中文摘要：

控压钻井过程中，实时控制井底压力主要靠调节和控制井口回压。通过分析控压钻井中的瞬变过程，建立了各过程中的多相流计算模型，并利用有限差分法对模型进行了求解。通过仿真算例分析了采取控压钻井时井口回压随时间的变化规律，讨论了返出钻井液增量、气相渗透率、排量、钻井液密度、初始井底压差、井深和黏度等对井口回压的影响规律。结果表明：返出钻井液增量越大，井口施加的回压也越大；在返出钻井液增量一定的条件下，气相渗透率、排量、钻井液密度、初始井底压差、井深和黏度对井口回压均有影响，气相渗透率越大、排量越小、钻井液密度越小、初始并底压差越大、井越深、钻井液黏度越小，气体到达井口时需要施加的回压峰值也越大。

英文摘要：

It is mainly relied on adjusting and controlling wellhead back pressure to control bottom hole pressure in real time during managed pressure drilling（MPD）. The MPD wellhead back pressure computational model was established based on multiphase flow theory and principle of MPD, and computed using finite difference method. The variations of wellhead back pressure in MPD were analyzed by simulation examples. Factors impacting the wellhead back pressure were studied, including increment of return drilling fluid, gas phase permeability, discharge capacity, drilling fluid density,well depth,initial bottom hole differential pressure and viscosity. The simulation results showed that the larger increment of return drilling fluid, the greater wellhead back. When increment of return drilling fluid was constant,discharge capacity, drilling fluid density, and initial bottom hole differential pressure impacted wellhead back pressure significantly. The wellhead back pressure is higher with smaller discharge capacity and drilling fluid density, and greater initial bottom hole differential pressure. The effect of gas phase permeability,viscosity and well depth is small.