COAL SEAM GAS
Some basics in economics, geology and hydrogeology as applied to eastern Australia
Acknowledgements for data sources: Peter Flood, Carey Bradford, Anita Andrew
Coal seam gas (CSG) is natural gas• Natural gas – what is it, how does it form and
where does it occur? Natural gas is dominated by methane CH4. May have small amounts of other hydrocarbons, CO2, N2.
• It is a colourless, odourless gas that will burn at concentrations of 5-15% in air.
• In nature, it mostly forms by decomposition of organic material (e.g. in landfills, swamps, sediments and organic-bearing rocks).
• Methane is an attractive fuel as it is easy to distribute and on burning produces much less CO2 on a weight basis than coal (the C/H ratio is 0.25 versus >1.4 for black coal).
Natural gas in rocks• Economic concentrations of natural gas occur in sedimentary
basins where it has formed by decomposition of organic material deposited at the time of sedimentation (marine and terrestrial sources). Most economic sources are late Palaeozoic to Neogene in age (e.g. 400 Ma to 10 Ma), and gas is forming in modern sediments
• Three major types of gas occurrence are found in sedimentary rock basins:
Conventional gas, hosted in porous and permeable rocks such as sandstone and limestone, and commonly associated with oil
Shale gas, hosted in “tight” fine grained shale
Coal seam gas, hosted in coal (mostly in black coal).
Methane hydrate
• A huge potential resource of natural gas is locked up in modern marine sediments in the form of methane hydrate (properly termed methane clathrate CH4.5.75H2O, an ice-like substance forming in cold-water conditions)
The oil and gas window
Most natural gas is generated from sedimentary rocks buried to considerable depth and subjected to heat and pressure. The gas “window” overlaps that of oil, but most forms at higher temperature.
Black coal in eastern Australian sedimentary basins has been subject to temperatures (e.g. >100°-150°C) that generated considerable methane
A brief interlude on shale gas
• Production only just commenced in Australia, and there are potential large resources (e.g. Cooper, Canning Basins).
• Forms by decomposition of organic material originally deposited in marine mud, when this material is lithifiedinto shale, and methane is generated by heat and pressure.
• Shale is a “tight” rock and acts as a barrier to fluid flow (whether that be water, oil or gas)
• To economically extract gas, shale needs to be fractured (“fracked”) following directional drilling and use of high pressure water, sand and small amounts of added chemicals (see later)
Shale gas
Large resources currently being developed and exploited in the USA
This is resulting in the USA changing from being an energy importer to exporter and affecting world politics
‘00s to ‘000 m
Directional drilling
Coal seam gas
• Formed during and subsequent to the coalificationprocess from original organic material. The source rock (particularly black coal), is also the reservoir
• Gas is absorbed on to coal and constrained by water pressure
• Optimal reservoir depth 250-1000 m
• Gas can be released by drilling into, and dewatering the coal (by releasing pressure)
• Methane drainage has occurred for many decades in the underground coal mining industry to reduce the risk of gas blowouts and methane explosions
CSG is generated as primary or secondary gas during and subsequent to
the process of coalification of organic material
CSG can form by thermal and biological processes
During the earliest stage of coalification biogenic methane generated as a
by-product of microbial action (primary biogenic gas)
Subsequently, thermogenic methane forms with burial and temperatures
>50°C
Later, biogenic methane can form by reduction of CO2 from shallow
groundwaters (secondary biogenic gas)
Gases produced are adsorbed onto micropore surfaces and stored in
cleats, fractures and other openings in coal, and also in groundwaters
within the coal beds
Coal seam gas
Coal seam gas: derived from coal maturation and subsequent biogenic processes
Coal thin section Coal SEM image
From Pells 2012
Coal seam gas
In Australia, large CSG resources in the Surat and Sydney-Gunnedah
and Bowen Basins. Industry grew rapidly in Qld for supplying gas as
liquefied natural gas (LNG) exports. Limited use for local supply.
Saline water storage
From Kelly, 2012
Environmental concerns
include:
• storage of saline waters at
surface and potential for
contamination
• disturbance of shallow aquifers
that could be used for water
supplies
• gas, salt and chemical entry
into aquifer waters
• fugitive emissions
• disposal of salts from
desalination plants
The economic drivers• since 1999
increasing world
energy need,
especially
growing major
economies (e.g.
China, India)
saw rising price
of oil
• June 2015 to
March 2016 WTI
crude fell from
$US105 to
$US33 BBL -
viability of shale
gas and CSG?
what happens
next?
