Mercedes Mullins
Natural gas is a fossil fuel formed from the remains of plants, animals, and microorganisms over millions of years. It is composed primarily of methane, with smaller amounts of natural gas liquids, carbon dioxide, and water vapour. The extraction of natural gas involves locating geological formations likely to contain deposits, such as shale, sandstone, and other sedimentary rocks, through seismic surveys. Once a potential site is identified, an exploratory well is drilled, and the quality and quantity of natural gas are assessed. The extraction process, known as hydraulic fracturing or fracking, involves pumping a mixture of water, sand, and chemicals into the rock under pressure to release the gas. Natural gas is used for electricity generation, as fuel, and in industrial processes, but its extraction and consumption contribute to climate change and pose health and safety challenges.
| Characteristics | Values |
|---|---|
| How natural gas is formed | Natural gas is a fossil fuel formed from the remains of plants, animals, and microorganisms that lived millions of years ago. Under oxygen-free conditions, these organic materials were subjected to intense heat and pressure underground, causing them to thermally decompose and transform into natural gas. |
| Composition | Natural gas primarily consists of methane (CH4), but it also contains smaller amounts of natural gas liquids (NGLs), carbon dioxide, water vapor, and other compounds. |
| Extraction methods | Natural gas is extracted through drilling wells into subsurface rock formations. In recent years, hydraulic fracturing or "fracking" has been used to extract gas from low-permeability formations, such as shale. |
| Processing | Before being used as fuel or in manufacturing, natural gas undergoes processing to remove impurities such as water, ethane, butane, propane, pentanes, hydrogen sulfide, carbon dioxide, and other gases. |
| Environmental impact | Natural gas is considered a cleaner-burning fuel compared to other fossil fuels, producing lower amounts of harmful emissions like nitrogen oxides and sulfur dioxide. However, its extraction and consumption contribute to climate change, and leaks during the extraction and distribution processes can lead to methane emissions. |
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What You'll Learn
Locating natural gas deposits
Geologists and geophysicists use technology and knowledge of the properties of underground natural gas deposits to gather data that can be interpreted and used to make educated guesses about the location of deposits. Two-dimensional seismic imaging is a technique where geophysicists use data collected from seismic exploration activities to develop a cross-sectional picture of the underground rock formations. They interpret the seismic data, including vibration recordings, to develop a conceptual model of the composition and thickness of the various layers of rock underground. This process is used to map underground formations and make estimates based on geologic structures to determine the likelihood of deposits.
Another technique using seismic data is called 'direct detection', which was discovered in the mid-1970s. 'Bright spots', or white bands, on seismic recording strips can indicate deposits of hydrocarbons. The porous rock that contains natural gas reflects stronger seismic reflections than water-filled rock, allowing for the detection of natural gas reservoirs. However, this method is not completely reliable as not all 'bright spots' contain hydrocarbons, and not all hydrocarbon deposits are indicated by white strips.
Three-dimensional seismic imaging can be used in conjunction with other exploration techniques to more accurately locate petroleum reservoirs and place wells to be drilled. This technique is more costly and prolonged than 2-D imaging as it requires data from thousands of locations. Four-dimensional seismic imaging can further increase recovery rates by providing information on the depletion of the reservoir over time.
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Drilling and testing
Once a promising site is identified, the drilling process can begin. The first step is to prepare the site by clearing and levelling the land, followed by setting up the necessary infrastructure, such as access roads, safety barriers, and safety procedures. A drilling rig is then assembled on-site, and a well is drilled straight down into the ground. This initial borehole, known as the surface hole, extends to a depth below the deepest known aquifer to avoid polluting water sources. A steel casing is cemented in place to protect the aquifer.
The next stage involves drilling the main well. This process typically takes about 50-60 days and includes feeding steel pipe into the well while using drilling mud to manage pressures, gather information about rock layers, and cool the drill bit. Safety equipment, such as a blowout preventer, is also installed to prevent the unexpected release of natural gas or oil.
After drilling, the completion process begins. This involves perforating the steel pipe to connect the well bore to the natural gas reservoir. Additional techniques like hydraulic fracturing or steam flooding may be applied to enhance recovery. Hydraulic fracturing, also known as fracking, involves pumping a high-pressure mixture of water, sand, and chemicals into the well to create cracks in the rock and release the trapped natural gas.
Once the drilling and completion processes are completed, testing is performed to assess the quality and quantity of natural gas available. If the results are favourable, production wells are drilled to extract the natural gas. These wells can be drilled vertically or horizontally, depending on the characteristics of the natural gas-bearing formations. In conventional natural gas deposits, the gas flows easily up through the wells to the surface, while unconventional natural gas, found in shale and other sedimentary rock formations, requires hydraulic fracturing to break up the rock and release the gas.
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Hydraulic fracturing
Fracking involves injecting a mixture of water, chemicals, and sand at high pressure into impermeable rock formations, causing the rock to crack and release the gas trapped within. This technique is used to extract gas from tight pores or small cracks in the rock, which would otherwise be difficult to access.
