ENERGY AND THE ENVIRONMENT
ENERGY AND THE ENVIRONMENT PHSC 1014
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Date Created: 10/02/15
ESA21 Environmental Science Exercises Fossil Fuels Natural Gas Introduction History In the world of fossil fuels natural gas is often the overlooked ugly duckling It gets lumped in with oil as in oil and gas industry even though the discussion usually centers upon oil It does not help that gasoline which is derived from oil is shortened to gas In many people s mind the gas in oil and gas refers to gasoline and not natural gas However natural gas has much to offer as an energy source that makes it preferable to other forms of fossil fuels It burns much cleaner than coal or oil and it produces far less carbon dioxide for each unit of energy Its simple chemical nature makes it a much better source to use in high efficiency fuel cells than either coal or gas As a usable energy source natural gas really has only one stumbling block but it is a major one it is hard to transport and store Ifthe transport or storage system is not completely sealed natural gas will leak Further both systems must be able to withstand high pressures in order to compact the natural gas into a reasonable space These problems have kept natural gas from widespread usage throughout history even though its existence has been known about for a long time Like coal and oil natural gas has been used for several millennia The earliest records ofthis date back to 200 BC when the Chinese developed a crude system of bamboo pipes to transport gas to burners to evaporate brine to make salt1 However it was not until largescale pipe systems were developed in the 1800 s that natural gas began to see extended use Initially it was used for lighting in homes and buildings The increased production of electricity in the late 1800 s led to a decline in this usage although there became a growing demand throughout the 1900 s for its use to heat homes water and cook Most of this usage of natural gas was near the wells that produced it due to the lack of longrange pipelines or transport In 1925 the first allwelded pipeline over 200 miles in length was built running from Louisiana to Texas The growth in such pipeline networks and the cheap price of natural gas led to an expansion in its use Between the turn of the century and 1970 usage and production of natural gas increased fiftyfold However production of natural gas in the US peaked in 1973 and by 1980 we began to import natural gas from other countries Today about 15 percent of our natural gas comes from other countries mostly through pipelines from Canada Usage Over the last century the use of natural gas has become more diversified In 2002 226 trillion cubic feet of natural gas were used in the US Table 1 shows a list ofthe different uses ofthis amount of natural gas As you can see natural gas has come a long way from being used primarily to provide lighting The greatest use today is in the industrial sector as an ener y source and as a chemical feedstock for such things as fertilizer The second greatest use is for generating electricity This is a growing sector as the creation of new turbine generators that burn the gas in an engine and then use the exhaust to boil water results in power plant efficiencies of 5060 Most of the Table 1 US Natural Gas Consumption2 remaining natural gas is used for heating hot water and cooking in homes and companies Table 1 also shows a few other uses of natural gas A very small portion ofthe total amount is used in cars and trucks as an alternative fuel to gasoline This usage results in reduced emissions from automobiles However the sparse usage for this less than 1 means that it makes a very small dent in the amount of air pollution The remaining 74 is used to extract the natural gas remove condensates and such and push it through the pipelines This wasted energy lowers the overall efficiency of natural gas While it is a decent amount of energy to waste it is still far lower than the amount of energy that is wasted in both the oil and coal sectors for refining and transportation The US is the world s largest consumer of natural gas due in large part to our large supplies and our ample pipeline network for getting the gas to market Many countries do not have a delivery system which severely limits its usage there and often results in natural gas from wells there being burned at the wellhead Still natural gas is the third largest commercial fuel source worldwide accounting for 23 percent of global energy consumption In 2002 there was a total of Table 2 WorldWide Usage 20023 903 trillion cubic feet of it consumed Table 2 shows the top five consumer countries of natural gas As you can see the US and Russia use much more natural gas than any other country Creation Natural gas is composed primarily of methane CH4 It does contain other chemical species such as butane and propane lfthe mixture is comprised only of these species it is called dry natural gas as there will be no liquid components at standard pressure and temperature There might also be some other organic components such as pentanes that are mixed in with these species These heavier species are normally liquid at standard temperature and pressure and comprise what is called natural gas liquids Natural gas might also be mixed in with nonhydrocarbon compounds such as water vapor carbon dioxide and hydrogen sulfide If so it forms what is called wet natural gas and requires some processing before it can be used Natural gas comes from the decomposition of organic matter just like oil and coal Unlike oil and coal though it can come from almost any organic matter whereas coal comes only from plant matter and oil comes almost exclusively from plankton and microplankton remains Natural gas can come from both of these sources as well This is why you often find it associated with both oil wells and coalmines Natural gas can also come from unconventional sources as well It is produced by dead plant matter decay in