DOE Regional Partnerships Find New Use for Unmined Coal

Jul 18, 2008 - DOE Fossil Energy Newsalert

The Midwest Geological Sequestration Consortium (MGSC), one of seven regional partnerships created by the U.S. Department of Energy to advance carbon sequestration technologies, has begun injecting carbon dioxide (CO2) in a groundbreaking field project in Wabash County, Ill. The project represents a promising strategy for safely storing this greenhouse gas while simultaneously increasing natural gas production in the region.

The pioneering project is the first of the Regional Carbon Sequestration Partnerships to inject carbon dioxide into a coal seam in the United States.

The Phase II pilot project, headed by the Office of Fossil Energy's National Energy Technology Laboratory (NETL) and the Illinois and Indiana State Geological Surveys, is testing the viability of turning unmined coal deposits into a source of useable energy by extracting natural gas, specifically coalbed methane, trapped in the coal. The bituminous coals of the Illinois Basin have a high content of methane making the Wabash County site a choice location for the project. The Illinois State Geological Survey estimates that there is up to 3.6 billion tons of storage capacity and over 10 trillion cubic feet of recoverable coalbed methane from unmined coal seams in the Illinois Basin.

Traditionally, operators drill production wells and, in a process called dewatering, pump water out of the coals to extract the gas. MCSG scientists are turning this research pilot project into a two-for-one opportunity by coupling the gas extraction with CO2 sequestration. Dewatering does not work well with carbon sequestration; it limits the amount of CO2 that can be sequestered because the dewatering process creates a low-pressure environment for the injected CO2 that reduces storage capacity.

The Wabash County project eliminates the need for dewatering. The project is designed to use one injection well and three production wells. Trucked-in CO2 is pumped through a heater and injected into the coal seam as a gas, increasing the pressure underground and desorbing the coalbed methane. Methane and CO2 make perfect partners; CO2 is preferentially adsorbed, meaning that, as the CO2 flows through the coal seam, methane is displaced from the surface of the coal in favor of the CO2.

This method presents a major challenge: coal swelling. As CO2 is injected, coal swells to absorb the gas. CO2 molecules are larger than methane, and the coal can absorb three molecules of CO2 for every molecule of methane that is released. Injecting too much CO2 at once can lower the permeability of the coal, and it has the potential to reduce the injection rate and limit the overall amount of CO2 that can be injected and sequestered into the seam.

To alleviate coal swelling, MGSC scientists are field testing a new approach: injecting the CO2 in pulses or cycles. CO2 is injected for 8- to 24-hour periods followed by a similar duration of shut-in to let the CO2 soak. This gives the CO2 time to adsorb, the pressure to dissipate, and avoids any pathway congestion or roadblocks. At the end of the test, researchers anticipate up to 250 tons of CO2 to be injected over 3 months.

In addition to the benefits of enhanced methane recovery, this project will also help demonstrate that geologic sequestration is a safe and permanent method to mitigate greenhouse gas emissions into the atmosphere. The Wabash County project will monitor the injected CO2 both in the lab and in the field, measuring changes in CO2 injectivity, the amount of CO2 that is retained by the coal, and the amount of methane gas that is displaced by CO2.

The project is one of six small-scale pilot field tests being conducted by the MGSC during the current validation phase of the Regional Carbon Sequestration Partnerships program, which is managed by NETL. During this phase, field tests are being conducted to validate the most promising sites to deploy sequestration technologies. In addition to the Wabash County coalbed-methane project, other field tests are determining the ability of some oil fields to sequester CO2 while enhancing oil production, and they are examining the injection of CO2 into saline formations a mile or more below the surface.

The MGSC is one of seven regional partners in a nationwide network to help determine the best approaches for capturing and permanently storing gases that can contribute to global climate change. Led by the Illinois State Geological Survey at the University of Illinois, the MGSC, in coordination with the Indiana and Kentucky Geological Surveys, is investigating CO2 sequestration options for the 60,000 square mile Illinois Basin, a subsurface geologic feature which underlies most of Illinois, western Indiana, and western Kentucky.