When drilling into soft clay stratum, the drilling speed is fast, the displacement is small, and the mud performance is not good, especially the viscosity and shear force are too high, which is easy to cause mud bag. In addition, when drilling, the mud is short circuited and the drilling continues after stopping the pump, resulting in dry drilling and mud bag of the bit.

After the mud bag of the bit, the operation is abnormal, the drilling is broken and skipped, the drilling rate decreases significantly, the rotary table load increases, the pump pressure increases slightly, and the drilling tool is stuck when moving.

After the mud bag of the bit is found, the first thing to do is to ream frequently, or high-speed reaming, light pressure drilling and improve the displacement. Secondly, the mud shall be handled as soon as possible according to the downhole and formation conditions. If the treatment is invalid, trip out immediately. When tripping out, use low speed to prevent sticking in case of obstruction. If necessary, connect Kelly to circulate mud and pull out by reverse reaming. Mud shall be poured frequently during tripping out. If mud cannot be poured, Kelly shall be connected in sections to circulate mud.