深水双梯度钻井井口回压实时优化与最大钻进深度预测

Real-time optimization of wellhead backpressure and prediction of maximum drilling depth in deepwater dual-gradient drilling

为实现更大的钻进深度,本文建立了井口回压实时调节优化模型,模型通过优化实时钻进过程中的井口回压,达到实时优化井筒压力剖面的效果,从而实现更大的钻进深度。通过实例对比了回压恒定和回压实时调节两种条件下的优化结果,并分析了不同钻井参数对回压优化结果和最大钻进深度的影响,研究结果表明:与回压恒定条件下的最优化结果相比,井口回压实时调节优化模型优化了钻进过程中的井口回压,使井筒压力剖面可以更好地适应地层窄安全压力窗口,实现了更大的钻进深度;利用井口回压实时调节优化模型后,可进一步减小随钻井底压差,从而有利于储层保护和钻井提速;相比于空心球注入体积分数和排量,最大钻进深度受分离器与钻头间距和纯钻井液密度的影响更为明显。

In order to achieve greater drilling depth,a real-time adjustment optimization model of wellhead backpressure was established.The model achieves a real-time and optimal wellbore pressure profile by optimizing wellbore back pressure during the real-time drilling process.Then a greater drilling depth can be achieved.The optimization results under two conditions;constant backpressure and real-time adjustment of backpressure,were compared by examples,and the influence of different drilling parameters on the optimization results of backpressure and maximum drilling depth under real-time adjustment of backpressure was analyzed.Research results show that compared with the optimization results under the condition of constant backpressure,the real-time adjustment model of wellhead backpressure can optimize the wellhead backpressure in the drilling process so that the wellbore pressure profile can better adapt to narrow safe pressure margins,which can achieve greater drilling depth.Moreover,the real-time adjustment optimization model of wellhead backpressure can further reduce the bottom-hole pressure difference,which is conducive to reservoir protection and increase of ROP.Compared with the volume fraction of hollow spheres and displacement,the maximum drilling depth is more affected by the distance between the separator and bit and the density of pure drilling fluid.