Essential Aspects in Probabilistic Cost and Duration Forecasting for Subsea Multi-well Abandonment: Simplicity, Industrial Applicability and Accuracy

Abstract

There are a large number of subsea fields on the Norwegian Continental Shelf approaching the end of their lifetime and, hence, require to be abandoned. In order to improve cost efficiency, a combination of rig-based and rigless technologies will be employed to accomplish distinct phases for subsea well abandonment. A correct picture of expenditures and duration for the field abandonment is an important aspect in budgetary planning for every company.Although the probabilistic approach has become a standard method compared to the deterministic approach for time and cost forecasting, complexity of the probabilistic approach compared to the deterministic method might still be a hindrance for using this approach. In this paper, a simple excel-based program is developed for probabilistic cost and time estimation of subsea multi-well abandonment. This model is aimed to provide an applicable and simple means for industry to estimate cost and time of subsea well abandonment. The structure of this program is based on the Oil and Gas UK Guideline on well abandonment cost estimation. This is presented in a way capable of being replicated easily. In addition a summary of vessel based technologies available for subsea well abandonment together with a brief description of operation sequences for well abandonment are presented.The inclusion of dependencies into cost and time forecasting model is a challenging issue which needs to be addressed in order to achieve a correct picture of possible outcomes. In the second section of this paper, different approaches to address dependencies among different operations are also investigated together with a comparison and a discussion on the benefits and the disadvantages associated with each approach. This will be implemented for a case example wherein different rigless technologies are utilized to complete multi-well abandonment.