Abstract

The traditional need to carry out all well operations from a rig can be expensive and delays valuable well construction programmes. Rigless intervention, including the use of subsea wireline lubricators and installing subsea Xmas trees on wire, utilising a Dynamically Positioned (DP) intervention vessel has long been accepted in some areas of the world as a cost-effective and efficient alternative to traditional rig-based methods.

In 2005 it was recognised internally that the ability to intervene without a traditional rig would be of potential future benefit. An aspirational work programme was developed including both well operations such as subsea Xmas tree (SSXT) change out, well abandonment and production enhancement operations was developed. The scope generated was sufficient to justify the mobilisation of a suitable vessel and the necessary specialist equipment such that these operations could be completed. It was also recognised that the vessel would offer further options for construction support, commissioning start up support and field maintenance activities. The actual 1st job undertaken of SSXT installation on Vincent project was not recognised as a possibility until late 2006.

To date 7 SSXT installation operations have been completed successfully in approx. 370m of water on the Vincent field in Australia, this was followed by wireline intervention to commission wells for operation to/from the host facility. A number of plugged and abandoned wellheads were also severed and recovered from the seabed. The vessel was also utilised extensively for other subsea operations. Operations are ongoing to complete the expansion of the Vincent project and a number of production enhancement opportunities are being planned for the near future including PLT surveys, water shut offs, and Gas-lift valve installation.

This paper will detail the operations undertaken and the issues to be managed to ensure safe and cost-effective execution. Furthermore the paper examines the unique challenges of translating experience gained to date to the Asia-Pacific region, to deeper water depths, and will discuss the lessons learnt from the planning and operations phases of the project. These will include details of the modifications required to the vessel to convert her from her previous role as a large Supply Vessel (PSV), including the critical elements of the conversion required in order to ensure appropriate Class registration and the successful award of an Australian Safety Case covering all safety critical operations.

Lastly the paper will examine the potential benefits Rigless intervention can offer and the additional cost benefits of incorporating other non-well related activities into the vessel programme.

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