WEEK 9 - Fossil Fuels Flashcards
How is coal formed?
From plant material that builds up in low-energy places like swamps.
What happens during early decay?
Decay uses up oxygen, making the surrounding water oxygen-poor, which helps preserve the plant material.
How does burial affect coal?
As the plant material is buried deeper, heat and pressure remove other elements, increasing the carbon content.
What are the types of coal based on heat/pressure?
- Lignite = low-grade coal (barely “cooked”)
- Anthracite = high-grade coal (heavily “cooked,” almost a metamorphic rock)
Where are coal fields found in Canada?
Coal fields mark areas where ancient swamps once bordered the shores of old seas.
What is petroleum made from?
Petroleum (oil and natural gas) comes from the remains of plankton, mostly marine algae.
Why is coal grade higher near mountains?
Because the buried plant material was more heavily pressed and “cooked” by heat and pressure.
How is petroleum formed?
- Plankton remains break down into hydrocarbons (oil and gas) in oxygen-free, organic-rich mud
- The mud hardens into shale
What is a “source rock”?
A source rock is the shale that contains the original organic matter where oil and gas formed.
How is oil and gas formed from organic matter?
Oil and gas form when large organic molecules break down into smaller ones rich in hydrogen and carbon—a process called cracking.
What is biogenic gas?
A natural gas made by microbes as they break down organic matter.
What is the “oil window”?
The temperature range (~60°C to 120°C) where most oil forms from organic matter.
What is thermogenic gas?
Natural gas formed by heat breaking down oil into very small molecules, like methane.
How does oil and gas migrate underground?
Oil and gas move from the source rock into permeable rocks like sandstone.
What happens if oil and gas aren’t trapped underground? (No Barrier)
- If oil and gas don’t hit an impermeable rock, they keep rising to the surface.
- At the surface, they can be broken down by microbes, meaning they are lost as usable resources.
How is oil and gas trapped underground?
If oil and gas hit an impermeable rock (like shale), it acts as a seal, trapping them in the permeable reservoir rock below.
NOTE: Impermeable rock doesn’t let fluids pass through
What is an oil trap?
- An oil trap is a natural setup in the Earth where oil and gas can collect in large amounts underground.
- It allows the oil and gas to stay trapped and not escape to the surface.
What is a reservoir in an oil trap?
- The reservoir is the layer of rock that holds the oil and gas.
- It’s usually made of sandstone or other rock that lets oil and gas move through (called permeable rock).
What keeps oil and gas from escaping in an oil trap?
- A layer called the seal or caprock sits above the reservoir.
- It’s made of impermeable (non-porous or watertight) rock that blocks the oil and gas from rising.
What are common types of oil traps?
- Anticline fold traps – forms when rock layers bend upward into an arch shape.
- Fault-bounded traps – forms when rock layers are shifted and sealed by a fault.
- Stratigraphic traps – forms when oil and gas are sealed by changes in rock type or layer shape.
What do all oil traps have in common?
- Oil and gas collect in one specific area underground.
- The top of the reservoir rock (where oil and gas are stored) is sealed by an impermeable caprock that stops the oil and gas from escaping.