The economic drivers
• Increasing world energy need, especially growing major economies: China, India
• Natural gas (including CSG) is viewed as being convenient, less polluting than coal or oil, and potentially more abundant
• Although not a new industry in Australia, CSGdevelopment has really only grown since 2005, with the impetus being the LNG export market
• Over 70% of Queensland’s domestic gas supply is CSG, only 6% in NSW: potential for growth in supplying households, industry and for power generation
• In 2013, 4840 CSG wells in Qld and 230 in NSW
The economic drivers• NSW has a problem situation where most of its gas supply to
1 million customers is conventional gas (Cooper Basin), with the resource diminishing and contracts ending by 2017. New Bass Strait gas contract with AGL in 2015. Customers will pay more.
• Current and potential employment and investment benefits. In Queensland, projects underway employ 18 000 people and generate $1 bn p.a. in royalties to the Qld govt.
• A caveat: since 2014, the world economic outlook has become weaker and demand for energy resources (thermal coal, gas, oil) has decreased, resulting in lower prices and loss of economic viability for some operations.
• In Queensland, LNG developments and exports are delayed and less viable, and in NSW, abandonment of Gloucester Basin and Camden operations by AOG. Santos “hunkering down” in Narrabri area
Sydney-Gunnedah-Bowen, Surat and Galilee Basins are main focus
Australian sedimentary basins with CSG potential
Australian CSG reserves
• Reserve life is ≈150 years at current rates of production,
but production is projected to increase with the
establishment of the CSG LNG industry
• Australia has substantial subeconomic demonstrated
resources and large inferred resources – Qld has 92% of the reserves, NSW 8%
– reserves in the Surat (69%) and Bowen (23%) basins with small
amounts in the Clarence-Moreton (1%), Gunnedah (4%),
Gloucester and Sydney basins
• CSG uses are growing
– pipeline gas or as a fuel for on-site electric power generation
– pipeline gas to regional centres and cities as power generation,
industrial facilities and mains gas
– LNG for export
Australian CSG
Reserves
On a world basis, Australia is well endowed with unconventional gas (e.g. CSG)
Why does CSG only occur here?
• Must have the appropriate sedimentary rocks (e.g. coal) and geological conditions
• Many other parts of Australia are underlain by sedimentary rocks, but these either do not have the source materials, or they have been subject to heat and pressure that have destroyed gas potential
• CSG does not occur in igneous and metamorphic rocks that underlie about half of continental Australia
• There is essentially NO CSG potential in the New England region of northern NSW due to the above factors and community group concerns about “CSG Mining” in the region are baseless
CSG in southern Queensland and northern NSWIn southern
Queensland, CSG mainly occurs in the
Walloon Coal Measures of the SuratBasin (which is a lobe
of the Eromanga/Great Artesian Basin), with a
resource also in the underlying Bandanna
Formation of the Bowen Basin
Productive aquifers of the Surat Basin are shown in blueand aquitardsshown in brown
CSG in southern Queensland and northern NSW
Productive aquifers of the Surat Basin are shown in yellow, aquitards in greyand brown
Namoi alluvium
In northern NSW, CSG mainly occurs in coal measures of the Gunnedah Basin, underlying
the Surat Basin
CSG in Sydney Basin
1.5
2.0
2.5
3.0
1.0
0.5
250 200 150
Permian Triassic Jurassic Cretaceous Tertiary
100 Time (Ma)
Dep
th s
ub
-sea (
km
)
50 0
0
-0.5
-1.0
Missing section
Wianamatta Gp
Mittagong Fm
Hawkesbury SS
Narrabeen Gp
Illawarra Coal Measures
Shoalhaven Gp
Sea level
ISO-VR
0.5
0.6
0.7
0.8
1.0
1.3Burial history the
Sydney Basin Faiz et al. 2006
Faiz & Hendry 2006
CSG in Sydney Basin
1.5
2.0
2.5
3.0
1.0
0.5
250 200 150
Permian Triassic Jurassic Cretaceous Tertiary
100 Time (Ma)
Dep
th s
ub
-sea (
km
)
50 0
0
-0.5
-1.0
Missing section
Wianamatta Gp
Mittagong Fm
Hawkesbury SS
Narrabeen Gp
Illawarra Coal Measures
Shoalhaven Gp
Sea level
ISO-VR
0.5
0.6
0.7
0.8
1.0
1.3
A
B C
Exploring for CSG: directional drilling has
revolutionised the industry
Downhole steerable drilling motor and drill bit
Directionally drilled borehole
Several directional wells can be completed from the one site. The drilling process might follow on from preliminary exploration involving a seismic survey
OLD
NEW
From Pells, 2012
Drilling involves considerable friction, thus drill fluid additives are used
Exploring and testing for CSG• Exploration takes place in known coal basins• Drill core of coal is recovered for testing• Laboratory testing of coal core takes place to
determine gas yield and flow rate.
