页岩气钻井岩屑运移规律仿真分析

Simulation Analysis of Cuttings Migration in Shale Gas Drilling

页岩气水平井钻井过程中岩屑在重力作用下极易在斜井段及水平段中沉积形成岩屑床,清洁难度大,进而导致井底高摩阻、高扭矩和阻卡,严重时造成卡钻、钻具断落井下安全事故。基于液固两相流理论,建立了三维井眼环空岩屑运移模型,通过控制变量法分别分析了钻杆转速、排量、岩屑粒径、偏心度、井斜角度等因素变化对环空井筒岩屑体积分数及运移轴向速度的影响规律。研究结果表明:随着转速和钻偏心度增大,岩屑体积分数降低及轴向速度增大;岩屑粒径增大,岩屑体积分数增加及轴向速度降低;随着井斜角降低,岩屑体积分数降低及轴向速度增加。可见提高转速、钻井液排量和控制钻头破坏岩屑粒径大小有利于提高井眼清洁,降低井下安全事故。

During the drilling process of shale gas horizontal well,under the influence of gravity,cuttings are easy to deposit in the inclined and horizontal sections to form cuttings bed,which is difficult to clean.It may casue prolems as high friction,high torque and jamming at the bottom of the well,and serious accidents such as sticking and drilling tool breaking down the well.Based on the theory of liquid-solid two-phase flow,a three-dimensional model of cuttings migration in annulus were established.By controlling variable method,the influence of the change of drill pipe speed,displacement,cuttings particle size,eccentricity,deviation angle and other factors on the volume fraction of cuttings in annulus wellbore and the axial velocity of cuttings migration was analyzed.The results show that the volume fraction and axial velocity of cuttings decrease with the increase of rotary speed and drilling eccentricity,the volume fraction and axial velocity of cuttings decrease with the increase of cuttings diameter,and the volume fraction and axial velocity of cuttings increase with the decrease of well inclination.It can be seen that methods as increasing rotation speed,drilling fluid displacement and controlling the size of rock debris damaged by bit can improve borehole cleaning and reduce downhole safety accidents.