1. Shale pore pressure anomaly. drilling fluid pressure is less than the pore pressure, the shale porosity in the liquid will go to the well, with the formation of different pore size and permeability , the    water wells will peel off, block and collapse.

2. Shale by tectonic stress (prestressing) caused by wellbore instability. Such as formation dip, faults and fracture zones prone to collapse and so on

3. Low intensity rock at formation pressure side to the internal displacement of the borehole, soften, then wash wells because streams from erosion and fall into the wells under drilling collision, resulting in wells collapse.

4.  Too much of sand underground will make the water well hole collapse