偏心环空中Robertson-Stiff流体的波动压力计算模型

Computational Model of Fluctuating Pressure of Robertson-Stiff Fluid in Eccentric Annulus

用窄槽流动模型模拟流体在偏心环空中的流动,结合流体流动的控制方程和Robertson-Stiff流体的流变方程,建立了稳态层流条件下的波动压力计算模型。利用自适应的辛普森积分法对其进行了数值求解,并对波动压力的影响因素进行了分析。结果表明,建立的Robertson-Stiff流体在偏心环空中的波动压力计算模型预测结果准确,采用的数值求解方法精度高,与已有的偏心环空波动压力计算模型结果对比误差在10%以内;在井眼环空处于完全偏心的情况下,波动压力梯度降低为同心环空的50%左右;当流性指数和管柱井眼尺寸比较大时,要对起下钻的速度严格限制。

The flow of fluid in eccentric annulus is simulated using narrow slot flow model,the fluid flow fluctuation pressure model in eccentric annulus under steady laminar flow condition is establish based on the control equations of fluid flow and the rheology equation of Robertson- Stiff fluid. The numerical solution of the fluctuation pressure model is obtained using adaptive Simpson integral method,and the influence factors of the fluctuation pressure are analyzed. It is shown that the computational model of the Robertson- Stiff fluid flow fluctuation pressure in eccentric annulus is accurate,and the adopted numerical method is of high accuracy. Compared with the calculation results of existing models,the prediction error of the model is lower than 10%. The fluctuating pressure gradient in total eccentric annulus is about 50% of that in concentric annulus. The tripping speed should be strictly limited when the flow index and the size ratio of string to hole are relatively large.