Coal

Question 1

Formation?

Answer 1

• Carboniferous coal swamp
• Low grade metamorphism
• Forest
• Heat and increased pressure throughout as buried
• Peat
• Lignite
• Bituminous Coal
• Anthracite (Most energy)
• Graphite (energy lost here – decrease in mass through compression)

Question 2

Formation requirements?

Answer 2

• Abundant land plants
• Anaerobic decomposition of plant debris favoured by near-surface water table
• Rapid basin subsidence and sediment accumulation
• Intermittent high clastic input (burial)
• Deltas provide ideal conditions – especially elongate or birdsfoot deltas – form where marine currents/waves are weak allowing delta progradation as a series of lobes
• Others: valley bogs/fens; blanket bogs

• Differential rock compaction – compaction varies by rock type

Question 3

Coalfield of Britain and Ireland:

Answer 3

• Location controlled by Carboniferous paleogeography in region of rifted continental crust between highlands massif and marine Cornwall-Rhenish basin (rift, sag and infill)
• Advanced Variscan deformation from S also stopped southward advance of deltas; most coalfields weakly affected by Variscan deformation (esp S Wales and Kent)
• Coalfiled sandwiched between regional Caledonian and Variscan unconformities
• Post-Carboniferous coal exists but not much
• Peat: NW Britain (25% of electricity in Ireland)

Question 4

History of Coal exploitation in the UK:

Answer 4

• Roman Times
• C 12-14th Bishops of Durham
• C 17th Long Wall Mining – Pig Iron
• Pre-1800 Tynesdide – Pits 40% recovery
• C 18th – Deep mining
• 1913 – peak coal
• 1947 – NCB formed
• 1984 Miners Strike
• North Sea exploration
• 1994 Wearmouth closed
• 2015 last deep pit closes

Question 5

Resource and Reserves?

Answer 5

Resource: total in place (mass)
Reserve:
• That which can be extracted
• Technical – Recoverable using available technology
• Proven – fully funded and recoverable using extant development
• Probable – typically the most likely recoverable
• Possible – typically the P10 reserve or equivalent

Question 6

Cooke re-evaluated coal resources:

Answer 6

•	Due to oil+ gas wells and better techniques
•	1977 – 190 billion tonnes
•	2011 4177 billion tonnes
o	Onshore 774
o	Offshore 3403
•	Offshore accounts for most difference

Question 7

What is CBM?

Answer 7

•	Source
o	Free gas (methane) in coal cleats
o	Methane dissolved in water 
o	Water also in pore spaces
•	Fractures rocks to increase permeability and flow
•	Uses well – more safe and efficient than traditional mining
•	Submersible pump – pumps gas and water up pipe from coal seam
•	Water and gas separated
Stages:
•	Dewatering stage – production slow
•	Stable production phase
•	Decline stage

Question 8

Characteristics compared to conventional gas exploration:

Answer 8

•	CBM
o	Low permeability 
o	Cleat dominated
o	Peak 0.3mmscf/d (low production rates)
o	Many wells
o	Co-produced wells – have to treat
•	Convenctional gas
o	Low to high permeability
o	Matrix dominated
o	Min (NSea) 20mmscf/d
o	Few wells
o	No water production

Question 9

Pros of CBM?

Answer 9

• CBM is just 5% calorific value output of coal
• Exploration for CBM wells is cheap
• Production of the wells is inexpensive as the coal seams that are used are shallow, making the wells cost effective
• The methane gas produced by CBM is normally the same grade methane as normal natural gas and can therefore be fed directly into gas pipelines for domestic supply

Question 10

Cons of CBM?

Answer 10

• Danger of causing land subsidence by extracting groundwater that can lead to depressurisation and compaction of coal units in the subsurface
• Co-produces water

Question 11

Enhanced Coal Bed Methane?

Answer 11

• Carbon dioxide pumped into seams
• CO2 adsorbed and methane desorbed
• Dating the process seems to be self-limiting

Question 12

UCG?

Answer 12

• 2 wells drilled into coal seam and interconnected
• Oxygen injected, promotes reaction
• Syngas (making hydrogen and carbon monoxide + minor methane and CO2)
• Could be a ‘multi-storey’ operation

Question 13

Pros of UCG?

Answer 13

• UCG promises to release 70% of coal’s calorific value
• UCG wells do not co-produce water
• UCG produces a mixture of useful sources of energy, such as synthetic gas, for electricity production or industrial heating, suitable amounts of hydrogen for the production of hydrogen gas, synthetic natural gas and synthetic diesel.
• UCG also offers the opportunity of being combined with carbon capture and sequestration

Question 14

Cons of UCG?

Answer 14

• Can cause the subsidence through the production of underground fires
• UCG also carries the risk of burning contaminants, such as the shutdown of the Cougar Energy project in Kingaroy, Australia where monitoring wells detected too much benzene, a highly flammable agent that could have led to significant underground fires