swamps and rice fields Animals such as cattle and termites produce large quantities as a byproduct of digestion These sources though cannot be tapped for energy use Other unconventional sources such as landfills manure digesters and wastewater treatment plants are used to produce natural gas China produces enough gas from manure digesters to provide cooking and lighting for over 6 million homes In the US we have over 340 landfill gas projects that can produce over 1000 MW of electrical power These unconventional sources fall under the heading of renewable sources of energy as they are using waste products that will continue to be produced Conventional sources unfortunately are not renewable as the rate of their production far exceeds the rate at which they are being produced Fig 1 Jefferson County Landfill DOE Production and Reserves The production of natural gas peaked in the US in 1973 In that year over 22 trillion cubic feet of natural gas were produced from wells almost all of which were in the lower 48 states Production fell off rapidly in the late 1970 s and reached a low of 16 trillion cubic feet in 1986 Soon after this low was reached the price of natural gas began to fall being cut in halfwithin four years This low price helped to spur increased demand for the natural gas which experienced a steady increase in production throughout the 1990s US production has been leveling off in recent years with the increase in demand being met by importing natural gas from Canada and a few other countries quot5 Natural Gas Pruductinn Production IcF 1970 1980 1590 2000 2010 Yeir Fig39 2 U39S39 ProdUCtion of natural gas The majority of natural gas production in the US comes from Texas 50 TCF Louisiana 13 TCF and the federal waters offshore of these two states 44 TCF Together they account for over 10 trillion cubic feet of natural gas which is more than half ofthe 193 trillion cubic feet produced in 2002 Behind these two regions the largest production comes from New Mexico 15 TCF Oklahoma 15 TCF and Wyoming 14 TCF More accurately we really should clarify this and say that these are the largest producers that send natural gas to market Over 3 trillion cubic feet of natural gas are withdrawn from wells in Alaska However because of the lack of an available pipeline to handle shipping this much natural gas from the North Slope region the natural gas is pumped back into the ground for storage While pipelines have been proposed to ship the natural gas down to the lower 48 states the cost of such a venture has made the probability ofthis becoming a reality any time soon zero These production ratios between the various states closely matches the ratio of proven reserves of natural gas By most estimates the US has between 180 190 trillion cubic feet of natural gas in proved reserves Ofthis about one quarter 50 TCF is in the state of Texas or in the federal waters offshore of it while another 28 TCF is in Louisiana or in the federal waters offshore of it Behind these two regions come Wyoming 20 TCF New Mexico 17 TCF Oklahoma 15 TCF and Colorado 14 TCF This accounts for about threefourths ofthe proved reserves between these six states These ratios of production and reserves also account for why most of the natural gas consumption in the US occurs in the South and West As we stated previously the worldwide consumption of natural gas is a little over 90 TCF a year The largest producing country is Russia 21 TCF followed quickly by the US 19 TCF These two alone produce almost half ofthe world s output After them production values for other countries fall off quickly Canada is the world s third largest producing country with 65 TCF per year while the United Kingdom is fourth with 38 TCF per year5 What is interesting is that these are not all of the countries with the largest proven reserves of natural gas Russia leads the world with reserves of about 1700 TCF However Iran 940 TCF and Qatar 760 TCF have reserves that far outstrip the sums ofthe US and Canada 60 TCF6 As we said before the lack of an infrastructure that can get the natural gas from the wellhead to market makes the availability of this energy supply to consumers impossible in many countries It is this lack of infrastructure that causes more than 3 TCF of natural gas a year to be vented or flared into the atmosphere Coal Bed Methane This picture ofthe world s supply of natural gas can be radically altered by two fairly new potential sources of natural gas coal bed methane and methane hydrates Coal bed methane is exactly what it sounds like it is natural gas that is trapped within coal seams The natural gas mostly methane got there during the coal creation process as some of the plant matter was broken down by pressure heat and bacteria Unlike some deposits of natural gas in Colorado and Wyoming this methane did not migrate from the coal seam to become lodged in sedimentary rocks nearby Due to the large amount of surface area inside the coal that can trap the gas the coal seam can store up to six or seven times what a conventional rock formation will hold This means thatthese formations could produce vast quantities of natural gas It is estimated that there is about 700 TCF of coal bed methane in the us with about 100 TCF El c al ems of this being recoverable with today s technology so far there is only about 185 proved reserves of H9quot 339 current coal bEd memane pr ducu n coal bed methane 4 This would increase our reserves of natural gas by over 60 7 Besides the potential increase in reserves coal bed methane has a few other characteristicsthat makes it desirable Natural gas that is associated with petroleum reserves is usually found at depths that are about 14 miles deep within the Earth This means that drilling to get to these reserves is very costly Furthermore the pressures found at these depths means that pore spaces within the rocks is usually very tight causing low permeability in the rock and harming production Coal bed methane on the other hand is usually found at very shallow