Gas is absorbed into coal and is at least partly released along fracture systems (cleat) when pressure is reduced.
Drilling also provides data on reservoir pressure, gas and water production and water composition
Extracting CSG
CSG is produced via cased wells. The drill hole is cased with steel and cemented in place to prevent escape of gas and associated formation water into shallow aquifers and at the wellhead
Gas and water entry into the bottom of the cased hole
Double steel casing with cement infill
Extracting CSG• Water is pumped out of
the coal seam aquifer thus reducing the pressure. Gas is desorbed from coal and released. Produced water and gas are separated at the wellhead
• “Fracking” (hydraulic fracturing) of the coal seam aquifer has been used in about 20% of CSG wells in eastern Australia in order to improve rate of gas extraction
Composition of a typical fracking fluid used in Australia
Some of the above chemicals include sodium hypochlorite and hydrochloric acid (as used in domestic swimming pools), acetic acid (vinegar) and disinfectants. Use of partly water-soluble benzene derivatives (BTEX chemicals) is banned in Australian jurisdictions. Other scientific considerations are that coal seams are not in hydrologic connectivity with other aquifers (due to aquitards) and huge dilution factors are involved
Produced (formation) water compositions• CSG-associated water is commonly brackish, with a range of 200-
10000 mg/L TDS (compare typical drinking water of <500 mg/L TDS). Values in RED exceed ANZECC guidelines for stock water
Data for 126 CSG formation waters
in Surat and Bowen Basins,
Queensland
Waters are essentially Na-Cl-HCO3 types, with
low Ca, Mg, K, SO4, metals
pH 7.7-9.4 BTEX <2 ppb
Cl 29-5360 ppm Zn Most <0.5ppm
SO4 <1-105 ppm Cd ≤0.005 ppm
HCO3 58-5280 ppm Cu Most <0.02ppm
Na 18-4270 ppm Pb Most <0.01 ppm
Ca 1-324 ppm As ≤0.02 ppm
Mg <1-302 ppm Hg <0.0001 ppm
K <1-276 ppm U ≤0.001 ppm
Fe <0.1-350 ppm V ≤0.03 ppm
B 0.2-3.5 ppm Ni Most <0.02ppm
F 0.1-3.7 ppm Cr Most <0.02 ppm
Mn Up to 5.7 ppm Mo Most <0.02
Water and CSG extraction over time
Predicted gas and water production from a CSG well: time frame is up to 20 years
Community concerns about water and CSG extraction
1. aquifer drawdown
2. aquifer contamination from CSG-associated
waters (e.g. salinity, BTEX chemicals, gas,
heavy metals, F, B)
3. disruption to, and potential local sterilisation of
current farming and grazing practices
4. threat to native flora and fauna
5. fugitive emissions of methane from wells and
pipelines (powerful greenhouse gas)
6. end of well life
Environmental consequences of water and CSG extraction
• Potential for aquifer interference, e.g. is there significant connectivity between CSG aquifers and shallow aquifers used by rural industries, towns, etc?
• Hydrological modelling of the Surat Basin in southern Queensland by non-corporate organisations (University of Southern Queensland, Queensland Water Commission) has demonstrated the likelihood of limited drawdown of water levels in productive aquifers over decadal periods
• This is due to presence of abundant aquitards in the Basin sequence and that the amounts of water withdrawn represent a tiny fraction of the total groundwater resource
Hypothesised risks to aquifers from dewatering
Remember that in the real-world situation (e.g. Surat Basin), many of the overlying units are aquitards
Testing for aquifer interaction
• potential for aquifer interference, e.g. is there significant
connectivity between CSG aquifers and shallow aquifers
used by rural industries, towns, etc?
