Download Carbonaceous Deposits

Carbonaceous Deposits
Chapter 6
Carbonaceous Deposits
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Introduction
Hydrocarbons
Coal
Fossil Energy (Consumption)
Summary
Introduction
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Buried organic matter undergoes
diagenetic transformations due to
increased pressure and temperature
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Terrestrial plants -> peat -> coal
Organic matter (terrestrial/marine) ->
hydrocarbons
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Type (gas or oil) depends on temperature and
kerogen type
Kerogen – set of complex organic compounds,
composed of varying proportions of C, H, and O
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Introduction
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“Fossil Fuels” supply most of world’s
energy demands
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Oil (Petroleum)
(Natural) Gas
Coal
Organic carbon reservoirs on Earth
Hydrocarbons
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Buried organic matter undergoes
diagenesis during burial
Hydrocarbons - naturally occurring organic
compounds comprising hydrogen and
carbon
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can be as simple as methane [CH4], but many
are highly complex molecules
Can be in solid, liquid or gaseous form
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<- Methane
Butane ->
www.worldofmolecules.com
Hydrocarbons
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Petroleum – liquid hydrocarbon
accumulations
Natural gas – gaseous hydrocarbon
accumulations
Bitumen – solid (or nearly so)
hydrocarbons formed during hydrocarbon
generation, alteration, or other means
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Pore fill (“cement”)
Hydrocarbons
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Hydrocarbons generated from “source
rocks”:
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Rich in organic matter, if heated will generate
oil and/or gas
Typical source rocks contain ~ 1% organic
matter
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Usually shale or limestone
Rich source rocks may have as much as 10 %
organic matter
E.g., Condensed sections, shaley lakes
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Typical Weight % Organic
Matter
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Mudrocks 2.1%
Limestones 0.29% (sometimes higher)
Sandstones 0.05%
Black shales 3-10%
Oil or kerogen shales >25%
Coals >70%
Hydrocarbons
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The amount of organic matter is
important, but so is the type of organic
matter
In general, terrestrial organic matter
tends to generate natural gas, marine
organic matter will generate oil
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Also depends on temperature
Use atomic ratios (H, C, O) to
characterize organic matter type
van Krevelen plot
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Petroleum Maturation
Geothermal
Gradient
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Hydrocarbons
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Once hydrocarbons are generated, they
tend to migrate upwards/laterally until they
reach either the surface (seeps) or a barrier
(seal)
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Oil and gas are less dense than water
Migration can occur in phases:
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Primary – oil/gas expelled from source rocks
Secondary – subsequent oil/gas migration
Structural traps
Stratigraphic traps
Hydrocarbons
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Most hydrocarbons are produced from
conventional accumulations
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Discrete accumulations, usually with a downdip
water contact from which hydrocarbons may
be extracted using “traditional” development
practices
Middle East – proven reserves 673 Billion
barrels (~65% world’s total)
World petroleum demand: ~75 million barrels
day
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Distribution of Sedimentary Rocks
Oil Reserves
Oil Consumption
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Hydrocarbons
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Large amounts of hydrocarbons are present
in unconventional accumulations.
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A broad class of hydrocarbon accumulations of
a type that has historically no been produced
using traditional development practices.
E.g., tight-gas reservoirs, gas shales, oil shales,
tar sands, coalbed methane
More oil in tar sands/heavy oil deposits of
Alberta than in Saudi Arabia
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?2.5 trillion barrels (estimates vary considerably)
Distribution of
tar sands in
Alberta
Hydrocarbons
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Heavy oil and tar sands deposits of
Western Canada are thought to be formed
of Devonian oil that migrated up and into
shallow Cretaceous sands
Bacterial degradation eliminated the lighter
hydrocarbons, leaving heavy residue
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Makes them hard (i.e., expensive) to produce
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Coal
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Start Here
Coal forms from organic plant material on
land
Plant material accumulates in swamps,
commonly in a tropical or semi-tropical
environment
The organic material is buried
progressively, leading to increases in
temperature and pressure
Age of Coal Deposits
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Late Carboniferous Period
Wicander and Monroe, 2001
A Carboniferous coal swamp
•Note the ferns and horsetails
…and the dragonfly!
