Natural gas is a combustible mixture of hydrocarbon gases.
Natural gas is abundant and when burned, gives off a great deal of energy with fewer emissions than many other sources. Compared to other fossil fuels, natural gas is cleaner burning and emits lower levels of potentially harmful byproducts into the air.
It is formed primarily of methane, it can also include ethane, propane, butane and pentane. It is a fossil fuel used as a source of energy for heating, cooking, and electricity generation.
Natural gas is found in deep underground rock formations or associated with other hydrocarbon reservoirs in coal beds and as methane clathrates. It was discovered thousands of years ago in China, and has been a resource ever since.
Petroleum is another resource and fossil fuel found in close proximity to and with natural gas. Most natural gas was created over time by two mechanisms: biogenic and thermogenic. Biogenic gas is created by methanogenic organisms in marshes, bogs, landfills, and shallow sediments.
Deeper in the earth, at greater temperature and pressure, thermogenic gas is created from buried organic material.
When wet natural gas is produced, it must be processed to separate the different components it contains, such as water and hydrocarbons.
Natural gas liquids (NGLs), such as butane, ethane (ex. used to make plastics) and propane, are other forms of hydrocarbons, which can be used for many different products.
Butane is commonly known as the flammable liquid in handheld lighters, propane is often used for heating in homes or as a fuel source for grills and propane is a chemical building block found in many different kinds of plastic products we use every day.
Also, the propane and other lighter compounds found in the LNGs may be marketed as liquefied petroleum gas (LPG), and heavier hydrocarbons may be made into gasoline (petrol).
The average American citizen will come into contact with at least one product each day which can trace its roots back to wet natural gas.
Everything from phone cases to food containers to tires to gasoline to fibers inside every kind of carpet is derived in part from a natural gas liquid.
Dry natural gas is essentially made up entirely of methane, and not much else. This means that the methane will burn at correct temperatures for use in things like our stoves, in vehicles and in manufacturing processes.
Dry natural gas can also be used on our area of extraction to power vehicles, drilling rigs and other operations involving the industry, which reduces the need for using other fuels like gasoline and diesel.
After minimal processing, dry natural gas flows into pipelines which are strategically placed across the country delivering it to homes, businesses, manufacturers, agricultural centers and power generation plants.
The methane separated from the wet gas mixture also flows into these pipelines.
Natural gas recently overtook coal as the largest source of electric production in the United States, which in turn has helped to decrease our country’s carbon emissions to levels not seen in decades.
Main Components of Natural Gas
Natural gas is stripped down to methane before being used by consumers. It is the most rich component of pure natural gas, which is highly combustible and can be used for a wide range of energy purposes.
The chemical formula of methane is CH4 with molecular weight of 16 gram/mole.
Before methane can be burned, it first has to be stripped from the natural gas that’s found in oil wells, gas wells and condensate wells. Once processed from the natural gas, it is used for generating electricity through gas and steam turbines.
It is also sent to homes through pipelines where it’s used for cooking, heating, air conditioning and other important home activities.
The chemical formula of methane is C2H6 with molecular weight of 30 gram/mole. Ethane is the next most abundant component of energy found in natural gas. It is a hydrocarbon and a byproduct of petroleum refining.
With a higher heating value than methane, it is used in several ways after being isolated from natural gas.
Once separated from natural gas, ethane is often used to produce ethylene and polyethylene products. In turn those are used to produce packaging, trash liners, insulation, wire and other consumer products.
Propane is an abundant energy source found in natural gas and is processed in gas or liquid form. The chemical formula of methane is C3H8 with molecular weight of 44 gram/mole.
Often found in pipeline gas, propane can be used for a variety of purposes.
Frequently, it is used for fueling engines, cooking with stoves and for central heating within the home or larger buildings. Propane is also used for many barbecue grills due to its high-energy output and portability.
Some buses and larger vehicles are fueled on propane, and many homes also use the gas for fueling the furnace, water heaters and other essentials.
Butane is found in natural gas, butane is not as abundant as other hydrocarbons, but it is still a viable energy source and can be used for a variety of purposes.
