What is Natural Gas

    Natural gas is a mixture of hydrocarbons formed from fossilized organic material from millions of years ago. Methane is the primary component of natural gas and it is tasteless, odorless, and colorless. Because of its properties, a chemical compound, mercaptan (which has the odor of rotten eggs), must be added to ensure its detection.

    Methane is a hydrocarbon, or a class of organic molecules that only contain hydrogen and carbon. Once burned, many hydrocarbons produce large amounts of heat energy and this is used to generate electricity. While natural gas is a nonrenewable resource, it is considered a "cleaner" type of energy because it produces less carbon dioxide (CO2) than coal or gasoline once burned. However, burning natural gas does not remove our dependence on fossil fuels for energy and CO2 is still produced into the air we breathe.

    Over time, the combination of dead organic material, heat, and pressure created not just methane, but several other forms of fossil fuels. The big ones we see today include coal and oil. Sometimes these other resources are discovered when exploring for natural gas. As stated earlier, natural gas is a mixture of methane, which we call "dry gas" and other hydrocarbons called "wet gases." Wet gases are other compounds in natural gas that include ethane, butane, propane, etc. These wet gases are very useful resources that can be converted into other fuels and materials. For example, the use of petrochemical plants, or "cracker plants", would enable the conversion of extracted ethane into ethylene, which is used extensively in the production of plastics.




Types of Gas Resources

Resources
Schumann, Jon;  Vossoughi, Shapour; Unconventional gas resources in the U.S.APorous Media and Its Applications in Science, Engineering, and Industry, AIP Conference Proceedings, 1453, 301-306 (2012).





Six Types of Unconventional Gas

Shale Gas

    Shale gas is a fine-grained rock that was formed from the mud or clay at the ocean's bottom. The gas trapped within shale is contained in both naturally occurring fractures and attached to clay surfaces in the shale itself. In December, 2008, the Potential Gas Committee projected the total natural gas resources in the United States at approximately 1,836 trillion cubic feet. In the North East, the Marcellus and Utica shale formations underlay areas of New York, Pennsylvania, Ohio, West Virginia, and portions of Virginia and Maryland. While shale gases have been known to be located 500 to 11,000 ft beneath the surface, the gas trapped in the Marcellus formation is closer to 6,000 - 9,000 ft deep. Some of the other large shale gas reserves in the U.S. include the Barnette, Haynesville, and Fayetteville formations. Because of the geologic nature of shale, the gas is scattered in the rock formations and has very poor ability to flow. This requires hydraulic fracturing methods, which utilize horizontal drilling, water, sand, and chemicals to break apart the shale enough to allow the gas to escape to the surface.

Shale Gas - Hydraulic Fracturing

    The hydraulic fracturing process involves drilling straight down until the shale formation containing the natural gas is reached. Then the drill changes direction and begins drilling horizontally within the shale formation. After the drill is removed, a well casing that consists of multiple layers of concrete and steel is placed from the surface to below underground aquifers to prevent waste discharge into groundwater. Farther down into the shale layer, charges are placed in the horizontal well and detonated to fracture the rock.

    Once drilling is complete, the next stage is where the extraction process gets its name. The shale must be hydraulically fractured, or "fracked", to ensure the detonated fractures remain open for the gas to escape to the surface. As part of this process, a mixture of 2-6 million gallons of water, sand, and chemicals, known as “frackwater,” is injected into the drilled well at high pressure. Sand particles keep the fractures open and the chemicals are used to kill unwanted bacteria and prevent corrosion. Natural gas escapes to the surface through the drilled well, along with portions of the original frackwater solution.

    This "produced water" contains both the original chemicals used in hydraulic fracturing as well as many other naturally occurring substances that have leached into the water while injected underground. After being exposed to the deep shale formations, the frackwater solution absorbs high concentrations of minerals (>100,000 ppm total dissolved solids), heavy metals like barium and strontium, and sometimes radioactive elements such as uranium, thorium, and radium. This waste water is stored within on-site tanks or ponds until it can be transported to a deep well injection site. Unfortunately, the gas rises out of the well at such high pressures, it has to be burned off in a process called "flaring" to allow the gas to be safely extracted. This is also a method used by gas companies to burn off impurities in the natural gas as it first escapes to the surface.

    In order to lower land use and environmental footprint on the surface, several wells can be drilled and fracked on a pad. This allows drillers to extract gas from the shale in any direction (see right). Because fracking uses so much water, some drilling companies are attempting to reuse the produced water to frack other wells.

Tight Gas

    Tight gas gets its name from the tight rock formations in which it is located. Extraction of natural gas from these tight rocks is very expensive and requires fracturing and acidizing. The Energy Information Administration estimates 310 trillion cubic feet of tight gas could possibly be extracted in the United States. The Montney formation in British Columbia, which is estimated to hold up to 800 trillion cubic feet of gas, is largest tight gas formation in North America.

