Probabilistic Cost and Time Estimation of Rigless Plug and Abandonment

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With a high demand for plug and abandonment (P&A) of subsea wells in the future on the Norwegian continental shelf, industry is challenged to find alternatives and rigless technologies that can make P&A operation more cost-effective and -efficient. Light-well-intervention vessels (LWIVs) can take over some parts of P&A operations and release semisubmersible rigs to function in the drilling and completing of new wells. This paper covers potential and experience of LWIVs in P&A.


The P&A work of a single well can be separated into three distinct phases: reservoir abandonment, intermediate abandonment, and removal of the wellhead and the casing strings a few meters below seabed (Oil and Gas UK 2011). Different vessels and technologies will be applied for these phases, which are also affected by the complexity of the well. It is also expected that these P&A phases to some extent will be performed in multiwell campaigns in which issues such as learning effects and correlations have to be considered.

The deterministic approach for time and cost estimation is a simple, traditional method, and the results can be transferred easily. There are some limitations associated with the deterministic approach, such as the yielding of biased results and, sometimes, the inability to capture the full range of outcomes.

On the other hand, the probabilistic approach has been recognized recently as a common and preferred technique for time and cost estimation, compared with the deterministic approach. This approach presents a nonbiased technique for time and cost forecasting and allows for inclusion of uncertainty into the model, covering the correct range of possible outcomes.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 169203, “An Investigation of Different Approaches for Probabilistic Cost and Time Estimation of Rigless Plug and Abandonment in a Subsea Multiwell Campaign,” by Fatemeh Moeinikia and Kjell Kåre Fjelde, SPE, University of Stavanger; Arild Saasen, SPE, Det Norske Oljeselskap ASA and the University of Stavanger; and Torbjørn Vrålstad, SPE, SINTEF, prepared for the 2014 SPE Bergen One Day Seminar, Bergen, Norway, 2 April. The paper has not been peer reviewed.
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Probabilistic Cost and Time Estimation of Rigless Plug and Abandonment

01 January 2015

Volume: 67 | Issue: 1


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