Monitoring the CO2 injection site: K12-B

The K12-B gas field is located in the Dutch sector of the North Sea. The top of the reservoir lies approximately 3800 meters below sea level, and the ambient temperature of the reservoir is over 127 °C. The K12-B gas field has been producing natural gas from 1987 onwards and is currently operated by GDF SUEZ E&P Nederland B.V. The natural gas has an initial CO2 content of 13%, which is relatively high. Since the start of the gas production the CO2 component has been separated from the natural gas stream on-site and since 2004 part of the separated CO2 is re-injected into the gas field. In 2004 a demonstration project commenced where CO2 was re-injected into K12-B. The goal was to investigate the feasibility of CO2 injection and storage in depleted natural gas fields. More than 6 years later CO2 injection is still taking place and numerous monitoring techniques have been applied in order to get a better understanding of various aspects of underground CO2 storage in nearly depleted gas fields. Over the years monitoring activities have mainly focused on the well integrity and on the behavior of the CO2 in the well and reservoir. The cap rock present at K12-B consists of hundreds of meters of rock salts from the Zechstein Super Group. The most likely migration pathway for any gas, should migration occur at all is therefore along the well bores. Establishing the conditions of wells is of great importance for safety issues. Some of the tools which have been used will be discussed. Another goal for the various monitoring activities is to gain a better understanding of the behavior of the CO2 in the injection wells and the migration of the CO2 in the reservoir. How the CO2 migrates in the reservoir is important as regards the assessment of the potential for enhanced gas recovery (EGR) by CO2 injection.