Wireline (Slickline) is one method of running various measuring instruments and tools into petroleum wellbores. Basically, subsurface devices are attached to the end of a long spool of wire, instruments are then lowered down hole and winched back up.
A lubricator (several sections of pipe) is attached to the top of a wellhead BOP. A grease valve and pulley are mounted on top of the lubricator to run the wire through. Tool strings are then pulled up into the lubricator, before running in and out of the wellbore.
The winch is usually mounted on a truck but can be skid mounted for remote operations. A drop spool can also be employed if instruments need to be hung down hole (i.e. inside casing, no tubing installed within which a collar stop or dart could be landed).
Four basic types of wire are employed. Also called slickline, solid steel wire is for normal use while solid stainless steel wire is for sour service. Braided wire comes in either solid core, for heavy duty use, or e-line in which the braid is wrapped around a coaxial cable for electric control of downhole tools and instruments (i.e. formation and production logging).