Search

A pilot site for CO2 storage in coal seams was set-up in Poland, as has been reported on previous GHGT conferences. This site consisted of one injection and one production well. About 760 ton of CO2 has been injected into the reservoir from August 2004 to June 2005. Breakthrough of the injected CO2 was established, which resulted in the production of about 10% of the injected CO2 by the production well in this period. A follow-up EC project, MOVECBM, aimed at determining the storage performance of the reservoir, i.e. whether the injected CO2 was adsorbed onto the coal or whether it was still present as free gas in the pore space. The injection well was used for this purpose, because the production well had to be abandoned for permitting reasons. Several operational periods can be defined between the last injection in June 2005 and the abandonment of the well in October 2007. In the first period the well was shut-in to observe the pressure fall-off, followed by a decrease of pressure at the wellhead by releasing gas in a controlled way in the first months of 2006. The amount and composition of the gas were measured. As a result of the pressure reduction, the well flooded with water. A production pump was placed on the former injection well, enabling active production from the coal from March to September 2007. Results of these operations showed that whereas the gas production rates were as expected based on the experience with the production well, the water production was remarkably low. Further, the gas composition showed a predominance of CO2 over CH4 during the gas release that changed gradually into a predominance of CH4 over CO2 during the production phase. Although stabilization was not reached within the production period, the composition approached a 60% methane, 40% CO2 ratio. This indicates that the exchange of these gases is more complex than often envisaged. After removal of the pump the well was filled with water, which ceased the gas release. This indicates that the pressure in the reservoir was back to its original, hydrostatic, state. As the total volume of CO2 produced was only a fraction of the amount that was injected, it can be concluded that the CO2 was taken up by the coal and is currently adsorbed. This gives confidence in the long-term stability of the injected CO2. In conclusion, the field demonstration in Poland has been a successful experiment. Lessons learned in this demonstration indicate that the volumes that can be injected in low permeability coal seams (