Geopressurized Zones

    These zones of gas are very deep (10,000 - 25,000 ft) and under incredible pressure. A geoprocessurized zone is formed when clay containing natural gas is compressed over porous materials like silt or sand. Such a compression causes the gas to seep into the porous material beneath the clay. While these zones of highly pressurized gases are problematic for current drilling technologies, it is estimated that they could contain up to 5,000 - 49,000 trillion cubic feet of gas.

Deep Gas

    These sources of natural gas are exactly as the name implies, very deep and expensive to extract. Such gases can be at depths of 15,000 ft or more. Because of its depth, deep gas are not currently preferable in comparison to other much shallower conventional and unconventional gas formations.

Methane Hydrates 

    Methane hydrates exist in the arctic permafrost areas and consist of methane pockets trapped in frozen water. According to the U.S. Geological Survey, it is estimated that these methane hydrate regions could contain more carbon than the entire world's source of oil, coal, and non-methane hydrates combined.

Coal-Bed Methane




The Importance of Natural Gas

    Natural gas is an important resource for both chemical and energy industries. In December, 2008, the Potential Gas Committee projected the total natural gas resources in the United States at approximately 1,836 trillion cubic feet. With such a large reserve or resources beneath our feet, many believe this could reduce our dependence of foreign oil. One of the large reservoirs of natural gas lies in the Marcellus and Utica shale formations in Northeastern America. Because the natural gas is located in the shale formations, unconventional drilling is used with a fracturing method known as hydraulic fracturing, a.k.a. "fracking". Large stores of methane gas can be extracted for generating electricity while other wet gases can be used to create other chemical feed stocks.

Chemical and Agricultural Industry

    Both methane and wet gases can be used as chemical feedstocks. With the use of a steam reformer, methane can be converted to syngas, or synthesis gas, which consists of hydrogen (H2) , carbon monoxide (CO), and sometimes carbon dioxide (CO2). 

CH4 + H2O ⇌ CO + 3 H2

    Steam reformation requires high temperatures of 700 - 1100 °C and the use of nickel catalysts. The syngas produced from this process is critical for the production of ammonia and methanol. Most ammonia is used in fertilizers but it is also used to synthesize a wide range of other chemical compounds and commercial products:

 Nylon Petroleum Refining  Rubber Production  Household Cleaning 
 Clothing   Air-conditioning  Refrigeration

    Methanol is one of the most important chemical compounds in the chemical industry. It is used as the basis for thousands of products and hundreds of chemicals. Some of the materials produced from methanol include:

 Plastics  Safety glass laminate Refrigerants 
 Synthetic fibers  Adhesives  Windshield fluid
 Paints  Solvents  Particle board
 Resins  Carpeting  Pigments and dyes
 Magnetic film  Insulation  

    The other wet gas components of natural gas (ethane, propane, butane, etc.) can be used as chemical feedstocks when subjected to cracking (see right and below).




Energy Production



Resources

Cunningham, William P.; Cunningham, Mary Ann, Principles of Environmental Science Inquiry and Applications, McGraw-Hill Companies, Inc., Seventh Edition, 2013.






Examples of natural gas components








    
    There are two types of natural gas that can be extracted: (1) Conventional Gas and (2) Unconventional Gas:

Conventional Gas
    
    Gas reservoirs are usually trapped on top of oil reserves within a rock layer. Extraction of conventional gas is relatively easy and once the drilling is complete, the gas can escape to the surface (see picture left).

Unconventional Gas

    Natural gas reserves that cannot flow and are trapped in rock layers like shale or coal bed seams in such a way that the gas is tightly bound the rock formation. Drilling for unconventional gas is more complex and requires hydraulic fracturing to break apart rock formations so that enough gas can become free and flow to the surface. Because the natural gas is trapped in rock formations, the rock must be fractured for the gas to escape. Unconventional drilling is used to extract resources like methane hydrates, shale gas, deep gas, tight gas, and coal-bed methane (see picture left). There are six types of unconventional gas: shale gas, deep gas, coal bed methane, tight gas, methane hydrates, and geopressurized zones.






























    Between 360 to 290 million years ago, dead organic matter from swamps was buried and the intense heat and pressure from moving tectonic plates caused the formation of coal deposits with trapped methane gases. Because coal is more porous than other natural gas deposits and has a larger internal surface area, it can hold up to 6 - 7 times more gas. Coal-bed methane (CBM) is extracted from coal seams that are usually too deep for mining. Depending on the depth, vertical or vertical drilling is applied to acquire methane. It is estimated that 160 - 700 trillion cubic feet of CBM is stored under the United States alone. Some of the largest CBM sites in the U.S. include the Powder River Basin located in Wyoming and Montana, the San Juan Basin in Colorado and New Mexico, the Uinta Basin in Utah, and several other sites in Kansas and Virginia. The methane is allowed to escape these underground formations after the water around the coal seam is pumped out. Unfortunately, this water is high in salinity and contains harmful elements like barium, iron, arsenic, and manganese. This produces a serious risk to the surrounding environment because the high salinity water can deplete soil nutrients, cause erosion, kill plants, cause sedimentation, temperature changes, and pose a risk to drinking water.




