Numerical Simulation Study On The Throttle Effect Of Wellbore Double Throttling

In the process of oil and gas exploitation,due to the existence of a special area of "high pressure and low temperature",hydrates are easily formed in the wellbore to adhere to the inner wall of the tubing,causing the tubing to freeze and block,which seriously affects the efficiency of oil and gas exploitation.Therefore,based on the theory of fluid mechanics and heat transfer,this paper conducts numerical simulation studies on the throttling process in critical and subcritical flow states respectively,reveals the temperature and pressure change laws under different working conditions before and after throttling,establishes a temperature and pressure prediction model before and after throttling,and proposes a double throttling design method.The results show that:(1)In the critical flow throttling process,the pressure ratio after throttling and pre-throttle pressure is less than the critical pressure ratio,and the downstream pressure wave of the throttling will not affect the upstream pressure through the throttling nozzle,and the output of the critical throttling process is related to the pre-throttle pressure,which has nothing to do with the post-throttling pressure,and the influencing factors of the mouth flow model mainly include the pressure before the inlet,the gas-liquid ratio and the diameter of the nozzle.(2)In the process of subcritical throttling,the pressure ratio after throttling to the pressure before throttling is greater than the critical pressure ratio,and the downstream pressure fluctuations of throttling cross the throttling nozzle,which affects the upstream pressure fluctuations,and the pressure prediction model of the subcritical throttling process is not only related to the pre-throttle pressure,but also related to the postthrottle pressure,which is quite different from the critical flow process model.(3)The design of the double throttling device combines the two independent systems of downhole throttling and wellhead throttling through the pressure and temperature model of the wellbore,and synthesizes the prediction model of hydrate generation to obtain a double throttle with the control of hydrate generation.This paper provides theoretical guidance for solving the problem of hydrate freezing and plugging and improving the efficiency of wellbore mining.