Well logging

Well logging is technique used in the oil (petroleum) & gas industry for recording rock properties and thereby finding hydrocarbon zones in the formation (below the earth's crust). Logging procedure starts with lowering a 'logging tool' inside oil well (or hole) down to the total hole depth to determine what kind of the rock/s constitute the formation and gives an estimate to where the oil and gas (hydrocarbon) zones are. Logging tools developed over the years basically determine the hydrocarbons present in the pore spaces of the rocks by formation evaluation measuring the electrical properties, acoustic, radioactive etc., of the rocks or fluids. Logging, or recording the rocks/oil gas zones is done when the lowered logging tool is pulled out of the hole. This data recorded is put on to a 'Well Log'. Well logging is usually performed when the total depth of the hole is drilled, which could range in depths from 1000 ft to 25,000 ft (or more).

Another kind logging technique used is 'Mud Logging'. A Mud Logger works when an drilling going on. The Mud Logger analyzes the rock samples coming out of the circulating mud/fluids off 'flow line' from the drill string/pipe. Similar to a Well Log, a 'Mud Log' is prepared by the Mud logging company. A mud log displays the Gas present in the formation by using Gas Chromatograph techniques. A mud log also describes the formation geology.

The 'Well and the Mud Log' are transferred in 'real time' to the operating company which uses these logs to decide how much hydrocarbon reserves they have in the well and how long can it produce economically.

Major well logging and mud logging companies

Both these jobs are performed by Oil & Gas Service companies. Well Logging companies are – Schlumberger, Halliburton, Baker Hughes Mud logging companies – Geoservices, Baker Inteq (part of Baker Hughes), Datalog.