Carbon Dioxide Geo-storage & Sequestration

Question 1

Stabilisation wedges:

Answer 1

• Emission predictions split into 7 25-Gt wedges
• There is time for tech to catch up
• Achieve all 7 wedges and the interim goal will be achieved

Question 2

Ways to achieve these wedge futures:

Answer 2

• Increase fuel economy of two billion cars from 30 to 60 mpg
• Cut electricity use in homes, office and stores by 25%
• Add twice today’s nuclear output to displace coal
• Increase wind power 40-fold to displace coal
• Increase solar power 700-fold to displace coal
• Stop all deforestation
• Install CCS at 800 large coal-fired power plants

Question 3

Is CCS a Panacea?

Answer 3

• 2017 emissions are 32.5 Gt CO2
• 25 Gt would take 650 million barrels per day of CO2 CCS
• Not likely to be a panacea
• Could remove 2 wedges
• Costs £25-60 per tonne CO2 (2006)

Question 4

Traditional CCS method?

Answer 4

• Capture
• Compression
• Transport
• Inject/store

Question 5

Other technologies:

Answer 5

• Pre-combustion
o Capture converts the fossil fuel into a mixture of hydrogen and CO2 and then separates the CO2, leaving the hydrogen to be used as a clean CO2- free fuel
o Yields H2 (clean fuel) and CO (potential petrochemical feedstock)
o Currently fewer than 20 power stations worldwide
o UCG – could yield massive environmental dividends

• Oxyfuel
o Capture burns the fossil fuel in pure oxygen rather than air. This raises the combustion temperature and produces CO2 and steam. The CO2 can then be isolated by condensing and then removing the steam
o Yet to be fully commercialised
o Efficient for CO2 capture at 99%
o High electricity consumption for oxygen unit

• Post-combustion
o Capture removes CO2 from the dilute, low pressure exhaust gases using solvents
o Can be retro-fitted
o Most of the worlds fossil fuel power plants
o UK CCS competition aimed at post-combustion – cancelled
o Drax – Yorkshire attempting

Question 6

CO2 Storage – where?

Answer 6

• Depleted gas and oil fields
o Including CO2 Enhanced oil and gas recovery
• Depleted gas fields – extracted at low pressure – could have caused fracturing and failing – can we still sequester?
• Deep saline aquifers
o Global estimates of 10,000 billion tonnes of CO2 storage capability
o 175 billion tonnes of storage would allow us to halt the rate in growth of global emission for around 50 years
• Unminable coal seams
o Coal will adsorb CO2 and release methane
• Enhanced CBM – currently self-limiting
• Coal goaf (void space after extraction)
o Goaf is up to 2000 times more permeable than deep saline aquifers
o Ash reacts vigorously with CO2 forming solid carbonates
o A sealing layer of net strata compression always develops above goaf panels, offering a tight seal above the CO2 storage zone

Question 7

Limiting technology?

Answer 7

• Data Density
• Site Capacity
• Site Injectivity
• Reservoir and Seal Reactivity
• Site integrity
• Site monitoring – needed even after setup

Shrinking infrastructure in the North Sea means that CO2 sequestration and EOR there is becoming less viable

Question 8

CO2 Enhanced Oil Recovery

Answer 8

• CO2 production from eastern UK could ‘power’ CO2 EOR in the North sea for 10-15 years per project
• Allows for
o Improved security of oil supply
o Infrastructure usable for carbon capture
o Increased tax revenues over current projections

Question 9

Convection enhanced dissolution:

Answer 9

• Eventually the CO2 will dissolve into the residing brine
• Prior to dissolution, CO2 is expected to be less dense than the residing brine
• Dissolution into the brine is then controlled by Henry’s law and diffusion. This is a slow process (100s of years)
• However increased CO2 concentration in the brine leads to increased density
• Hence we expect buoyancy driven convection to enhance mass transfer by up to an oder of magnitude

Question 10

Residual trapping

Answer 10

• The brine, being a wetting fluid adheres to the sides of the pore due to surface tension
• As brine moves upwards CO2 is displaced
• But as the brine passes through the pore throat, some of the CO2 is trapped

Question 11

Cosmic Ray Muon Tomography

Answer 11

• Charged, very penetrating particles created by cosmic radiation striking the atmosphere
• Loss through ionisation when travelling through matter
• Can be deflected when travelling through high atomic number materials
• Penetrate 2km of rock
• Lasts less than 2 micro-seconds
• To see where CO2 is moving

Question 12

Potential risks of geo-storage

Answer 12

• CO2 and CH4 leakage
o Frequency well failure after injection unknown
o Frequency cap rock failure is unknown
o Chance on CO2 is generally low for coal seams and highest from deep saline aquifers
o Health hazards to people and animal
o Marine ecosystem impact unknown
o Affect soil and ground water quality
o Make CO2 ineffective as mitigation option
• Seismicity
o Chance unknown, can be controlled through controlling injection pressure
o Damage to buildings and infrastructure
o Cap rock damage, which might cause CO2 leakage
• Ground movement
o Chance unknown
o Could cause damage to buildings
o Seismicity
• Displacement of brine
o Chance unknown
o Rise in water table
o Increase salinity drinking water resources