Natural Gas
When the chemical composition of petroleum is such that it exists in the gaseous or vapor state at normal temperature and pressure, it is called natural gas. Natural gas is generally colorless and odorless, usually weighs less than air, and chemically is a much simpler mixture of hydrocarbons than are petroleum liquids. Methane, ethane, propane, and butane are names of selected hydrocarbon components within natural gas. The primary component of most natural gas is methane. But be careful not to confuse natural gas with natural gasoline, a colorless liquid obtained from petroleum.
As mentioned, natural gas is usually colorless and odorless; however, the natural gas you burn in your home does have an odor. This odor is the result of chemicals like mercaptan, a sulfur compound, that have been intentionally added to the gas so a leak can be detected easier. The process of adding chemicals to natural gas to purposefully give it an odor is called stenching.
Although most components of natural gas are in the gaseous slate at normal temperature and pressure, these compounds can become liquid by raising the pressure and/or lowering the temperature. When natural gas reverts (condenses) from a vapor state to a liquid state, the resulting liquids are called condensates or distillates.
Most conventional forms of exploiting hydrocarbons are aimed at recovering the liquid and gaseous states of petroleum (oil and natural gas, respectively). Infrequently, nonconventional efforts are directed toward recovering semisolid and solid petroleum deposits like tar. Heavy oil recovery (extremely thick liquid petroleum) uses both conventional and nonconventional techniques.
Units of Petroleum Measurement
In the early days of Col. Drake's discovery, petroleum liquids were measured in "hogsheads," a unit of measure equal to 63 gallons. Today, petroleum liquids are measured and sold in barrels. A barrel of oil is equivalent in volume to 42 U.S. gallons, or about half the volume of an average bathtub.
Why does a barrel have 42 gallons rather than, say, 40,45, or 50? Well, it's probably a carryover from the days when oil was transported from well to refinery by horse and wagon. An open-top barrel or drum had considerable loss of contents by spillage, seepage, or evaporation during transport. To help counteract this loss, the producer had to give the transporter 2 extra gallons for every 40 gallons of sales. Today, oil losses are not as high as 2 gallons out of 42, but the 42-gallon barrel has survived and is the national standard for oil measurement
Natural gas measurement is more complicated because gas is compressible. Therefore, the volume that any gas occupies depends on the pressure and temperature applied to the gas when it is measured. Natural gas is measured by the standard cubic foot (scf). A standard cubic foot is the volume occupied by a gas at approximately atmospheric pressure and at a temperature of 60°F. Gas flow rates can…