wireline log, borehole log. The product of a [[survey]] operation, also called a survey, consisting of one or more [[curve|curves]]. Provides a permanent record of one or more physical measurements as a function of depth in a well bore.
Well logs are used to identify and [[correlate]] underground rocks, and to determine the mineralogy and physical properties of potential reservoir rocks and the nature of the fluids they contain.

(1) A well log is recorded during a [[survey]] operation in which a [[sonde]] is lowered into the well bore by a [[survey cable]]. The measurement made by the downhole instrument will be of a physical nature (i.e., electrical, acoustical, [[nuclear]], thermal, dimensional, etc.) pertaining to some part of the wellbore environment or the well bore itself.

(2) Other types of well logs are made of data collected at the surface; examples are core logs, [[drilling time log|drilling-time logs]], [[mud]] sample logs, hydrocarbon well logs, etc.

(3) Still other logs show quantities calculated from other measurements; examples are [[movable oil plot|movable oil plots]], computed logs. etc.