Title: Exploratory study of some potential environmental impacts of CO₂ sequestration in unmineable coal seams

Authors: Sheila W. Hedges, Yee Soong, J. Richard McCarthy Jones, Donald K. Harrison, Gino A. Irdi, Elizabeth A. Frommell, Robert M. Dilmore, Curt M. White

Addresses: US Department of Energy, National Energy Technology Laboratory (NETL), P.O. Box 10940, Pittsburgh, PA 15236-0940, USA. ' US Department of Energy, National Energy Technology Laboratory (NETL), P.O. Box 10940, Pittsburgh, PA 15236-0940, USA. ' US Department of Energy, National Energy Technology Laboratory (NETL), P.O. Box 10940, Pittsburgh, PA 15236-0940, USA. ' US Department of Energy, National Energy Technology Laboratory (NETL), P.O. Box 10940, Pittsburgh, PA 15236-0940, USA. ' US Department of Energy, National Energy Technology Laboratory (NETL), P.O. Box 10940, Pittsburgh, PA 15236-0940, USA. ' US Department of Energy, National Energy Technology Laboratory (NETL), P.O. Box 10940, Pittsburgh, PA 15236-0940, USA. ' US Department of Energy, National Energy Technology Laboratory (NETL), P.O. Box 10940, Pittsburgh, PA 15236-0940, USA. ' US Department of Energy, National Energy Technology Laboratory (NETL), P.O. Box 10940, Pittsburgh, PA 15236-0940, USA

Abstract: An initial investigation into the potential environmental impacts of CO₂ sequestration in unmineable coal seams has been conducted, focusing on changes in the produced water during enhanced coalbed methane (ECBM) production, using a CO₂ injection process (CO₂-ECBM). A high volatile bituminous coal, Pittsburgh No. 8, was reacted with synthetic produced water and gaseous carbon dioxide at 40°C and 50 bar to evaluate the potential for mobilisation of toxic metals during CO₂-ECBM/sequestration. Microscopic and X-ray diffraction analysis of the post-reaction coal samples clearly show evidence of chemical reaction and chemical analysis of the synthetic produced water shows substantial changes in composition. These results suggest that changes to the produced water chemistry and the potential for mobilising toxic trace elements from coal beds are important factors to be considered when evaluating deep, unmineable coal seams for CO₂ sequestration.

Keywords: geological sequestration; carbon dioxide; CO₂ sequestration; carbon sequestration; coal bed methane; environmental impact; unmineable coal seams; toxic metals; water chemistry; toxic trace elements.

DOI: 10.1504/IJEP.2007.014232

International Journal of Environment and Pollution, 2007 Vol.29 No.4, pp.457 - 473

Published online: 26 Jun 2007 *

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