Design And Analysis Of Preset Full-size Restrictor

With the rapid development of China's economy,the consumption of energy has increased dramatically.Coal,oil and natural gas,as commonly used energy sources,play a very important role in the energy structure.However,coal and oil cause great pollution to the environment,while natural gas,as a highly efficient and environmentally friendly energy source,can be vigorously developed and utilized to greatly protect and improve the environment and further alleviate energy pressure.But there are two problems in the extraction and transmission of natural gas.Firstly,the pressure of the pipeline is high.Generally,the pressure of gas wells is very high.The equipment of gas production at the wellhead and gas transmission pipeline are under high pressure environment,which requires high pressure of equipment and pipeline,has potential safety hazards,and has high development cost.Secondly,hydrate is easy to form.Under high pressure environment,natural gas is easy to form hydrate,which causes pipeline blockage and seriously affects the exploitation and transmission of natural gas.Based on the principle of downhole throttling,the formation conditions of hydrate was studied,the preset restrictor of full diameter and retractable air nozzle and its supporting tools were designed,the restrictor and its key parts were calculated,the distribution model of wellbore pressure and temperature was established,and the two important parameters of downhole throttling models,the inner diameter of the nozzle and the minimum depth of penetration,are calculated.Finally,the fluid flow around the nozzle is simulated.The main research works of this paper is as follows:(1)The properties,formation mechanism,influencing factors,prevention measures and prediction methods of hydrate are described.The principle of downhole throttling and critical flow conditions of throttling are studied.The characteristics of surface throttling and downhole throttling are compared.(2)Based on the research of downhole throttling technology,a kind of the preset restrictor of full diameter and retractable air nozzle and its supporting tools are designed,and the engineering design drawing and three-dimensional model of the restrictor and its supporting tools are completed.The working process of delivery,fishing,blowing off the air nozzle and sand control cover of the preset downhole choke is described.Finally,the design and strength analysis of the main parts of the preset throttle,such as air nozzle,lock block,connector,sand control cover are completed(3)According to the principle of downhole throttling,the inflow state model of natural gas from reservoir to bottom of well,the wellbore pressure and temperature model of natural gas from bottom of well to before and after throttling to wellhead,the throttling,depressurizing and cooling model of natural gas passing through the stage of throttling device are derived,and the downhole throttling parameters are calculated.Finally,the gas well throttling model is established by using PIPESIM gas well analysis software,and the influence of throttling parameters on daily production,wellbore pressure,temperature and hydrate is analyzed(4)By using Fluent software and gas-liquid two-phase flow model,the flow state of natural gas near the gas nozzle is simulated,and the change rules of the parameters such as speed,pressure,temperature,density of natural gas near the gas nozzle are analyzed.The effects of different nozzle diameter and length on the flow field are studied to find the minimum length of the nozzle,so as to realize the standardization of the nozzle length and facilitate the design,processing and replacement of the nozzleThe preset restrictor of full diameter and retractable air nozzle designed in this paper can meet the design requirements,reduce the pressure of natural gas wellhead,reduce the pressure of wellhead equipment and surface gas transmission pipeline,remove the high-pressure safety hazards,effectively avoid hydrate formation,improve the production efficiency of gas wells,and finally solve the two problems in the production and transmission of natural gas.It can provide some reference for the safety production of gas well.