An expression which applies to a method developed for the purpose of logging highly deviated holes and holes with serious bridging problems. At the present time, systems such as this involve the use of drill pipe to carry specially designed well-logging tools through highly deviated boreholes or past wellbore constrictions to a depth where logging can be performed. A survey cable connects the downhole logging instrument to the surface where the measurements are recorded.

Usually, this is an operation designed for performing openhole surveys below a surface- or protective casing string, but can be used for performing some cased-hole surveys as well. Examples are Slant-hole Express and Toolpusher.