How Fossil Fuel Was Formed And Utilized: Contrary to what many people believe, fossil fuels are not the remains of dead dinosaurs. In fact, most of the fossil fuels found today were formed millions of years before the first dinosaurs. Fossil fuels, however, were once alive. They were formed from prehistoric plants and animals that lived hundreds of millions of years ago.
Think about what the Earth must have looked like 300 million years or so ago. The land masses we live on today were just forming. There were swamps and bogs everywhere. The climate was warmer. Trees and plants grew everywhere. Strange looking animals walked on the land, and just as weird looking fish swam in the rivers and seas.
Tiny one-celled organisms called proto-plankton floated in the ocean. When these living things died, they decomposed and became buried under layers and layers of mud, rock, and sand. Eventually, hundreds and sometimes thousands of feet of earth covered them. In some areas, the decomposing materials were covered by seas, and then the seas dried up and receded.
During the millions of years that passed, the dead plants and animals slowly decomposed into organic materials and formed fossil fuels. Different types of fossil fuels were formed depending on what combination of animal and plant debris was present, how long the material was buried, and what conditions of temperature and pressure existed when they were decomposing.
For example, oil and natural gas were created from organisms that lived in the water and were buried under ocean or river sediments. Long after the great prehistoric seas and rivers vanished, heat, pressure, and bacteria combined to compress and “cook” the organic material under layers of silt.
In most areas, a thick liquid called oil formed first, but in deeper, hot regions underground, the cooking process continued until natural gas was formed.
Over time, some of this oil and natural gas began working its way upward through the earth’s crust until they ran into rock formations called “caprocks” that are dense enough to prevent them from seeping to the surface. It is from under these caprocks that most oil and natural gas is produced today.
The same types of forces also created coal, but there are a few differences. Coal formed from the remains of trees, ferns, and other plants that lived 300 to 400 million years ago. In some areas, such as portions of what is now the eastern United States, coal was formed from swamps covered by sea water.
The sea water contained a large amount of sulfur, and as the seas dried up, the sulfur was left behind in the coal.
Today, scientists are working on ways to take the sulfur out of coal because when coal burns, the sulfur can become an air pollutant. Some coal deposits, however, were formed from freshwater swamps which had very little sulfur in them. These coal deposits, located largely in the western part of the United States, have much less sulfur in them.
All of these fossil fuels have played important roles in providing the energy that every man, woman, and child in the United States uses. With better technology for finding and using fossil fuels, each can play an equally important role in the future.
WHAT IS COAL?
Coal looks like a shiny black rock. Coal has lots of energy in it. When it is burned, coal makes heat and light energy. The cave men used coal for heating, and later for cooking. Burning coal was easier because coal burned longer than wood and, therefore, did not have to be collected as often. People began using coal in the 1800s to heat their homes.
Trains and ships used coal for fuel. Factories used coal to make iron and steel. Today, we burn coal mainly to make electricity.
COAL IS A FOSSIL FUEL
Coal was formed millions of years ago, before the dinosaurs. Back then, much of the earth was covered by huge swamps. They were filled with giant ferns and plants. As the plants died, they sank to the bottom of the swamps. Over the years, thick layers of plants were covered by dirt and water. They were packed down by the weight.
After a long time, the heat and pressure changed the plants into coal. Coal is called a fossil fuel because it was made from plants that were once alive! Since coal comes from plants, and plants get their energy from the sun, the energy in coal also came from the sun.
The coal we use today took millions of years to form. We can’t make more in a short time. That is why coal is called nonrenewable.
COAL IS OUR MOST ABUNDANT FUEL
The United States has more coal reserves than any other country in the world. In fact, one-fourth of all the known coal in the world is in the United States. The United States has more coal that can be mined than the rest of the world has oil that can be pumped from the ground. We have enough to last more than 250 years. Currently, coal is mined in 25 of the 50 states.
Coal is used primarily in the United States to generate electricity. In fact, it is burned in power plants to produce more than half of the electricity we use. A stove uses about half a ton of coal a year. A water heater uses about two tons of coal a year. And a refrigerator, that’s another half-ton a year. Even though you may never see coal, you use several tons of it every year. Coal is not only our most abundant fossil fuel, it is also the one with perhaps the longest history.
A BRIEF HISTORY OF COAL
Coal is the most plentiful fuel in the fossil family and it has the longest and, perhaps, the most varied history. Coal has been used for heating since the cave man. Archeologists have also found evidence that the Romans in England used it in the second and third centuries (100- 200 AD).
