Evaluation of the CO2 Leakage Risk Along the Abandoned Wells in the French Context

This paper presents a classification system, adapted from the Watson and Bachu (2007) one, to estimate the leakage risk along the abandoned wells in the French context. The selected criteria of this classification are the wellbore type (with/without casing that intercepts the aquifer where the storage will take place), the abandonment date (before/after 2000 which corresponds to a significant improvement in the French wellbore abandonment regulation), the top level of primary cementation, the deviation of the wellbore, and the drilling date (before/after 1980). The input data necessary to establish the classification are mostly available. When a data is missing, we have considered either: 1) a most prejudicial option assuming that the maximum value is considered; 2) or less prejudicial option where the criterion does not affect the calculated risk category. The results show a great variability of the risk when one moves from the most prejudicial option to the less prejudicial one. This emphasizes the primary importance of the management of the lack of data in this kind of study. Thus, without any additional information, the evaluation of the CO2 leakage risk along the abandoned wells should at least exhibit the two extreme values that respectively correspond to the less and the most prejudicial options.