Almost everywhere that drillers find crude oil, they find it under a pocket of gas. Still more gas is dissolved in the oil. When drillers go deep, the gas may be under pressure that causes it to shoot to the surface, as it did at the Macondo well, causing the Deepwater Horizon disaster.
The gases of crude oil are hydrocarbons, simple small molecules for the most part, that float over a deposit of crude. Several hydrocarbon gases have well-known names because they are common in everyday life: methane, butane, propane, and ethane.
Methane was the treacherous firedamp of old Wales, the odorless invisible menace that suddenly ignited in the coalmines, killing hundreds at their work on the pit face in the dark. Mine explosions still happen, and firedamp still causes some of them. Methane is marsh gas too, that probably lights the ghostly phosphorescent ignis fatuus, the flickering will-o-the wisp that leads travelers astray in the dark.
Chemically, methane is CH4, the smallest, lightest hydrocarbon, used as natural gas in modern homes and factories. It burns relatively cleanly, creating far fewer particulates than heavier hydrocarbons, but 5 to 15 percent mixed in ordinary air makes a mixture that explodes.
Natural gas is mostly methane, but sometimes holds a trace of other hydrocarbon gases too. The commercial product is scented with mercaptans, vile-smelling compounds containing sulfur, because in its natural odorless form a leak can suffocate the unwary. Natural gas is cheap and efficient, which is why a network of natural gas pipelines covers America.
Butane, C4H10, is stable, non-corrosive, and extremely flammable. It exists in two main forms, the straight chain of n-butane, and iso-butane, a branched molecule. Both are classed as alkanes. Alkanes are made of carbon and hydrogen linked together by single bonds in molecules that have no rings.
Butane lighters may be the commonest disposables. Lighters used to be filled with naphtha, but butane smells better, and the manufacture of a disposable butane lighter is a simpler and less expensive proposition.
Butane is used as a propellant in many aerosols. Unfortunately, some inhale this propellant seeking euphoria, which can lead to brain damage or sudden death.
Butane is also used in camp stoves (mixed with propane) and in refrigerators and freezers. It has replaced Freon as a refrigerant in many applications because it does not harm the ozone layer. However, it does not work well as a direct substitution for Freon, because older equipment is not designed to use it properly.
Propane is used as vehicle fuel in the form of LPG. Most often vehicles that run on propane are part of fleets, with special arrangements made for their fueling and maintenance. Propane also runs barbecues, some welding torches, and camp stoves. In some areas, it is used in home heating.
Like methane and butane, propane is an alkane, and is usually found with them in natural gas deposits. Its formula is C3H8.
The propane supply is flexible, because its production is a by-product of natural gas production and crude oil cracking. The cracking that divides crude oil into its components is easily tuned to provide more or less propane or other hydrocarbons as needed. In addition, huge amounts of propane (and other gases) are stored underground in Texas, Alberta, and Kansas, to avoid fluctuations in supply.
As well as its work-a-day applications, propane is the primary fuel that lifts hot air balloons.
Ethane (C2H4) is the second largest component of natural gas. It used to be burned as fuel along with methane, but now it is separated out, cracked into ethylene, and used in petrochemicals. Ethylene becomes plastic, the most widely used type of plastic in the world. It is also turned into synthetic detergents, gasoline additives, anti-freeze, and polystyrene. It can also become an anesthetic, and an agent used in ripening fruit.
These are not the only hydrocarbon gases, but they are the ones in widest use. Methane heats our homes and businesses. Butane is important in the packaging of convenience foods, and also in earth-friendlier air conditioners. Propane runs some public transit, and runs barbecues. Ethane has countless uses, from packaging to cleaning supplies. Each of these hydrocarbon gases is essential to life as we currently live it.