This paper presents the HAZID/HAZOP [1,2,3,4] applied in risk analysis for the Cascade 5 well and this methodology main results, including possible failure or deviation events during the well construction, their causes and detection resources, consequences, criticality, and recommendations for mitigating safety risks.

The HAZID/HAZOP is a systematic method to analyze step by step each well operation, mapping possible deviation processes and proposing recommendations either to prevent causes or mitigate consequences.

The probabilities of some final events in the phases Liner 10”, Logging 12.25” and contingencies, were out of the ALARP (as low as reasonably practicable) [1] levels of risk tolerance, and it was recommended the improvement of the safeguards in these phases using BOP tests program designed.

The greater number of subsea control system failures compared to those that occurred on surface testing is believed to be primarily due to system complexity and hydrostatic issues that come into play in deeper water.

It is important to keep in mind that control system failures are discovered during function tests. In fact, a very large percentage of all failures could have been identified with only a simple function test.

It is important to distinguish between those failures that are found from pressure and those found from function testing.

In this study it was calculated the interval of tests of the security system (BOP) for the period of 100 days of mission, in order to get an average unavailability within the ALARP level (10e−8, 10e−4).

Following this approach it may be possible to avoid kicks and blowouts, saving costs and time in the well construction process.

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