The life cycle of an oil well contains several phases, such as design, construction (drilling, completion and evaluation), production, intervention and abandonment. Moreover, each phase includes its particular operational modes (e.g., in the intervention phase there are wireline and coiled tubing operations). One of the main concerns during each phase refers to the risk of uncontrolled hydrocarbon flow to the environment, which is mitigated by measures that ensure well integrity through the use of well barriers. In this sense, the concept of two independent well barriers, reinforced by standards such as NORSOK D-010, leads the efforts in the industry, but does not clearly addresses the risks.
A failure in the well barrier elements leads to undesired events involving oil flow to the environment, damages to equipment and personnel loses. However a full comprehension of how these events contribute to the risk should take into account factors regarding the operational conditions. For instance, when the wellbore is exposed, an influx of hydrocarbons tends to release a biggest amount of oil to the environment than when the completion is installed. Additionally, older wells tend to sustain a smaller pressure when compared to other wells in the beginning of their life cycles — what also impacts on the consequences of undesired hydrocarbon flows. Nonetheless, these accidents should be pondered by their probability of occurrence for a full addressment of the risk.
In order to contribute to a risk-oriented view of issues related to well integrity, this work presents a customized Preliminary Risk Analysis framework. The simultaneous combination of well barrier elements failures constitutes the base of the analysis, which is complemented by control and monitoring measures. Hazards are also described according to their operational conditions, allowing treating this aspect separately.