Survivability Risk Assessment During Hydrocarbon-Related Accident Events For Subsea Well Intervention Operations From Smaller Non-Drilling Ship-Shaped Vessels
- Fleur Royes (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE International Conference on Health, Safety and Environment in Oil and Gas Exploration and Production, 12-14 April, Rio de Janeiro, Brazil
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 1.10 Drilling Equipment, 5.1.2 Faults and Fracture Characterisation, 3.2.2 Downhole intervention and remediation (including wireline and coiled tubing), 1.6 Drilling Operations, 4.1.2 Separation and Treating, 1.7 Pressure Management, 7.2.1 Risk, Uncertainty and Risk Assessment, 3 Production and Well Operations, 1.7.5 Well Control, 4.2.4 Risers, 4.2 Pipelines, Flowlines and Risers, 4.1.5 Processing Equipment
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The recent emphasis in performing electric line and coiled tubing operations on subsea trees from ship-shaped vessels smaller than conventional drilling units has introduced a new set of challenges in keeping people safe during major accident events. The most significant of these is preventing the impairment of escape, evacuation and rescue facilities during uncontrolled hydrocarbon accident events, such as, releases originating from the well or, in the case of coiled tubing operations, from the return of pumped and well fluids to surface.
Open water wireline systems by their nature do not involve such risks, however coiled tubing operations involve a conduit between the well and the vessel and, depending on the nature of the preventative measures incorporated in the design of the intervention system, exceeding the allowable impairment frequencies is possible. Adopting the design principles of an open water wireline intervention package to coiled tubing operations where the wellbore is restricted subsea during operations provides distinct advantages as the probability of an accident event is significantly reduced.
Reducing the probability of hydrocarbon related events is critical in the design of the well intervention package and the consequent safety of the system and its operations. This is because well intervention vessels, unlike typical offshore vessels such as semi-submersibles and drillships, do not provide the same inherent protection as traditional offshore vessels against these types of accident events.
This paper presents how to manage the safety of personnel during hydrocarbon related accident events during well intervention operations on an intervention vessel as a function of the design of the invention system in consideration of the consequences for the identified accident events. The paper also assesses the safety associated with each type of intervention system and the vessel of operation relative to each another in terms of impairment frequencies.
There are numerous technical solutions and vessels used for well intervention operations, each with their own technical challenges relative to the management of accidental well releases for the preservation of life. The risks associated with electric line and coiled tubing intervention activities on subsea trees from semi-submersibles and drillships are well known and are in large part managed through the design of the vessels, whereas the execution of the same activities from smaller ship-shaped non-drilling vessels is in its infancy and therefore the risks associated with the activities are not yet fully understood within the industry.
There are several criteria used for determining the acceptability of risks associated with activities within the industry. Some of the more common measurements of risk are fatality risks and impairment frequencies of the escape, evacuation and rescue (EER) facilities. Since fatality risks are highly sensitive to the manning of a facility, a true comparison between the different intervention systems and the use of these on different vessels is difficult. Therefore, the more appropriate tool is
comparison of the EER impairment frequencies. By assessing and comparing the EER impairment frequencies associated with intervention activities on subsea trees the key risk drivers will be readily identifiable, as will the acceptability of each of the systems on the nominated vessels.
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