Lecture 6_ fossil fuels and our changing planet (1).pdf

Lecture 6: fossil fuels and our changing planet Fossil fuels: ● A hydrocarbon-containing material of biological origin, sourced in the solid earth, that can be source of energy ○ May include such material as coal, petroleum, natural gas, oil sand and heavy oils ○ Fossil fuels may be burned to produc...

Lecture 6: fossil fuels and our changing planet Fossil fuels: ● A hydrocarbon-containing material of biological origin, sourced in the solid earth, that can be source of energy ○ May include such material as coal, petroleum, natural gas, oil sand and heavy oils ○ Fossil fuels may be burned to produce energy, but this reaction releases CO2 into the atmosphere ○ >80% of primary energy production by humans is through fossil fuels ○ Petroleum may be refined into other products such as plastics, textiles, paints, fertilizers ● Hydrocarbons ○ Dead organic matter from plants and animals ○ Energy originally from the sun stored in organic carbon ○ Under the right pressure and temperature, will form some type of hydrocarbon ○ Deposited and trapped in the Earth’s crust ● Future ○ Oil ■ 33% of current energy use, 22 billion barrels per year current reserves > 1,000 billion barrels estimate undiscovered 500 billion barrels consumption projected to increase ○ Coal ■ 30% of energy use, abundant current reserves > 800 gigatons (equivalent to 4,500 billion barrels of oil) ■ Expansion has been growing ■ Contains impurities (sulfur, mercury, arsenic) ● Depends on how it is formed (e.g. eastern canada high in sulfur because formed in ocean) ○ Gas ■ 24% of energy use ■ Current reserves 180 trillion cubic meters (equivalent to 1,000 billion barrels) Extracting petroleum: ● Production types ○ Pumping ○ Steam injection ○ Strip mining ■ E.g. Alberta tar sands ● Petroleum or “crude oil” is a liquid that can be pumped out of the ground ● Human causes of increasing earthquake events ○ Fracking / hydraulic fracturing ■ A method used to extract natural gas and oil from deep underground ● Usually in a rock type called shale that holds the hydrocarbons more closely ● Process involves injecting large amounts of water, sand, and chemicals into a wellbore ● The injected fluid helps to prop open the fractures, while the sand acts as a proppant to keep the fractures from closing when the pressure is released ● These fractures allow the trapped gas or oil to flow more freely and be extracted ■ Environmental concern: impact on groundwater ● Migration of fracking fluid directly into groundwater ● Flowback of contaminated wastewater at the surface ● Methane leaks into groundwater ■ Fracking also induces seismicity ● Injection of fracking fluids into the ground can change the stress field around the fractured layers ● This can cause slip/motion on the fractures → release of acoustic energy as a small earthquake ● In most cases, magnitudes are in the range M1-M3 ● E.g. fracking induced major events: M4.7 in NW BC in 2015; M4.0 in texas in 2018; M5.7 in China in 2017 What does combustion of petroleum mean for the Earth system: ● The issue in global change is whether humans significantly disturbing Earth’s carbon cycle ○ I.e. combustion of fossil fuels moves carbon (in the form of carbon dioxide) to the atmosphere ○ Cars are just one source of emission of greenhouse gases that are influencing the planet’s climate ● Commercial gas ○ 87 octane is approximately 87% octane and 13% heptane ○ 92 octane is approximately 92% and 8% heptane ● Ideal combustion of pure octane ○ 2C8H18 + 25O2 → 16CO2 +18H2O ● Realistic combustion ○ Fuel + air (N, O2) → unburned HC’s + NxO + SOx + CO + H2O + CO2