幂律流体偏心环空流动中的波动压力修正模型

摘要

During drilling process,annular flow in wellbore was usually eccentric annular flow of power-law fluid. However,Burkhardt's formula is widely used in the field only worked for concentric annular flow, where there would be a large error when it was applied to calculate surge pressure in eccentric annular flow. In the paper, the effect of annular ratio and eccentricity on surge pressure in eccentric annular flow of power-law fluid was analyzed in the paper through CFD calculation. And the results showed that surge pressure decreased with the increase of eccentricity when annular ratio was large;but it increased first and then decreased with the increase of eccentricity;numerical fitting method was used to set up the functions of eccentricity and annular ratio referred to constant coefficient and mud cohesion coefficient in Burkhardt's formula,which extended the application scope of Burkhardt's formula where it can be used to calculate the surge pressure in eccentric annular flow of power-law fluid. In the end, the extended formula was checked with data in reference paper,and the error was less than 9%.%在石油钻井过程中,井眼环空中的流动多为幂律流体偏心环空流动.Burkhardt公式仅适用于同心环空流动,用来计算偏心环空流动中的波动压力时存在较大误差.通过CFD数值计算,分析了环空比和偏心度对幂律流体偏心环空中波动压力的影响.结果表明:在大环空比的情况下,波动压力随偏心度增大而减小；在小环空比时波动压力随着偏心度增大而出现先增大后减小的趋势.建立了Burkhardt公式中的常系数和泥浆粘附系数与环空比和偏心度之间的函数关系,从而扩展了Burkhardt公式的适用范围,使之可以计算幂律流体偏心环空紊流流动的波动压力.将扩展型Burkhardt公式的计算结果与文献中的数据进行了对比,误差＜9％.