Topic 5: Fossil Fuel Energy Flashcards
What is the most general path of the carbon cycle?
- CO2 in the atmosphere, taken into trees and plants via photosynthesis
- organisms in the ocean take in Co2
- carbon goes back into the atmosphere at night, via respiration
- soils give carbon back to the atmosphere via decay
oceans give some carbon back to the atmosphere - burning fossil fuels and cement production produces a ton of carbon to the atmosphere
What is the carbon cycle?
- how carbon is exchanged between reservoirs via interconnected pathways
- includes terrestrial biosphere, geosphere, hydrosphere, and atmosphere
Where is carbon stored/exchanged in the terrestrial biosphere and geosphere?
terrestrial: plants and animals, freshwater systems, and soil carbons
geosphere: fossil organic carbon in sedimentary sequences. Carbon in carbonate rocks and other igneous bodies
Where is carbon exchanged in the hydrosphere and atmosphere?
hydrosphere: marine biota, lots of dissolved carbon in the deep ocean, slowly is exchanged with the atmosphere. Ocean is the largest active carbon reservoir
atmosphere: atmospheric CO2, igneous outgassing, combustion, etc.
What is a carbon sink? carbon source?
Sink: takes in more carbon than it puts out. Oceans and forests are huge carbon sinks
Sources: puts out more carbon than it takes in. Weathering of rocks, melting permafrost, agriculture, and abuse of fossil fuels are all climate SOURCES
What are the three common formation processes for fossil fuels?
- Biogenesis
- Catagenesis
- Metagenesis
What is biogenesis?
- first stage in fossil fuel formation
- breakdown of complex organic materials by archaea, after burial under anoxic conditions
- archaea produce methane
- this occurs in shallow sedimentary settings
What is catagenesis?
- the second stage in fossil fuel formation
- “cracking” - chemical breakdown of organic kerogens to form hydrocarbons
- times, temperature and pressure dependent process
- produces bituminous coal, petroleum, methane. ect.
- occurs in medium to deep sedimentary settings
What are kerogens?
- mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks, halfway stage to full hydrocarbon
What is metagenesis?
- the third and final stage to fossil fuel formation
- low grade burial and regional metamorphism
- water is expelled from pore spaces in the rocks, liquid hydrocarbons expelled
- production of thermogenic methane (called dry gas - cause it has very little water in it
- everything that is NOT carbon gets driven off at methane, increase in carbon content
- occurs in deep sedimentary or orogenic settings
What is “jet”? the two kinds?
Jet is high pressure alteration of wood from trees of the family Araucariaseae
- soft jet is carbon compression in freshwater
- hard jet is carbon compression in salt water
there were no coals before the _______, because…..
there were no coals before the Devonian, because this is when evolution of terrestrial plants occurred.
pre- Mesozoic coals were denominated by _________, while mesozoic and paleogene coals were dominated by __________
pre- Mesozoic coals were denominated by ferns and scale-trees, while mesozoic and paleogene coals were dominated by _flowering plants and trees
What are the two coal types?
- Humic coals
- sapropelic coals
What are humic coals?
- coal made from fibrous plant debris
- contains Macerals, which is a lustrous black mineral-like material.
- formation is: Plants —> Peat —> lignite —> bituminous coal
What are sapropelic coals?
- formed from sapropels, fine-grained featureless algal debris
- forms in anoxic lakes, pools, ponds
- no oxygen, rich nutrients
How does coal formation occur in a swamp setting?
- organic debris accumulates in wet anoxic environment
- the low oxygen and acidity limit the decomposition of anything that sinks to the bottom
- typically has high peat accumulation in temperate regions.
How does coal formation occur in a transgression-regression setting?
- transgression: relative to sea level rise, covers land up
- regression: relative to sea level fall, exposes previously covered land
- interbedded coal and shallow marine clastic and carbonate sequences
- considerable lateral variation of coal deposits that reflects variations in swamp environments
what were some of the major coal-forming periods?
- carboniferous (max coal production, lots of vegetation)
- jurassic to paleogene (second major coal forming interval)
Where is modern coal accumulated?
- florida, virginia, coastal areas of canada, ireland, scandinavia
Why are there no long-term coal accumulation in temperate regions today?
- due to glacial activity
- glacial isostatic sea level change
what is the post-depositional modification part of coal formation?
