Apparatus and method for evaluating a wellbore, in particular a casing thereof

The apparatus for evaluating a wellbore (5) while drilling comprises a logging tool (11) held on a drill string (1) and is adapted to obtain data from the wellbore (5) while moving the drill string (1) including the logging tool (11) uphole and out of the wellbore (5). The logging tool (11) includes a memory (23) for storing obtained data and an on-board power supply battery (25). A computer (31) being positioned at a surface level of the wellbore (5) is adapted to obtain the data from the memory (23) when the logging tool (11) is also positioned at the surface level. The logging tool (11) is adapted to perform a minimum power-consuming sleep mode with a data obtaining and storing function being disabled and the computer (31) is adapted to transmit a wake-up signal downhole to enable the data obtaining and storing function of the logging tool (11) just prior to tripping out the drill string (1) from the wellbore (5). The wake-up signal preferably is a mud pulse signal sent through the drilling fluid used when drilling the wellbore (5).