幂律流体在偏心环空中流动的Hanks稳定性参数

在水平井的钻井和固井作业中,井的环空是偏心环空,而偏心环空不同于圆管和同心环空,它是几何边界不规则的区域,从而给判定非牛顿流体在偏心环空中流动的稳定性带来了巨大的困难。利用幂律流体在偏心环空中流动的数值解,研究汉克斯(Hanks)稳定性参数,得到了如下重要规律:Hanks稳定性参数的最大值和最小值分别在偏心环空的最宽边和最窄边处,符合已有的实验观察结论;Hanks稳定性参数的最大值和最小值总是在靠近钻柱壁的位置处,即层流的失稳点总是从钻柱壁附近开始发生,然后发展到整个环空,这点对钻井和固井是极端不利的;偏心越严重,则在偏心环空的最宽边和最窄边处的最大Hanks稳定性参数相差越大,一般大于5~100倍,这充分地说明了偏心时最宽边处早已是紊流但是最窄边却仍然是层流,符合实验和工程实际情况。表明了汉克斯(Hanks)稳定性参数对水平井的钻井和固井作业中水力参数的科学设计具有重要应用价值。

Hanks Stability Parameter of Power Law Fluid Flow in Eccentric Annulus

When drilling and cementing,the annulus of the horizontal well is eccentric.Different from round tube or concentric annulus,the eccentric annulus has a irregular geometry boundary and thus it is very difficult to determine the stability of non-Newtonian flow.Hanks stability parameter was analyzed according to calculate the numerical solution of power law fluid flow in eccentric annulus and some important conclusions were obtained as follows: In the eccentric annulus,the maxim of Hanks stability parameter was obtained at the most broad side and the minimum was obtained at the most narrow side.The conclusion was coincident with conventional experimental observations.The maxim and minimum were always at the point near the drill string wall,i.e.instability point of layer flow initiated near the drill string wall and then expanded whole annulus.This instability point was extremely adverse.The more severe of excenter,the more significant difference presented between the maxim and the minimum which was more than 5-100 fold generally.That gave a clear indication that the most narrow side was still layer flow while the most broad side was turbulent flow.And that was also coincident with the experiments and the practices.It was proved by the study that the Hanks stability parameter was very helpful to hydraulics optimization of horizontal well for the drilling and cementing practice.