Research On Gas Liquid Separation Technology And Supporting Equipment For Natural Gas Hydrate Exploitation

In the process of offshore NGH(Natural gas hydrate)exploitation by depressurization method,droplets in the gas may affect lift and recovery.Based on this phenomenon,gas liquid separation scheme and overall process scheme of mining is designed,which is suitable for offshore NGH vertical well.This scheme uses two packers to seal the reservoir and is designed with concentric string,which is based on depressurization method and the technique of drain and gas recovery by electric submersible pump.After the gas carrying droplets passes through the wellbore sealed by two packers,sand control device and gas-liquid separation device,the gas and liquid are separated and lifted separately.The liquid is discharged through the tubing and the gas is discharged through the annulus of tubing and casing.In order to select a reasonable gas-liquid separation method,the separation efficiency and adaptability of the three gas-liquid separation methods of helical separator,axial-flow separator with guide blades and tubular separator are analyzed in different gas-liquid ratios.In contrast,helical separation is more suitable for downhole gas-liquid separation of NGH,which has better adaptability for small flow rate.According to the gas hydrate well conditions,the working parameters and physical parameters are calculated under the condition of downhole temperature and pressure.On this basis,the structure of the helical gas-liquid separation device is designed,which follows design principles and requirements.Based on the extracted fluid region,a reasonable gas-liquid separation model of hydrate is established by using DPM(Discrete Phase Model)and EWF(Eulerian Wall Film)model,which can simulate the process of droplet fragmentation,polymerization and secondary transport.In order to obtain the structure parameters of the helical separation device with better separation effect,the influence rules of the pitch,the number of turns and the outer diameter of the helical tube on the separation performance were obtained.Based on this rule,through the steepest climbing experiment,the optimization center is determined as follows: pitch is 60mm;number of turns is 9;and outer diameter of helical tube is 110 mm.The experimental design of response surface and particle swarm optimization algorithm are determined,which take high separation efficiency and low pressure drop as optimization objectives.The optimized results are as follows: pitch is 70mm;number of turns is 10;and outer diameter of helical tube is115 mm.Combined with the structural design and parameter optimization results of hydrate gasliquid separation device,the experimental prototype structure and indoor gas-liquid separation experiment bench scheme are designed.Then,the gas-liquid separation experiment was carried out in the laboratory.On the one hand,the experiment can detect the separation performance of the helical separation device under the optimized parameters;on the other hand,the accuracy of two phase coupling analysis model can be verified by comparing the indoor experiment and numerical simulation results.The results showed that: the deviation between the numerical simulation and the laboratory experiment is small,and the gas-liquid separation calculation model can simulate the gas-liquid separation process accurately;the gas-liquid separation device with the structure parameters has effective separation performance under the working condition of the example.