http://www.uky.edu/KGS/coal/coal_information.htm
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Coal
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Rank
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increasing temperature of formation
and loss of volatiles
Grade
„ a function of ash and sulfur
content
Energy Value of Coal Ranks
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Distribution of U.S. coal
“Purple” – mostly Pennsylvanian coal
Trend continues up into Maritimes
Strip mining coal – Nova Scotia
Coal Reserves
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Fossil Energy
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“Fossil energy” meets ~80% of primary
demand
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http://www.energie-schweiz.ch/internet/00480/?lang=en
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Oil, gas, coal
By 2030 demand will be ~ 66% higher
than now
Issues: environment (pollution, global
warming, etc.), reserves, alternative
energy sources
Oil consumption, 1980-2020
• Note the
accelerating trend
for transportation…
• …more cars, and
especially in the
developing world,
as it develops
106 barrels/day = 3.65 x 108 barrels/yr = 2.1 x 1015 BTU/yr (approx)
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Our remaining petroleum
(Conventional wisdom…)
• Currently we consume
oil and gas at a rate of
2.35 x 1017 BTU/yr
• There are 2.78 x 1019
BTU of oil and gas
remaining
• This leaves us 118
years
• Peak production has
passed or will pass
soon
Our remaining petroleum
(An Oilpatch View…)
http://www.cspg.org/CSPG_RESERVOIR_JULY_2003.pdf
• Many estimates of
remaining potential
ignore unconventional
accumulations that
are huge
• Also ignores
improvements in
technology –
finding/producing
• There is cause for
“cautious optimism”
•Many people in the oil patch will be retiring in the
next decade
•Who will replace them? (we need to keep finding
the stuff for the next several decades!)
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Global coal consumption, 19702020
• Some predictions see an
increased reliance on
coal…
Coal consumption
• …especially in the
developing world…
• …but coal is a dirty,
polluting resource…
• …so we have a problem
Problems with burning of coal
• The main problem is SO2 and CO2
emissions.
• Toxic trace element emissions, such as
arsenic, beryllium, selenium, thorium,
vanadium
• Also, problems of acid mine drainage,
subsidence, mine fires, black lung disease
Clean coal technologies
• 1. Precombustion burning: cleaning of coal
using micro-organisms to remove sulfur
• 2. Combustion-enhancing technologies
• 3. Conversion technologies
• 4. Post-combustion cleaning: SO2 scrubbing
using limestone which reacts with the gas
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Coal - World consumption
1970-2020
• Between 2000 and
2020, the world will
be consuming coal at
a rate of 5 x 109 to 9
x 109 short tons/year
• With global reserves
of 1.088 x 1012 tons,
this leaves us with
about 120 to 220
years’ worth of coal
(at 2000-2020 rates
of consumption)
Fossil Energy
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For better or worse, and until a cheap,
available alternative source of energy
can be found, we will continue to rely
on fossil fuels to supply global energy
demands
Summary
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Upon burial, organic matter undergoes
diagenesis due to increases in pressure
and temperature
Hydrocarbons are generated from
kerogen
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Marine and terrestrial organic matter
Type (oil/gas) depends on type of organic
matter and temperature
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Summary
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Once generated, hydrocarbons tend to
migrate upwards until they either seep
at the surface or are trapped
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Structural, stratigraphic traps
Thick accumulations of terrestrial plant
material can be transformed into coal
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Need reducing environment
Plant material -> peat -> coal
Much of world’s coal is Late Paleozoic
Summary
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Most of humanity’s energy needs are
satisfied by the combustion of fossil
fuels
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~80%
Despite concerns about environment &
future availability of fossil energy, no
cheap substitutes are available
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Humanity’s dilemma…
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