环空螺旋流场中岩屑运动条件的分析

ANALYSIS OF CUTTINGS TRANSPORT ACTION IN THE HELICAL FLoW OF ECCENTKIC ANNULUS

由岩屑床面的几何特征及颗粒的受力特性分析得出，床面颗粒以滚动的方式起动，根据这一起动机理，从分析岩屑颗粒在螺旋流场作用力、重力及颗粒间的相互作用等条件下的力平衡出发．并考虑颗粒的薄膜水及粘结力的作用，建立起定向斜井内环空螺旋流作用下岩屑运移的临界水力条件．根据此水力条件，从理论上说明了斜井内岩屑运移最困难、最危险的井段在井斜角３０°＜θ＜５５°～７０°内，它由岩屑床面形态即岩屑大小及形状等因素决定，而与流场条件无关．这一结论与实验中观察到的规律一致．

According to the characteristics of bed surface geometry of cuttings and forcesacting on the cuttings,it is pointed out that the starting motion of particles on cuttings bed surfaces is in the form of rolling. Based on this mechanism,the critical condition of motionin the helical flow of directionally deviated-well annulus is derived from analysis the forces. such as hydraulic force,gravity,collision and cohension of film water.The theoretical analyses indicate that the worst well section for cutting cleaning is in the position of deviatedangle of 30°<θ<55°～70°。The worst section can be determined with the bed surfaceproperties of cuttings,such as cuttings sizes and shapes,etc,Flow field condition has no effecton it.This conclusion is confirmed on many experiments.