In the 1700s, the English found that coal could produce a fuel that burned cleaner and hotter than wood charcoal. During the 1300s in North America, the Hopi Indians used coal for cooking, heating and to bake the pottery they made from clay. Coal was later rediscovered in the United States by explorers in 1673. The Industrial Revolution played a major role in expanding the use of coal.
A man named James Watt invented the steam engine which made it possible for machines to do work previously done by humans and animals. Mr. Watt used coal to make the steam to run his engine. During the first half of the 1800s, the Industrial Revolution spread to the United States. Steamships and steam-powered railroads were main forms of transportation, and they used coal to fuel their boilers.
In the second half of the 1800s, more uses for coal were found. During the Civil War, weapons factories were beginning to use coal. By 1875, coke (which is made from coal, and is not the same as CocaCola) replaced charcoal as the primary fuel for iron blast furnaces to make steel. The burning of coal to generate electricity is a relative newcomer in the long history of this fossil fuel.
It was in the 1880s when coal was first used to generate electricity for homes and factories. By 1961, coal had become the major fuel used to generate electricity in the United States. Long after homes were being lighted by electricity produced by coal, many of them continued to have furnaces for heating and some had stoves for cooking that were fueled by coal. Today we use a lot of coal, primarily because we have a lot of it and we know where it is in the United States.
COAL MINING AND TRANSPORTATION
Most coal is buried under the ground. If coal is near the surface, miners dig it up with huge machines. First, they scrape off the dirt and rock, then dig out the coal. Th is is called surface mining. After the coal is mined, they put back the dirt and rock. They plant trees and grass.
The land can then be used again. This is called reclamation. If the coal is deep in the ground, tunnels called mine shafts are dug down to the coal. Machines dig the coal and carry it to the surface. Some mine shafts are 1,000 feet deep. This is called deep mining, or underground mining.
In the mine, coal is loaded in small coal cars or on conveyor belts which carry it outside the mine to where the larger chunks of coal are loaded into trucks that take it to be crushed (smaller pieces of coal are easier to transport, clean, and burn). The crushed coal can then be sent by truck, ship, railroad, or barge.
You may be surprised to know that coal can also be shipped by pipeline. Crushed coal can be mixed with oil or water (the mixture is called a slurry) and sent by pipeline to an industrial user.
CONVERTING COAL INTO ELECTRICITY
Nine out of every 10 tons of coal mined in the United States today are used to make electricity, and nearly half of the electricity used in this country is coal-generated electricity. Electricity from coal is the electric power made from the energy stored in coal. Carbon, made from ancient plant material, gives coal most of its energy. This energy is released when coal is burned.
We use coal-generated electricity for:
- and much more!
The process of converting coal into electricity has multiple steps and is similar to the process used to convert oil and natural gas into electricity:
1. A machine called a pulverizer grinds the coal into a fine powder.
2. The coal powder mixes with hot air, which helps the coal burn more efficiently, and the mixture moves to the furnace.
3. The burning coal heats water in a boiler, creating steam.
4. Steam from the boiler spins the blades of an engine called a turbine, transforming heat energy from burning coal into mechanical energy that spins the turbine engine.
5. The spinning turbine is used to power a generator, a machine that turns mechanical energy into electric energy. This happens when magnets inside a copper coil in the generator spin.
6. A condenser cools the steam moving through the turbine. As the steam is condensed, it turns back into water.
7. The water returns to the boiler, and the cycle begins again.
Electricity-generating plants send out electricity using a transformer, which changes the electricity from low voltage to high voltage. Th is is an important step, as it gives electricity the jolt it needs to travel from the power plant to its final destination. Voltages are often as high as 500,000 volts at this point.
Electricity flows along transmission lines to substation transformers. These transformers reduce the voltage for use in the local areas to be served. From the substation transformers, electricity travels along distribution lines, which can be either above or below the ground, to cities and towns.
Transformers once again reduce the voltage—this time to about 120 to 140 volts—for safe use inside homes and businesses. The delivery process is instantaneous. By the time you have flipped a switch to turn on a light, electricity has been delivered.
COAL’S ROLE IN OUR ELECTRICAL SUPPLY
Natural gas and oil are also used to make electricity. How does coal compare to these other fossil fuels? In terms of supply, coal has a clear advantage. The United States has nearly 300 billion tons of recoverable coal. That is enough to last more than 250 years if we continue to use coal at the same rate as we use it today.
