ABSTRACT:

A very quick evolution has occurred during the last few years concerning production risers in general and hybrid risers in particular, as far as oil production in deepwater contexts is concerned. Raising the produced hydrocarbon stream from the sea floor to the ocean water surface keeps being so far affected (together with the mooring system) by the actual water depth (when not using dynamic positioning systems, of course), while other parameters proper of the related floating units normally depend both on the production throughput level and on the amount of required storage. With particular attention devoted to cold offshore oil reservoirs producing from shallow targets (e.g. located in the Mediterranean Sea area and / or in West Africa), thus emphasising the importance of the thermal properties of the riser system, a global risk analysis has been developed (and some results are here presented) in order to point out potential dangers or critical roles played by any of the system components and possible environmental consequences, depending on the geographical area (as already done by the Authors in several previous publications mainly concerning FPSO systems & similar ones). As well, comprehensive discussion is also carried out nowadays, debating how different approaches to Safety Case development can be compared and then merged into more general methodologies, as it is today encouraged and more and more often required. As a matter of fact, it can be said that - with respect to other and previous riser system kinds - the safety assessment of the here examined hybrid riser system has shown that a marked attitude does and should exist to better equalise the risk levels, without concentrating highest risk and criticality conditions inside single components (as it keeps happening for other kinds of risers or riser components, e.g. the flex joint for the steel catenary risers). Preliminary results are here provided and discussed, coming from an applied study (which is in progress) foreseen over a 3-year schedule. Suggestions and personal contributions are provided too, for potential system development purpose.

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