Unit 2 Lecture 10: Energy Resource - Fossil Fuels

fossil fuels

energy sources that formed from the remains of once-living organisms

• oil (petroleum)

• natural gas

• coal

nonrenewable energy sources

the processes by which they form are so slow that they are not replaceable on a human timescale

what causes the differences in physical properties among the various fossil fuels?

differences in the starting materials from which the fuels formed and in what happened to those materials after the organisms died and were buried within the Earth

coal

formed from remains of swamp plants above sea level compressed by sediments as ocean levels rose and fell millions of years ago

heat and pressure inside the Earth turns plant remains into coal through different stages:

1. peat

2. lignite

3. bituminous

4. anthracite (metamorphic rock)

why does the grade of coal improve as time, pressure, and heat increase?

the percentage of carbon increases as the stages progress

environmental impacts of coal

emits

• sulfur dioxide (acid rain, respiratory illnesses)

• nitrogen oxides (smog, respiratory illnesses)

• particulate matter (smog, haze, respiratory illnesses, lung disease)

• carbon dioxide (primary GHG produced from burning fossil fuels = heats atmosphere)

uses of coal

• generate electricity

• domestic heating fuel

• manufacturing in industries

how do petroleum (oil) and natural gas form?

1. marine organisms die and bury in the ocean floor sediments

2. overtime get covered by sediments and prevented from decay

3. remains of this organic matter get buried over millions of years

4. heat and pressure turns the remains into oil and gas

oil trap

a geologic environment that allows for economically significant amounts of oil and gas to accumulate underground

what are the 2 basic conditions of geologic structures that act as oil traps?

1. reservoir rock

2. cap rock

reservoir rock

porous, permeable rock that yields petroleum and natural gas in sufficient quantities to make drilling worthwhile

cap rock

virtually impermeable to oil and gas

halts the upwardly mobile oil and gas and keeps both from escaping at the surface

ex: shale

2 common oil traps

1. anticline

2. fault trap

shale gas extraction (fracking)

• Shale is a dense, tight rock formation where natural gas is trapped in tiny pores. Because the rock has very low permeability, the gas cannot flow naturally to a well on its own.

• Engineers drill vertically thousands of feet underground and then curve the drill to run horizontally through the shale layer to capture more gas.

• A high-pressure mixture of water, chemicals, and sand is pumped into the well.

• The high pressure cracks the shale rock, and the sand grains hold the tiny fractures open so the trapped gas can escape and flow up the well

methane hydrates

an unconventional natural gas source

an ice-like substance that forms under high pressure and low temperatures, trapping molecules of a gas like methane in a cage-like crystalline structure called a clathrate.

how to tap methane hydrates safely is not yet clear.