Thermodynamic and Kinetic Processes associated with CO2- Sequestration and CO2-Enhanced Coalbed Methane Production from unminable Coal Seams Von der Fakultät für Georessourcen und Materialtechnik der Rheinisch -Westfälischen Technischen Hochschule Aachen zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften genehmigte Dissertation vorgelegt von Dipl.-Geol. Andreas Busch aus Koblenz Berichter: Univ.-Prof. Dr. R. Littke Univ.-Prof. Dr. Dr. h.c. D.H. Welte Tag der mündlichen Prüfung: 13.05.2005 Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar to my parents ACKNOWLEDGEMENTS First of all, I would like to thank my supervisors, Prof. Dr. R. Littke and Dr. B.M. Krooß for the opportunity to complete this thesis and for the best study conditions, one can imagine. Especially the given opportunity to attend numerous national and interna- tional meetings and conferences as well as to perform a three months stay at CSIRO Australia raised my motivation exceedingly. In addition to the very intense and helpful exchange of ideas with my supervisors, it allowed me to discuss the issues of my research with scientists from many countries. Furthermore, I gratefully acknowledge Prof. Dr. Dr. h.c. D. H. Welte for co- supervising this thesis. I would like to give my special regards to Y. Gensterblum, who introduced me in many aspects of petrophysical laboratory work and who was always interested in discussing the results of the experiments. His patience in explaining the basics of gas chromatography, volumetric sorption experiments, lab-automation as well as the small and big things in daily laboratory life improved this thesis tremendously. Since the major part of this thesis has been conducted in the scope of an EU project (RECOPOL), I acknowledge the help and support of all partners associated in this project. Among these partners, I would like to express my thanks to Dr. H. Pagnier and F. van Bergen who co-ordinated the project as well as to the fellows at TU Delft (K.-H. Wolf, Dr. H. Bruining, N. Siemons and S. Mazumder) and IFP Paris (Dr. D. Bossie-Codreanu). Prolific research is only possible with fruitful co-operations. I gratefully acknowledge Dr. X. Choi (CSIRO Petroleum Division, Melbourne, Austra- lia) for supervising me for three months in his department. His friendliness and pa- tience helped me to understand the principles of reservoir simulation and reservoir modeling. In this context I would like to thank the Heitfeld-Foundation for financial support. Productive research is also only possible with people that usually not appear as au- thors on a publication but that give support in various time consuming administrative subjects. Therefore, I would like to thank D. Kanellis and R. Wuropulos for giving me this support. 5 Furthermore, I enjoyed all the time being surrounded by the students and staff at the “Lehrstuhl für Geologie, Geochemie und Lagerstätten des Erdöls und der Kohle (LEK)” at RWTH Aachen University. This conglomerate of open-minded and down-to- earth people made work a leisure activity. Among these people, I would like to ex- press my special thanks to R. Mildenberger (sample preparation) and my office- mates K. Müller, J. Hollenstein and Dr. D. Prinz (in chronological order) for all the small and big things not related to research. Among the former, I would like to thank Dr. D. Prinz for being able to explain gas sorption on coal “in a different way”. I would also like to thank all my friends for pretending to understand what my re- search is all about and for helping me to forget about it. My parents, to whom I would like to dedicate this thesis, and my brother are thanked for supporting me over all the long years of education. This thesis could only be writ- ten because they always accepted my views and my decisions. And finally, I would like to thank E. Holuscha for her inspiration. 6 ABSTRACT The present thesis investigates the thermodynamic and kinetic processes associated with gas sorption (CO2, CH4) on coal. It is incorporated into a research field which studies CO2-sequestration in combination with CO2-enhanced coalbed methane pro- duction in unminable coal seams. This combination is regarded as a viable and promising option to reduce anthropogenic CO2-emissions. At the moment numerous world-wide research projects investigate the feasibility of this concept under different geological and technical conditions. Among these pro- jects, the RECOPOL-project („Reduction of CO2 Emissions by means of CO2 Storage in the Silesian Basin in Poland”) is working on a European level and includes labora- tory experiments, reservoir modeling, and geophysics as well as a field test in the Upper Silesian Basin in Poland. As a partner in this broad international consortium, it was the task to perform single- and mixed-gas sorption experiments on coals from the test site under the prevailing in situ reservoir conditions. Further coal samples from different coal basins all over the world have been integrated into this study to strengthen gained results and to address the diversity of coal samples in terms of