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Enhanced Coalbed Methane Recovery

Enhanced Coalbed Methane Recovery. Iman Mansourine November 18 th ,2003. 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

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Enhanced Coalbed Methane Recovery

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  1. Enhanced Coalbed Methane Recovery Iman Mansourine November 18th,2003

  2. 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

  3. Principal points of the presentation: • Coalbeds reservoirs characteristics • - Geologic sequestration of CO2 in coalbed reservoirs

  4. Coalbed reservoirs characteristics

  5. Coalbed Reservoir GasContent • 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 > 95%

  6. Characteristics of Coalbed reservoirs • Coalbed are characterized by their dual porosity: • Primary porosity: micropores • Secondary porosity: macropores ( fractures) Source: Van Der Meer

  7. Coal flow mechanisms Source: Law

  8. 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

  9. Gas recovery conventional vs. coalbeds Source: ARI 2002

  10. Productive stages of a coalbed methane well Source: ARI 2000

  11. 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.

  12. Geologic sequestration of CO2 in coalbeds

  13. 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

  14. Reducing Greenhouse Gas Emissions Using Enhanced Coalbed Methane (ECBM) Source: Gunter, 1998

  15. Reservoir mechanisms Gas Sorption Isotherm Source: ARI,2000

  16. Reservoir mechanisms Coalbed Adsorption Phenomenon Source: Reeves

  17. Reservoir mechanisms Source: Reeves

  18. Reservoir mechanisms Source: Reeves

  19. 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

  20. 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

  21. 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

  22. 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

  23. Worldwide ECBM (Sequestration) Projects Source: ARI 2002

  24. Global Assessment of CO2-ECBM/ Sequestration Resources/Capacity Source: ARI 1998

  25. The potential for technically-recoverable CBM Source: ARI

  26. Detailed Examination of US CO2-ECBM/Sequestration Potential Source: DOE/ARI study (2003)

  27. Largest Pilots to Date: San Juan Basin • The world’s first experimental pure CO2-ECBM recovery pilot • The second field demonstration site Source: SPE 48881 Location of CO2/N2 pilots, San Juan Basin

  28. Allison Unit Well Pattern • 4 CO2-injection wells. • 9 methane production • wells. Source: SPE 48881

  29. 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

  30. Allison Unit Production Source: ARI, 2003

  31. 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

  32. Comparison of Numerical Simulators for Greenhouse Gas Storage in Coalbeds (Law etal.) • 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

  33. 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

  34. 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

  35. 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

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

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

  38. 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

  39. 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

  40. THE END

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