Charles R. Nelson¹

(1) TICORA Geosciences, Inc, Arvada, CO

ABSTRACT: Geologic Controls on the Carbon Dioxide Sequestration Capacity of Coal Deposits

The geologic sequestration of carbon dioxide generated from the combustion of fossil fuels by injection into deep subsurface coal deposits is a proposed concept for reducing the buildup of this harmful greenhouse gas in the earth's atmosphere. The physical sorption of carbon dioxide within the coal micropores is the primary sequestration mechanism. Subsurface coal deposits throughout the world are recognized geologic traps or reservoirs for sorbed phase natural gas which, in turn, demonstrates their inherent potential for sequestering sorbed phase carbon dioxide for geologically long time intervals. A unique feature of this geologic sequestration concept is that the carbon dioxide sorption process promotes the desorption of any sorbed phase natural gas present in the coal micropores. The revenue obtained by the recovery and sale of this liberated natural gas would partially offset the overall carbon dioxide sequestration process cost.

This paper compares the effects of pressure, moisture content and coal rank variation on the carbon dioxide and methane sorption properties of coals from the U.S. Rocky Mountain region and elsewhere. Carbon dioxide and methane sorption capacities progressively increase as coal rank increases but the methane sorption capacity exhibits significantly greater sensitivity to coal rank variation than does the carbon dioxide sorption capacity. The results also indicate that the ratio of the carbon dioxide sorption capacity to that of methane progressively decreases as the pressure, moisture content and coal rank increase. The site-specific characterization of these types of interdependent relationships is essential for defining the carbon dioxide sequestration capacity of subsurface coal deposits.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado