控压钻井泥浆帽设计方法研究

Research on Mud Cap Design of Managed Pressure Drilling

控压钻井可以较为精确地控制整个井筒环空压力剖面,能有效解决钻井过程中出现的井涌、井漏、井塌、卡钻等多种井下故障,但在起钻之后不能仅靠调整井口回压平衡地层压力,需要注入高密度泥浆帽。为满足控压钻井起钻泥浆帽注入过程中井底压力恒定,必须设计出合理的泥浆帽密度和高度。为此,基于起下钻过程中的井筒压力控制原理和控压钻井起下钻工艺,建立了控压钻井泥浆帽密度和高度的计算模型,提出了一种维持控压钻井起钻过程井底压力恒定的泥浆帽密度和高度的设计方法,并以塔里木油田某井为例评价分析了泥浆帽密度和高度对井口回压控制的影响,并指出设计泥浆帽密度和高度时应综合考虑各种因素,在泥浆帽注入和驱替过程中实时控制井口压力,以维持井底压力恒定。

The MPD can precisely control the hydraulic pressure profile throughout wellbore annular. It can effectively solve a variety of complicated situations such as well kick, lost circulation, well collapse, pipe-sticking and others,while the high density mud cap must be filled in because only adjusting the wellhead back pressure can not balance the reservoir pressure after tripping out. In order to keep constant downhole pressure during tripping,densi- ty and height of mud cap must be reasonably designed. For this reason, a model for calculating and analyzing the pa- rameter of filling in mud cap in MPD is constructed based on borehole hydraulic pressure controlling theory and MPD tripping technology. A MPD design measure for keeping a constant downhole pressure during tripping is pro- posed. Using wells of Tarim Oilfield as examples,influence of density and height of mud cap on wellhead backpres- sure controlling was analyzed. The factors, which should be considered in designing density and height of mud cap, were pointed out, and the wellhead pressure should be real-time controlled during injection and displacing for mud cap in order to keep constant downhole pressure.