双梯度钻井关键工具及井筒压力动态变化规律

为了解决注空心球双梯度钻井中分离器的分离效率不高的问题,对井筒压力的动态变化规律进行了研究。设计了能够对空心球实现高效分离的过滤分离器,并通过数值模拟与室内试验进行了验证,过滤分离器最高分离效率可以达到98.5%。建立了空心球分离进入环空时所产生的波动压力数学模型,结合该模型并考虑空心球的体积分数、钻井液排量、分离器位置以及机械钻速的动态变化,进一步建立了井筒压力动态变化的数学模型。基于钻井数据进行了算例计算和影响因素分析。研究结果表明:在分离器位置处,井筒压力分布存在明显拐点,而环空中钻井液密度分布存在突变;通过动态调节空心球体积分数和分离器位置等关键参数可以灵活调节环空中轻质钻井液的密度大小、液柱长度以及随钻井底压力的大小,从而实现对随钻井底压力的实时预测。研究结果可以为窄压力窗口条件下的安全钻进提供理论基础与技术支撑。

Key Tools and Dynamic Variation of Wellbore Pressure in Dual-gradient Drilling

In order to solve the problem of low separation efficiency of separator in hollow sphere injected dual-gradient drilling, the dynamic variation of wellbore pressure was studied. A filter separator capable of efficiently separating hollow spheres was designed and verified by numerical simulation and laboratory test, and the highest separation efficiency can reach 98.5%. The mathematical model of fluctuating pressure generated by the separation of hollow sphere into the annulus was built;combined with the model and considering the dynamic variation of the volume fraction of hollow sphere, the drilling fluid displacement, the separator position and the rate of penetration, the mathematical model of dynamic variation of wellbore pressure was further built. Based on drilling data, case calculation and influential factor analysis were carried out. The research results show that the wellbore pressure distribution has an obvious inflection point at the position of the separator, while the distribution of drilling fluid density in the annulus has an abrupt change;by means of dynamically adjusting the key parameters such as the volume fraction of the hollow sphere and the position of the separator, the density of unweighted drilling fluid in the annulus, the length of the liquid column and the bottom pressure while drilling can be flexibly adjusted, and thus realize the real-time prediction of the bottomhole pressure while drilling. The research results provide theoretical basis and technical support for safe drilling under narrow pressure window conditions.