Enhanced Coalbed Methane Recovery

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Enhanced Coalbed Methane Recovery

• Iman Mansourine
• November 18th,2003

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Introduction

• Coalbed methane is the natural gas that is both
  generated and
• stored in coal seams
• Coal is the most abundant energy source in the
  world, and it is a
• major source of hydrocarbons particularly gas
• - Methane represent more than 90-95 of the gas
  volume
• Coalbed methane has become a significant
  component of U.S.
• natural gas supplies, 7 of total US natural
  gas production
• The injection of CO2 in coalbeds is the most
  attractive option
• the CO2 is stored and at the same time the
  recovery of coalbed
• methane is enhanced

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Principal points of the presentation

• Coalbeds reservoirs characteristics
• - Geologic sequestration of CO2 in coalbed
  reservoirs

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Coalbed reservoirs characteristics
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Coalbed Reservoir Gas Content

• Gas Storage Mechanisms
• Free gas within natural fractures
• Dissolved gas in water within natural fractures
• Adsorbed gas within the coal matrix

Total gas Volume
Free Gas Volume
Dissolved Gas Volume

Adsorbed Gas Volume


Typically gt 95
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Characteristics of Coalbed reservoirs

• Coalbed are characterized by their dual porosity
• Primary porosity micropores
• Secondary porosity macropores ( fractures)

Source Van Der Meer
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Coal flow mechanisms
Source Law
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Characteristics of Coalbed reservoirs

• The coalbed porosity and permeability changes as
  
• reservoir pressure is lowered and gas
  production occurs.
• The permeability of coal vary in two basic ways
• 1- Phase-relative permeability effects
• 2- Change in the effective stress within the
  seams
• Coalbeds can hold 2-3 times as much gas as
  conventional
• sandstone reservoirs.

Source ARI, 2002
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Gas recovery conventional vs. coalbeds
Source ARI 2002
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Productive stages of a coalbed methane well
Source ARI 2000
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Characteristics of natural gas in coal

• - The natural gas found in coal is "sweet" not
  "sour" as it does not
• contain hydrogen sulphide
• - It is generally pure methane with small amounts
  of carbon dioxide
• and nitrogen
• It is of near-pipeline quality when produced and
  requires
• minimal processing and,
• - It is generally produced at lower pressures
  than conventional
• natural gas.

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Geologic sequestration of CO2 in coalbeds
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Why?

• Coals have the ability to physically adsorb
  large volume
• of CO2 in a highly concentrated state
• Coals are frequently located near large point
  sources
• of CO2 emissions
• The injection of CO2 into coal seams enhances
  the
• commercial methane recovery process

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Reducing Greenhouse Gas Emissions Using Enhanced
Coalbed Methane (ECBM)
Source Gunter, 1998
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Reservoir mechanisms
Gas Sorption Isotherm
Source ARI,2000
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Reservoir mechanisms
Coalbed Adsorption Phenomenon
Source Reeves
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Reservoir mechanisms
Source Reeves
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Reservoir mechanisms
Source Reeves
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CO2 sources
Three CO2 sources may be used within CO2-ECBM
recovery Operations 1- Natural High pressure
CO2 from underground reservoirs is likely to
be the lowest cost source 2- Potential
industrial CO2 sources including gas-fired plants
and other large industrial plants 3-
Anthropogenic sources that currently are being
vented to the atmosphere
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Effects Coal Properties and Operational
Parameters ( SPE 78691)

• Purpose Determine which operational parameters
  are
• important to adjust for coals with different
  physical properties
• in order to maximize the amount of CO2
  remaining in coalseams

• How? Use of PSU-COALCOMP, a dual-porosity coalbed
  
• methane simulator, to model primary and
  secondary production
• of methane from coal, for a variety of coal
  properties and
• operational parameters

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Effects Coal Properties and Operational
Parameters ( SPE 78691)

• Three properties affect the performance of the
  sequestration
• process
• The sweep efficiency well geometry
• The reservoir pressure level
• The degree of departure from chemical
  equilibrium between the
• gasses and the coal the sorption time constant

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Effects Coal Properties and Operational
Parameters ( SPE 78691)
Results