The process of hydraulic fracturing usually begins with drilling a well vertically down to the depth of the rock formation containing the natural gas. The drilling then turns horizontal, extending for thousands of feet within the rock layer. Steel casings are inserted into the well, creating a barrier between the rock and the casing. Small holes are made in the casing to allow for the injection of the fracking fluid.
The fracking fluid, consisting of water, chemicals, and sand, is then pumped into the well at high pressure. This creates new fractures in the rock or widens existing ones, allowing the natural gas to escape. The gas flows out of the pores and into wells that funnel it to the surface for gathering, processing, and transportation.
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Processing natural gas
Natural gas is a fossil fuel formed from the remains of plants, animals, and microorganisms that lived and were deposited in an oxygen-poor environment millions of years ago. It is composed primarily of methane, with smaller amounts of natural gas liquids (NGLs), carbon dioxide, water vapour, and other compounds. Before natural gas can be used as a fuel or in industrial processes, it undergoes processing to remove impurities and separate the methane from other components. This processing is essential to ensure the gas meets specified requirements, such as pipeline quality specifications for transmission companies.
The extraction process for natural gas can vary depending on the geological formation from which it is sourced. Conventional natural gas is extracted by drilling wells into subsurface rock formations. In contrast, unconventional natural gas, found in tiny pores within shale, sandstone, and other sedimentary rocks, is extracted using hydraulic fracturing or "fracking" technology. This process involves pumping a pressurised mixture of water, sand, and chemicals into the rock to increase its permeability and release the gas trapped within.
During the extraction and processing of natural gas, several impurities and compounds must be removed. These include water, ethane, butane, propane, pentanes, and higher molecular weight hydrocarbons. Additionally, toxic compounds like hydrogen sulfide, which may be converted into pure sulfur, carbon dioxide, and water vapour, are also eliminated. In some cases, helium and nitrogen may be present and require removal as well.
The processed natural gas, with its high methane content, is then ready for use in various applications, such as fuel for heating, cooking, and electricity generation. It also serves as a raw material in industrial processes, including plastic production. However, it is important to acknowledge that natural gas extraction and consumption contribute to climate change and pose unique health and safety challenges for workers due to the release of radioactive isotopes and toxic compounds during the process.
Overall, the processing of natural gas involves the removal of impurities, separation of desired compounds, and ensuring compliance with specific requirements to make it suitable for transportation and utilisation in various sectors.
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Environmental impact
Natural gas, a fossil fuel, is considered a relatively clean-burning fuel source. However, its production and use have significant environmental and safety considerations. The extraction, transportation, refining, and burning of natural gas contribute to climate change, air and water pollution, and health issues.
The burning of natural gas emits fewer air pollutants and carbon dioxide than coal or petroleum products for the same amount of energy. However, natural gas is composed mainly of methane, a potent greenhouse gas that is 34 to 84 times more effective at trapping heat than carbon dioxide over a 20-year period. Leaks occur throughout the natural gas system during extraction and transportation, and studies have shown high rates of methane leakage. This undermines natural gas's reputation as a cleaner fuel and contributes significantly to global warming.
The combustion of natural gas also produces nitrogen oxides, which are precursors to smog, and small amounts of sulfur, mercury, and particulates. Air pollution from burning fossil fuels has been linked to asthma, cancer, heart disease, and premature death. Globally, fossil fuel pollution is responsible for one in five deaths, with 350,000 premature deaths in the United States in 2018 attributed to fossil fuel-related pollution.
Additionally, the extraction of natural gas through hydraulic fracturing (fracking) has environmental implications. Fracking requires large amounts of water, which can impact aquatic habitats and water availability for other purposes. The use of hydraulic fracturing fluid, which may contain hazardous chemicals, poses a risk of contaminating surrounding areas through spills, leaks, or faulty well construction.
The environmental impact of natural gas extends beyond its immediate effects. The development of unconventional gas can affect local and regional air quality, and the infrastructure required for a transition to natural gas as a bridge fuel may slow down the adoption of truly renewable energy sources. Furthermore, the extraction and burning of natural gas contribute to ocean acidification, with about a quarter of the carbon dioxide emitted being absorbed by the oceans, altering their chemistry.
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Frequently asked questions
Natural gas is a fossil fuel formed from the remains of plants, animals, and microorganisms that lived and decomposed millions of years ago. It is composed primarily of methane (CH4), a highly flammable compound, along with smaller amounts of other gases and liquids.
Natural gas is formed through either biogenic or thermogenic processes. The thermogenic process involves organic matter being heated and compressed deep underground over millions of years, breaking down carbon bonds and converting it into hydrocarbons. The lightest of these hydrocarbons exist as gas under normal conditions and are collectively called natural gas.
Geologists use seismic surveys on land and in oceans to locate potential natural gas deposits. These surveys create and measure seismic waves to understand the underlying rock formations. If a site shows potential, an exploratory well is drilled and tested to determine the quality and quantity of natural gas present.
Natural gas is extracted from the ground in its gaseous form. Energy companies use hydraulic fracturing, or fracking, to break up rock formations and release the gas. They pump a mixture of water, sand, and chemicals under pressure into the rock, allowing the gas to flow into wells and be brought to the surface.