But what about costs? The mining, transportation, electricity generation, and pollution-control costs associated with using coal are increasing, but both natural gas and oil are becoming more expensive to use as well. This is, in part, because the United States must import much of its oil supply from other countries.
It has enough coal, however, to take care of its electricity needs, with enough left over to export some coal as well. The cost of using coal should continue to be even more competitive, compared with the rising cost of other fuels. In fact, generating electricity from coal is cheaper than the cost of producing electricity from natural gas.
In the United States, 23 of the 25 electric power plants with the lowest operating costs use coal. Inexpensive electricity, such as that generated by coal, means lower operating costs for businesses and for homeowners. This advantage can help increase coal’s competitiveness in the marketplace.
CLEANING UP COAL
Coal is our most abundant fossil fuel. The United States has more coal than the rest of the world has oil. There is still enough coal underground in this country to provide energy for the next 250 years or more. But coal is not a perfect fuel.
Trapped inside coal are traces of impurities like sulfur and nitrogen. When coal burns, these impurities are released into the air. While floating in the air, these substances can combine with water vapor (for example, in clouds) and form droplets that fall to earth as weak forms of sulfuric and nitric acid. Scientists call it “acid rain.”
There are also tiny specks of minerals—including common dirt—mixed in coal. These tiny particles don’t burn and make up the ash left behind in a coal combustor. Some of the tiny particles also get caught up in the swirling combustion gases and, along with water vapor, form the smoke that comes out of a coal plant’s smokestack. Some of these particles are so small that 30 of them laid side-by-side would barely equal the width of a human hair.
Also, coal like all fossil fuels is formed out of carbon. All living things—even people—are made up of carbon. (Remember—coal started out as living plants.) But when coal burns, its carbon combines with oxygen in the air and forms carbon dioxide. Carbon dioxide is a colorless, odorless gas, but in the atmosphere, it is one of several gases that can trap the earth’s heat.
Many scientists believe this is causing the earth’s temperature to rise, and this warming could be altering the earth’s climate. Sounds like coal is a dirty fuel to burn. Many years ago, it was.
But things have changed. Especially in the last 20 years, scientists have developed ways to capture the pollutants trapped in coal before they can escape into the air.
We also have new technologies that cut back on the release of carbon dioxide by burning coal more efficiently. Many of these technologies belong to a family of energy systems called “clean coal technologies.”
HOW DO YOU MAKE COAL CLEANER?
Actually there are several ways. One way is to clean the coal before it arrives at the power plant. This is done by simply crushing the coal into small chunks and washing it. Another way is to use “scrubbers” that remove the sulfur dioxide (a pollutant) from the smoke of coal-burning power plants.
HOW DO SCRUBBERS WORK?
Most scrubbers rely on a very common substance found in nature called “limestone.” We literally have mountains of limestone throughout the United States. When crushed and processed, limestone can be made into a white powder. Limestone can be made to absorb sulfur gases under the right conditions—much like a sponge absorbs water.
In most scrubbers, limestone (or another similar material called lime) is mixed with water and sprayed into the coal combustion gases (called “flue gases”). The limestone captures the sulfur and “pulls” it out of the gases. The limestone and sulfur combine with each other to form either a wet paste (it looks like toothpaste!), or in some newer scrubbers, a dry powder.
In either case, the sulfur is trapped and prevented from escaping into the air.
THE CLEANEST COAL TECHNOLOGY —A REAL GAS!
We can even turn coal into a gas—using lots of heat and water—in a process called gasification. When coal is turned into a gas, we can burn it and use it to spin a gas turbine to generate electricity. The exhaust gases coming out of the gas turbine are hot enough to boil water to make steam that can spin another type of turbine to generate even more electricity. But why go to all the trouble to turn the coal into gas if all you are going to do is burn it?
A big reason is that the pollutants in coal—like sulfur, nitrogen and carbon dioxide —can be almost entirely cleaned up when coal is changed into a gas. In fact, scientists have ways to remove 99.9 percent of the sulfur and small dirt particles from coal gas.
Gasifying coal is one of the best ways to clean pollutants out of coal. Another reason is that the coal gases don’t have to be burned. They can also be used as valuable chemicals. Scientists have developed ways to turn coal gases into everything from liquid fuels for cars and trucks to plastic toothbrushes!
COAL AND CLIMATE CHANGE
Carbon dioxide (CO2) is a colorless, odorless gas that is produced naturally when humans and animals breathe. The main source of man-made CO2 emissions, however, is the burning of fossil fuels (oil, natural gas and coal) for energy production.
