大斜度井偏心环空钻柱旋转对岩屑运移的影响

Effect of Drill String Rotation in Eccentric Annulus of High Angle Deviated Well on Cuttings Movement

在钻井过程中,当液流速度小于岩屑悬浮运移速度时,岩屑容易在大斜度井段沉降并形成岩屑床,导致钻柱卡钻、高摩阻和扭矩、低机械钻速等问题。建立大斜度偏心环空三维物理模型,采用结构网格划分环空流体域,用滑移网格模拟钻柱旋转。基于欧拉固液两相流模型和Realizable k-ε紊流模型,考虑钻井液对岩屑的举升力、岩屑加速产生的虚质量力以及固液间的动量交换,模拟了钻柱旋转条件下井斜角、岩屑注入浓度、钻井液速度和黏度对岩屑运移的影响。研究表明:钻柱旋转使得岩屑床床面沿旋转方向倾斜,沿井眼呈不对称分布状态,并能够显著减小环空岩屑浓度,其变化幅度受钻井液入口流速、井斜角、钻井液黏度和岩屑注入浓度的影响,但当转速达到某一临界值后,旋转作用效果将减弱。研究结果可为采取合理措施提高岩屑运移效率提供参考。

In the course of drilling,when the flow stream velocity is lower than the suspension moving velocity of cuttings,the cuttings are easily settled in the high angle deviated well section and form cuttings bed,leading to the problems like drill string sticking,,high friction and torque and low rate of penetration. In this paper,3D physical model of high angle deviated eccentric annulus was built,structural grid was used to divide the annulus fluid domain,and sliding grid was used to simulate the drill string rotation. Based on Euler solid- fluid two- phase flow model and realizable k- ε turbulence model,after having considered the lifting power of drilling fluid to cuttings,the virtual mass force resulted from the acceleration of cuttings and the momentum exchange between solid and fluid,this paper simulated the effect of of hole angle,cuttings influx concentration,drilling fluid velocity and viscosity on the cuttings movement under the circumstances of drill string rotation. The study results showed that the rotation of drill string made the surface of cuttings bed incline along the rotation direction,forming an unsymmetrical distribution state along the wellbore,and could apparently reduce the annular cuttings concentration; the rangeability was affected by the inlet flow rate of drilling fluid,hole angle,drilling fluid viscosity and cuttings influx concentration,but when the rotation rate achieved a critical value,the effect of rotating effort would weaken. The study results can provide reference for adopting rational measures to improve the cuttings movement efficiency.