Device and method of determining rate of penetration and rate of rotation

A device for determining a rate of penetration and/or rate of rotation of a drilling assembly or logging tool while drilling or logging a wellbore, the device being coupled to at least a sensor array for measuring logging data related to at least one property of a zone surrounding the wellbore, and comprising a memory buffer and at least one processing module, wherein the processing module of the rate of penetration and/or rate of rotation determining device is arranged to:

• at respective first and second time instant, acquire and store into the memory buffer a first logging data frame using a first array of sensors and a second logging data frame using a second array of sensors, the logging data relating to at least one property of a zone surrounding the wellbore, the second logging data frame overlapping at least partially the first logging data frame,
• compare the first and second logging data frames,
• determine a relative change in depth and/or azimuth between the first and second logging data frames, and
• calculate the rate of penetration and/or rate of rotation based on the relative change in depth and/or azimuth determined and a difference between the first and second time instants.