为解决深水窄压力窗口安全钻井问题,设计了一种基于井下分离的新型深水双梯度钻井方式,通过室内实验验证了井下分离的有效性和实现井筒双梯度的可行性,对钻进过程中的动态井筒压力进行计算,并针对该钻井方式建立了钻井参数（包括分离器位置、分离效率、注入体积分数、钻井液密度、井口回压、排量）优化模型。通过实例分析了不同控制参数条件下及不同窄安全压力窗口下的钻井参数优化问题,结果表明井筒压力剖面得到优化,可适应深水窄压力窗口,实现更大钻进深度;利用最优化模型,可以获得更小的钻井井底压差,从而提高钻速,同时保护储集层;优化过程中始终保证动态变化的井筒压力在安全压力窗口内,可有效避免因压力不平衡导致的井下复杂情况。图8表4参18
To ensure safe drilling with narrow pressure margins in deepwater, a new deepwater dual-gradient drilling method based on downhole separation was designed. A laboratory experiment was conducted to verify the effectiveness of downhole separation and the feasibility of realizing dual-gradient in wellbore. The calculation of dynamic wellbore pressure during drilling was conducted. Then, an optimization model for drilling parameters was established for this drilling method, including separator position, separation efficiency, injection volume fraction, density of drilling fluid, wellhead back pressure and displacement. The optimization of drilling parameters under different control parameters and different narrow safe pressure margins is analyzed by case study. The optimization results indicate that the wellbore pressure profile can be optimized to adapt to the narrow pressure margins and achieve greater drilling depth. By using the optimization model, a smaller bottom-hole pressure difference can be obtained, which can increase the rate of penetration (ROP) and protect reservoirs. The dynamic wellbore pressure has been kept within safe pressure margins during optimization process, effectively avoiding the complicated underground situations caused by improper wellbore pressure.
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