考虑气体悬浮的关井井筒压力计算方法

A wellbore pressure calculation method considering gas entrapment in wellbore shut-in condition

钻井过程中发生气侵后,侵入井筒内的气体以气泡形式分布在井筒中。当气泡浮力不足以克服因钻井液屈服应力产生的阻力时,气泡将会悬浮在钻井液中。通过试验研究不同钻井液屈服应力、气泡几何尺寸下气体极限悬浮体积分数,根据试验结果拟合气泡极限悬浮体积分数预测模型,建立关井条件下考虑气体悬浮影响的井筒压力计算方法。结果表明:在屈服应力为0~22.4 Pa时,模型预测结果与试验结果相比误差小于7%;与现场实测数据对比,套压峰值误差为1.51%,关井后同一时刻套压值误差小于3.5%;模型可用于气侵关井后有气体悬浮时井筒压力精确计算。

After gas intrusion occurs during drilling,the invading gas is distributed in the wellbore in the form of bubbles.When the buoyancy of the bubble is insufficient to overcome the resistance caused by the yield stress,the bubble will be entrapped in the drilling fluid.The ultimate gas entrapment concentration under different yield stress and bubble geometry was carried out experimentally.By fitting the experimental results,a prediction model of ultimate gas entrapment concentration was obtained,and a wellbore pressure calculation method by considering the effect of gas entrapment under shut-in conditions was established.It is found that the error between model prediction and experimental results is less than 7%when the yield stress ranges from 0 to 22.4 Pa.Compared with the field data,the relative error of the calculated peak casing pressure error is 1.51%and of the casing pressure on the same time after shut-in is not exceed 3.5%.The wellbore pressure after shut-in can be accurately calculated by the established model.