Definition - What does Well Log mean?
A Well Log is a detailed record of the geological formation during the drilling of a borehole. A well log is prepared by either taking samples through visual inspections or with the aid of measuring instruments lowered into the borehole. Logs prepared using visual inspections are called geological logs whereas logs prepared with the help of inspection instruments are called geophysical Logs.
Petropedia explains Well Log
Well Logs are generally prepared in order to evaluate hydrocarbon deposits. In order to perform this evaluation, testing of rock and fluid formations at different locations is conducted and the data is recorded on the logs. The device that is used to conduct well testing is called logging tool and it can be attached to a thin wire called wireline, which carries this tool to the necessary depth within the borehole to conduct testing on quantity and location of hydrocarbons beneath the earth’s surface. This tool gathers all data and sends it to the control room where the well logs are prepared.