• hydrological modelling to assess the potential drawdown of
water levels in productive aquifers over decadal periods;
aquitards in the basin sequence will limit the amounts of
water withdrawn
• active monitoring of groundwater impacts
– water chemistry
– ground surface levels
Environmental consequences of water and CSG extraction
Examples of potential water drawdown levels due to CSG extraction in the Surat Basin over decades from QWC hydrological modelling study. Does not take into account (a) natural recharge, or (b) drawdown due to other water users (e.g. agriculture)
Environmental consequences of water and CSG extraction
• In Surat Basin, 1500 GL water would be extracted with CSG production over 20 years (i.e. 75 GL p.a.)
• This is about 1/40000th of the water in the Great Artesian Basin (Surat Basin is part)
• Does not take into account (a) natural recharge (880 GL p.a.), or (b) other uses of Basin water for agriculture, town water supplies, etc.
• By legislation in Queensland, CSG producers are required to make good any impact on water supply
• water produced from coal seams is
highly variable in quality (potable to
saline) and quantity
• disposal options: evaporation dams (no
longer permitted), reverse osmosis (RO)
treatment, re-injection into suitable deep
aquifers (treated or untreated), direct
use of water for power station cooling,
coal washing, stock
• salts can be used a commercial source
of salt, soda ash and chlorine
• RO water is required for drinking water
standards and is used for stock,
augmentation of town supply, irrigation
of crops and tree plantations, industry,
dust suppression – supplements and
augments GAB groundwater
Aquifer contamination
Impact on farming
and native flora and fauna
• Apart from water issues there are other impacts including:
• Effects of land clearing on native flora and fauna
• Disturbance of farming and grazing operations
• infrastructure and access roads
• microseismic disturbance from fracking and water removal: allegations that earthquakes are caused
• surface subsidence
Geoscience Australia geodetic network to monitor ground
surface response to resource extraction in Surat Basin
From Garthwaite et al. (2015)
Landowners and CSG companies
• all underground resources
are owned by the Crown
• landholders have legal
rights − access, negotiation
and compensation
• CSG companies cannot
enter land without consent
and must negotiate on
placement of infrastructure
• sites must be rehabilitated
at the end life
• land owners are entitled to
financial compensation for
CSG activities
Surat BasinTara, Queensland
Fugitive greenhouse gas emissionsBackground methane values:
• methane seepage to the
atmosphere from
sedimentary basins
containing coal deposits is
commonplace
• emissions globally from
geological sources 60−80
Mt/a with 13−29 Mt/a from
seeps and micro-seeps (Etiope et al. 2012)
• sources are primarily located
along coal basin fringes
associated with coal outcrop
and subcrop formations
What are fugitive emissions?
IPCC Guidelines for National Greenhouse
Gas Inventories: Energy Sector - includes
CH4, CO2 and N2O (from combustion)
• Conventional oil and gas
(equipment and well leaks etc.)– exploration
– production
– venting and flaring
– processing
– storage
– distribution
• Coal mining – seam gas− underground mining (ventilation air,
drainage)
− open-cut mining
− post-mining
− abandoned mines (only underground)
CSG Fugitives
currently not counted in
National Inventory but
fugitives from CSG
under scrutiny
industry rapidly growing
with large export CSG
LNG proposed/underway
LNG projects proposed in
Queensland
total capacity 50−60 Mt pa
1000’s of wells and long
distance pipelines
potential for significant fugitive
emissions
little reliable data available
most studies based on life cycle
assessment
results sensitive to assumptions
Remember, methane is generated naturally by ruminant animals (20% of emissions in Australia), anaerobic vegetation decomposition, landfill, sewage treatment plants, flatulence, etc.
End of well life?
• wells are expected to be
productive for ≈ 20 years
– not much experience
– site dependant
• small footprint of well with
directional drilling and
multi head wells
• pipelines are buried
underground
• requirement to seal well
and rehabilitate site
• can well life be extended?
Potential environmental impacts - summary
• Aquifer drawdown
• Aquifer contamination from CSG-associated waters (e.g. salinity, BTEX chemicals, gas, heavy metals, F, B)
• Fugitive emissions of methane from wells and pipelines (powerful greenhouse gas)
• Disruption to, and potential local
sterilisation of current farming and
grazing practices
• Threat to native flora and fauna (just
like farming, grazing, roads, urban sprawl)
Attempting to dispel myths- a difficult task for the scientist
• Unfortunately, good science and media- and politics-driven agendas do not mix well
• Factual information can be ignored or selectively used to suit the arguments of protagonists
• Fear, ignorance and political
opportunism make media
stories, whereas scientific
information and logic don’t
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