• For short time constants as injection pressure
  is increased
• CO2 sequestrated and methane produced both
  increase,
• regardless to the size of the injection wells
• For large time constants
• - Increasing injection pressure in the longer
  injectors decreases
• performance
• - For short injectors increasing injection
  pressure continues to
• improve performance
• The dependence of CO2 sequestrated on injector
  length is
• minimal for the higher injection pressures

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Worldwide ECBM (Sequestration) Projects
Source ARI 2002
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Global Assessment of CO2-ECBM/ Sequestration
Resources/Capacity
Source ARI 1998
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The potential for technically-recoverable CBM
Source ARI
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Detailed Examination of US CO2-ECBM/Sequestration
Potential
Source DOE/ARI study (2003)
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Largest Pilots to Date San Juan Basin

• The worlds first experimental pure CO2-ECBM
  recovery pilot
• The second field demonstration site

Source SPE 48881
Location of CO2/N2 pilots, San Juan Basin
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Allison Unit Well Pattern

• 4 CO2-injection wells.
• 9 methane production
• wells.

Source SPE 48881
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Allison unit CO2 injection

• - The Allison pilot utilizes approximately 3
  MMcfd of naturally
• occurring CO2 produced from at McElmo Dome
  across the
• San Juan basin
• Bottom Hole pressure of about 1100 psi, safely
  below the
• the formation fracture gradient
• High purity (99)
• - Essentially dry

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Allison Unit Production
Source ARI, 2003
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Comparison of Numerical Simulators for Greenhouse
Gas Storage in Coalbeds (Law et al.)

• To model CBM production processes, many features
  have to be
• taken into account
• Dual porosity nature of coalbeds
• Darcy flows of gas and water in the natural
  fracture system
• Diffusion of a single gas component at the coal
  surface
• Coal matrix shrinkage due to gas desorption

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Comparison of Numerical Simulators for Greenhouse
Gas Storage in Coalbeds (Law et al.)

• Five numerical simulators are being compared for
  their capability
• to model CO2 storage project
• Stars, Computer modeling group
• GEM, Computer modeling group
• Eclipse, Schlumberger Geoquest
• GCOMP, BP-Amoco
• SIMED II, Commonwealth Scientific and Industrial
  Research
• Organization
• Only Stars and GCOMP are conventional oil and gas
  simulators

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Comparison of Numerical Simulators for Greenhouse
Gas Storage in Coalbeds (Law et al.)

• The comparison is based on field test data of
  coalbed reservoir
• in Alberta, Canada
• Description of Test Problem Sets
• - A single well test with pure CO2 injection
• - CO2 injection/CBM production in an
  inverted five-spot
• pattern

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Comparison of Numerical Simulators for Greenhouse
Gas Storage in Coalbeds (Law et al.)
Problem set 1 Single well CO2 injection test

• - Cylindrical (r-?-z) grid system
• 29 x 1 x 1
• Operating conditions
• 15-day CO2 injection period
• 45-day shut-in period, pressure falloff
• 60-day production period
• 62.5-day shut-in period, pressure build up

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Comparison of Numerical Simulators for Greenhouse
Gas Storage in Coalbeds (Law et al.)
Problem set 2 5-Spot CO2 injection/ CH4
production process Rectangular (x-y-z) grid
system 11 x 11 x 1
Operating conditions 182.5-day injection
rate 182.5-day production rate
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Comparison of Numerical Simulators for Greenhouse
Gas Storage in Coalbeds (Law et al.)
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Comparison of Numerical Simulators for Greenhouse
Gas Storage in Coalbeds (Law et al.)
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The benefits of ECBM

• Sequestration of CO2 in coal is a promising
  market-based
• environmental solution that can reduce
  greenhouse gas emissions
• while increasing coalbed methane recovery
• Increase in total reserves
• Recovered methane can be used as fuel for
  electricity and
• hydrogen generation

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The benefits of ECBM

• Alternatively, the record gas can be sold for
  profit, re-affirming
• coal as the fuel of choice for power plants
• Reduction of emitted CO2, a contributor to
  global warming and
• long-term climate instability
• The greatest impact of CBM may be in countries
  such as
• Australia, China and India where coal is the
  primary energy
• source and conventional natural gas are small

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THE END