Consol Energy has signed a contract with the US Department of Energy to demonstrate a novel drilling and production process that creates sequestration sinks for carbon dioxide in unmineable coal seams, produces usable coalbed methane and reduces potential methane emissions to the atmosphere.
In the seven-year project, CONSOL Energy will use a technology known as "slant-hole" drilling to drain methane from coal seams not suitable for mining. Carbon dioxide (CO2) will then be injected into the coal seam to test the capacity of coal seams to sequester CO2, a greenhouse gas, following stimulation of methane production.
"A unique feature of this particular project is that slant-hole drilling also will be used to drain coalbed methane simultaneously from a mineable coal seam overlying the unmineable seams. The mineable seam will be sealed off before CO2 injection begins, so that CO2 does not infiltrate the mineable seam," said Dr. Frank Burke, CONSOL Energy's vice president for research and development.
"Removing coalbed methane from the mineable seam helps ensure the safety of subsequent mining operations, and it recovers methane that would otherwise have been vented to the atmosphere," Burke said.
Thus, the technology provides the dual greenhouse-gas-reduction benefits of sequestering CO2 in the unmineable seams and avoiding emissions of methane from the mineable coal, Burke said.
"Slant-hole drilling promises to be a more productive and much lower cost alternative to more conventional vertical frac wells for this application," he said. "We believe this process will be effective in most coal seams, especially those that are not suitable for conventional vertical fracturing.
"This demonstration will provide much-needed data on the technical and economic potential for CO2 sequestration, and could permit early commercialization of a potentially economic method for coalbed methane management," Burke said.
CONSOL Energy's proposal is to drain coalbed methane from a mineable coal seam and multiple underlying unmineable coal seams. Upon drainage of 50-60 percent of the coalbed methane, some of the production wells will be used for CO2 injection to sequester the CO2 in the unmineable seam, while stimulating additional methane production.
The slant-hole technique involves drilling a vertical production well through the targeted coal seams, and then intersecting that hole with a guided borehole, drilled from the surface, which deviates from the vertical hole to extend up to 3000 ft horizontally in the coal seams. This allows methane production and CO2 sequestration over a large extent of the reserve from relatively few surface locations.
In full commercial application, a typical five-hole, four-seam pattern could sequester up to 9 billion ft3 of CO2, and avoid 1.5 billion ft3 of methane emissions, while producing 6 bcf of methane.
Burke said CONSOL Energy would demonstrate the technology in a three-well, two-seam section, using commercial scale (3000-ft) slant-hole completions.
Edited from various sources by Sam Dodson
Read the article online at: https://www.worldcoal.com/cbm/18062014/alternative_cbm_drilling_technology_with_consol_energy_cbm53/