A Study of Possible Solutions for Cost Efficient Subsea Well Abandonment

There is a large number of subsea production wells offshore Norway approaching the end of their lifetime. Considering high spread rate of semisubmersible rigs, abandonment operations of these wells will be quite expensive. Moreover, Plug and abandonment (P&A) can easily contribute with 25% of the total costs of drilling for exploration wells offshore Norway. Hence it is of great importance to seek approaches and solutions to reduce the P&A cost. This paper reviews some possible new ways and also alternative technologies as the solutions to cut down the P&A expenses. Some of these technologies are now being used offshore Norway. In the first section of this paper, challenges of performing P&A operations offshore Norway together with the main cost drivers are discussed. It is then briefly argued how to consider issues such as barriers setting depth, cementing depth and logging in the design and well construction phases to ease or avoid future P&A challenges. For hydrocarbon exploitation in the Barents Sea and Arctic regions it is important to take into account the P&A phase in the early stage of planning and development. Light well intervention vessels as alternatives to semisubmersible rigs are recognized of being the largest contributor to cost saving. It will then be discussed to what extent vessel technologies can cut down the expenses for subsea abandonment. New ways of performing P&A can be another contributor to cost saving. It is shown how research and testing can assure the operators of new ways for performing P&A. Retrieval of production tubing is a challenging suboperation such that it imposes significant cost to subsea well abandonment. There have been performed studies on how P&A could be performed with tubing left in hole and it is of interest to pursue this further. We will investigate how the abandonment operations can be simplified and be more cost efficient if the production tubing can be left inside the well where the basic assumptions for being able to do it is accounted for. In addition, some complexities in abandonment operations can cause additional cost. An example of such complexities can be the need to establish two permanent barriers for potential permeable zones in overburden. It will be demonstrated how much can be saved with respect to cost if the regulations allow to ease some parts of abandonment operations. In this study, a probabilistic approach as a systematic tool to produce unbiased results is applied to quantify cost savings of new alternatives compared to the traditional ones.