CML双梯度钻井井筒温压场与泥浆帽优化

Optimization of mud cap and the field of wellbore temperature and pressure in CML dual gradient drilling

可控泥浆液面(CML)双梯度钻井作为一种应用于深水环境的控压钻井新方法,掌握其井筒流动规律对于控压钻井工艺设计具有重要意义,目前在该方面缺乏系统性的研究。为了探究CML双梯度钻井瞬态井筒温度与压力的分布规律,同时对窄压力窗口条件下的泥浆帽高度进行优化设计,根据CML双梯度钻井的工艺特点与钻井液循环流动特征,建立了井筒温度场和压力场物理模型以及瞬态井筒温压耦合场数学模型,利用有限差分和循环迭代方法对模型进行离散和求解。结果表明,钻井液循环过程中井筒内存在6个不同的传热区域,泥浆帽段环空内钻井液不参与对流换热,返回管线内的钻井液温度分布与海水温度分布相似;水下泵出口压力等于泥浆帽静液柱压力与泵压之和,随着泥浆帽高度增大,水下泵的泵压呈递减趋势;在给定压力窗口条件下,获得了钻井循环和停泵时的最优泥浆帽高度。该研究可以为CML双梯度钻井技术的理论研究与控压钻井工艺设计提供一定的参考。

Controlled mud level(CML)dual gradient drilling is a new method of pressure control drilling applied in deepwater environments.Mastering the wellbore flow pattern is crucial for the design of pressure control drilling technology,and there is currently a lack of systematic research in this area.In order to explore the distribution law of transient wellbore temperature and pressure and optimize the design of mud cap height under narrow pressure window conditions for CML dual gradient drilling.Based on the process characteristics of CML dual gradient drilling and the circulating flow characteristics of drilling fluid,physi-cal models of wellbore temperature and pressure fields,as well as mathematical models of the coupled transient wellbore temper-ature pressure fields have been established.Finite difference method and cyclic iteration method are used to solve the model by discretization.The results indicate that there are six different heat transfer zones in the wellbore during the drilling fluid circula-tion process.The drilling fluid in the mud cap annulus does not participate in convective heat transfer,and the temperature distri-bution of the drilling fluid in the return pipe is similar to that of seawater.The outlet pressure of the underwater pump is equal to the sum of the static liquid column pressure of the mud cap and the pump pressure.As the height of the mud cap increases,the pump pressure of the underwater pump shows a downward trend.Under the given pressure window conditions,the optimal mud cap height during drilling circulation and pump shutdown was obtained.This study can provide a certain reference for the theo-retical research and pressure control drilling process design of CML dual gradient drilling technology.