The behavior of oil well cement at downhole CO2 storage conditions: Static and dynamic laboratory experiments
Résumé
One of the major technological issues for CO2 injection is the long-term behavior of the cement-based materials used to ensure the overall sealing performance of the storage wells. When water is present, the CO2 injected can react chemically with the cement (i.e. carbonation). The objectives of our experimental program are to assess the kinetics and phenomenology of the changes that occur in class-G Portland cements exposed to CO2-enriched aqueous fluids at 8 MPa and two different temperatures (90 °C and 140 °C). The experimental program presented in this paper consists of two carbonation tests (static tests) and a coupled chemo-mechanical test (dynamic test) which were performed on similar class-G cement and similar CO2-rich water. The main preliminary results show a carbonation front progressing from the fluid-sample interface towards the sample centre. The front moves faster at 140 °C than 90 °C because of the different carbonation process involved at this higher temperature. The results of a coupled chemo-mechanical test with injection of CO2-saturated water show that the CO2 flow rate in the cement rapidly decreases, finally resulting in carbonation clogging of the cement sample. They seem consistent with reported field observations.