Natural Gas

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Natural Gas Th e same factors that promote the formation of petroleum also help in the formation of natural gas. It is therefore expected that natural gas is found at locations near oil fi elds, oft en in association with petroleum (thus its name associated or dissolved gas). It is liberated when oil is brought to the surface in the same manner that carbon dioxide gas is liberated when someone opens a carbonated drink. If the gas diff uses through the pores of sedimentary rocks and accumulates in a reservoir other than the oil reservoir, the gas is called non-associated gas. Up to only a few decades ago, most natural gas discovered was fl ared off or reinjected into the ground, as it was considered to be of litt le use. Its use increased during the latt er half of the twentieth century, as it proved to be a convenient and relatively clean fuel to be burned in gaseous burners for space heating and cooking (Figure 7-19). Natural gas is primarily methane (CH4), but a certain percentage of heavier hydrocarbons such as ethane (C2H6), propane (C3H8), butane (C4H10), and a small amount of pentane (C5H12) and hexane (C6H14) are 28 George, R L, “Mining for Oil,” Scientifi c American, March 1998. 29 Duncan, D. C., and Swanson, V. E., “Organic-rich shale of the United States and world land areas,” US Geological Survey Circular 523, 1965. 30 “Annual Energy Outlook 2006,” Energy Information Energy, February 2006. Figure 7-19 Natural gas, the cleanest of all fossil fuels. Figure 7-18 The huge equipment used in strip-mining operations illustrates the dramatic impact that mining has on neighboring communities. 165 Chapter 7 - Fossil Fuels Table 7-8. Total Natural Gas Endowment (bbo equivalent)* World US Cumulative production Undiscovered reserves Reserve growth (inferred) Remaining (proven)reserves Total Endowment 292 866 610 799 2567 142 88 59 29 318

  • For defi nitions refer to Table 7-5.

Source: USGS World Producti on Assessment 2000 ( htt p:// also present. At normal temperature and pressure, pentane and hexane are liquid, but in elevated temperatures and pressures underground, they become gas and fl ow out with other gases. Commercial natural gas is primarily a mixture of methane and ethane. Th e propane and butane are liquefi ed and sold separately as liquefi ed petroleum gas (LPG) or “bott led” gas. For a long time, many producer countries used to burn natural gas at the well. Th is was very wasteful and caused huge environmental problems. Because of its lower density, it costs about four times as much to transport natural gas through pipelines as it does for crude oil; these gases are liquefi ed and shipped to their destinations as liquefi ed natural gas (LNG) in huge cryogenic containers aboard large tankers and ocean liners. Reserves, and Resources Th e total amount of available natural gas is shown in Table 7-8. Roughly two-third of all natural gas reserves lie in Russia and the Middle East (Table 7-9). Th e United States with 193 trillion cubic feet has a litt le more than 3% of the world’s natural gas reserves.31 Because natural gas is relatively clean, its rate of consumption is increasing by an average of 2.8% annually, faster than other sources of fossil fuels (Figure 7-20). If consumption continues to grow at this rate, natural gas reserves remain available for another 75 years. However, this number is believed to be optimistic, as natural gas substitutes coal and petroleum in an eff ort to reduce the eff ect of greenhouse gases.32 Besides wells, however, there are other sources of natural gas such as hydrates that if they could be extracted, would provide energy for many hundreds of years. Hydrates are icy deposits of crystallized natural gas and water, buried under the extreme pressures and cold temperatures of the deep oceans and Arctic permafrost that have been formed by the disintegration of certain bacteria. It is estimated that gigantic hydrate fi elds around the world contain twice the energy of all other forms of fossil fuels combined. Th ese reserves are virtually untapped, as there are major obstacles that have to be overcome before the reserves can be accessed. Any major changes in temperature or pressure may be capable of breaking down the material, releasing huge amounts of methane – a very potent greenhouse gas (See box “Th e Deadly Lake”).33 Th e cost of extraction is prohibitively high and the natural gas, even if it is extracted, has to be transported thousands of miles from Arctic regions before it can be used. One solution is to convert it to liquid synthetic fuel, such as methanol, before it is sent through pipelines. 31 Energy Information Agency Fact Sheet, htt p:// 32 Meadows, D., Limits to Growth: 30-Year Update, Chelsea Green Publishing Company, 2002, p. 94. 33 A few petroleum geologists have gone so far as to blame the loss of ships and airplanes in the Bermuda Triangle on sudden pulses of methane gas released from a hydrate layer below the Atlantic Ocean. As the ocean boils with a sudden squirt of methane bubbles, ships can be swallowed before having time to make distress calls, and plane engines might be choked by the rising plume of methane gas. Table 7-9. World Proven Natural Gas Reserves as of Jan. 1, 2006 Country Total Recoverable Reserves (trillion cubic feet) Percentage of the Total Russia 1680 30.5 Iran 971 15.9 Qatar 911 14.9 Saudi Arabia 241 3.9 UAE 214 3.5 Other Mid.East 223 4.1 US 193 3.1 Rest of the World 1,679 24.1 Total 6112 100 Source: Energy Informati on Agency, 2006. Figure 7-20 The outlook for worldwide natural gas consumption Source: Energy Informati on Agency, 2005. 􀀒􀀐􀀐 􀀑􀀕􀀐 􀀑􀀐􀀐 􀀕􀀐 􀀐 􀀴􀁒􀁉􀁌􀁌􀁉􀁏􀁎􀀀􀀣􀁕􀁂􀁉􀁃􀀀􀀦􀁅􀁅􀁔 􀀨􀁉􀁓􀁔􀁏􀁒􀁙 􀀰􀁒􀁏􀁊􀁅􀁃􀁔􀁉􀁏􀁎􀁓 􀀓􀀖 􀀕􀀓 􀀗􀀓 􀀘􀀗 􀀙􀀐 􀀑􀀐􀀐 􀀑􀀑􀀖 􀀑􀀓􀀔 􀀑􀀕􀀐 􀀑􀀖􀀕 􀀑􀀙􀀗􀀐 􀀑􀀙􀀘􀀐 􀀑􀀙􀀙􀀐 􀀒􀀐􀀐􀀐 􀀒􀀐􀀐􀀑 􀀒􀀐􀀐􀀕 􀀒􀀐􀀑􀀐 􀀒􀀐􀀑􀀕 􀀒􀀐􀀒􀀐 􀀒􀀐􀀒􀀕 166 Converting natural gas to liquid fi rst requires breaking its chemical bonds using steam, heat and a nickel-based catalyst to produce a mixture of carbon monoxide and hydrogen known as syngas. Th is process is called steam reforming. Syngas is then blown over various catalysts to transform it into gasoline, diesel, and other liquid hydrocarbons.


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