depths of anywhere from a couple of hundred feet to maybe a mile This greatly reduces the price of drilling The lower pressure at these depths means that natural gas can more readily flow from the coal which increases production and further reduces costs Coal bed methane does have some problems especially when one considers the effect on the environment Most shallow coal beds still contain a large amount of water This water tends to block the pore spaces in the coal and decreases flow rates of natural gas to the well One way to increase the flow rate is to draw offthe water and thereby open up the pathways for natural gas to flow This produced water is often saline in nature which makes its disposal problematic Allowing the waterto runoff on the surface will increase the salinity of local water ecosystems and radically affect the local plant and wildlife population Injecting the water back into the ground increases expenses which decreases the profitability of the wells Either way the drawing off of the water will lower the local groundwater which can have affects on local communities Currently our knowledge of extraction of natural gas from coal beds is still in its infancy We do not understand how best to produce natural gas from these areas nor do we know what environmental damage will be done by doing so Much more research is needed to properly understand the particulars of this situation Unfortunately there are many forces that are pushing the extraction from coal beds right now which could cause huge problems in the nearfuture Metha ne Hyd rates Another potentially large source of natural gas is methane hydrate formations These are solid crystalline features that are composed of a combination of methane water ice and other gases The methane and gases are trapped in the lattice structure of the water ice which like coal beds can hold much more natural gas than normal rock features These hydrate formations are usually found on the ocean floor where there is high pressure and nearfreezing temperatures This usually requires water depths greater than 300 feet Knowledge about these structures is quite slim For one thing we are not sure how they form It could be that the methane is produced by bacteria nearthe seafloor that are decomposing organic sediments Fig Diagram of methane in ice lattice However it might also be that the methane originates from oil deposits deep within the Earth that leaks to the sea floor bottom through faults and cracks Either way it is still unknown how the methane gets trapped within an ice lattice The lack ofthis knowledge means that we have no idea what conditions would be favorable for their formation This limits our ability to search for such structures Another matter that is unknown about methane hydrates is their stability The ice lattice structure is fairly delicate being much more fragile than a sedimentary rock would be that contains natural gas If the hydrates should breakdown it would cause a massive release of methane into the atmosphere By some estimates there is 3000 times the amount of methane in hydrate formations than is found in the atmosphere currently Given the size of these deposits and the ability of methane to absorb infrared radiation this could increase the greenhouse effect dramatically Further the decay ofthese hydrates on the ocean bottom could cause massive landslides which would cause problems for any extraction facility built nearby This lack of knowledge about the stability ofthe hydrate formations prevents us from building any type of extraction facility at this time Lastly we have no idea how much methane hydrate there is in the world The USGS estimates that there is twice the amount of carbon to be found in methane hydrate deposits as there is in all other fossil fuels combined However this estimate is made with scant information and could very well be wild speculation There is better data for the existence of methane hydrates in certain locations Mappings by the USGS of offshore North and South Carolina reveal the possible existence of a 1300 TCF methane hydrate deposit lfthis is true and if it could be extracted safely it would represent a 700 increase in the current natural gas deposits in the US At current consumption rates this would be a 70year reserve of natural gas While the potential for methane hydrates as an energy source are quite high our current lack of knowledge about their properties limits our ability to pursue Much more research is required before we attempt to exploit them as a source Additional Reading The following link discusses research on methane hydrates The site is maintained by the Department of Energy and also contains links to additional resources Topic National Methane Hydrate Program Summary Contains information about methane hydrate research Link httpwwwnetl doegovscnghydrate Department of Energ y The following Department of Energy website is a clearinghouse for information about natural gas Topic Natural Gas Information Navigator Summary Clearinghouse for information aboutnatural gas Link httptontoeiadoe govdnavngngsumtopasp Department of Ene rov The following is an opinion piece on the state of natural gas in the world It provides background information as well as projections for what the future holds um um Topic Natural Gas Primer quot1quot Summary Opinion pieceon the state of natural Gas quot Link httpwWwhubbertpeakcomgyasp rimer Hubbert Peak References 1 httQwwweiadoegovkidsmilestonesnaturalgashtml January 10 2004 2 httQtontoeiadoegovdnavngXlsng cons sum nus m dxls January 10 2004 3 httQwwweiadoegovemeuieatable13html January 10 2004 4 US Crude Oil Natural Gas and Natural Gas Liquids Reserves 2002 Annual Report Department of Energy Energy Information Administration 2002 5 httQwwweiadoegovemeuieatable41html January 10 2004 6 httQwwweiadoegovemeuieatable81html January 10 2004 7 Coal Bed Methane Potential and Concerns USGS Fact Sheet FS123 00 October 2000 8 4 httQmarineusgsgovfactsheetsgashydratestitlehtml January 10 200 John M Pratte 2004