rank, maceral composition, and moisture. Experiments have been performed on 14 different coal samples. Analytical tempera- tures were 22, 32 and 45°C at pressures up to 230 bar (23 MPa). The thesis is divided into three major chapters, each of them dealing with a different, well defined question: • The first part contains measurements that arose from a Round Robin initiated by the US Department of Energy. The different laboratories were supposed to inves- tigate five different samples from the Argonne Premium Sample Programme. Measurements performed included CO2 single-gas isotherms on dry coals at 22°C and pressures up to about 50 bar (5 MPa). Additionally, CH4 experiments under the same experimental conditions as well as CO2/CH4 mixed-gas sorption experiments at 45°C and pressures up to 180 bar (18 MPa) have been carried out. The emphasis of the study was to compare single- and mixed-gas sorption experiments and to perform a detailed characterisation of the five different sam- ples. • The second part investigates the kinetics of gas sorption on coal. To address this issue, CO2 and CH4 adsorption/diffusion experiments on one coal sample from the Upper Silesian Basin in Poland have been conducted on different grain sizes and temperatures (32 and 45°C) as well as on dry and moist coals. The emphasis of this chapter was to obtain qualitative differences between the different meas- 7 urements as well as to derive a kinetic model which describes gas sorption on coal by a simple and realistic formulation that can readily be implemented in exist- ing reservoir simulators. • The third part concentrates on the preferential sorption from CO2/CH4 gas- mixtures on coal. Measurements have been performed on ten different coal sam- ples at 45°C and pressures up to 230 bar (23 MPa). Dry and moisture- equilibrated coals as well as different source gas compositions have been used. The emphasis here was to demonstrate dependencies of different coal properties (rank, maceral composition, and moisture content) and different pressure ranges on the preferential sorption behaviour of coal. The main results of the three studies can be summarised as follows: o The ratio of CO2/CH4 sorption capacities from single-gas measurements varies strongly and is not constant as stated in several previous studies. o The sorption capacities of mixed-gases (CO2/CH4) can not be calculated from single-gas experiments. o The sorption rate for CO2 is always faster than for CH4. Sorption rates decrease as grain sizes and moisture contents increase and temperature decreases. o The sorption kinetics can be described by a simple, semi-empirical 1st-order ki- netic model under the assumption of a fast and a slow sorption process. o Preferential adsorption of CO2 and preferential desorption of CH4 occurs, against general expectations, only in some instances and is dependent on coal proper- ties. o The preferential sorption from a CO2/CH4 gas mixture on coal varies widely and only shows minor trends with different ranks and maceral compositions. o The source gas composition does not influence the preferential sorption behav- iour. The moisture reduces and the inertinite content increases the selectivity for CO2. 8 ZUSAMMENFASSUNG In der vorliegenden Studie wurde die Thermodynamik und Kinetik der Gassorption (CH4, CO2) an Kohle untersucht. Sie ist eingebunden in ein Untersuchungsfeld, wel- ches die CO2-Sequestrierung sowie die dadurch angeregte Flözgasförderung in nicht-abbaubaren Kohleflözen betrachtet. Diese Kombination wird als eine viel ver- sprechende und realisierbare Option der Reduzierung anthropogener CO2- Emissionen betrachtet. Verschiedene weltweite Forschungsprojekte beschäftigen sich zurzeit mit dieser Fra- gestellung unter diversen geologischen und technischen Voraussetzungen. Unter diesen Projekten greift das RECOPOL-Projekt („Reduction of CO2 Emissions by means of CO2 Storage in the Silesian Basin in Poland”) auf europäischer Ebene und beinhaltet Laboruntersuchungen, Lagerstättenmodellierung, Geophysik sowie einen Feldtest im Oberschlesischen Kohlebecken in Polen. Als Partner in diesem weit gefassten, internationalen Konsortium stellte sich uns die Aufgabe, Einzel- und Mischgasexperimente an Kohlen aus dem Untersuchungsge- biet und unter den dort vorherrschenden in situ Bedingungen durchzuführen. In die Untersuchungen wurden weitere Kohleproben aus verschiedenen weltweiten Lokali- täten integriert, um gewonnene Erkenntnisse konkretisieren zu können, und um der Vielseitigkeit der Kohlen (Reife, Mazeralzusammensetzung, etc) gerecht zu werden. Die diversen Messungen wurden an 14 verschiedenen Kohlen durchgeführt, wobei Temperaturen von 22, 32 und 45°C und Drücke bis 230 bar (23 MPa) gewählt wur- den, um den Lagerstättenbedingungen gerecht zu werden. Es wurden sowohl Feuch- te-äquilibrierte als auch trockene Kohleproben verwendet. Die Arbeit gliedert sich in drei Teile, jeweils unter dem Gesichtspunkt unterschiedli- cher, konkreter Fragestellungen: • Der erste Teil beinhaltet Messungen aus einem Ringversuch, initiiert durch das US Department of Energy.