Is this 5 letter word really that scary?, page-56

For those who are interested, the main component of drilling mud is bentonite. It is mixed with various other fluids to make drilling 'mud'. Bentonite absorbs water and when it does it forms a 'gel' or clay which is strongly resistant to hydrostatic pressure. Fluids and bentonite are transported to the drilling rig from the supply base by the rig support vessels, although the NTP would have had a good supply on-board when it mobilised. Amongst other things, bentonite is also used in civil engineering applications to stop excavations from collapsing for the same reason its used in offshore drilling. Useful stuff.