Geoenergy and CCS Flashcards
Reasons for energy gluts?
- 1930s depression
- 1940s Post WWII austerity
- 1970s OPEC
- 1980 Iran/Iraq war
- 1985 – oil price crash
- 2008 – global recession
Previous thoughts on age of earth?
- In 1862 William Thompson (Lord Kelvin) calculated that a molten Earth would take between 20 and 400 million years to cool to its present state*
- In 1903 Pierre Curie & Albert Laborde announced that radium produces enough heat to melt its own weight of ice in an hour.
- Arthur Holmes (Durham University, first Reader in Geology 1924-1943) produced the first credible age of the Earth data using radiometric dating and in 1931 The British Association for the Advancement of Science came to a consensus that the Earth was a few billions of years old.
Current ideas on heating of Earth?
- Much of the internal heat of the Earth is thought to come from the decay of radioactive thorium.
- Thorium-232 is the main natural radioactive isotope. It decays to Lead- 208 via alpha decay* and has a half-life of 14 billion years.
- The Earth still has about 85% of the thorium it had when it formed.
Uranium?
• Used for nuclear power – not thorium
• Crustal abundance 2ppm – thorium 12ppm
• Uranium 235 is the only naturally occurring fissile isotope
o Capable of nuclear chain reaction
• No life on Mars = no radioactivity = no mantle, no magnetic field, no atmosphere
• Why is thorium not used?
o Uranium by-product is plutonium = used for weapons
o Thorium actually has a better chain reaction but technology not viable
Energy from Nuclear?
• 1kg 235U converted via nuclear processes releases 7.2x1013 joules
• 1kg coal burned releases 2.4x107 joules
o Weight for weight uranium releases 3,000,000x more energy than coal
Geothermal basics? and Iceland vs UK? Types?
Causes:
• Convection in mantle
• Emplacement of granites
Iceland: 30 high temperature systems: T>250 degrees C
UK:
• Only area higher than 120 millawatts per m2 is South West – Cornwall – granites – high abundance of thorium
• Average heat flow in Whin Sill in north
• Average thermal gradient 26 degrees per km
Types Shallow • Hydrothermal Systems o Confined to areas of high heat flow on plate boundaries • Engineered geothermal systems o Redruth, Cornwall
Petroleum basics
Petroleum (oil and gas – fluids)
• Alkanes – CnH2n+2
• Alkenes – CnH2n
• Aromatic – CnH2n-6
Condensate – gas at high temp in earth – condenses to liquid at surface
Oil, gas and coal form from the heating (during burial) of plant remains
• Oil & gas mainly form from soft tissue such as algae (sea weed)
• Coal forms from woody tissue
• >100oC to form oil & >150 oC to form gas
Forming petroleum accumulations?
Forming petroleum accumulations • Source: Where the oil forms • Reservoir – rock from which we can produce the oil • Seal – What stops the oil leaking to the surface • Trap – shape of the oil container in the Earth (inverted) Source: • Preservation of organic matter (plant remains) o Anoxic conditions • Peat bogs • Black sea • Lake Tanganyika o Typical environments: • Silled basins • Shallow seas • Coastal upwelling • Stratified lakes Reservoir: • Permeable or very fractured • Sand • High porosity Seal: • Fine grained, low permeability • Mudstones (shale’s), salt o Desert and temperate lakes o Rivers and deltas o Shallow and deep seas o Salt and mudstone • Salt will anneal itself to stop fracture = best Traps: • Domes (anticlines) • Fault blocks • Salt diapirs Migrations and timing: • If petroleum migrates from the source rock before a trap is formed or a seal is deposited then no petroleum accumulation will form • The oil and gas will leak to surface and be biodegraded
Coal formation?
Coal • Forest • Heat and increased pressure throughout as buried • Peat • Lignite • Coal
Future ideas?
For the future: how to safely tap vast gas hydrate deep water but shallow subsea depths – 160x more energetic than oil
