mud logging
n.— «Tecton provides on-site rig monitoring and mud logging for the geothermal drilling industry. Mud logging is the term for testing and keeping track of the microscopic nature of rock and the presence of liquid in wells during the drilling process.» —“Geothermal driller ThermaSource acquires Tecton Geologic of Windsor” by Loralee Stevens Business Journal Sept. 9, 2008. (source: Double-Tongued Dictionary)