摘要
脆性泥页岩在钻井过程中受到钻头机械碰撞等容易造成井壁部分崩落,井眼形状偏离理想的圆形,按照圆形井眼研究地层坍塌规律会带来一定误差。为此,将真实井眼近似为椭圆形状,分析得到井壁应力分布模型,利用"弹性-应变软化-塑性"模型预测井壁坍塌压力,对影响脆性泥页岩直井井壁坍塌失稳因素进行敏感性分析,并利用有限元软件建模分析椭圆形井眼的塑性损伤破坏特性。研究结果表明:与常规圆形井眼相比,椭圆形井眼坍塌压力较高,且由于椭圆长轴端点处周向应力集中程度随椭圆度增加而增大,椭圆形井眼坍塌压力也随椭圆度的增大而进一步提高;脆性泥页岩塑性损伤破坏表现为局域化的破坏断裂带形式,而不是相对均匀的塑性区。研究结果对更好地认识脆性泥页岩的坍塌失稳机理有一定的指导意义。
Mechanical collision is easy to cause brittle mud shale to collapse from a wellbore during drilling operation,and make the shape of the wellbore deviate from an ideal circle,so studying the collapse law according to a circular wellbore will bring certain errors.Treating a real wellbore as an approximate ellipse,this paper analyzed the model of stress distribution on the well wall,used a“elasticity-strain softening-plasticity”model to predict the collapse pressure on the wall,analyzed the sensitivity of the factors causing the collapse of the borehole,and modeled plastic damage and failure characteristics of elliptical boreholes using the finite element software.The results show that,compared with a conventional circular wellbore,the collapse pressure on an elliptical wellbore is higher,and as the circumferential stress concentrated at the end of the long axis increases with the increase of ellipticity,the collapse pressure increases too;plastic damage to brittle mud shale is shown as a local fractured zone,rather than a relatively uniform plastic zone.These findings are references to better understanding the collapse and instability mechanism of brittle mud shale wells.
作者
刘海龙
张磊
谢涛
张启龙
林家昱
Liu Hailong;Zhang Lei;Xie Tao;Zhang Qilong;Lin Jiayu(Tianjin Branch of CNOOC(China)Co.,Ltd;State Key Laboratory of Efficient Development of Offshore Oil)
出处
《石油机械》
北大核心
2020年第5期28-33,共6页
China Petroleum Machinery
基金
“十三五”国家科技重大专项“渤海油田高效开发示范工程”(2016ZX05058)。
关键词
脆性泥页岩
椭圆形井眼
坍塌失稳规律
应变软化
椭圆度
brittle mud shale
elliptical wellbore
collapse and instability law
strain softening
ellipticity
