Pore pressure in shale is more than hydrostatic pressure; however, the well does not flow because shale is impermeable. While drilling through pressured shale formation, pressure in shale causes fractures of shale due to stress cracks.
Pressure in shale causes fractures of shale due to stress cracks.
Shale finally falls into the well and results in stuck pipe incident.
Shale falling into the well.
