Coal Bed Methane Development

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Coal Bed Methane Development

• Tom Myers, PhD
• Hydrologic Consultant
• Western Mining Action Network
• Sept. 29-Oct. 1, 2005

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What is coal bed methane?

• Standard natural gas CH4
• Methane forms along with coal
• It is held in the cleats with the coal
• Substantial water pressure needed to keep methane
  in the coal 400 to 1000 ft ?

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Process of Developing CBM

• Relieve pressure to release methane by removing
  water
• Domestic wells completed in seams produce methane
  due to drawdown caused by nearby pumping
• 6-7 times more natural gas than in traditional
  natural gas fields

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Set of wells in southeast MT
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What Happens to Developed Water?

• Most developed water is
• Discharged to surface water
• Discharged to containment pond
• Land applied for evaporation

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Discharge to Impoundment in Wyoming Disposal by
evaporation, percolation or sometimes diverted to
LAD
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What are hydrologic impacts?

• Groundwater depletion
• Water table drawdown
• Decreased flow to springs and streams
• Groundwater Contamination
• - Methane in the groundwater
• - Seepage of disposed CBM water
• Surface Water
• - Water quality Excess Sodium or Salt
• - Wasted water
• - Changing channel shape

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How much water produced?
Gallons per minute/ WELL
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How much water?

• In Montana
• 25000 wells in Powder River basin
• Up to 9,000,000 acre-feet
• No water right!
• In Wyoming
• Up to 50000 wells in PRB

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Effects of Withdrawing That Much Water2003
Drawdown in Wyoming PRBNorth to Left
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Lets look at more details

• Hydrology of coal effects of depletion
• Quality of water being discharged effects on
  rivers/stream/plants.
• Alternatives to wasting the water

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Coal Seam Hydrology

• Low Porosity 0.02
• Relatively high conductivity 1 to 20 feet/day
• CBM producers are confined under significant
  pressure
• Thickness to as much as 90 feet

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• Montana Powder River Basin
• Many coal seams down to 1800 feet
• Coal seams relatively small proportion of total
  thickness
• Dietz up to 100 feet thick

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Coal Seams as a Source

• Coal seams a major source of water in the PRB of
  Montana.
• Thin conductive seams with low porosity lead to a
  rapid expansion in the effects of drawdown.

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Effects of CBM Pumping

• Rapid Drawdown.
• Effect on adjacent aquifer?

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Effects of Coal Mining
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Unaffected hydrology
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CBM effects on hydrology
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Coal Seams Next to Tongue River
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Effects of Discharge to Surface WaterWater
Quality

• Surface Water Quality
• Effects on Irrigation/Stockwater Usage
• Changing Riparian Ecosystems to more salt
  tolerant system

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Water Quality of CBM Water
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Salt and Sodium Effects on Irrigated Soils
Sodium Adsorption Ratio Proportion of Sodium
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Recommend Most Sustainable Practice

• Reinjection into aquifers depleted by CBM
  production.
• Injection or percolation into depleted aquifers
  with water treatment as required protecting
  and/or enhancing water quality.
• Replace other uses where quality allows.
• Surface discharges with water treatment as
  required resulting in improved stream flows with
  adequate mitigations against negative impacts.

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Hydrology effects with Reinjection
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Not Recommended

• Evaporation of water resulting in loss of
  resource.
• Injection or percolation into aquifers where
  water quality is deteriorated and negative
  hydrological impacts occur.
• Land application that creates negative impacts on
  soils and water quality
• Direct discharges that degrade water quality and
  negatively impact downstream users or result in
  loss of resource.