Acta Montanistica Slovaca Ročník 11 (2006), mimoriadne číslo 1, 116-119 Use of carbon dioxide in underground natural gas storage processes Stanislaw Nagy 1 Používanie CO 2 pri procesoch uskladövania plynu v podzemí The possibility of use of carbon dioxide in gas storage processes is presented. The model of mixing process between CO 2 and methane in porous media is given. The process of injection of carbon dioxide into a lower part of storage near the water –gas contact is modeled. The example of changes in the mixing zone is presented and discussed. Key words: carbon dioxide, gas storage processes, porous media, near the water Introduction The research project related to the“Use of carbon dioxide in underground natural gas storage processes” is executed in two phases. In the first stage, the study of diffusive and dispersive mixing processes (CO 2 /stored natural gas) in classic gas storages and the study of adsorption-diffusive processes in coal bed layers in selected abandoned hard coal mines is given. The second stage is related to a numerical study of mixing processes. Carbon dioxide designated to be used in storage processes could be obtained in separation processes from flue gases that come from sources of a CO 2 emission point (power plants, thermal-electric power stations, chemical factories, steel mills, etc.). Following technologies are available for the capture of carbon dioxide: chemical absorption, cryogenic process, physical absorption, membrane technologies. Basically, four methods of CO 2 storage in geological structures could be distinguished: 1. storing in oil depleted reservoirs and exploited gas storages 2. storing in aquifer structures 3. storing in coal beds linked with an enhancement of methane exploitation (ECBM) or construction of a storage in abandoned hard coal mines 4. storing in depleted and exploited oil reservoirs CO 2 in storage processes The easiest process, using CO 2 in a natural gas storage process in the depleted natural gas reservoirs, is the exchange of classic gas cushion (buffer volume) for another cushion which partly involves CO 2 . Such using of carbon dioxide could be economically justified: the costs of separation, transport, compression and the injection of CO 2 could be diminished by the possibility of natural gas reception from the top parts of storage. Besides obvious ecologic and economic benefits, the uncertainty of the composition of the natural gas exploited from an underground storage should also be considered. This issue will be the first point of the research project. The matter of storing in coal beds linked with the enhancement of exploitation (ECBM) or the erection of a storage in abandoned hard coal mines is the second basic problem in the research project. ECBM-CO 2 in the upper silesian basin of Poland (RECOPOL) The RECOPOL project is an EC-funded research and demonstration project to investigate the technical and economic feasibility of storing CO 2 permanently in subsurface coal seams (Pagnier et al., 2004). The main aim of the project was to demonstrate that the CO 2 injection in coal under European conditions is feasible and that the CO 2 storage is a safe and permanent solution. This is the first field demonstration experiment of its kind in Europe. The development of the pilot site in the Upper Silesian Basin (Fig. 1) in Poland began in summer 2003. One of the existing coal bed methane wells was cleaned up, repaired and put back into production (Fig. 9). A new injection well was drilled at 150 m from the production well. After the completion of the well with casing, cementing and perforations, the perforated zones were tested. A baseline cross borehole seismic 1 dr. hab inž. Stanislaw Nagy, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Cracow, Poland, stanislaw.nagy@agh.edu.pl (Recenzovaná a revidovaná verzia dodaná 6. 10. 2006) 116