Natural gas, refrigerated liquid with high methane content

Petroleum is the mixture of gaseous, liquid, and solid hydrocarbons (although the term is often restricted to the non-gases) derived from chemical reactions on prehistoric animal and vegetable matter which occurs as reservoirs in sedimentary rocks from which it is extracted. Petroleum (8002-05-9) syn. crude oil or petroleum oil also contains inorganics such as compounds of sulphur, nitrogen, oxygen, metals, etc. 

Natural gas (8006-14-2) is the gaseous component of petroleum. It is mostly methane with some ethane and smaller quantities of propane, butane, carbon dioxide, hydrogen sulphide, nitrogen, helium, and other gases. It is distributed in commerce as compressed or liquefied natural gas (LNG) for fuel and other purposes. 

Crude oil is processed in refineries by distillation, cracking, reforming, alkylation, polymerization, and other methods to generate gases, distillates, residuum, and sludges from which an enormous number of petroleum products 

The author was unable to find a reference for why an oil well sampling device might be charged with a compressed or liquefied gas. 

In addition to natural gas a number of gases are associated with petroleum  

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