Cost and safety efficient plugging and abandonment of subsea wells by a smaller vessel

Abstract

The main objective of this thesis is to evaluate challenges in satisfying rules and regulations set by regulatory bodies, constrains related to the well status as well as the limitation of technology available to perform plugging and abandonment activities. IOSS and NCA have joined resources in development of state of the art technology especially for full commercialization in P&A operations. It is required to provide suitable technical solutions to show to the authority that P&A for shut in well category 2&3 can normally be performed safely and successfully by fit for purpose intervention facilities as accomplished by drilling rigs. This will be a favorable solution for oil operating companies taking into consideration their determination toward IOR philosophy for subsea wells. Safety authorities require a good quality of P&A operation that provides an eternal sealing arrangement to isolate reservoir fluids migration up to the sea surface. Therefore primary strategy was to establish a clear understanding of the state of a shut in well to be abandoned and the means to establish barriers to control well pressure prior to commencement of the P&A campaign as required by the authorities. A thorough study of guidelines related to selection and location of WBE is dealt with, especially the technology available for deployment of tools downhole when setting plugs. This forms the design bases for top side equipment capability needed for handling heavy lifts of subsea WCP packages, SLIS or riser system and BHA while performing P&A activities. Based on evaluation of the state of the art of technology available today and exploration of the scope of work required to be accomplished on P&A operation for shut in well category 1 to 3, it is recommended that permanent abandonment by use of small intervention facilities be done since is as well economically a viable solution. The major constrain in this work was the limitation in acquiring technical information for P&A operation since most of the information and experience available is not well shared in the industry and lack of supporting literature. It was necessary to gather technical information from experienced personnel who directly have been involved or performed P&A operations. This was a challenge and led into set back in the thesis work since most of the crew dealing with WOI operations was located offshore.