Storage sites associated with depleted oil and gas reservoirs may contain many abandoned wellbores in addition to potentially unidentified wellbores. These wellbores have historically variable quality and quantity of cement that will have undergone ranging degrees of degradation. Wellbore performance in a single wellbore is dependent on the wellbore events (i.e. pressure and temperature changes) that occur within the life of the wellbore (Fourmaintraux et al., 2005; Gray et al., 2007).

There is significant uncertainty surrounding the integrity of existing wellbores due to a lack of data. Successful implementation of carbon capture and storage (CCS) will depend on solving the small-scale leakage problem associated with localized flow along wellbores. Our knowledge of oil wellbore performance under different life stages of a well is still weak. Consequently, each wellbore is unique and general conclusions about well integrity are difficult to ascertain from analyzing only a single well. Each wellbore is considered as a risk and robust tools are needed to allow for the assessment of the performance for wellbores and investigate wellbore leakage mechanism.

In this paper, a full lifecycle methodology is proposed to assess wellbore integrity as a measure of the risk of leakage. The methodology identifies the key elements to model the wellbore element and incorporates the use of a statistical approach to better understand the uncertainty in the risk estimation and interaction between various parameters controlling the model.

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