钻井液密度窗口下限的三维数值计算格式

为了得到准确的安全泥浆窗口,结合有限单元法提出了用于计算钻井液密度窗口下限三维数值解的数值计算格式.计算包含了井孔轨迹全长的油田区块整体模型的应力场,利用有限元子模型技术逐点计算井孔轨迹上关键点的泥浆窗口下限值.在数值求解过程中,施加足够泥浆压力保持井孔围岩处于弹性状态,并施加反向载荷形成实际卸载,逐步试算求出泥浆窗口的下限值.利用一个包含直井段和90°转角圆弧段井孔轨迹的简单井孔模型,计算了沿井轴全长各处不同井孔倾角对应的泥浆窗口下限值数值解,并把该数值解和利用经典解析解取得的结果作了比较,证明了算法的有效性.

3D numerical calculation scheme for lower bound of density window of drilling mud

In order to obtain the accurate safe mud window, a numerical calculation scheme for 3D numerical solution of lower bound of density window of driling mud was proposed in combination with the finite element method. The stress field of whole model for the oil field region including the total length of wellbore trajectory was calculated. With the finite element submodel technique, the lower bound values of mud window were calculated point by point for each key location along the wellbore trecjotory. In the numerical solution process, enough mud pressure was applied to keep the wellbore surrounding rock at eastic state, an inverse load was imposed to form the practical unloading, and the lower bound values of mud window were gradually obtained. With a simple wellbore model including the wellbore trajectories at both vertical section and 90° curved section, the lower bound values of mud window corresponding to different wellbore inclination angles along the total length of wellbore trajectory were calculated. Moreover, the numerical solution was compared with the results attained with the conventional analytical method. And thus, the effectiveness of the numerical calculation scheme is proved.