Riser Systems for Economic Deepwater Well Intervention

Riser Systems for Economic Deepwater Well Intervention
June 1996
S. Hatton

Floating production with subsea completions is currently acknowledged as the favoured technology for development of marginal and deepwater reserves. It is a technology that has been in existence for over 10 years but has only recently been widely adopted in favour of more technologically complex systems such as TLPs and SPARs which facilitate surface completions.

Floating production with subsea completions offer a number of key advantages such as a fast track schedule, low CAPEX to first oil and phased development. In the current economic climate these factors are an essential factor in maximising the NPV of an asset allowing project status to be achieved. Additionally, floating production is seen as a low risk solution, since the technology is well proven and can accommodate design changes without severe impact and is flexible to meet the completion and drilling requirements of a wide range of reservoir configurations.

Unfortunately nothing is usually perfect and there is normally a down side. For floating production, the down side is primarily the high through life cost of well intervention and workover operations. Unlike the TLP and SPAR where well intervention can be conducted directly from the production facility, subsea completions require mobilisation of a rig to conduct workover of subsea step out wells. This method of workover is costly, due to high rig rates and long mob/demob durations, particularly if the intervention is unplanned. Future workover costs will increase, due to the increase in rig rates which is predicted over the next decade, particularly in deep water and also as developments move into harsh environments Learn more at www.2hoffshore.com which increases intervention durations and complexities. This may have a dramatic effect on the economics of existing subsea developments which may have been justified on the basis of lower rig rates.

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