Relocation of existing jacket platform in western offshore of india ‎

Abstract

ONGC (Oil & Natural Gas Corporation Limited) started its hunt for “Black Gold” in the Indian western offshore region in 1976 and is ‎currently operating more than 285 fixed steel platforms in water depths ranging between 25-‎‎90m. Many of the existing wells on the platforms have matured over a period of time, resulting ‎in decline of productivity, even after employing usage of Improved Oil Recovery ‎‎(IOR)/Enhanced Oil Recovery (EOR) techniques. Considering the techno-commercial ‎constraints for offshore development, IEOT-ONGC has taken up a study for re-location of ‎existing non-producing offshore platform to a newer location. The structural adequacy of the ‎existing structures at new locations has been ascertained for ‎‎100 year return period extreme ‎storm conditions for 8 different directions and other design loads as per API RP ‎‎2A ‎‎(WSD) (Ref. 1), considering in-situ met-ocean and soil conditions in the new field. The structural integrity ‎assessment ‎procedure explores the need ‎for ‎strengthening/mitigation measures in case the inherent capacity of the structure to ‎withstand ‎the incoming loading is not sufficient at the new site of installation. For relocation of ‎existing jacket platforms to new locations at different water depths in ‎western ‎offshore of India, ‎a general philosophy for foundation design has been developed considering installation of ‎plinth platform for relocation to field where water depth is higher than existing one and ‎installation of insert piles and extra clamp-on skirt piles, if required, where water ‎depth at ‎relocation is similar to existing water depth for the platform.‎ In this paper, relocation ‎methodology of existing well head platforms for use at new locations in Western offshore of ‎India at similar or different water depths has been discussed ‎covering foundation philosophy, well plugging and abandonment (P&A), ‎decommissioning and refurbishment aspects.