The chemical formula of methane is C4H10 with molecular weight of 58 gram/mole. Isolated during natural gas processing, butane makes up around 20 percent of natural gas composition.
It is often a component in automobile gas. Refrigeration units and lighters also use a large amount of butane as fuel. Aerosol cans use butane as a propellant, but this has been flagged as harmful to the environment.
Where is natural gas found?
Natural Gas is mainly extracted from the petroleum deposits deep beneath the earth. In fact, it occurs just above the layer of crude oil, as gases are lighter than oil. It is formed through the same process through which petroleum is formed.
High temperatures and pressure leads to the conversion of the remains of plants and animals buried under the earth into naturally occurring gas along with petroleum and coal. Gas reservoirs differ greatly, with different physical variations affecting reservoir performance and recovery.
In a natural gas (single-phase) reservoir it should be possible to recover nearly all of the in-place gas by dropping the pressure sufficiently. If the pressure is effectively maintained by the encroachment of water in the sedimentary rock formation, however, some of the gas will be lost to production by being trapped by capillarity behind the advancing water front.
Therefore, in practice, only about 80 percent of the in-place gas can be recovered. On the other hand, if the pressure declines, there is an economic limit at which the cost of compression exceeds the value of the recovered gas.
Depending on formation permeability, actual gas recovery can be as high as 75 to 80 percent of the original in-place gas in the reservoir. Associated gas is produced along with the oil and is separated at the surface.
Unconventional gas reservoirs
Substantial amounts of gas have accumulated in geologic environments that differ from conventional petroleum traps.
This gas is termed unconventional gas and occurs in “tight” (i.e., relatively impermeable) sandstones, in joints and fractures or absorbed into the matrix of shales, and in coal seams.
Unconventional gas sources are unconventional only in the sense that, given current economic conditions and states of technology, they are more expensive to exploit and may produce at much slower rates than conventional gas fields.
However, as technology changes or as conventional sources become relatively expensive, some unconventional gas becomes easier and relatively cheaper to produce in quantities that can fully complement conventional gas production.
Such has been the case with tight gas, shale gas, and coal-bed methane.
Tight gas occurs in either blanket or lenticular sandstones that have an effective permeability of less than one millidarcy (or 0.001 darcy, which is the standard unit of permeability of a substance to fluid flow).
These relatively impermeable sandstones are reservoirs for considerable amounts of gas that are mostly uneconomical to produce by conventional vertical wells because of low natural flow rates.
However, the production of gas from tight sandstones has been greatly enhanced by the use of horizontal drilling and hydraulic fracturing, or fracking, techniques, which create large collection areas in low-permeability formations through which gas can flow to a producing well.
Shale gas was generated from organic mud deposited at the bottom of ancient bodies of water. Subsequent sedimentation and the resultant heat and pressure transformed the mud into shale and also produced natural gas from the organic matter contained in it.
Over long spans of geologic time, some of the gas migrated to adjacent sandstones and was trapped in them, forming conventional gas accumulations.
The rest of the gas remained locked in the nonporous shale. In the past the production of shale gas was generally too slow to be profitable, but now wells can be drilled horizontally for long distances through the shale beds, and the formations can be stimulated by hydraulic fracturing to enhance gas production greatly.
About 25 percent of the gas produced in the United States comes from shales, and that proportion is expected to rise to 50 percent before the mid-21st century.
Considerable quantities of methane are trapped within coal seams. Although much of the gas that formed during the initial coalification process is lost to the atmosphere, a significant portion remains as free gas in the joints and fractures of the coal seam; in addition, large quantities of gas are adsorbed on the internal surfaces of the micropores within the coal itself.
Since coal is relatively impermeable, the existing fracture systems of seams that contain rich reserves of methane are sometimes stimulated by fracking in a manner similar to shales and tight sandstones.
Geo-pressured fluids and methane hydrates
Geo-pressured reservoirs exist throughout the world in deep, geologically young sedimentary basins in which the formation bear a part of the overburden load. The fluid pressures can become quite high, sometimes almost double the normal hydrostatic gradient.
Methane hydrates have been found in sandstones from polar regions and in sand and mud sediments from continental margins. Techniques for extracting the methane in an economically viable and environmentally sustainable manner are under exploration.