the recording of information derived from examination and analysis of formation cuttings made by the bit and of mud circulated out of the hole. A portion of the mud is diverted through a gas-detecting device. Cuttings brought up by the mud are examined under ultraviolet light to detect the presence of oil or gas. Mud logging is often carried out in a portable laboratory set up at the well.

this includes routine geological examination of drill cuttings from a well, plus a record of the variations in drilling rate, mud pumping pressure, depths of formation changes and an analysis of the mud for oil and gas traces.

Hydrocarbon well logging. The analysis of samples of the circulated drilling fluid (or mud) and formation cuttings to detect signs of fluids which have entered the mud from the formations. Hydrocarbons may be detected by fluorescence, by chromatographic analysis, gas, and other ways. Also, the mud may be monitored for salinity and viscosity. Plots of such data often include a sample log and a drill time curve.