Storing carbon dioxide (CO2) in deep geological formations is one part of the carbon capture and storage (CCS) process. The process of storing CO2 into deep geological formations is defined as geological CO2 sequestration or CO2 geo-sequestration. Injecting CO2 into a reservoir does not guarantee safe storage because CO2 could leak back to the surface and/or may contaminate specific strata where other energy, mineral and/or groundwater resources are present. Two mechanisms control assurance of storage integrity, which are containment within the geological structure and minimizing the potential for wellbore leakage (Espie, 2005).

This study is concerned with describing the wellbore leakage mechanism utilizing wellbore element, which will be extended to the whole wellbore system. To get a better chance of success in practice, successful CCS depends on the small-scale leakage problem associated with localized flow along wellbores. Our knowledge of wellbore performance for storage purposes is still weak.

The paper is the first of a series to model wellbore element analytically by introducing wellbore sealing efficiency index. Wellbore sealing efficiency can be used as a ranking criteria between different wellbore elements in the same well and/or different wells in the same locality. Moreover, safety performance of wellbore element can be assessed.

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