Transient simulation of the blowing-out process of the air pockets in vertical wellbore

For a better control of drilling flow, it is important to grasp the changing rule of well-head parameters during blowout. In this study, we develop a one-dimensional ideal transient model composed of a set of governing equations, and a numerical code is developed by Fortran based on the model. The method of characteristics is employed to transform the nonlinear coupled differential equations to ordinary ones. The simulation results indicate that the effect of well depth on the outlet velocity of wellhead is more significant than that of hydraulic diameter, fluid density and slug unit length.