Carbon dioxide is important for plants and animals, but if too much of it is produced, it can build up in the air and trap heat near the earth’s surface. This is called the greenhouse effect.
To clean CO2 from power plants, scientists have been studying how to capture the CO2 coming up a power plant’s smokestack before it gets into the air. The CO2 can then gathered, transported, and eventually stored deep underground or in the ocean, where it’s supposed to sit for a long, long time.
Scientists are even studying ways to recycle the CO2 into new materials. The technical name for this process is carbon capture and storage, or carbon sequestration.
It is expected that coal and other fossil fuels will remain a major energy source for years to come. Many environmentalists believe that capturing and storing CO2 from power plants, combined with other efforts, could help fight climate change. Scientists continue to research and develop carbon sequestration technologies.
It is important to make sure these new processes are environmentally acceptable and safe. For example, scientists must determine that CO2 will not escape from under the ground, or contaminate drinking water supplies. Carbon capture and storage is an exciting area of research and development for today’s scientists.
WHAT IS NATURAL GAS?
Raw natural gas is a mixture of different gases. The main ingredient is methane, a natural compound that is formed whenever plant and animal matter decays. By itself, methane is odorless, colorless, and tasteless. As a safety measure, natural gas companies add a chemical odorant called mercaptan (it smells like rotten eggs) so escaping gas can be detected. Natural gas should not be confused with gasoline, which is made from petroleum.
WHERE IS NATURAL GAS FOUND?
Like petroleum, natural gas can be found throughout the world. It is estimated that there are still vast amounts of natural gas left in the ground. However, it is very difficult to estimate how much natural gas is still underground. New technologies are helping to make the process a little easier and more accurate.
Recent estimates show that most of the world’s natural gas reserves are located in the Middle East, Europe, and the former U.S.S.R., with these reserves making up nearly 75 percent of total worldwide reserves. Roughly 16 percent of the reserves are located in Africa and Asia and another 4 percent in Central and South America.
The United States makes up almost 4 percent. While the United States may only have a small percentage of natural gas when compared to worldwide reserves, there is still plenty in the country to last for at least another 60 years or longer, as a lot of gas may be undiscovered or unrecoverable with today’s technologies.
Natural gas is produced in 32 states. The top producing states are Texas, Oklahoma, New Mexico, Wyoming, and Louisiana, which produce more than 50 percent of U.S. natural gas.
USES FOR NATURAL GAS
For many years, natural gas was considered worthless and was discarded by being burned in giant flares. But it wasn’t long before it was discovered as a useful energy source. Today, approximately 24 percent of the energy consumption of the United States comes from natural gas. More than one-half of the homes in the country use natural gas as their main heating fuel.
Natural gas is a colorless, shapeless, and odorless gas. Because it has no odor, gas companies add a chemical to it that smells similar to rotten eggs. This way you can tell if there is a gas leak in your house. Natural gas is also an essential raw material for many common products, including paints, fertilizers, plastics, antifreeze, and medicine.
We also get propane—a fuel often used in many barbecue grills—when we process natural gas.
DRILLING FOR NATURAL GAS
The exploration for and production of natural gas is very similar to that of petroleum. In fact, natural gas is commonly found in the same reservoirs as petroleum. Because natural gas is lighter, it is often found on top of the oil.
And like oil, some natural gas flows freely to wells because of the natural pressure of the underground reservoir forces the gas through the reservoir rocks. These types of gas wells require only a “Christmas tree,” which is a series of pipes and valves on the surface that are used to control the flow of gas. Only a small number of these free-flowing gas formations still exist in the U.S. gas fields.
Most now need some type of pumping system to extract the gas still trapped in the underground formation. One of the most common is the “horse head” pump, which rocks up and down to lift a rod in and out of a well bore, bringing gas and oil to the surface.
Often the flow of gas through a reservoir can be improved by creating tiny cracks in the rock, called fractures, that serve as open pathways for the gas to flow. In a technique called “hydraulic fracturing,” drillers force high pressure fluids (like water) into a formation to crack the rock.
A “propping agent,” like sand or tiny glass beads, is added to the fluid to prop open the fractures when the pressure is decreased.
Natural gas can be found in a variety of different underground formations, including: shale formations; sandstone beds; and coal seams. Some of these formations are more difficult and more expensive to produce than others, but they hold the potential for vastly increasing the nation’s available gas supply.
