Natural gas is one of the earth’s most valuable natural resources and a major source of the world’s energy supply. It is believed that gas was first discovered by the Chinese, who noticed gas escaping from just beneath the earth’s surface. Realizing the burning properties of this gas, the Chinese piped it though bamboo reeds over short distances and used it as a fuel source, and much later as an “eternal flame.”
Today, natural gas is among the cleanest of all fossil fuels. It is hard to visualize, as it is colorless, odorless and shapeless in its natural form. What makes it so valuable is that it is highly combustible and environmentally pretty friendly. In other words, when it is burned, it releases a lot of energy, but relatively few potentially harmful byproducts into the air.
Invisible superpower
The word “gas” conjures many connotations. Upon hearing or reading it, our minds might jump to the gas we pump into our vehicles to make them run – gasoline. Or, we might think of the gas used by heavy duty trucks and large machinery – diesel. While these commonly are referred to as “gas,” they are petroleum-based liquids with far greater and more complex carbon molecule chains. But when we’re talking about natural gas, we are referring to a different natural resource found below the earth’s surface that we use every day – to generate electricity, light our cities, heat our homes, power our factories and run our appliances. In liquid form, it is an essential raw material (also known as propane) used to fire up backyard barbeque grills, as an agent in fertilizers that produce an abundant harvest, as well as an ingredient in paints and plastics, numerous chemicals and even in medicines.
2017 Domestic natural gas consumption by sector (based on billion cubic feet )
Measuring the invisible
Although we can’t see, smell, taste or touch raw natural gas, we can measure it, and in several different ways. The energy content of natural gas (as well as other forms of energy) can be measured in British thermal units (Btus). A Btu is the amount of energy needed to heat one pound of water by one degree Fahrenheit. Natural gas is also measured in cubic feet. One cubic foot equals roughly 1,000 Btus. Another term used in measuring natural gas is billion cubic feet (Bcf); one Bcf equals around one trillion Btus. Here’s a look at the various terms and what they represent.
Natural gas conversion
| Unit | Cubic Feet | Btus |
|---|---|---|
| 1 cf | 1 cv | 1,024 Btus |
| 1 mcF | 1,000 cf | 1,024,000,000 Btus |
| 1 Bcf | 1 billion (1,000,000,000) cf | 1.024 trillion Btus |
| 1 TcF | 1 trillion (1,000,000,000) cf | 1,024 quadrillion Btus |
Producing natural gas
Natural gas can be produced both conventionally and unconventionally. Conventional exploration for oil and gas has been the focus of most exploration and production companies over the course of the last century. Conventionally produced gas has been drilled and gathered from depths of less than 1,000 feet to more than 35,000 feet. In recent years, advanced drilling exploration and extraction technologies have enabled greater access to deep reservoirs, although due to increased temperatures and pressures (to say nothing of the time involved) drilling at great depths is still a costly operation. However, most of the growth in supply today comes from shale, or a combination of other lower-quality reservoir rocks.
Shale is a fine-grained, sedimentary rock that is composed of clay and tiny particles of other minerals, such as quartz and calcite, and organic materials derived from plants and animals that died while the precursor sediments were being deposited. “Shale gas” is locked in small pores inside the shale, which must be hydraulically fractured to release the gas (or oil, as the case may be). Gas is also being produced from “tight gas sandstone” – low-quality, mostly non-porous and impermeable rock. Gas is also associated with coal beds, and “coal bed methane” has been targeted at several locations around the world, most notably in the U.S., China and Australia.
Originally, natural gas was gathered as a byproduct of traditional oil production, which involved drilling vertically into geological formations where oil and gas have been found for decades. The gas was depressurized and released as oil was brought to the surface.
However, transporting natural gas requires access to pipelines. In the absence of nearby pipelines, natural gas is considered essentially without value and is simply burned off (or “flared”) from a pit near the well. It is safer and environmentally more prudent to flare gas than to let it escape into the atmosphere. Flaring still occurs in parts of the U.S., and more so in developing countries where markets and infrastructure are lacking.
That is changing in the U.S., however, due to extensive pipeline infrastructure build-out currently taking place. Increasingly, quantities of natural gas lacking a nearby market are quickly and efficiently being transported from producing regions to areas of consumption through a complex.
Accessing gas that is trapped inside rock has always presented challenges. Hydraulic fracturing (pioneered in the 1940s) involves using highly pressurized water, sand and other liquids to fracture the rock and free the gas. However, until a few years ago, the majority of shale gas (and oil) remained commercially unviable.
But advancing technologies have created new ways for extracting unconventional gas that have radically changed the U.S. energy picture. The combination of two extraction techniques – the hydraulic fracturing mentioned above and a technique called horizontal drilling (which came into use in the 1980s) – has revolutionized the production of large, unconventional shale formations in a number of states.
Once considered of little value to gas drillers because their natural gas was nearly non-extractable, these same shale reservoirs can now economically yield abundant amounts of gas for decades to come.
