Oil and Natural Gas

Intro

Colorado contains abundant oil and natural gas resources and reserves as well as a plethora of oil and gas fields throughout the state. A summary of these deposits is included in two CGS RockTalks on oil and the Niobrara Formation. Natural deposits of oil, or petroleum, include a variety of liquid compounds (crude oil), comprised of varying proportions of carbon and hydrogen (hydrocarbons), and gaseous hydrocarbons (natural gas) commonly comprised of methane and other constituents (e.g. ethane, propane, and butane). Minor amounts of nitrogen, oxygen, sulfur, and other trace elements are also present in petroleum. These non-renewable fuels are likely the result of decomposition and burial of organic matter produced by either marine or terrestrial plants and/or animals that died long ago. The formation of oil and natural gas from organic material is a complicated process. Petroleum geologists refer to the geologic elements and processes that are essential for natural oil and gas formation as a “petroleum system.” Generally, the geologic elements of petroleum systems include several components: source rocks, migration pathways, and reservoir rocks, seals, and traps. Geologic processes create each of these elements – specific factors associated with these elements determine if and where a commercial deposit may exist (Magoon, 1988).

At the end of 2019, Colorado contains ~1.56 billion barrels of proven oil resources and ranks 8^th in the U.S. for proven oil reserves. In 2020, Colorado produced ~171.5 million barrels of oil. Currently, in 2020, 29 counties produced oil with most produced from Weld County (~138 million barrels) followed by Adams, Broomfield, Rio Blanco, Arapahoe, Garfield, and Jackson counties (produced a combined ~17.6 million barrels of oil in the same year).

Oil

For kerogen to be transformed into oil, it must be buried to a depth where the temperature and pressure are sufficiently high to convert the kerogen into oil. The place where the depth is sufficient to achieve this, is called the “oil window”. Oil shale which contains only kerogen was never buried deeply enough to generate oil. Therefore, humans must artificially convert the kerogen in oil shale into oil at high temperatures.

Oil shale is different from shale oil. People are increasingly developing shale oils such as the Bakken shale oil in North Dakota and Niobrara shale oil in Colorado. These strata were buried deeply enough to convert the kerogen into oil. However, substantial quantities of the generated oil remained in the source rock, rather than migrating out of the source rock into a more conventional reservoir rock. So, oil companies are successfully using fracking technology and horizontal drilling to extract the oil from these units of shale oil. As of 2020, most of the oil production in Colorado is from these unconventional resources such as the Niobrara Formation in Weld County.

Natural Gas

Natural gas, in itself, might be considered an uninteresting gas—it is colorless, shapeless, and odorless in its pure form. Quite uninteresting—except that natural gas is combustible, abundant in the United States, and when burned gives off a great deal of energy and few emissions. Compared to other non-renewable fuels, natural gas is cleaner burning and emits lower levels of potentially harmful byproducts into the air. We require energy constantly, to heat our homes, cook our food, and generate our electricity. It is this need for energy that has elevated natural gas to such a level of importance in our society, and in our lives.

At the end of 2019, Colorado contains 24,115 billion cubic feet (Bcf) of proven natural gas resources and ranks 7th in the U.S. for proven natural gas reserves. In 2020, 36 counties produced natural gas producing ~2,064 Bcf of natural gas (including coalbed methane). Currently, in 2020, most natural gas in Colorado is produced from Weld County (~953.8 Bcf) followed by Garfield (~424.9 Bcf), La Plata (~220.8 Bcf), Rio Blanco (~100.0 Bcf), Las Animas (~41.7 Bcf), and Mesa counties (~40.5 Bcf).

Natural gas is a non-renewable fuel. Like oil and coal, this means that it is, essentially, the remains of plants and animals and microorganisms that lived millions and millions of years ago. But how do these once living organisms become an inanimate mixture of gases?

There are many different theories as to the origins of non-renewable fuels. The most widely accepted theory says that non-renewable fuels are formed when organic matter (such as the remains of a plant or animal) is compressed under the earth, at very high pressure for a very long time. This is referred to as thermogenic methane. Similar to the formation of oil, thermogenic methane is formed from organic particles that are covered in mud and other sediment. Over time, more and more sediment and mud and other debris are piled on top of the organic matter. This sediment and debris puts a great deal of pressure on the organic matter, which compresses it. This compression, combined with high temperatures found deep underneath the earth, breaks down the carbon bonds in the organic matter. As one gets deeper and deeper under the earth’s crust, the temperature gets higher and higher. At low temperatures (shallower deposits), more oil is produced relative to natural gas. At higher temperatures, however, more natural gas is created, as opposed to oil. That is why natural gas is usually associated with oil in deposits that are 1 to 2 miles below the earth’s crust. Deeper deposits, very far underground, usually contain primarily natural gas, and in many cases, pure methane.