Recent research is exploring how to obtain and use gas from these sources. Some of the work has been in Devonian shales, which are rock formations of organic rich clay where gas has been trapped. Dating back nearly 350 million years (to the Devonian Period), these black or brownish shales were formed from sediments deposited in the basins of inland seas during the erosion that formed the Appalachian Mountains.
Other sources of gas include “tight sand lenses.” These deposits are called “tight” because the holes that hold the gas in the sandstone are very small. It is hard for the gas to flow through these tiny spaces. To get the gas out, drillers must first crack the dense rock structure to create ribbon-thin passageways through which the gas can flow.
Coalbed methane gas that is found in all coal deposits was once regarded as only a safety hazard to miners but now, due to research, is viewed as a valuable potential source of gas.
STORAGE AND DELIVERY OF NATURAL GAS
Once natural gas is produced from underground rock formations, it is sent by pipelines to storage facilities and then on to the end user. The United States has a vast pipeline network that transports gas to and from nearly any location in the lower 48 states. There are more than 210 natural gas pipeline systems, using more than 300,000 miles of interstate and intrastate transmission pipelines.
There are more than 1,400 compressor stations that maintain pressure on the natural gas to keep it moving through the system. There are more than 400 underground natural gas storage facilities that can hold the gas until it is needed back in the system for delivery to the more than 11,000 delivery points, 5,000 receipt points, and 1,400 interconnection points that help transfer the gas throughout the country.
MEETING OUR FUTURE NATURAL GAS NEEDS
Natural gas is an important energy source for the U.S. economy, providing 24 percent of all energy used in our Nation’s diverse energy portfolio. A reliable and efficient energy source, natural gas is also the least carbon-intensive of the fossil fuels.
Historically, the United States has produced much of the natural gas it has consumed, with the balance imported primarily from Canada through pipelines. The total U.S. natural gas consumption is expected to increase from about 23 trillion cubic feet today to 24 trillion cubic feet in 2035.
Production of domestic conventional and unconventional natural gas cannot keep pace with demand growth. The development of new, cost-effective resources such as methane hydrate can play a major role in moderating price increases and ensuring adequate future supplies of natural gas for American consumers.
Methane hydrate is a cage-like lattice of ice inside of which are trapped molecules of methane, the chief component of natural gas. If methane hydrate is either warmed or depressurized, it will revert back to water and natural gas. When brought to the earth’s surface, one cubic meter of gas hydrate releases 164 cubic meters of natural gas.
Hydrate deposits may be several hundred meters thick and generally occur in two types of settings: under Arctic permafrost, and beneath the ocean floor. Methane that forms hydrate can be both biogenic, created by biological activity in sediments, and thermogenic, created by geological processes deeper within the earth.
While global estimates vary considerably, the energy content of methane occurring in hydrate form is immense, possibly exceeding the combined energy content of all other known fossil fuels. However, future production volumes are speculative because methane production from hydrate has not been documented beyond small-scale field experiments.
LIQUEFIED NATURAL GAS
Another way to ensure the United States has enough natural gas to meet demands is through importing gas from foreign countries. Currently, most of the demand for natural gas in the United States is met with domestic production and imports via pipeline from Canada.
However, a small but growing percentage of gas supplies is imported and received as liquefied natural gas (LNG). A significant portion of the world’s natural gas resources are considered “stranded” because they are located far from any market. Transportation of LNG by ship is one method to bring this stranded gas to the consumer.
LNG is produced by taking natural gas from a production field, removing impurities, and liquefying the natural gas. In the liquefaction process, the gas is cooled to a temperature of approximately -260 degrees F at ambient pressure. The condensed liquid form of natural gas takes up 600 times less space than natural gas.
The LNG is loaded onto double-hulled ships which are used for both safety and insulating purposes. Once the ship arrives at the receiving port, the LNG is typically off -loaded into well-insulated storage tanks. Regasification is used to convert the LNG back into its gas form, which enters the domestic pipeline distribution system and is ultimately delivered to the end-user.
In 2008, the United States imported 352 billion cubic feet (Bcf ) of LNG from a variety of exporting countries but primarily from Trinidad and Tobago. There are currently nine LNG import terminals located along the Atlantic and Gulf coasts.
The mainland terminals are: Everett, Massachusetts; Cove Point, Maryland; Elba Island, Georgia; Freeport, Texas; Sabine Pass, Louisiana; Cameron, Louisiana; and Lake Charles, Louisiana. The off shore terminals are Gulf Gateway Energy Bridge in the Gulf of Mexico and Northeast Gateway, located off shore Boston.