Just How Important is Russian Gas for Europe?-Business- dw.de


Cracking Hydrocarbons

A petrochemical plant, or cracker plant, uses steam to "crack" or break hydrocarbons into smaller, more useful, hydrocarbons. For example, the wet gas ethane can be cracked into PVC, vinyl chloride, ethylene glycol, styrene, and polystyrene products. Such processes require massive amounts of energy but they are very important for the chemical and agricultural industries.




    Natural gas is a nonrenewable resource but it is the cleanest fossil fuel at our disposal. Currently, natural gas is most commonly being used to heat our homes and businesses. With such a surplus of natural gas resources, it is a potential for fueling transportation and offsetting our dependence on much dirtier fuels like oil and coal. This is very important because our current method of burning coal and oil to meet increasing energy demands is causing in devastating impacts on climate and the environment.

    Like natural gas, oil and coal are extracted from underground and while there are many methods, they all have serious impacts on our ecosystems and pose serious threats towards human health. Oil extraction is also dangerous because of its persistence in the environment if a spill occurs. Whether by train, vehicle, pipeline, boat, or drilling operations, oil spills seem to occur frequently around the world. Some of the largest oil spills here in the U.S. have been the 1989 Exxon Valdez and the 2010 BP Deep Water Horizon incidents. The latest controversy is the extraction of Tar Sands Oil from Canada and transportation of such material to the U.S. via the Keystone Pipeline.

    The environmental impact from accessing oil and coal reserves is serious but  even more issues reside in burning these fossil fuels. Burning oil and coal to provide electricity creates solid, liquid, and gaseous waste. Each form of waste is equally dangerous but the air emissions produced from burning fossil fuels is directly related to the issue of climate change. For years scientists have been warning about the increasing concentration of atmospheric greenhouse gas concentrations and their impact on global climate. The Intergovernmental Panel on Climate Change (IPCC) issued an assessment report in 2007 that included the results of 6 years of work by 2,500 scientists and represented a consensus of more than 90 percent of all scientists working on climate change. Their conclusion at 90 percent certainty is that the observed climate change is being caused by human activity. IPCC also projected the future of global climate change. They predicted that global temperatures will increase about 2-4 C by 2100. They also predicted that by the end of the century, sea levels will rise 1-2 meters. 

    Greenhouse gases are gases that have the ability to absorb infrared radiation (heat) from our sun. These gases are naturally present in our atmosphere and help keep our planet warm by regulating the amount of heat that remains trapped on the planet. However, the balance of greenhouse gases in the atmosphere has been offset due to burning fossil fuels, which emit these gases. The The three major greenhouse gases are CO2 , CH4 , and N2O. Some of the major sources of CO2 include burning fossil fuels, cement production furnaces, and the burning of forests and grasslands. About 3 billion tons of CO2 is taken up by terrestrial ecosystems and about 2 billion tons are absorbed by the oceans, leaving an annual atmospheric release of about 4 billion tons of  CO2 per year. Natural gas, or CH4 , is less abundant than carbon dioxide but it absorbs 23 times as much infrared energy per molecule. Methane is produced anywhere organic matter decays without oxygen, especially underwater. Some sources include ruminant animals, wet-rice paddies, coal mines, landfills, wetlands, and leaking pipelines. Nitrous Oxide (N2O) is produced mainly by chemical reactions between atmospheric nitrogen and oxygen, which combine in the presence of heat from internal combustion engines. 

    The effects of human caused climate change are already noticeable as the frequency and strength of drought, wildfires, storms, and rising sea levels are all increasing. In the years to come, all of these factors are going to have major impacts on agriculture, disease, and damage to infrastructure. 

    Because of the threat climate change poses, natural gas is currently the cleanest fossil fuel we can burn because it emits far less CO2 or other toxic particulate matter in comparison to coal or oil. While this helps, it does not solve the problem we face with greenhouse gas emissions.

    Methane (CH4) is more efficient at trapping radiation than CO2 and according to the EPA, pound for pound, CH4 impacts climate change twenty times greater than that of CO2 over a one hundred year period. So methane does burn cleaner than coal in the terms of producing less CO2, but on its own, methane is a greater threat to climate change than CO2 due to its large contribution to the greenhouse gas footprint.