Simulation Of The Overflow Process Of High Temperature And High Pressure Gas Well

The downhole environment of high temperature and high pressure gas well is generally complex,and the safety density window is narrow,so we need to accurately control the real-time change of downhole pressure.Once gas invasion occurs,the miscible density,the flow status and the pressure of fluid that flows into the wellbore are constantly changing during the process of flows out of the wellhead.It has a fast flow speed when reaches the wellhead,and it is difficult to control.The gas invasion rate and the bottom hole pressure interact with each other in the overflow process.However,most of the current multiphase flow models of the wellbore are built based on the hypothesis that the velocity of gas invasion is constant.It is inaccurate to reflect the whole process of the occurrence and development of the overflow,and there is a big error compared with the actual situation.It is urgent to research the new flow model of the multiphase flow in the wellbore so as to better understand the mechanism of the overflow of the high pressure gas well.In this paper,based on the theory of heat transfer and thermodynamics,the heat transfer process of formation and wellbore was studied,and the transient temperature field prediction model in the process of drilling was established,and the influence of output volume and cycle time on the temperature distribution of the wellbore was calculated.Based on the principle of conservation of mass and momentum,the continuity equation and momentum equation of gas-liquid two phase flow were established.Considering the coupling relationship between the wellbore pressure and the gas invasion,the multiphase flow model of the wellbore was established by combining the status changes of the gas-liquid two phase flow during the move process.The finite-difference method was used to solve the equations and front of multiphase flow.was tracked.The calculation results of model combined the coupling between wellbore pressure and gas invasion rate was compared with that of ordinary model to show the necessity of coupling.The simulation results show that the highest point of wellbore temperature is not at the bottom of the well,but a depth near the bottom of the well.The circulating temperature of the bottom hole decreases with the increase of the circulating time.In the process of overflow development,the rate of gas invasion increases with the increase of circulation time,and the velocity of annular mixed phase of drilling fluid increases continuously during the process that upward to wellhead.When the gas was circulated to the position near the wellhead,the velocity of annular mixed phase of drilling fluid increases rapidly,and the increment of the mud pool increases.The calculated results of the velocity of transient gas invasion and constant gas invasion are quite different.Even if the thickness of reservoir is drilled even increases slightly,the increased range of the invasion of gas invasion is obvious.During drilling process,we should control the drilling rate when we encounter high permeability or high gas bearing stratum when it is difficult to accurately predict the formation pressure,which will provide enough time for monitor and control overflowThe multiphase flow model of the wellbore in this paper can be used to predict the flow law of multiphase flow in the wellbore during the overflow process.And it is aimed to provide a theoretical basis for the establishment of a reasonable overflow monitoring and control scheme in scene.