Presentation on theme: "Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 22 Energy."— Presentation transcript:
Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 22 Energy and Material Resources from the Earth
Fig. 22.3 Photosynthesis and Fossil Fuels The Carbon Cycle
Fossil fuels Decayed organic material (plants) Must have relatively rapid burial FOSSIL FUELS ARE A NONRENEWABLE RESOURCE
Hydrocarbons—oil and gas Oil formation 1) Relatively large quantity of organic matter 2) Rapid burial (before oxidation) 3) Subsequent chemical reactions [f(P,T)] transform decaying organic matter into hydrocarbons.
How do oil and gas deposits form? Production of large amounts of organic material (mainly microscopic plants and bacteria) Preservation in a reducing (oxygen-poor) depositional environment (e.g., restricted ocean basin) Burial causes increased heat and pressure, resulting in maturation (the physical and chemical breakdown of organic matter into a liquid or gaseous hydrocarbon compounds) in a source rock.
There’s more: Migration of fluids out of the source rock into a more permeable reservoir rock. Trapping of fluids must occur by encountering an impermeable seal. In short, you need – Production – Preservation – Maturation – Migration – Trapping
Thermal conditions of oil formation Relatively narrow temperature range: ≈50–200°C (also depends on time) Temperature and duration determine type of hydrocarbon: oil wet gas dry gas gone Duration of process could last millions of years
Environments of oil formation Continental shelf Continental rise Some nonmarine basins
Reservoirs For oil to be useful, it must accumulate in concentrated and accessible areas. Such spots are called reservoirs. Accumulation is possible because oil and gas are low-density fluids that can migrate through the pore space in rocks.
Reservoirs To create a reservoir, the migration of the fluids is retarded by cap rock. Cap rocksReservoir rocks shalesandstone gypsumlimestone salt limestone
Trap Combination of cap rock and reservoir rock favorable for petroleum accumulation Stratigraphic trap Structural trap
Dry Holes Many potential reservoirs exist that are free of hydrocarbons. Source rocks may have enough organic matter but may never have been hot enough.
Oil distribution Most oil is found in Cenozoic rocks, which have the best chance of preservation (erosion, metamorphism).
How do we explore for oil? Map surface geology (use surface geometry to interpret subsurface conditions) Seismic exploration (good way to get lots of information but subject to interpret) Drilling, coring (more detailed information from smaller area—like seismic, very expensive)
How much oil is left? Proven reserves: 700 billion barrels (over half in Middle East) Petroleum resources: 2 trillion barrels 1997 consumption: ~70 million barrels per day At this rate reserves will last between 25 and 80 years.
This assumes no increase in the rate of consumption, but Between 1985 and 1995, consumption of oil in the world increased by 16%. The increase in Latin America was 30%. The increase in Africa was 40%. The increase in Asia was 50%.
Fig. 22.10a Peter Kresan Strip Mining Coal in Pennsylvania
Fig. 22.10b Peter Kresan Reclaimed Land in Pennsylvania
Alternatives to fossil fuels 1. Nuclear energy Advantage: virtually inexhaustible supply Disadvantage: dangerous waste
After R.E. Gephart, 1998 Possible Nuclear Waste Contamination
Alternatives to fossil fuels 2. Solar energy Advantage: virtually inexhaustible supply Disadvantage: very expensive with current technology
Fig. 22.11 Ned Gallate/The Stock Market Solar Cells
Alternatives to fossil fuels 3. Geothermal energy Advantage: cheap and clean Disadvantages: cannot be transported long distances
Geothermal energy Must have a concentrated heat source near the surface: magma chamber with porous rocks above Cool water pumped into hot rocks, hot water or steam extracted (rocks may be as cool as 80°C) Producing: Iceland, France Experimenting: New Mexico, California
Fig. 22.12 Pacific Gas and Electric Geothermal Energy to Electricity
Mineral deposits If deposited in concentrated volume, we get veins or lodes. If deposited in large volume, we get disseminated deposit. grade: The relative quantity of ore in an ore body (gold ≈0.05 oz/ton)
Mineral deposits hydrothermal deposits: minerals deposited from hot waters usually associated with igneous intrusions These fluids carry “low temperature ions”; when the fluids cool off (near surface) the solubility goes down and minerals with Pb, Fe, Hg, Cu, Zn, Ag, Au, etc. are precipitated.