在华北大平原进行煤田地质勘探或石油普查勘探时,由于第四纪冲积表土及第三纪粘土砾石层较厚(一般均在300~500米),岩性极为松软,局部井壁易于扩大,形成灯罩形,使钻杆产生弯曲回转,增大钻杆的弯曲应力和扭力,这就是断钻杆的主要地方,给钻探施工工作带来了极大困难,工人中流传着“不 During coal prospecting or petroleum census exploration in the North China Plain, the Quaternary Alluvial and Tertiary clay gravel layers are thick (generally, 300 to 500 meters), the lithology is extremely soft, the partial wellbores are easy to expand, The formation of the lampshade, the drill pipe bending rotation, increase the bending stress and torque drill pipe, which is the main place to break the drill pipe, drilling work has brought great difficulties, the workers circulating "not