Supported by the last events, it can be observed that safety must be the major concern in the activities developed in oil and gas well construction. However, safety assessment during the well construction process is not a trivial issue. Available risk evaluation approaches are based on static analyses of existent systems, not allowing a dynamic evaluation of the risk at each alteration of circumstances.

This work proposes the use of quantitative and dynamic risk assessment (QDRA) to assess the degree of safety of each planned job. The QDRA is a type of "safe job analysis" approach, developed to quantify the "degree of safety" in the entire well construction process, as well as during maintenance activities. The proposed methodology presents the definitions of "barrier" and "integrated barriers set (IBS)", as well as the modeling technique showing their relationships and it compares it with the analysis presented at Norwegian standard (NORSOK D-010).

This technique has been applied not only during the planning stages of well construction but also during workover to analyze the number of available IBSes for each operation. The greatest advantage of this technique is that it can be applied during the planning stages of well construction and maintenance, where the effects of hazard on the job sequence are important unknowns.

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