Numerical simulation of wellbore gas-liquid phase transition based on Lattice Boltzmann method

Whenever gas kick occurs, gas flows in mixture with the flowing drilling fluid or migrate upwardly when drilling fluid is suspended. When wellbore temperature and pressure are higher than the critical temperature and pressure of natural gas, natural gas is in a supercritical state. In the process of gas migration along the wellbore, gas volume will gradually increase due to the decrease of wellbore temperature and pressure. At the critical point, phase behavior changes and gas volume increases very rapidly, which can bring great harm to well control; what is worse, it may lead to well blow out. Therefore, it is of great significance to analyse the effects of phase change characteristics of the supercritical fluid on well control safety. Due to the huge advantages and strong adaptability of Lattice Boltzmann method (LBM) to solve gas-liquid two-phase flow problem with complicated and changeable phase interface, wellbore gas-liquid phase transition based on inter-particle interaction of LBM method is researched in this paper. Simulation results show that different initial densities of mixed fluid have significant influence on gas and liquid phase distribution after phase transition. Continuous gas is formed in phase change position of a wellbore when initial density of mixed fluid is less than the critical density. And gas change in phase behaviour migrates along the wellbore as bubbles when initial density of mixed fluid is greater. Research results not only improve the understanding of gas-liquid phase transition mechanism, but also can provide some valuable attempts to promote the application of LBM method in wellbore gasliquid two-phase flow.