As of July 2009, the government reported 34 new or expanded facilities that have been approved or proposed to serve U.S. markets.
If you could look down an oil well and see oil where Nature created it, you might be surprised. You wouldn’t see a big underground lake, as a lot of people think. Oil doesn’t exist in deep, black pools. In fact, an underground oil formation—an “oil reservoir”—looks very much like any other rock formation.
Oil exists in this underground formation as tiny droplets trapped inside the open spaces, called “pores,” inside rocks. The pores and the oil droplets can be seen only through a microscope. The droplets cling to the rock, like drops of water cling to a window pane.
WHERE IS OIL FOUND?
Oil reserves are found all over the world. However, some have produced more oil than others. The top oil producing countries are Saudi Arabia, Russia, the United States, Iran, and China.
In the United States, petroleum is produced in 31 states. Those states that produce the most petroleum are Texas, Alaska, California, Louisiana, and Oklahoma.
While the United States is one of the top producing countries, its need for petroleum surpasses the amount it can produce; therefore, a majority of our oil (close to 60 percent) must be imported from foreign countries. The country we import the most oil from is Canada, followed by Saudi Arabia, Mexico, Venezuela, and Nigeria.
USES FOR PETROLEUM
You are probably already familiar with the main use for petroleum: gasoline. It is used to fuel most cars in the United States. But petroleum is also used to make many more products that we use on a daily basis. A majority of petroleum is turned into an energy source. Other than gasoline, petroleum can also be used to make heating oil, diesel fuel, jet fuel, and propane.
It can also be turned into petrochemical feedstock—a product derived from petroleum principally for the manufacturing of chemicals, synthetic rubber, and plastics. It is also used to make many common household products, including crayons, dishwashing liquids, deodorant, eyeglasses, tires, and ammonia.
DRILLING FOR OIL—EXPLORATION
The first step to drilling for oil is knowing where to drill. Because it is an expensive endeavor, oil producers need to know a lot about an oil reservoir before they start drilling. They need to know about the size and number of pores in a reservoir rock, how fast oil droplets will move through the pores, as well as where the natural fractures are in a reservoir so that they know where to drill.
While in the past it may have taken a few guesses and some misses to find the right place to drill, scientists have discovered new ways to determine the right locations for oil wells. Using sound waves, scientists can determine the characteristics of the rocks underground. Sound travels at different speeds through different types of rocks.
By listening to sound waves using devices called “geophones,” scientists can measure the speed at which the sound waves move through the rock and determine where there might be oil-bearing rocks. Scientists can also use electric currents in place of the sound waves for the same effect.
Scientists can also examine the rock itself. An exploratory well will be drilled and rock samples called “cores” will be brought to the surface. The samples will be examined under a microscope to see if oil droplets are trapped within the rock.
DRILLING FOR OIL—PRIMARY RECOVERY
Once the oil producers are confident they have found the right kind of underground rock formation, they can begin drilling production wells. When the well first hits the reservoir, some of the oil may come to the surface immediately due to the release of pressure in the reservoir.
Pressure from millions of tons of rock lying on the oil and from the earth’s natural heat build up in the reserve and expand any gases that may be in the rock. When the well strikes the reserve, this pressure is released, much like the air escaping from a balloon. The pressure forces the oil through the rock and up the well to the surface.
Years ago, when the equipment wasn’t as good, it was sometimes difficult to prevent the oil from spurting hundreds of feet out of the ground in a “gusher.” Today, however, oil companies install special equipment on their wells called “blowout preventers” that prevents the gushers and helps to control the pressure inside the well.
When a new oil field first begins producing oil, the natural pressures in the reservoir force the oil through the rock pores, into fractures and up production wells. This natural flow of oil is called “primary production.” It can go on for days or years. But after a while, an oil reservoir begins to lose pressure.
The natural oil flow begins dropping off and oil companies must use pumps to bring the oil to the surface. It is not uncommon for natural gas to be found along with the petroleum. Oil companies can separate the gas from the oil and inject it back into the reservoir to increase the pressure to keep the oil flowing.
But sometimes this is not enough to keep the oil flowing and a lot of oil will be left behind in the ground. Secondary recovery is then used to increase the amount of oil produced from the well.
DRILLING FOR OIL—SECONDARY RECOVERY
Imagine spilling a can of oil on a concrete floor. You would be able to wipe some of it up, but a thin film of oil might be left on the floor. You could take a hose and spray the floor with water to wash away some of the oil. This is basically what oil producers can do to an oil reservoir during secondary recovery.