- compaction and bacterial and fungal attack
- lots of compression
- production of methane, co2, ammonia (gases escape)
What is coalification?
- the physical and chemical modification of peat into coal
- burial, biochemical reactions, increasing heat and pressure
- Rank: Peat –> lignite –> bituminous –> anthracite
- as this rank increases, the more oxygen gets driven off
- general decrease in moisture and distinguishable plant remains
- increase in macerals, density, calorific value
what are some of the deep mining ways to mine coal?
Room and pillar mine: however this only removes 50% of coal as a lot needs to be left behind so that the cave doesn’t collapse and can only be done on flat-line resources
Continuous mining machines: back and forth moving armored rotary cutter, removes nearly all coal, as the cutter advances the overlying bedrock is let down
What are some of the surface mining ways to mine coal?
Open pit/Strip mining: surface exposure with the removal of overburden, excavation, and then backfilling/landscaping
Augering: drilling a hole into horizontal coal beds, 50% recovery of coal, may be used where overburden is too thick for open mining
What are some acid mine environmental issues with coal mining?
- sulfur issues: original plant content contains sulfur, this can make sulfuric acid eventually
- poisoned aquatic systems
- sulfur burning: Pyrite within coal isn’t removed fully, burns alongside sulfur compounds, produces acid rain.
What is an environmental issue associated with coal mining and production?
- Enhanced greenhouse effect from co2 release
- causes climate warming
- ocean acidification from carbonic acid
- carbonic acid attacks calcium carbonate shells of marine organisms, destroys ecosystems
What are some negative post-mining effects of coal mining?
- subsidence (collapse and cave ins of shallow room and pillar subsurface mines)
- coal fires (underground fires that can last for years and consume vast amounts of coal, many negative environmental effects)
Currently, peat production is most concentrated in…
- northern temperate climates
- Russia, and ireland
Is Peat a renewable resource? why or why not?
- Technically considered a renewable resource, if it is managed well!
- can re-grow, and takes 5-10 yrs to reharvest
What issues are there with modern peat energy production?
- may cause problems with habitat destruction and site rehabilitation
- economically, not as valuable as other electricity sources, peat has much less energy than other fossil fuels as it is less carbon concentrated
- burning peat for energy still pollutes the atmosphere, creates acid rain
What is petroleum?
- Oil produced from photosynthetic marine planktonic mirco algae
- algae die, its debris floats to the bottom of the ocean and gets trapped within marine sediments
- rich in lipids, proteins, and carbohydrates. Simpler carbohydrates than coal.
- low in cellulose and lignin
How is Petroleum formed?
- Biogenesis and diagenesis (Conversion of some hydrocarbons to methane by archaea, in shallow settings)
- catagenesis (compaction and water expulsion, organic material to kerogen and then liquid petroleum, some methane produced)
- metagenesis (Lots of methane produced, residual left overs into graphite)
What is produced in all stages of petroleum formation?
methane
Where is petroleum found? How does it move/get trapped?
- very little petroleum is found in the source rocks. It doesn’t stay where it is formed.
- petrol migrates into permeable and porous strata, rocks that have void or pore spaces (these are called reservoirs)
- petroleum moves up, but is confined (trapped) by impervious layers, where it accumulates over time.
What are common reservoir rocks for petroleum? common trap rocks?
sandstones or limestones for reservoirs
shales for trap rocks
How do we exploit/produce/mine petroleum? What are the typical methods?
- Early methods included finding it at natural seeps in the ground
- later methods included cable tool drills, which is percussion drilling
- rotary drilling, which is much more modern and ‘higher’ tech’
What is rotary drilling? Explain how it can exploit petrolem/oil
- includes a complex three-cone rotating drill bit that is attached to a rotating pipe.
- drilling fluid is pumped down to prevent blowouts and act as lubricant
- rock debris is flushed back up hole
- components of drilling rig include a turntable, kelly pipe, derrick and swivel, pumping system, and blowout preventer
What options are available if you cannot drill directly down for rotary drilling?
directional drilling
- steerable drilling techniques, used with swivel joints and down hole motors
- to be able to access oil-bearing strata more efficiently
- access reserves from inaccessible locations
- can use multiple drills from the same site
- useful in offshore oil fields
What are the types of recovery methods for oil/petroleum?