Natural gas can also be formed through the transformation of organic matter by tiny microorganisms. This type of methane is referred to as biogenic methane. Methanogens, tiny methane-producing microorganisms, chemically break down organic matter to produce methane. These microorganisms are commonly found in areas near the surface of the earth that are void of oxygen. These microorganisms also live in the intestines of most animals, including humans. Formation of methane in this manner usually takes place close to the surface of the earth, and the methane produced is usually lost into the atmosphere. In certain circumstances, however, this methane can be trapped underground, recoverable as natural gas. An example of biogenic methane is landfill gas. Waste-containing landfills produce a relatively large amount of natural gas from the decomposition of the waste materials that they contain. New technologies are allowing this gas to be harvested and used to add to the supply of natural gas.

Natural Gas Constituents

Natural gas is a combustible mixture of hydrocarbon gases. While natural gas is formed primarily of methane, it can also include ethane, propane, butane and pentane. The composition of natural gas can vary widely, but below is a chart outlining the typical makeup of natural gas before it is refined.

In its purest form, such as the natural gas that is delivered to your home, it is almost 100% methane. Methane is a molecule made up of one carbon atom and four hydrogen atoms, and is referred to as CH₄. The distinctive smell that we often associate with natural gas is actually an odorant called mercaptan that is added to the gas before it is delivered to the end-user. Mercaptan aids in detecting any leaks.

Natural gas is found underground, although sometimes it leaks to the surface. Oil and gas are often found together in underground traps. Oil floats on water and natural gas floats on oil. Because of these density contrasts, oil and gas rise in a reservoir until they are trapped at the highest point. When the trap is a fold, it can create a commercial accumulation underground. In a case like this, it is possible to produce the oil and/or gas without producing any water, which is good for a variety of reasons. Since 1978, the industry has learned how to produce natural gas from coals. This is called coalbed methane production, or CBM. As of 2020, about 11% of our natural gas production in Colorado is from CBM.

For hundreds of years, natural gas has been known as a very useful substance. The Chinese discovered a very long time ago that the energy in natural gas could be harnessed and used to heat water. In the early days of the natural gas industry, the gas was mainly used to light street lamps, and the occasional house. However, with much improved distribution channels and technological advancements, natural gas is being used in ways never thought possible.

There are so many different applications for this non-renewable fuel that it is difficult to provide an exhaustive list of everything it is used for. And no doubt, new uses are being discovered all the time. Natural gas has many applications, commercially, in your home, in industry, and even in the transportation sector! While the uses described here are not exhaustive, they may help to show just how many things natural gas can do.

Natural gas is one of the most popular fuels for residential heating. In 2000, according to the American Gas Association (AGA), 51 percent of heated homes in the U.S. (or 49.1 million households), used natural gas heating. In addition to heating homes, natural gas can also be used to help cool houses, through natural gas powered air conditioning. Some examples of other natural gas appliances include space heaters, clothes dryers, pool and jacuzzi heaters, fireplaces, barbecues, garage heaters, and outdoor lights. Commercial uses of natural gas are very similar to residential uses. The commercial sector includes public and private enterprises, like office buildings, schools, churches, hotels, restaurants, and government buildings. The main uses of natural gas in this sector include space heating, water heating, and cooling. For restaurants and other establishments that require cooking facilities, natural gas is a popular choice to fulfill these needs.

Natural gas has a multitude of industrial uses, including providing the base ingredients for such varied products as plastic, fertilizer, anti-freeze, and fabrics. Natural gas is consumed primarily in the pulp and paper, metals, chemicals, petroleum refining, stone, clay and glass, plastic, and food processing industries. These businesses account for over 84 percent of all industrial natural gas use. Natural gas is also used for waste treatment and incineration, metals preheating (particularly for iron and steel), drying and dehumidification, glass melting, food processing, and fueling industrial boilers. Natural gas may also be used as a feedstock for the manufacturing of a number of chemicals and products. Gases such as butane, ethane, and propane may be extracted from natural gas to be used as a feedstock for such products as fertilizers and pharmaceutical products.

Natural gas has long been considered an alternative fuel for the transportation sector. In fact, natural gas has been used to fuel vehicles since the 1930’s! There are about 110,000 NGVs on U.S. roads today and more than 12 million worldwide. There are about 1,000 NGV fueling stations in the U.S. – and about half of them are open to the public. Most natural gas vehicles operate using compressed natural gas (CNG). This compressed gas is stored in a similar fashion to a car’s gasoline tank, attached to the rear, top, or undercarriage of the vehicle in a tube shaped storage tank. A CNG tank can be filled in a similar manner, and in a similar amount of time, to a gasoline tank.

Natural gas, because of its clean burning nature, has become a very popular fuel for the generation of electricity. In the 1970’s and 80’s, the choices for most electric utility generators were large coal or nuclear powered plants; but, due to economic, environmental, and technological changes, natural gas has become the fuel of choice for new power plants.