvious effect on the conversion rate of hydrate(i.e.the final hydrate production);the hydrophobic interface can not only increase the formation rate of hydrate,but also significantly increase the conversion rate of hydrate which means increase the final hydrate production.At the same time,because of the hydrophobic interface,it is difficult for hydrate to adhere to the wall of the pipe,and plugging is hardly occur.The influence of different concentration of ethylene glycol(MEG)inhibitors on the growth and plugging of hydrate in pipelines was quantitatively analyzed.The minimum dose range without plugging of hydrate pipelines was initially determined under the experimental conditions of initial pressure 4.5 MPa and temperature 8?.When the mass fraction exceeds0.2,it is difficult to form hydrate;when the mass fraction is about 0.1,the hydrate is non-uniformly dispersed in liquid phase.When it is below 0.05,plugging still occurs.