Deployment of dedicated riserless well intervention (RLWI) vessels to perform a number of light-weight plug and abandonment (P&A) operations on subsea wells (also called pre-P&A) is now being used systematically in the North Sea as an alternative to modular offshore drilling units (MODUs). This paper describes the scope of work, project specific equipment and activities performed by RLWI vessels in preparation for the final abandonment by the MODU in two case studies, offshore Norway (Troll Osberg Gas Injection and Glitne fields). Based on the lower costs of RLWI compared to a MODU (Fjaertoft et al. 2011) and the shorter P&A operational times (Moeinikia et al. 2014), it is estimated that these case studies saved the Operator between 58.5 and 78 USD million.

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