钻井液密度窗口下限的3维数值计算格式.pdfVIP

钻井液密度窗口下限的3 维数值计算格式 沈新普1 (1.沈阳工业大学大学 建筑工程学院，辽宁省沈阳市 邮编；110870) 摘 要：为了得到准确的安全泥浆窗口，将结合有限单元法，给出用于计算钻井液密度窗口下限3 维 数值解的数值计算格式。首先计算包含井孔轨迹全长的油田区块整体模型的应力场，然后利用有限元 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，采用“先施加足够 泥浆压力保持井孔围岩处于弹性状态、然后施加反向载荷形成实际卸载”的方法，逐步试算求出这个 o 泥浆窗口下限。利用一个包括直井段和 90 转角圆弧段的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。并把数值界和利用经典解析解取得的结果作了比 较。 关键词：钻井液，泥浆窗口；坍塌压力；剪切破坏；数值计算格式；下限 3-D numerical calculation scheme for lower bound calculation of drilling mud density window SHEN Xin-pu 1 (1.School of Civil Engineering, Shenyang University of Technology, Shenyang, 110870, China) Abstract ：In order to obtain accurate safe mud weight window, 3-D numerical scheme for calculation of lower bound of driling mud ’s safe density window was proposed on the basis of Finite Element techniques. In this process, stress field of global model at field scale is calculated first. This global model consists of the region where the wellbore trajectory sites. Sumodeling technique of Finite Element Method is used to calculate the lower bound of mud weight window point by point for each key locations along the trecjotory of wellbore. A big value of mud weight is aplied to wellbore to keep the wellbore and its surrounding rock at eastic stress status. It is followed by an inverse load to form unloading to the previous mud weight. In this way, this value of lower bound of mud weight window is obtiend numerically. With a simple model of wellbore which consists of vertical section and 90o curved section, values of lower bound of mud weight window for points along the trajectory were calculated. These points are located at variuos values of incl