中文摘要：

合理的钻井液帽高度和密度对于维持起下钻过程中井底压力恒定至关重要。鉴于此,根据控压钻井钻井液帽工艺流程及钻井液帽设计原则,结合起下钻井筒瞬态波动压力计算模型,建立了控压钻井起下钻钻井液帽优化设计模型。以塔中某口水平井为例进行数值模拟计算,计算结果表明：随钻井液帽高度的增加,井底波动压力最大值呈线性增加;结合约束条件给出钻井液帽高度和密度的优化区间分别为1 265-1 930 m、1.34-1.48 g/cm^3,推荐采用钻井液帽优化区间的中间值（高度1 598 m,密度1.39 g/cm^3,波动压力极大值为0.84 MPa）作为现场作业参数。研究结果可为控压钻井钻井液帽作业参数的选取提供理论指导。

英文摘要：

Reasonable mud cap height and density are of vital importance on maintaining bottom hole pressure in tripping process. In this paper, an optimization design model is established for MPD tripping mud cap by using transient surge pressure calculation model of borehole based on process flow and design principle of MPD tripping mud cap. A horizontal well in Tazhong is taken as an example for numerical simulation and calculation. The results indicate that maximum bottom hole surge pressure rises linearly with increase of mud cap height ; optimized range of mud cap height and density is respectively 1 265 - 1 930 m and 1. 34 - 1. 48 g/cm^3 based on constraint conditions. It is suggested to take the median of mud cap optimized range （1 598 m height, 1. 39 g/cm^3 density and 0. 84 MPa maximum surge pressure） as the field operation parameter. The result can provide theoretical guides on selection of operation parameters for mud cap of MPD tripping.