differential sticking — Oil & Gas Glossary
A situation in which the drilling assembly (pipe, drill collars and bottomhole assembly) is stuck in filter cake that was previously deposited on a permeable zone. The pipe is held in the cake by a difference in pressures between the hydrostatic pressure of the mud and the pore pressure in the permeable zone. The force required to pull the pipe
Detailed Explanation
free can exceed the strength of the pipe. Methods used to get the pipe free, in addition to pulling and torquing the pipe, include: (1) lowering hydrostatic pressure in the wellbore, (2) placing a spotting fluid next to the stuck zone and (3) applying shock force just above the stuck point by mechanical jarring, or (4) all the above. The most common approach, however, to getting free is to place a spot of oil, oil-base mud, or special spotting fluid.