Coupling Analysis Of Wellbore Temperature And Pressure And Optimization Design Of Downhole Throttling Tool

Natural gas hydrate is easy to appear during the development of natural gas wells,which has a great impact on the production efficiency and scientific management of gas wells.Downhole throttling technology can be used because conventional surface throttling processes require heating and insulation devices,which will increase the economic cost and the risk at the wellhead.The throttle is installed in the wellbore at an appropriate depth to cool and reduce pressure on the airflow.Meanwhile,the formation heat is used to improve the airflow temperature to ensure that the gas temperature after throttling is higher than the hydrate formation temperature under the pressure condition.Based on the analysis of downhole throttling principle,based on the law of energy,mass and momentum conservation,combined with the radial heat transfer principle of the wellbore,and considering the interaction between fluid physical parameters and wellbore temperature and pressure,as well as the temperature and pressure coupling effect,the temperature and pressure coupling prediction model of the gas well is constructed.The model was solved by the fourth-order runge-kutta method and the MATLAB program was developed to obtain the distribution diagram of gas well temperature and pressure with well depth.Taking the depth of the throttle as the node,the gas well was calculated in sections according to the throttle temperature drop and pressure drop mathematical model,and the gas well parameter variation diagram was obtained under the throttling condition,and the influence of gas relative density and gas well production on temperature and pressure was analyzed.The main process parameters of the throttle are determined,including the reasonable depth of the throttle and the diameter of the nozzle,etc.By using the established model and program,the distribution of the fluid parameters along the well depth can be obtained.Considering that the fluid flow pattern around the throttle nozzle is very complex,and the sudden change in the diameter of the nozzle will cause the stable laminar flow to become turbulent,the fluid flow speed is accelerated,and the vortex is easy to be generated.Complex flow states can be described by two-dimensional method.With the help of Fluent software,after determining reasonable boundary conditions and corresponding parameters,numerical simulation was carried out on the throttle nozzle grid model to obtain the distribution of airflow velocity,pressure,temperature and density.In order to simplify the design and processing of the nozzle,the flow field simulation of the size structure of a total of 15 groups of throttling nozzles was carried out to select the most suitable size.