Fossil Fuels - Lecture Notes

Energy Consumption

A. Fundamental Sources of Energy

  1. Nuclear fusion: energy from sun

  2. Gravity: generated by anything with mass (hydroelectric)

  3. Nuclear fission: splitting uranium atoms

  4. Geothermal: energy from Earth’s interior

  5. Chemical energy stored in chemical bonds

B. How We Produce Energy

  • Fossil fuels: oil, gas, coal

    • have replaced biomass as major energy source

    • most is used to produce heat and electricity

C. Source we use for energy is dependent on EROI (Energy returned on Investment)

  • high for fossil fuels —> cheap and provide a lot of energy

Fossil Fuel Formation + Origin

  • Defining a fossil fuel: biomass energy that is buried within the earth where it is stored until it’s extracted and burned

B. How Fossil Fuels Form

  • Fossil fuels are formed from ancient organic matter

  • Fossil fuels form in anaerobic environments (without oxygen)

  • All fossil fuels are a type of kerogen

    • source of material for crude oil, natural gas, and coal

  • To produce a fossil fuel, organic matter must be rapidly buried and not oxidized

    • form organic molecules into hydrocarbons

      • types of hydrocarbons: methane, propane, butane, octane

Geology of Fossil Fuels

  • Age: most produced during Paleozoic time era (540-250 MYA)

  • Source rock: sedimentary

    • shale: oil shale

    • sandstone: tour sands

    • coal: coal seams

    • petroleum migrates upwards (less than water)

    • Oil trap: holds oil or gas

      • impermeable rock

  • Geographically

    • oceans, swamps, lakes, deserts, any biome sedimentary rocks exists

How Geologists Find Fossil Fuels

  • 1. Geologic maps of sedimentary rock and structures

  • 2. Based off surfaced maps and drill holes, geologic cross sections made

  • 3. Use geophysical techniques such as seismic reflection

  • 4. Once potential reservoir rocks are found, exploratory drilling begins

Geology of Fossil Fuels

  • Origin of coal, oil, and gas is related to the geologic cycle

  • These fuels are essentially stored solar energy in the form of organic matter that has not been exposed to oxidation

  • A. Coal: Made up of altered residue of plants that lived in ancient swamps. Found in lagoons, coastal plains, and deltas

    • form in swamp, where water and sulfured soil excludes much oxygen

    • plants partially decompose in oxygen - deficient environment and accumulate slowly to form layers of peat

    • sediment deposited and composes peat to form peat

    • burning coal accounts for 20% of US energy

    • grade of coal: determines value as a fuel, while sulfur content determines how it will pollute atmosphere

      • heat maximizes: bituminous

      • low sulfur: subbtuminous

    • coal is mined in strip mining and subsurface

      • acid mine drainage

  • B. Oil and Gas

    • Found in concentrated deposits which have been mined from wells, oil shales and tar sands

    • Next to water, oil is the most abundant liquid in Earth’s crust

    • Oil and natural gas, one derived from organic materials buried with marine or lake sediments

    • Where they form are locations’s that are subsiding with deposition basins where older sediment is buried by younger sediment subdues it to go to higher temperatures and pressure

    • Organic material is cooked to form hydrocarbons. As depth of burial temperature and pressure increases, the porosity of the source rock is reduced because of the compaction

      • 1-3 km

    • Source rock: shale, sandstone, fractured limestone or sandstone

    • Reservoir rocks: course grained permeable rocks that hydrocarbons migrate through

    • Trap rock: impermeable layer that traps oil and gas (cut + cline, fault, salt dome)

    • Oil and gas are formed in large deposits (oil and gas fields)

      • oil and gas is mined using pumping wells

      • oil can be recovered from earth materials like oil shale and tar sands

    • Environmental disruptions: oil spills, air pollution, acid rain

  • C. Tar Sands

    • Sandstone with thick accumulation of viscous oil

      • must heat rock, energy intensive

      • strip mining and drilling

  • D. Natural Gas

    • Methane and other volatile hydrocarbons

      • hydro-frecking

        • breaks rock to relative oil and gas

  • E. Coal

    • Decomposed and compressed vegetation, grade of coal determines fuel value and air pollutant potency

      • max heat: bituminous

      • low sulfur: sub-bituminous

      • strip and subsurface mines

Refining Fossil Fuels

  • Oil and gas must be processes after extraction

  • Refining: hydrocarbons are separated into different size classes and are chemically transformed into special fuels

Finding Fossil Fuels

  • Source rocks, reservoir rocks, trap rocks + structures, oil + gas fields, tour sands, oil shale, ocean drilling

  • B. Geologist Exploration

    • Make geologic maps of sediment rock

    • Make geologic cross sections

      • based on surface maps and drill holes

    • Geophysical techniques: more detailed view beneath surface

    • Once rock reservoir is found, drill from surface: exploratory drilling

Types of Fossil Fuels

  • A. Petroleum Oil

    • Sludge like mixture of hydrocarbons, formed from dead carbon material

  • B. Oil Shale

    • Strip mining and hydro-fading

    • Shale with organic matter that has not been decomposed to produce petroleum

      • must be heated to high temperatures to drill oil out

Fossil Fuel Resources

  • Are we running out?

    • We’ve used about half of our reserves

    • At current levels of production:

      • ~50 years of oil, 60 years of gas, 105 years of coal

    • New technology and discoveries can lead to increase in reserves

    • Peak oil: when rate of production peaks and then declines

Fossil Fuel Impacts

  • Habitat destruction due to mining

  • Air pollution from exhaust and emissions

  • Acid rain

  • Groundwater contamination

  • Oil spills

  • Deepwater 2010

  • Exxon Valdez 1989

In Class:

  • Sedimentary rock is the rock associated with fossil fuel formation