17.3 Fossil Fuels

GEOL1340

Fossil Fuels

Non-renewable energy sources formed from ancient organic matter buried over hundreds of millions of years.

Global Fossil Fuel Reliance

Fossil fuels account for over 60% of world electricity generation and the vast majority of primary energy consumption.

Environmental Impacts of Fossil Fuels

Combustion releases greenhouse gases driving air pollution, global warming, sea-level rise, and long-term public health issues.

Coal Definition

An organic sedimentary rock formed from the incompletely decayed remains of ancient terrestrial plant material.

Ideal Coal Formation Environment

Warm, humid climates combined with oxygen-poor (anoxic) swamp or wetland conditions to prevent full decay.

Coalification Rank Progression

Peat -> Lignite -> Bituminous Coal -> Anthracite.

Peat

Partially decayed, carbon-rich terrestrial organic matter accumulated in surface wetlands or swamps under oxygen-poor conditions.

Lignite ("Brown Coal")

Low-grade coal formed under shallow burial (few 100 m to 1,500 m) and temperatures up to ~50°C; compaction squeezes out water and air.

Bituminous Coal ("Soft Coal")

Intermediate coal formed under deeper burial (1,000 m to 5,000 m) and temperatures up to 150°C; higher carbon density and BTUs.

Anthracite ("Hard Coal")

Highest-grade coal formed via metamorphism at depths over 5,000 m, temperatures over 150°C, and tectonic deformation; highest carbon and energy content.

Over-Metamorphosed Coal

Metamorphism beyond anthracite converts carbon into graphite, which acts as a thermal/electrical insulator and cannot be burned as fuel.

The Carboniferous Period (~300–350 Ma)

Period when extensive coal formed globally because land plants expanded rapidly before specialized organisms (like fungi) evolved to break down lignin and cellulose.

Canadian Shield Coal Absence

Ancient continental cratons (Canadian Shield) contain no usable coal because any ancient organic matter was metamorphosed into graphite.

Thermal Coal

Lower-grade coal burned directly to generate electricity and heat.

Metallurgical (Coking) Coal

High-grade coal used primarily for manufacturing steel.

Highvale Mine

Canada's largest coal mine located in Alberta, feeding the Sundance and Keephills power stations.

Petroleum (Oil & Natural Gas) Origin

Formed primarily from microscopic marine organisms (plankton and algae) accumulating on stagnant seafloors/lakebeds.

Petroleum Source Rock

Organic-rich black shale formed when plankton-rich mud is buried and preserved in anoxic waters.

Kerogen

Waxy organic matter in sedimentary rocks that breaks down into hydrocarbons under elevated temperature and pressure.

Oil Window

Depth of 2–6 km and temperatures of 60°C–120°C (or 75°C–150°C) required to chemically convert kerogen into liquid oil.

Gas Window

Depths of 6–9 km and temperatures of 120°C–200°C where hydrocarbons crack into thermogenic natural gas (methane, CH4).

Biogenic Methane

Methane gas produced at shallow depths and low temperatures by anaerobic bacterial decomposition of organic matter.

4 Essential Components of a Petroleum System

Source Rock, Thermal Maturation, Reservoir Rock, and Trap & Seal (Cap Rock).

Reservoir Rock

High-porosity (storage capacity) and high-permeability (connected pathways) rock (e.g., porous sandstone or fractured limestone) storing oil/gas.

Cap Rock (Seal)

An impermeable rock layer (e.g., shale, dense evaporites, mudrock) that prevents fluids from escaping to the surface.

Petroleum Trap

A structural or stratigraphic geometry that halts upward migration of oil and gas (e.g., anticlines, fault traps, salt domes, stratigraphic pinch-outs).

Anticline Trap

An upward structural fold in rock layers that forms the most common petroleum trap.

Salt Domes

Low-density evaporite deposits that rise slowly toward the surface, deforming surrounding strata and creating hydrocarbon traps.

Density Stacking in Reservoirs

Fluids naturally layer inside a trap by density: Natural Gas on top, Crude Oil in the middle, and Water on the bottom.

Natural Oil Seeps

Occur when oil and gas migrate to the surface and escape because no trap or seal exists.

Seismic Surveys

Geophysics technique using sound waves to map subsurface sedimentary stratigraphy and locate potential petroleum traps.

Western Canadian Sedimentary Basin

Major Canadian geological structure holding roughly 10% of world oil reserves (light oil, natural gas, and oil sands).

Conventional vs. Unconventional Reserves

Conventional reserves migrate into porous reservoirs and are easily pumped; unconventional reserves (oil sands, shale gas) require specialized extraction techniques.

Oil Sands (Tar Sands)

Unconventional deposits of sand/clay mixed with highly viscous bitumen, exposed near the surface due to microbial alteration; abundant in Athabasca, Alberta.

Oil Sands Environmental Concerns

High natural gas consumption for steam processing, land devastation from strip-mining, toxic tailings ponds, and risk of groundwater contamination.

In Situ Extraction

Method of recovering deep oil sands by injecting steam underground to heat bitumen and lower its viscosity so it can be pumped.

Shale Gas

Natural gas trapped inside low-permeability shale rock that can only be extracted using hydraulic fracturing.

Hydraulic Fracturing ("Fracking")

Injecting water, sand, and chemicals under high pressure to crack impermeable reservoir rock and release trapped shale gas.

Fracking Environmental Risks

High water use, undisclosed chemical additives, risk of shallow aquifer contamination, and induced low-level seismicity (earthquakes).

Coal-Bed Methane

Natural gas (methane) trapped inside the pores of coal beds that can be extracted without mining the coal itself.

Uranium Classification

A nuclear energy resource hosted in clastic sedimentary rocks (e.g., Athabasca Basin, SK), NOT an organic fossil fuel.

Canada Uranium Standing

Canada is the world's 2nd largest producer of uranium.