气体钻水平井钻杆偏心对环空岩屑运移规律的影响

Effect of Drill Pipe Eccentricity to Annulus Cuttings Migration Law in Gas Drilling Horizontal Wells

气体钻水平井段,由于自身重力,钻杆倾向于下井壁,形成偏心环空,使得下环空岩屑运移困难,通过研究偏心环空正常携岩和岩屑床岩屑的运移规律对气体钻水平井井眼净化具有重要意义。针对钻杆偏心对气体钻水平井环空岩屑运移规律的影响问题,基于气固两相流理论,利用可视化实验并结合计算流体动力学(CFD)数值模拟方法对其进行了研究。从环空气体速度分布、岩屑速度分布和岩屑相对体积分数分布等方面分析了正常循环和下井壁沉积20 mm岩屑床两种工况,钻杆偏心对环空岩屑运移规律的影响。实验现象和数值模拟结果表明:正常循环时,随着偏心度不断增大,下环空气体和岩屑速度逐渐减小,气体携带岩屑的能力降低;当下井壁沉积20 mm岩屑床时,随着偏心度的增大,气流对岩屑床的扰动能力降低,使得下环空岩屑相对体积分数明显增大,岩屑床的最高剩余厚度逐渐增大。

The horizontal section of gas drilling,drill pipe tends to lower wall for gravity,forming an eccentric annulus,so that cuttings migration difficulties in the lower annular,researching normal cuttings carrying and the cuttings migration law of cuttings bed in the eccentric annulus are of great importance in wellbore cleaning for gas drilling horizontal wells. For the effect of drill pipe eccentricity to annulus cuttings migration law in gas drilling horizontal wells,based on gas-solid flow theory,a study was conducted by a visualization experiments and combined with computational fluid dynamics（ CFD） numerical simulation method. The effect of drill pipe eccentricity to annulus cuttings migration law in the drilling conditions of normal circulation and 20 mm cuttings deposition in lower wall were analyzed,from gas velocity distribution,cuttings velocity distribution,relative volume fraction distribution of cuttings in annulus and other aspects. Experimental phenomena and numerical simulation results show： in the drilling conditions of normal circulation,with increasing of the drill pipe eccentricity,decreasing of gas velocity and cuttings velocity in lower annulus,cuttings carrying capacity of gas is also decreased; 20 mm cuttings deposition in lower wall,with increasing of the drill pipe eccentricity,airflow disturbance ability of cuttings bed is decreased,so that the relative volume fraction of cuttings increased obviously in lower annular,gradually increasing the thickness of the remaining cuttings bed.