井底常压控制压力钻井设计计算

井底常压控制压力钻井(MPD)技术采用专用的控压装备,将井底压力控制在合理的范围内.建立井底常压MPD关于井口回压和钻井液密度的计算模型,运用迭代求解方法进行井口回压和钻井液密度的设计计算.利用该计算模型对克拉201井进行了实例分析,3 314 m处的环空压力对比表明,常规方式下无法设计合理的钻井液密度,采用井底常压法设计可保证环空压力在压力窗口之内;窄压力窗口段的回压和钻井液密度设计结果表明,采用井底常压法设计可安全钻穿2 800 m到目的层的井段,并可减少一层套管,节约建井成本.实例计算结果表明,MPD技术既降低了钻井液密度又满足了环空压力控制的需求,能精确地维持井底压力恒定,安全钻穿窄压力窗口地层,为优化井身结构、减少套管层次提供技术基础.

Design and calculation of a MPD model with constant bottom hole pressure

Bottom hole pressure can be maintained in a reasonable range by using the managed pressure drilling (MPD) technique with the special equipment. A calculation model is established for the back pressure and drilling fluid density of constant bottom hole pressure MPD, which are calculated by iterative method. The calculation model is applied to the well Kela 201. In the comparison of the annulus pressures at 3 314 m in the well, and the conventional drilling method cannot provide the appropriate drilling fluid density, but the constant bottom hole pressure MPD technique can make the annulus pressure within the pressure window. The design result of back pressure and mud weight of the narrow pressure window illustrated that the well can drill the target zone directly by using the MPD technique. It can simplify casing program and save drilling cost. The calculation example demonstrates that this technique not only reduces mud density, but also meets the demand of annulus pressure control. Narrow pressure window can be drilled. It provides a technical basis for optimizing well profile.