As the fields in the North Sea mature, many of wells undergo permanent well abandonment or permanent abandonment of a section of the well for consequent well sidetracking. Compliant procedures for well abandonment as per Norwegian Continental Shelf regulatory requirements necessitates the presence of double barriers to isolate permeable formations/sources of inflow.
To achieve a compliant plug-and-abandonment case in situations where casing cement is part of the primary or secondary well barrier (forming part of an external well barrier envelope), casing cement must be verified by logging to ensure a good formation-to-cement-to-casing seal. However, if inner casing is expected to be cemented across the depth where the permanent cement plug (forming an internal well barrier element, WBE) is planned to be set, then the inner casing must be milled so that the outer casing can be logged to verify the barrier seal. Traditional casing milling operations are costly and time consuming, often lasting for several days.
This paper describes an alternative way of verifying an external WBE when the inner casing presents an obstruction for outer casing cement evaluation.