Un-minable Coal Seams
Un-minable Coal Seams, or CO2-enhanced coal bed methane (CO2-ECBM) production, is a third storage option. The logic behind using these types of coal seams for storage is similar to that of using depleted oil fields for EOR. These coal beds contain large amounts of methane gas that, if released, can be captured and used for power generation or heating. By injecting CO2 into the coal seam, the methane contained in the surface pores of the coal is displaced and released. Laboratory measurements suggest that twice as much CO2 can be stored as methane was desorbed. However, since methane is also a greenhouse gas, all of the methane that is released must be captured and put to use for a greenhouse gas emissions benefit to occur. The revenue created by the capture of methane can help off-set CO2 injection costs. ECBM is still in the early stages of research and compared to storage in other reservoir types, coal seams appear to have a lesser capacity for storing CO2.
A CO2-ECBM pilot project developed by Burlington Resources (now ConocoPhilips) and BP is underway in the San Juan Basin in the southwestern United States. The project has achieved increased methane production. So far, no CO2 has been found in the capture methane gas indicating that CO2 is being stored in the coal seam. Lessons learned from this experiment will be looked to for future consideration of these coal seams as a storage option.