An estimate of the time to degrade the cement sheath in a well exposed to carbonated brine

Carbon sequestration in abandoned petroleum fields may be a short-term solution to reducing anthropogenic emissions of CO2. If sequestration is adopted on a large scale, it will be important to understand how CO2 may leak out of sequestration formations. Possible avenues for leakage are abandoned wells. The results of a set of cement degradation experiments were used to get a rough estimate of the rate of degradation of the cement that is used to construct and abandon wells when it is exposed to carbonic acid. The rates that were calculated give an estimate of the time to degrade 25 mm of cement under static conditions at pH and temperature conditions that one might expect in a sequestration formation. The results of the estimate indicate that it will take tens to hundreds of thousands of years to degrade 25 mm of cement.