斜直井段和水平井段中环空岩屑运移机理的研究

以岩屑颗粒单元为研究对象，通过分析偏心环空各区域中岩屑颗粒的主要受力，预测岩屑颗粒的运移趋势。通过数值计算，分析了在流核区和速梯区中井斜角、岩屑直径、钻井液返速等对岩屑运移的影响，以及静岩屑床面岩屑运移的基本条件及主要影响因素，对钻进中旋转钻柱能提高岩屑运移行程的机理给出了合理的解释。研究结果表明，增大钻井液返速和保持钻井中钻柱旋转是避免岩屑下滑的主要措施；在斜井段及水平井段中钻柱不旋转，环空岩屑的运移主要靠动岩屑床的作用；增大静岩屑床面液流边界层的速度梯度有助于减小静岩屑床厚度。

Transport mechanism of cuttings in annulus during deviated and horizontal drilling

A new approach was presented to predict the cuttings transport by choosing a cuttings cell as studying object and analyzing the forces acting on a particle in different areas of eccentric annulus. The effects of deviated angle of the well and paticle diameter, annular slurry velocity on cuttings transport were analyzed by numerical method. The basic conditions and the main affecting factors on the transport of cuttings on the uppermost layer of the stationary cuttings bed were described, and the mechanism of better hole cleaning by rotating pipe was interpreted reasonably. The results show that increasing the return velocity of drilling fluid and keeping drill string rotating are the measures to eliminate cuttings sllp. The cuttings transport mainly depends on the moving bed in horizontal and deviated well segments without the pipe rotating, the height of cuttings bed declines with the increase of velocity gradient of the fluid in attach-layer upon the stationary bed.