- primary recovery
- secondary recovery
- enhanced flow/recovery
What is primary recovery?
- the initial recovery process when extracting oil
- only recovers 20-30%
- natural pressure of the oil is pushed to the reservoir
- natural pressures arise from water dive, gas expansion, or dissolved gas evolution
What is secondary recovery?
- artificially simulated recovery of remaining oil in reservoir
- only 50% recovery possible
What are the 4 types of secondary recovery? explain them all
- water flooding (water from injection wells used to push oil towards production well)
- steam flooding (hot steam from injection wells lowers the oils viscosity, pushes it to the well)
- chemical flooding (light hydrocarbons injected to decrease oil viscosity, or chemicals injected to reduce oils tendency to stick to mineral grains)
- Gas reinjection (Natural gas is separated from recovered oil and reinjected to well to aid recovery)
What is enhanced flow/recovery of oil?
- third and final method to extract oil
- done if oil is very tightly filled in pore spaces, and has slow movement and is restricted
- two different methods to fix this: pumping acid, which dissolves gain cements and increases permeability, Or the more popular method which is fracking: highly pressurized water and sand pushed into injection wells to fracture rocks, allows oil to be freed. fissures are held open by sand particles
What is crude oil?
mixture of 1000’s of different hydrocarbon chains. Very variable
How can we refine crude oil? What are some methods?
- Distillation/fractionation
- cracking
- Alkylation
- Reforming
- Treatment
What is distillation/fractionation?
- one method to refine crude oil
- heating crude oil to evaporate hydrocarbons. All the hydrocarbons will condense back at different temperatures, so you can separate different hydrocarbons.
- typically done in a distillation tower, where lightest fractions (light gasoline) will be at the top of the tower, jet fuels and kerosene in the middle, and heavy residuum and asphalt are left at the bottom
What is cracking?
- a method of refining crude oil
- where heavy, complex hydrocarbons are broken down into smaller, lighter and more useful ones
- two kinds, thermal cracking and catalytic cracking
- both methods heat up the hydrocarbons and break them up into smaller molecular chains
What is Alkylation, reforming, and treatment?
- methods to refine crude oil
- Alkylation: Combines fractionation and cracking products to make gasoline. reverse process of cracking
- Reforming: Naphtha turned into high-octane gasoline
- treatment: final combination of materials from processing units
What is a less conventional method to refining and processing oil?
- By mining Kerogen-rich fine-grained clastic sedimentary rocks
- Artificially heating these rocks to convert them into oil (cracking)
How are oil shales made?
- blue-green algae accumulates in aquatic environments with silt and sediments under anoxic conditions
- thru burial and heating volatiles are removed
- the lipids in blue-green algae are converted to black kerogens
what are the types of modern excavation of oil shales
- surface open pit mining and processing, extracted rocks are crushed and heated in retort
- or in-situ retorting, where horizontal tunnel networks are drilled out on either side of the oil shale strata, and then rocks between are shattered by explosives or fracking, then lit on fire and kerogens are converted to oil and gas
What is bitumen? where can we find these tar/oil sands?
- Bitumen: dark hydrocarbon residue left behind after escape of more volatile components, rich in asphaltenes
- found in shallow, near-surface reservoirs where all other hydrocarbons have left
How do we extract/mine bitumen close to the surface?
- surface mining, which is most economic with less than 75m overburden.
- Overburden (clay, sand) cleared off oil and stored elsewhere. Strip mines are then used.
- After mining hot water and caustic soda (NaOH) added to sand to ‘liberate’ remaining bitumen.
- 2 tonnes of oil sand = 1 barrel of synthetic oil
How do we extract/mine bitumen deeper below the surface?
- any bitumen extraction deeper than 75km
- CHOPS: oil pumped out of ground, mix of bitumen and sand pumped out. Cheap, but poor recovery 5-10%
- CSS: “huff and puff” , hot steam injected over weeks/months. Sits for days - weeks to let heat soak in, mobilized bitumen then pumped out over weeks/months. when production declines, steam injected again. 20-25% recovery but steam expensive
- SAGD: Steam assisted gravity drainage. Horizontal wells drilled, one above formation one below. Steam injected to upper well, melts bitumen, which flows down to lower wellbore. Lots of water used, lots of energy used.
