Analysis of Well Design for Effective P&A of Production Wells
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Plugging and Abandonment (P&A) has long been given little im- portance in the oil industry as the activity does not generate values, and preparing for it to be efficiently carried out was overshadowed by the interest of providing an optimal well design for production of hydrocarbons. Moreover, P&A lay too far in the future and was thought of as a fixed and minor cost. This thesis deals with well construction, completion design and innovative abandonment technology as a way to reduce P&A expenditure. Slim well construction, monobore well completion and slen- der riser technology are investigated. Rigless abandonment methods involving wireline and coiled tubing for plugging both platform and subsea production wells are reviewed and compared. A rigless tech- nique is a technique which does not make use of heavy intervention rigs but of low specication or light well intervention vessels. Specif- ically, one of these techniques is given particular attention in this thesis, namely through-tubing abandonment. This technique com- plies with existing P&A standards, and is fully rigless. Data from a selected well program taken from a future subsea development is used as a case to illustrate the through-tubing abandonment con- cept and a plugging recommendation is carried out. Further, its risks and requirements are discussed. This development will be on the Brynhild field operated by Lundin Petroleum. Two tool designs for enhancing the capabilities of a light well intervention vessel to perform through-tubing abandonment are presented. The results are that the well construction and completion tech- niques discussed are benecial for a cost effective P&A and that through-tubing P&A is feasible with today's technology. However, specialized equipment needs to be used to meet various challenges. Rigless abandonment involves cheaper rig cost, but also more com- plex and delicate operations and this risk needs to be assessed and mitigated when planning for such an abandonment.