Andrew R. Scott1
(1) Altuda Geological Consulting, Austin, TX
ABSTRACT: Hydrogeologic Controls on Carbon Dioxide Sequestration in Coal Beds
The sequestration of carbon dioxide in coal beds has several advantages over other sequestration technologies. Slope instability potentially may result in the catastrophic release of carbon dioxide sequestered as hydrates in the deep sea, and precipitation of carbonate minerals associated with injection into saline aquifers may lower permeability near the well bore and inhibit further injection. Seal integrity and reservoir geometry and heterogeneity are important factors affecting the injection of carbon dioxide in abandoned oil and gas reservoirs, whereas carbon dioxide is strongly sorbed to the microporous coal matrix indicating that seal integrity is less important than in sandstone reservoirs.
Determination of the volume of carbon dioxide that may be potentially sequestered in coal reservoirs is a function of coal properties, reservoir conditions, and economics. Coal properties include coal swelling associated with carbon dioxide sorption, carbon dioxide sorption capacity, Langmuir volume and pressure, ash content, maceral composition, partial pressure of carbon dioxide (critical pressure), and the equilibrium between bicarbonate concentration in formation water and the coal surface. Reservoir conditions include pressure, temperature, in situ moisture, cleat and fracture spacing and geometry, and aperture size. Hydrogeologic economic factors include coal occurrence and distribution, proximity to carbon dioxide sources, depth to coal reservoir, and injection pressure. Quantification of carbon dioxide sequestration in coal reservoirs requires information on sorption capacity at reservoir pressure, temperature and in situ moisture conditions, reservoir pressure, coal thickness, an ash volume correction factor, permeability decrease with depth, and changes in permeability associated with coal swelling.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado