1. Barrier qualification
Barrier qualification should be based on evidence, not on the lowest-cost assumption. A mature well may appear to offer several options, including existing cement, a natural formation barrier such as creeping shale, or a new cement placement after casing recovery. Each option can change the amount of intervention required.
In one mature offshore abandonment campaign, logging showed shale movement behind casing. The result was encouraging, but the available evidence was not strong enough to qualify the interval as the long-term barrier assumed in the base plan. The campaign moved to a contingency design instead of trying to defend an assumption that could not be verified.
2. Well access
Access creates a different uncertainty. Historical completion drawings may show what was installed, but they cannot confirm what can still be moved after years of service. Solids, corrosion, deformed tubulars, degraded completion hardware and restrictions can change the recovery sequence.
In one casing-recovery operation, solids accumulation and mechanical restrictions forced the work into several stages, with additional cutting, cleanup, jacking and reevaluation before the abandonment objective could be achieved.
3. Contingency activation
Thus, contingencies should be designed into the base program, not added after a problem appears. A contingency has little value unless the conditions for using it are defined in advance.
Typical triggers include failure to verify a barrier, repeated inability to move or recover tubulars, unacceptable equipment response, or evidence that no longer supports the proposed barrier solution.
4. Technology and regulatory readiness
Technology should be treated the same way. Through-tubing cement evaluation can reduce uncertainty without first removing large sections of completion or casing. But the question is not whether a tool works in principle. The question is whether the evidence it produces is sufficient for the intended barrier decision and acceptable within the regulatory framework.
On the Norwegian Continental Shelf, permanent barriers must be verifiable. If a new method cannot demonstrate the required performance or equivalence, the campaign needs another path. Therefore, technology selection should start with the decision to be made, not with the tool.
