气体携岩对钻杆接头冲蚀规律研究

Study on the Erosion Law of Gas with Cuttings Against Tool Joint

针对气体钻井钻杆接头冲蚀严重易导致钻杆快速失效的问题,基于两相流计算流体动力学有限元法建立了气体携岩冲蚀18°斜坡钻杆的CFD仿真模型。根据此模型,系统地研究了钻杆居中、钻杆不同偏心程度、不同注气量以及不同钻速对岩屑颗粒冲蚀钻杆接头、岩屑颗粒运动轨迹和浓度分布以及环空气流速的影响。结果表明:(1)钻杆居中时,冲蚀速度对称分布,接头冲蚀比钻杆本体冲蚀严重,迎风坡面顶部附近出现最大冲蚀速度。同时,得到了接头最大冲蚀速度随岩屑质量流量及携岩速度的定量关系;(2)钻杆偏心时的最大冲蚀速度和接头宽流道环空一侧的冲蚀速度比钻杆居中时大,且偏心程度越高,接头环空窄流道一侧冲蚀区域越密集。钻杆偏心程度在30%～70%时,最大冲蚀速度由钻杆接头转移至钻杆本体。接头最大冲蚀速度分别在钻杆偏心0～30%、50%～70%和80%～90%时随携岩速度增加而增加,但在钻杆偏心30%～50%和70%～80%时最大冲蚀速度随接头环空宽流道岩屑浓度减小而减小。研究结果为预防钻杆接头冲蚀失效提供了理论依据,并在现场得到了应用。

Severe erosion against the tool joint always leads to rapid failure of the drill pipe in gas drilling. In order to understand the mechanism of this problem,we established the CFD model of the erosion of gas with cuttings against the drill pipe with 18＆#176; slope based on two phase fluid theory. According to this model,systematical studies have been made about the effects of different eccentricity,injection volume of gas,and drill rate on the erosion rate against the tool joint,and on the trajectory and distribution of cuttings and gas velocity. The results show that：at the first,when the drill pipe is in the cylindrical center of borehole,the distribution of erosion rate is symmetrical,the erosion against tool joint is more severe than against the drill pipes’ body and the maximum erosion rate is near the windward slope top. Meanwhile,the quantitative relationship between cuttings’ mass flow rate,gas velocity and the maximum erosion rate has been worked out. And then,the maximum erosion rate against the drill pipe and the erosion rate against the tool joint on one side of the wide flowpath are more severe when the drill pipe is eccentric. The maximum erosion is transferred from the joint to the drill pipes’ body when the drill pipe eccentricity from 30%to 70%. The maximum erosion rate against the tool joint increased with the increase of gas velocity when drill pipe eccentricity was at 0～30%,50%～70%and 80%～90%,respectively. But the maximum erosion rate against the tool joint decreased with the decrease of cutting concentration in wide flowpath when drill pipe eccentricity was at 30%～50%and 70%～80%,respectively. All the results from these studies provide the theoretical support for preventing failure of the tool joint and were applied in some oilfields.