They drill wells called “injection wells” and use them like gigantic hoses to pump water into an oil reservoir. The water washes some of the remaining oil out of the rock pores and pushes it through the reservoir to production wells. This is called “waterflooding.”
Let’s assume that an oil reservoir had 10 barrels of oil in it at the start (an actual reservoir can have millions of barrels of oil). This is called “original oil in place.” Of those original 10 barrels, primary production will produce about two and a half barrels.
Waterflooding will produce another one-half to one barrel. That means that in our imaginary oil reservoir of 10 barrels, there will still be six and a half to seven barrels of oil left behind after primary production and waterflooding.
In other words, for every barrel of oil we produce, we will leave around two barrels behind in the ground. This is the situation facing today’s oil companies. In the history of the United States oil industry, more than 195 billion barrels of oil have been produced but more than 400 billion barrels have been left in the ground.
DRILLING FOR OIL—ENHANCED OIL RECOVERY
Petroleum scientists are working on ways to extract the huge amounts of oil that are left behind after primary and secondary production. Th rough enhanced oil recovery (EOR) techniques, it may be possible to produce 30 to 60 percent of the reservoir’s original oil in place. Current research in EOR techniques includes:
• Thermal recovery, which involves the introduction of heat such as the injection of steam to lower the viscosity, or thin, the heavy viscous oil, and improve its ability to flow through the reservoir. Thermal techniques account for more than 50 percent of U.S. EOR production, primarily in California.
• Gas injection, which uses gases such as natural gas, nitrogen, or carbon dioxide that expand in a reservoir to push additional oil to a production wellbore, or other gases that dissolve in the oil to lower its viscosity and improve its flow rate. Gas injection accounts for nearly 50 percent of EOR production in the United States.
• Chemical injection, which can involve the use of long-chained molecules called polymers to increase the effectiveness of waterfloods, or the use of detergent-like surfactants to help lower the surface tension that often prevents oil droplets from moving through a reservoir. Chemical techniques account for less than 1 percent of U.S. EOR production.
The EOR technique that is attracting the most interest is carbon dioxide (CO2)-EOR. Injecting CO2—the same gas that gives soda pop its fizz—into an oil reservoir thins crude oil left behind, pressurizes it, and helps move it to producing wells.
When all remaining economically recoverable oil is produced, the reservoir and adjacent formations can provide sites for storage of CO2 produced from the combustion of fossil fuels in power plants and other processes that generate large amounts of CO2.
By capturing the CO2 emissions from these sources and then pumping it into depleting oil reservoirs, we not only increase the production from the well but store the CO2 underground to prevent it from being released to the atmosphere, where it may affect the climate.
The potential or CO2 sequestration in depleted oil and gas reservoirs is enormous. The Department of Energy has documented the location of more than 152 billion tons of sequestration potential in the United States and Canada from CO2-EOR. Currently, about 48 million tons of mostly naturally produce CO2 are injected annually for EOR operations in the United States.
When crude oil is removed from the ground, it does not come out in a form that is readily useable. Before it can be used, it must be refined, where it is cleaned and separated into parts to create the various fuels and chemicals made from oil. Within the oil are different hydrocarbons which have various boiling points, meaning they can be separated through distillation.
To do this, the oil is piped through hot furnaces and based on the hydrocarbon’s weight and boiling point, various liquids and vapors will be created. The lightest components, such as gasoline, will vaporize and rise to the top, where they will condense and turn back into liquids.
The heavier components will sink to the bottom. This will allow the components to be separated from each other and turned into their respective product or fuel. After the refinery, the gasoline and other fuels created are ready to be distributed for use. A system of pipeline runs throughout the United States to transport oil and fuels from one location to another.
There are pipelines that transport crude oil from the oil well to the refinery. At the refinery, there are additional pipelines that transport the finished product to various storage terminals where it can then be loaded onto trucks for delivery, such as to a gas station.
Sometimes the oil is located deep underneath the ocean floor and off shore drilling must be used to extract the crude oil. A platform is built to house the equipment needed to drill the well; the type of platform used will depend on a variety of characteristics of the location, including the depth of the water and how far underwater the drilling target is located.
A blowout preventer is used just like on wells built on land. This helps prevent petroleum from leaking out of the well and into the water. Currently, there are more than 4,000 active platforms drilling for oil in the Gulf of Mexico. While a majority of them are located in waters less than 200 meters (650 feet) in depth, nearly 30 are located in areas where the water is more than 800 meters (2,400 feet) in depth.
