考虑滑移效应的高密度水基钻井液流变特性

Rheological behaviors of the high-density water-based drilling fluid in consideration of slip effect

壁面滑移效应会影响高密度水基钻井液流变测量的准确性。基于同轴圆筒旋转黏度计的测量原理,从合理假设壁面滑移现象出发,提出了钻井液流变测量中壁面滑移效应的检测与校正方法,得出了有滑移效应的高密度水基钻井液真实流变特性的确定方法。采用两个不同环形间隙尺寸的圆筒测量系统,开展了考虑滑移效应的高密度水基钻井液流变测量实验,并分析了高密度水基钻井液流变特性与滑移特性。理论与实验研究表明,高密度水基钻井液流动时易出现壁面滑移现象,应消除滑移效应对流变测量的影响;无黏土高密度水基钻井液流变特性符合宾汉模式,其真实流变参数与不考虑滑移效应的表观流变参数存在显著差异;滑移速度与壁面剪切应力呈直线关系,且发生滑移的临界剪切应力很小。

A wall slip effect will affect the accuracy of rheological measurements of the high-density water-based drilling fluid.Based on the rheological measurement principle of a coaxial cylinder rotational viscometer,the present paper,according to a reasonable assumption of a wall-slip phenomenon,proposed a detection and correction method for the wall slip effect occurring in rheological measurements of the high-density water-based drilling fluid,and obtained an approach for determining actual rheological behaviors of the high-density drilling fluid with the presence of a wall slip effect.Rheological experiments considering a wall slip effect of the high-density drilling fluid were carried out by using both the original and the modified cylinder measurement systems of a six-speed rotational viscometer in different annular space size,and rheological properties and slip characteristics of the high-density water-based drilling fluid were analyzed.These theoretical and experimental studies suggested that a wall slip phenomenon occurred readily as the high-density water-based drilling fluid flowed,and its effect on rheological measurements should be eliminated.Rheological behaviors of the high-density water-based clay-free drilling fluid could be described with the Bingham model,and there existed a significant difference between actual rheological parameters and apparent ones that do not consider the presence of a wall slip effect.The slip velocity showed a linear correlation with the wall shear stress,and a critical shear stress for slide occurrence was quite small.