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]].