斜井岩屑运移临界环空流速力学模型

Mechanics model of critical annular velocity for cuttings transportation in deviated well

岩屑在大斜度井眼中主要以翻滚形式向井口方向运移,在低斜度井眼中主要以悬浮形式被钻井液举升至地面。通过岩屑受力分析建立两种运移机理作用下的岩屑运移临界流速计算力学模型,并提出保持倾斜井眼清洁的临界环空返速计算方法。将模型计算结果与现有试验数据进行了对比验证,结果表明:临界环空流速随井斜角变化趋势的模型预测结果与试验结果吻合较好,但由于模型计算和试验中判断形成岩屑床的准则不同,环空临界流速的模型计算值较试验值偏低;对实例井的井筒清洗分析结果与现场作业情况一致,验证了该模型的可靠性。

For the wellbore with high inclination, cuttings are transported to wellhead by a rolling form, while in the wellbore with a low angle, cuttings are suspended in drilling fluid and transported to the surface by a lifting form. On the basis of dynamics analysis on cuttings under two mechanisms, two corresponding models of critical velocity were developed. Based on the two models, a calculation method was constructed for determining the critical annular velocity to maintain hole cleaning. The trend of critical annular velocity varying with inclination predicted by critical annular velocity model was validated by comparison with old experimental results, and a good accordance was obtained. However, the predicted value of critical annular velocity is slightly lower than the experimental ones because of two different criteria on cuttings bed development. Its field application indicates also a good agreement between prediction and actual situations, which validated the reliability of this model.