STRATEGIC PETROLEUM RESERVE
Oil is a very important commodity to the United States. It fuels our cars and buses, as well as the machines at many factories and refineries. With a majority of the oil we use today being imported, what would happen if we weren’t able to get enough oil to keep up with the demand?
An oil embargo in the 1970s cut off the supply of oil imported to the United States from the Middle East leading to long lines at the gas stations and even some fuel shortages. While the idea of creating a stockpile had come up before, the embargo helped cement the idea that an oil reserve was in fact needed.
In 1975, Congress passed the Energy Policy and Conservation Act, which made it policy of the United States to establish a reserve of up to 1 billion barrels of crude oil. By 1977, oil was being delivered to the new Strategic Petroleum Reserve (SPR).
Currently, there are four SPR sites located in Texas and Louisiana, which have a total capacity to hold 727 million barrels of crude
oil (filled as of December 2009), making it the largest emergency oil stockpile in the world.
STORING THE OIL
At the SPR sites, the crude oil is stored in underground salt caverns. Salt caverns are carved out of underground salt domes by a process called “solution mining.” Essentially, the process involves drilling a well into a salt formation then injecting massive amounts of fresh water.
The water dissolves the salt. In creating the SPR caverns, the dissolved salt was removed as brine and either reinjected into disposal wells or more commonly, piped several miles off shore into the Gulf of Mexico. By carefully controlling the freshwater injection process, salt caverns of very precise dimensions can be created.
Besides being the lowest cost way to store oil for long periods of time, the use of deep salt caverns is also one of the most environmentally secure. At depths ranging from 2,000 to 4,000 feet (610 – 1,220 meters), the salt walls of the storage caverns are “self-healing.” The extreme geologic pressures make the walls rock hard, and should any cracks develop in the walls, they would be almost instantly closed.
An added benefit of deep salt cavern storage is the natural temperature difference between the top of the caverns and the bottom—a distance of around 2,000 feet. The temperature differential keeps the crude oil continuously circulating in the caverns, maintaining the oil at a consistent quality.
The fact that oil floats on water is the underlying mechanism used to move oil in and out of the SPR caverns. To withdraw crude oil, fresh water is pumped into the bottom of a cavern. The water displaces the crude oil to the surface. After the oil is removed from the SPR caverns, pipelines send it to various terminals and refineries around the nation.
FILLING THE SPR
Oil for the SPR can be purchased by the government from oil companies, as was done in the 1970s and the 1980s. In the late 1990s, the SPR also began using royalty-in-kind oil, which is oil that is given to the government by petroleum operators as payment on leases they hold on the federally owned Outer Continental Shelf in the Gulf of Mexico. Instead of paying for the leases with money, the companies give the government oil, which is then put into the reserves.
USING THE SPR
In an emergency, when a limited nation’s oil supply leads to an adverse impact on national safety or on the national economy, the president may order oil to be withdrawn from the reserve. The president can issue a full “drawdown” in which all the oil from the reserve is released.
A limited drawdown may be issued in times where the event threatening national energy supplies and the economy is less severe or expected to be of short duration. A limited drawdown has restrictions on the amount of oil that can be released, as well as for how long.
The president may also order a test sale, in which the process of releasing the oil into the marketplace is tested to ensure all personnel know the procedures for a drawdown and all equipment is operational. In the event of a drawdown, the Department of Energy—which manages the SPR—will offer a specific number of barrels of crude oil from the reserve for sale.
The department will select those companies to sell to and can begin delivering the oil within 13 days. Oil can be pumped from the reserve at a maximum rate of 4.4 million barrels per day for up to 90 days before the drawdown rate begins declining as the caverns empty out. At 1 million barrels per day, the reserve can release oil into the market continuously for nearly a year and a half.
There have been two emergency drawdowns from the reserve. The first took place in 1991 during the Persian Gulf War. In order to maintain a stabilized petroleum market during Operation Desert Storm, the government offered 33 million barrels of oil from the SPR for sale; a little more than 17 million barrels were bought and deliveries began within a month.
The second emergency drawdown occurred in 2005 after Hurricane Katrina damaged oil refineries in the Gulf Coast region.
The Department of Energy is also authorized to exchange oil from SPR. These exchanges have been used in the past to replace less suitable types of crude oil for higher-quality crude oil.
It has also been used for limited, short-duration actions to assist petroleum companies in resolving oil delivery problems, such as the CITGO/Conoco Exchanges in 2000, when a commercial dry dock collapsed, cutting off shipping channels to the refineries.