It is mainly relied on controlling the height of mud cap by adjusting mud pump to control bottom hole pressure in controlled mud cap drilling. The annular multiphase flow computational model was established based on multiphase flow theory and mud cap controlled drilling fundamental principle and then the model was computed by using finite difference approach. Through examples of simulation calculation, the effect of gas invasion time, discharge capacity, drilling fluid density, initial differential bottom hole pressure, gas phase permeability, well depth and drilling fluid viscosity on the height of mud cap were discussed. The result shows that the longer gas invasion time, the smaller discharge capacity, the smaller drilling fluid density, the greater initial differential pressure, the bigger gas phase permeability and the smaller drilling fluid viscosity, the height of mud cap which was needed to be adjusted is bigger. The peak value of the height of mud cap turns up much later with the deeper well when other conditions were unchangeable. The result provides the basis for adjusting the height of mud cap reasonably in controlled mud cap drilling.%在控制泥浆帽钻井过程中,主要通过泥浆泵调节泥浆帽的高度实现对井底压力的控制.以多相流理论和控制泥浆帽钻井基本原理为基础,建立了环空多相流计算模型,并利用有限差分法对模型进行了求解.通过仿真算例,讨论了气侵时间、排量、钻井液密度、初始井底压差、气相渗透率、井深、钻井液黏度等对泥浆帽高度的影响规律,结果表明:气侵时间越长、排量越小、钻井液密度越小、初始压差越大、气相渗透率越大、钻井液黏度越小,需要调整的泥浆帽高度越大；在其他条件相同的情况下,井越深,泥浆帽高度的峰值出现得越晚.研究结果为控制泥浆帽钻井过程中泥浆帽高度的合理调节提供依据.
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