Study On Solid-liquid Flow Characteristics In Hydrate Test Production Channel

As an ideal alternative energy source,natural gas hydrate is receiving more and more attention from all over the world.In recent years,countries around the world have successively carried out mining tests on proven hydrates,but in the process of seabed gas hydrate exploitation and transportation,whether it is a decomposition method represented by thermal excitation method or depressurization method,or used to break up seabed hydrates.The solid-state flow method in the form of solid-liquid two-phase mixed transport encounters flow safety problems such as the formation,secondary formation and blockage of hydrates in pipelines and wellbores,and because of the characteristics of hydrate reservoirs,there will be a lot of sand production.In order to ensure the flow safety in hydrate mining,it is of great significance to study the characteristics of solid-liquid two-phase flow in the hydrate test channel.In this paper,based on the field data,the OLGA simulation is used to compare the temperature and pressure distribution data along the wellbore with the hydrate formation temperature and pressure conditions.The problem of hydrate flow safety in the test channel is determined and explained.In order to grasp the characteristics of the solid-liquid two-phase flow in the perpendicular pipe,the hydrate formation and flow experiment of the pure water system was carried out by using the self-built hydrate high pressure loop containing the perpendicular pipe section.Sand particles were used as experimental materials to carry out sand-carrying experiments under the conditions of particle sedimentation,carrying and plugging in perpendicular tubes.Then based on the Open FOAM open source platform,based on the simplified dual Euler fluid model,a macroscopic flow model is built to simulate the hydrate-solid-liquid two-phase flow in the perpendicular tube.Based on the Open FOAM+CFDEM+LIGGGHTS platform,the perpendicular tube hydration is performed by the CFD-DEM coupling method.The solid-liquid two-phase flow is microscopically simulated to obtain the macroscopic and microscopic flow characteristics of the hydrate solid-liquid two-phase flow in the perpendicular tube.By perpendicular tube tube hydrate loop experiment and perpendicular tube sand deposition experiment,we get: As the hydrate formation increases,the viscosity of the slurry increases,the flow resistance of the hydrate slurry increases.The larger the flow rate,the greater the flow resistance and the greater the pressure loss.When the hydrate particle concentration is low,the flow resistance is affected.The flow rate is dominant in the factors,and when the hydrate particle concentration reaches a certain range,the hydrate concentration is dominant.The smaller the particle size,the slower the sedimentation.The critical carrying velocity of quartz sand with a grain size of 44 ?m is 0.0090 m/s,which is slightly larger than twice the sedimentation velocity.When the particles form a sediment plugging pipe section at the bottom of the vertical pipe,the flow channel at the elbow is widened as the flow velocity increases,and the sand particles are carried away from the bottom of the vertical pipe.When the flow velocity increases to a certain level,the flow channel area will not continue to expand despite the increase in flow rate.The macroscopic simulation study on the solid-liquid two-phase flow characteristics of the hydrate in the perpendicular tube shows that the established numerical model of the solid-liquid flow of the hydrate particles in the tube is reliable;the analysis of the simulation results results in the horizontal and vertical sections of the vertical tube.The distribution of hydrate particle concentration under different inlet phase fractions,particle sizes,and inlet flow rates.The larger the particle size is,the smaller the inlet phase fraction is,the more uniform the hydrate particle distribution is,and the smaller the maximum concentration is compared with the inlet phase fractional rate.As the velocity increases,the hydrate particle distribution unevenness first decreases and then increases,the maximum The concentration increases relative to the inlet phase fraction and decreases first.According to the simulation results,the quantitative relationship between the maximum particle concentration in the tube and the flow velocity and the inlet phase fraction is obtained,and the recommended range of safety conditions is given.The results of microscopic simulation of hydrate particles in perpendicular pipes show that the concentration distribution of the particles obtained through the microscopic simulation of cfd-dem in the three-dimensional space of vertical pipes is basically consistent with the macroscopic simulation results.In the vertical section,there is an obvious "high-density linear" particle distribution area along the direction of fluid flow at the junction between the elbow and the vertical section,extending into the vertical section.As the flow velocity increases,this phenomenon of particle density will disappear.