三维离散元在煤层水平井井壁稳定中的应用

为了阐明煤层中端割理和面割理等不连续面对井壁稳定的影响，利用三维离散元来分析煤层水平井井壁稳定，实现了在三维空间中对不连续面的仿真。在充分、真实反映煤岩割理特性的基础上，对煤层水平井进行了井壁稳定数值模拟分析。提出了虚拟节理和内外双层建模技术，虚拟节理技术可实现节理在各个方向的随机分布和动态的断裂分析，内外双层技术可降低计算量和消除边界的影响。模拟了沁水盆地3号煤层面割理和端割理的实际分布情况，最大程度反映了煤层的真实微观特征。通过分析井眼的走向、井径、井底压力和割理密度对井壁稳定的影响发现，当面割理的走向与井眼的走向相互垂直时，井壁最稳定；当两者相互平行时，井壁最不稳定。割理密度越大，井壁的稳定性越差；井径越大，井壁越不稳定。当不考虑渗流时，井底压力越大，井壁越稳定。

Application of the 3D discrete element method in the wellbore stability of coal-bed horizontal wells

Wellbore collapse is one of the main obstacles that prevent horizontal wells from the extensive use in coal seams.Coal rock mass has a great number of cleats and some fragmented zones,and is of low strength,so it is a great risk to drill in coal seams.Middle or high rank low-strength coal dominates in the Qinshui Basin,Shanxi Province.Hence,when water is used as a drilling fluid,it is easy for wellbore to collapse and the bottom hole assembly is readily buried underground.Especially for horizontal wells,the...