Abstract

This paper presents the results of a study examining the feasibility of a Conical Piled Monopod (CPM) offshore Northern Alaska in about 41m water depth, fairly competent soil conditions, and Multi Year Ice environment. The study was conducted jointly by ConocoPhillips Company based in Houston, Texas and Granherne Ltd, a KBR Company based in Leatherhead, UK. ConocoPhillips sponsored the study.

Two CPM concepts were considered, the Standalone CPM covered in this paper and a Dual Rig Jack Up (Gemini) Assisted CPM. The latter is the subject of another paper to be published later.

The CPM was configured for two drilling rigs, assuming topsides weights ranging from 35,000 tonnes to 45,000 tonnes and corresponding operating weights from 60,000 tonnes to 70,000 tonnes respectively. Ice loads were calculated using ISO 19906 formulae where possible, otherwise using references within the ISO 19906 code and specialist ice load advice (Ken Croasdale) where necessary.

The CPM has been shown to be feasible in the Alaskan Sea for the two ice conditions considered, 6m thick level ice and a very rare 25m thick ice island event. The ice island event represents a very conservative scenario and further data may allow its severity to be reduced. In addition, there will be many months, if not years, after discovery before an ice island can potentially impact the CPM.

The CPM has a large enclosed volume available, which could accommodate a potentially significant amount of oil storage. However, this has not been quantified within this study work.

The CPM concept eliminates or greatly minimizes the need for seabed preparation, being a pile supported structure. It also does not require solid ballast for resistance against sliding due to ice loads; these two characteristics of the CPM can have a major positive impact on the cost and schedule of an offshore Arctic project.

ConocoPhillips has a Patent Pending on the CPM concept.

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