ABSTRACT

In this study, a numerical model of a partial wellbore is developed by coupling computational fluid dynamics (CFD) with the discrete element method (DEM) in order to simulate the operation of a double-circulation system (DCS) in coalbed methane (CBM) well drilling, which is a novel technique used for cuttings transport. The values of the flow field are computed by a fluid solver and the motions of the particle phase are calculated by the DEM, for which an additional multi-sphere particle model is integrated. After verification of the model, the analysis centers on the working mechanism, the DCS parameters, and optimization of the angle θ of the injection nozzles, which is the most critical parameter affecting the efficiency of the DCS. Simulations reveal the working details of the DCS and prove its applicability to cuttings transport, especially in the curved and horizontal parts of the well. The effects of viscosity and particle size are investigated, and a low-viscosity drilling fluid is recommended. The optimal range for θ is obtained as 30° to 50°. This work provides a reference for the engineering application of DCSs, and by feedback from drilling sites the reliability of the results can be verified.

摘要

在这项研究中，通过将计算流体动力学（CFD）与离散元方法（DEM）耦合，建立了部分井眼的数值模型，以模拟煤层气（CBM）中双循环系统（DCS）的运行钻井，这是一种用于岩屑运输的新技术。流场的值由流体求解器计算，粒子相的运动由DEM计算，为此，集成了一个附加的多球粒子模型。在模型验证之后，分析集中于工作机理，DCS参数和角度θ的优化。这是影响DCS效率的最关键参数。仿真揭示了DCS的工作细节，并证明了DCS在钻屑运输中的适用性，尤其是在井的弯曲和水平部分。研究了粘度和粒度的影响，并建议使用低粘度钻井液。θ的最佳范围为30°至50°。这项工作为DCS的工程应用提供了参考，通过钻井现场的反馈，可以验证结果的可靠性。