HDD Machine common cases and solutions 08

Publication Date: 2020-12-31

The adverse effect of sand on the crossing construction

Due to the weak or no cohesive force between the sand particles, the original stress state is broken after the formation is drilled into the hole. The qualitative crossing construction of the sand layer is most prone to collapse accidents! During the drilling process If there is a hole collapse, the direct consequence is that the drilling tool is buried, causing the buried drill to “stuck” construction; if the hole collapse occurs during the dragging process, it may cause excessive dragging resistance or even failure! In the sand layer, the hole collapse The main reasons are as follows:

1 The stratum has little cementation. Once exposed, the original balance will be lost and collapse will occur;

2 Mud scour. During the drilling process, the mud is ejected from the nozzle at high speed, causing a strong impact on the sand layer and causing collapse;

3 Pull back to expand the hole (pull back to lay the pipe) too fast, open the pump too hard, and generate a large pressure in the hole;

4 The continuous collision of the drilling tool “squeezes the hole wall;

5 Excessive mud pressure will crack the formation and cause collapsed holes!