Reserves may be proved or potentially recoverable. Proved reserves refers to quantities of hydrocarbons estimated with reasonable certainty to be commercially recoverable from known accumulation under current economic conditions, operating methods and government regulations. Potentially recoverable resources describes volumes of natural gas that are potentially recoverable under existing and foreseen technological conditions. Today, the U.S. has one of the world’s largest known potentially recoverable natural gas resources.
Natural gas is composed primarily of methane (“dry” or “lean” gas) but also can include heavier compounds such as ethane and propane, among others, all of which have slightly different combinations of carbon and hydrogen in their molecular makeup. Natural gas can exist in a liquid state at underground pressures and then become gaseous at normal atmospheric pressure. Natural gas liquids (NGLs) are components of natural gas that are separated from the gas state in the form of liquids. Natural gas liquids are classified based on their vapor pressure, while natural gas has an intermediate vapor pressure. Natural gas liquids with a low vapor pressure are called condensates, and those with a high vapor pressure are called liquefied petroleum gas (also known as LPG or propane).
Natural gas is made up of naturally occurring hydrocarbons (a compound of hydrogen and carbon). The product of decomposed matter, hydrocarbons come in different molecular lengths and constructs, including straight chains, chains with branches, and complete rings. When broken down over time, hydrocarbons form crude oil or natural gas. Depending on the pressure and temperature in which they exist, hydrocarbons may be gaseous, liquid, semisolid or solid, according to how many carbon atoms they contain and whether they are under pressure or at atmospheric conditions. Propane and butane, for example, are liquids under pressure but are gases at atmospheric conditions.
Fossil fuels, deconstructed
As the table above illustrates, the hydrocarbons comprising natural gas have many uses. Methane (composed of one carbon atom and four hydrogen atoms) is the purist form of natural gas.
Although much of the gas produced is “dry” (almost entirely methane), wet natural gas requires processing at natural gas processing plants. That is where the liquids (water, liquefiable hydrocarbons and other impurities) are separated from the dry gas. Dry gas moves on through pipelines and is used to heat our homes and support electric power generation. Wet gas is further refined either at the same location or is piped to another location where it is “fractionated” primarily into ethane, propane, butane and natural gasoline. These natural gas liquids are then transported by interstate pipelines to petrochemical facilities, refineries or industrial plants depending on their use.
Ethane, propane and butane are feedstock (raw materials) used by the chemical industry to make various products, such as ethylene, which is used to help food ripen, in the manufacturing of certain types of plastics and as an inhalation anesthetic. Propane is used in home heating and cooking, while butane is used in lighters and added to gasoline to help reduce pollution. Natural gasoline is used as a solvent and thinner, and can be combined with other, higher-octane substances to create gasoline. It is also used to determine octane ratings in commercially made gasoline.
Natural gas value chain: From wellhead to end user
Source: Tortoise
Natural gas is transported to some industrial, commercial and electric generation customers from storage facilities via major interstate and intrastate pipelines, while others, including residential customers, get natural gas from a local regulated gas utility (also called a local distribution company) via local distribution pipelines. Some utilities are owned by investors while others are owned by local governments. The distribution companies obtain natural gas at transfer points on the major pipelines called “city gates.” There, the gas is depressurized and a sulfur-smelling odorant called mercaptan is added to make it easier to detect gas leaks. From the city gate, the gas flows through a vast network of smaller-diameter pipelines to homes and businesses.
Liquefied, compressed natural gas: acronyms galore
Liquefied natural gas (LNG) is made up of mostly methane that is cooled to approximately minus 260 degrees Fahrenheit and compressed to 1/600th of its size in its liquid state so that it can be transported to areas where it’s needed. Most often, LNG is transported by tanker ships to countries that consume more than they can produce or lack international pipeline access to import gas. Once this cool, compressed gas arrives at its destination, it is heated to return it to its original gaseous state. At that point, it can be transported by pipelines to homes and businesses. As global demand for gas increases and it gains in popularity, it is anticipated that global demand for LNG trade also will expand.
LNG Tanker
Compressed natural gas (CNG) is made by compressing natural gas until it is less than one percent of its volume at standard atmospheric pressure.
CNG and LNG are quickly growing in popularity as a fuel for powering fleets of vehicles, such as taxi cabs, buses, local delivery trucks, refuse and recycling trucks and other trucking fleets. The trucking industry, where millions of 18-wheelers transport all manner of goods across the U.S., is at the early stages of switching from petroleum to natural gas to power its vehicles, much to the benefit of both companies that make engines that run on natural gas, and for transporters, such as United Parcel Service and Federal Express, which stand to reap the rewards of markedly cheaper fuel.
CNG – powered bus
The switch from diesel to natural gas-fueled trucking is an emerging trend not only in the U.S., where attractive low natural gas prices are speeding the conversion, but in other countries as well.
Infrastructure constraints remain a key impediment; there currently are not enough fueling stations in place to make CNG-burning vehicles a convenient choice for most drivers, despite the fuel's lower cost and environmental benefits relative to gasoline.
North America's abundant natural gas is attractive to foreign customers in countries where it is far more expensive, as is the cost of electricity. While prices fluctuate, the map above provides an example of cost differentials of natural gas in the U.S., the U.K. and Japan.