Sorption and Desorption Processes of Methane and Carbon Dioxide from Coals and Shales - Experiments and Theory

Bernhard M. Krooss, Andreas Busch, Yves Gensterblum, and Dirk Prinz
Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Aachen, Germany

Physical sorption processes of hydrocarbon and non-hydrocarbon gases on coals and carbonaceous shales encouter increasing interest in the context of unconventional gas exploration and subsurface storage (sequestration) of CO₂.

During recent years experimental work has been performed in our laboratory to investigate sorption thermodynamics, kinetics, selectivity and fractionation processes of methane and CO₂ on coals of different type and rank and on shales of various compositions. Experiments have been conducted under high-pressure conditions (up to 25 MPa) at temperatures relevant for natural gas and coal basins. These studies have provided a database suitable for the development of numerical models on gas migration and storage. They have also revealed unexpected behaviour in terms of selectivity and relative sorption rates.

Generally, sorption and desorption of CO₂ to/from coals was found to proceed more rapidly than of methane. Although coals exhibit larger excess sorption capacities for CO₂ than for methane, certain coals showed preferential sorption of methane in the low-pressure range. Moisture content plays a crucial role in the sorption of gases on natural coals.

Selected results will be presented documenting the state of experimental work on gas sorption processes in sedimentary basins and implications for unconventional gas exploration.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas