Causes of well collapse:

1. The mud is not injected in time during tripping out, and the liquid column pressure is reduced, resulting in well collapse.

2. The drilling time is long, the mud performance is poor, especially the density is too low, the water loss is too large, and the shaft wall is unstable, which is easy to form Periodic well collapse.

3. Improper mud treatment, large amount of water added and formation collapse.

4. Long drilling stoppage time, mud sedimentation and deterioration of performance contribute to well collapse.

5. Unconsolidated formation and fractured formation with poor cementation are easy to be soaked by mud and weaken its cementation, resulting in well collapse.

6. The interbedding between quicksand layer, gravel layer and clay loses stability and a large section of well collapses.

Judgment of well collapse:

1. When drilling, the drilling is suddenly broken, the pump pressure rises or the pump is broken, the suspended load decreases, and even cannot rotate.

2. Mud backflow during tripping, serious reversal during shackle, stuck lifting, blocked lowering, broken pump during circulation, etc. are all well collapse phenomena.

Treatment method:

1. Maintain and restore the mud circulation as much as possible, and greatly move the drilling tool (rotating, lifting and releasing). Adjust mud performance, consolidate borehole wall and bring out collapsed rock blocks.

2. If the well in loose formation collapses, it will leak as soon as the pump is started and cannot be circulated. At this time, it is necessary to trip out as soon as possible, fill mud while tripping out, and lift up strongly within the safe load. After pulling out the drilling tool, handle it in line.

After the drilling tool is pulled out, prepare enough mud with good performance, and then run in and ream. Pay attention to the pump during reaming to prevent sticking until it is unobstructed.