In order to detect oil and gas in particular, well cuttings are examined with a low power stereo microscope, often using darkfield or pseudo-darkfield. The darkfield helps in identifying oil staining and the lithology of the borehole rocks. The lithology is a description of the rocks' physical characteristics visible in samples.
The oil and gas industries record rock and fluid properties to find hydrocarbon zones in the geological formations found in a borehole. The entire process will consist of lowering a logging tool into an oil well (hole) to measure the rock and fluid properties. Logging is performed as the logging tools are pulled out of the hole and data is recorded. The drilling depth when well logging can range from 500 feet to 35,000+ feet.
In the oil industry the well and mud logs are typically transferred to the operating company in real time, as these logs are used to make operational decisions about the well and to correlate information about the depths of surrounding wells.