14 Energy Resources Fossil Fuels

14 Energy Resources—Fossil Fuels

Questions for Review

1. A society’s level of technological development strongly influences its per-capita energy consumption. Explain.

As development increases, consumption of manufactured goods, elaborateness of housing, and use of mechanized transportation all increase, increasing per-capita energy consumption.

2. What are fossil fuels?

Fossil fuels are carbon-rich fuels formed from the remains of ancient organisms; they include oil, natural gas, coal, and the hydrocarbons in oil shale and tar sand.

3. Briefly describe how oil and gas deposits form and mature.

Microorganisms are buried in sediment. With moderate heating and time, the complex organic molecules are broken down into simpler, lighter hydrocarbons: first, waxes and tarry, asphaltic materials form; then these are broken down into successively lighter liquid and eventually gaseous hydrocarbons.

4. Compare and contrast past and projected U.S. consumption of petroleum and coal.

Coal was the first fossil fuel used, but it was quickly supplanted by petroleum once the latter was discovered. The result is that the United States has consumed about half its total petroleum resources but only a few percent of its coal. Remaining coal is projected to be enough to last for several centuries at modest consumption rates.

5. What is enhanced recovery, and why is it of interest? Give at least two examples of the method.

Enhanced recovery means getting more oil or gas out of already-exploited deposits. This is important because, currently, only about one-third of the amount initially present is extracted, especially with oil. Enhanced-recovery methods would, by definition, be applicable to deposits already found. Methods include artificial fracturing to increase permeability of reservoir rocks; the use of hot water or steam to warm oil, decreasing its viscosity and increasing extractability; and the use of gas under pressure to force out more oil.

6. Explain the nature of geopressurized natural gas resources, and note at least one obstacle to their exploitation.

Geopressurized natural gas is gas dissolved in deep pore fluids under high pressure. The depths and pressures involved make exploitation both costly and somewhat dangerous.

7. What are methane hydrates, and where are they found? Why are they both a substantial potential energy resource, and a concern with respect to global climate change?

Methane (or gas) hydrates are crystalline solids made of gas and water molecules, which are found in marine sediments and in arctic regions. From a fuel perspective, the resource may be huge, containing perhaps twice the carbon of all the other fossil fuels put together. However, if global warming destabilizes gas hydrates in arctic regions, this may release a good deal of methane into the atmosphere, and as methane is a potent greenhouse gas, this would increase greenhouse-effect heating.

8. What is coal? Why is it a less versatile fuel than oil, and how might its versatility be increased?

23 Coal is a solid, carbon-rich fuel formed from the remains of land plants. As a solid, its uses are limited (it cannot easily be used in airplanes or cars, for example), and it is also a rather dirty fuel that leaves a considerable ash residue when burned. Its versatility can be increased by gasification or liquefaction, which converts it to gaseous or liquid fuel that could be used like natural gas or gasoline, respectively.

9. What advantages does coal-bed methane have over other “unconventional” gas sources? Describe one problem associated with its extraction.

Using coal-bed methane converts a previously useless waste product (and potential pollutant) to a useful fuel. Coal beds are well mapped, so we also know where this resource is; and the technology to recover it exists. A potential problem is the water in coal beds, much of it saline or otherwise contaminated, that would also be extracted and requires careful disposal.

10. What air-pollution problems are associated particularly with coal, relative to other fossil fuels?

Coal ash can contribute to particulate pollution if not controlled. Also, the sulfur in coal forms sulfur gases that react in the atmosphere to produce sulfuric acid, a strong acid that is a respiratory irritant and identified as the major factor in acidifying rain beyond its natural weak acidity.

11. List and describe at least three potential negative environmental impacts of coal mining.

Underground coal mining is hazardous to the miners. There is also potential for surface collapse over the workings, and hard- to-extinguish mine fires. Strip-mining of coal disturbs a much greater land surface, and weathering of spoil banks may result in acid mine drainage.

12. What are oil shales and tar sands?

Oil shales are sedimentary rocks (not necessarily shales) that contain the waxy solid kerogen dispersed within them. Tar sands—usually sandstones—contain a thick asphaltic petroleum.

13. Oil shale and tar sand share several drawbacks. Cite and explain several of these.

The hydrocarbon is rather dispersed in each case, so a large volume of rock must be processed to extract a modest volume of fuel. The rocks would most likely be strip-mined, with attendant problems. A large volume of water is required to process these materials, and the rocks’ volume commonly increases during processing, leaving more waste rock to dispose of than the original volume mined out.