CO2 Stability of oilwell Cements on CCS wells

 
CCS is expected to play a prominent role in reducing the CO2 emission globally. At present, mainly legacy wells from oilfields which have been depleted and no longer produce are considered for CO2 disposal. This raises the question whether common API grade Portland cement can provide a century-long seal for CO2. In the presentation, at first an overview of ongoing and planned CCS projects is given, and technical details of CO2 capture, transportation and injection into the wellbore are explained. Furthermore, experimental as well as field results from ongoing CCS projects will be discussed. It is shown that different results on cement stability were obtained depending on specific wellbore conditions. However, it became evident that neat API oilwell cement is always subject to corrosion from supercritical CO2. A potential solution are cement blends of OPC and fly ash or slag. These SCM´s can improve CO2 resistance substantially. Moreover, a calcium aluminate-phosphate cement was found to be completely CO2 stable. The presentation also addresses the economic aspects of performing CCS in the North Sea.