Changes

Every now and again, the hole will collapse in on itself. This will happen where the earth stresses exceed the rock strength. Salt sections or shale sections at shallow depths containing water-sensitive clays are prone to this. Water-sensitive clays can expand by reacting with drilling fluids, particularly low salinity muds. This can cause the borehole wall to founder and bury the drill bit irretrievably. A decision may then be made to branch off from what hole is left, and this is called sidetracking.

Every now and again, the hole will collapse in on itself. This will happen where the earth stresses exceed the rock strength. Salt sections or shale sections at shallow depths containing water-sensitive clays are prone to this. Water-sensitive clays can expand by reacting with drilling fluids, particularly low salinity muds. This can cause the borehole wall to founder and bury the drill bit irretrievably. A decision may then be made to branch off from what hole is left, and this is called sidetracking.

Another problem that can occur is lost circulation, whereby the drilling mud is lost in large quantities into a fracture or a highly permeable interval. Adding fibrous material to the mud will solve the problem. This clogs up the lost circulation zone and prevents any further losses.

Another problem that can occur is lost circulation, whereby the drilling mud is lost in large quantities into a [[fracture]] or a highly permeable interval. Adding fibrous material to the mud will solve the problem. This clogs up the lost circulation zone and prevents any further losses.

==Well operations after drilling has ceased==

==Well operations after drilling has ceased==