- From source rocks rich in organic material from plants.
- From normal oils converted to gas due to excessive heat from deep burial.
- Natural gases fall into two categories:
(methane, ethane, propane, butane, & hydrogen). Methane is the most
abundant, comprising almost 80% of combustible gases. There are two
types of combustible gas: dry gas (usually from rock sources and
exposure to thermal and bacterial conditions) and wet gas (contains
higher hydrocarbons and is generally associated with oil accumulations).
75% of gas resources are combustible.
- Non-combustible (nitrogen, carbon dioxide, & hydrogen sulfide).
- Gas source rocks are more widespread and abundant than oil source rocks.
- Gas is being depleted at a much slower rate than oil due to the high cost of transporting gas (especially from remote areas).
much as 80% or more of gas is recoverable from a well/source versus
about 50% of oil since oil tends to adhere to the sand grains in the
is commonly re-injected into oil wells to maintain pressure and enhance
oil production. Once oil production falls to a low level, many then
convert the oil field into a gas field.
Natural Gas Basics
gas and crude oil are called hydrocarbons because both are composed of
carbon and hydrogen atoms. Natural gas molecules are generally shorter;
four carbon atoms or less. Crude oil molecules contain five or more
carbon atoms per molecule.
gas is both a clean burning fuel source and the primary feedstock into
the U.S. petrochemical industry. Raw natural gas in fields is processed
to separate the methane out from butane, propane, and large amounts of
ethane. The three heavier liquids are prone to condensation in natural
Natural Gas Liquids and Petrochemicals
– One carbon atom; chemical formula CH4. The principal use of methane
is as a fuel. The natural gas that is delivered to your home is almost
pure methane. Methane is also an upstream component of many important
– A primary raw material in automotive windshield wash and also used as
a racing fuel. Chemical derivatives of methanol also play an important
role in our everyday lives:
– Two carbon atoms; chemical formula C2H6. Ethane is the second-largest
component of natural gas, typically comprising up to 6% of the volume
of gas produced from a natural gas field.
– The vast majority of ethane is consumed in the production of ethylene
by steam cracking. Consumer products made from ethylene derivatives
represent a large part of the petrochemical industry here in the U.S.:
– Three carbon atoms; chemical formula C3H8. Truck fleets, forklifts,
barbecue grills, portable stoves and even the new Roush Ford F-150
pick-up use propane fuel. Propane’s octane rating is noticeably higher
than gasoline at 110.
Many homes not
connected to municipal (methane) gas pipelines use propane for their
appliances and furnaces. Other fuel uses for propane:
- Hot air balloons.
- Fuel for explosions and other special effects in theme parks and movies.
Butane – Four carbon atoms; chemical formula C4H10. Primary fuel uses for butane are:
- Bottled fuel for cooking and camping.
- Fuel for cigarette lighters.
- A propellant in aerosol sprays.
- As refrigerants.
Natural Gas Quality
Gas quality standards
vary depending on the pipeline system and are usually a function of
each pipeline system’s design and the markets that it serves. In
general, the standards specify that the natural gas be within a specific
range of heating value. In the U.S., gas must generally be should be
1.035 MMBtu per cubic foot of gas at 1 atmosphere and 60 °F.
Sour Gas –
Natural gas that contains detectable amounts of hydrogen sulfide (H2S)
is called sour gas. It’s a poisonous gas that is also very corrosive.
Hydrogen sulfide must be removed from raw gas by rather expensive
equipment at the well site to prevent corrosion damage to well site
pipes and equipment as well as to meet utility pipeline gas specs. As
H2S is particularly dangerous to humans, a typical pipeline limit for
hydrogen sulfide would be in the range of 4 parts per million per 100
standard cubic feet.
Sweet Gas – Natural gas that does not contain hydrogen sulfide is considered sweet gas.
Wet Gas – Wet
gas is natural gas that contains naturally liquid hydrocarbons (called
“condensate”) with the chemical composition of gasoline. Refineries pay a
slightly lower price for condensate than they do for crude oil because
the octane of condensate is very low.