Campaigns of Opportunity – Rigless Subsea Phase III Well Abandonment Operations in the UK Continental Shelf

Abstract

Subsea operations—from the need for multidisciplinary teams to delivering equipment and services in a harsh offshore environment—are inherently expensive. These costs are typically recovered through the reservoir production over a number of years. When production ceases, the cost of abandonment is absorbed as a liability, which leads to a stringent focus on cost efficiency. It is, however, an area where the opportunity to achieve significant cost savings through new technologies and an alternative approach to service vessel and campaign structure.

This paper describes a facilitating technology—the subsea wellhead connector, or SWC—that enables operators to undertake monohull and even rig-based subsea abandonment campaigns. Deviating from a semi-submersible rig to a monohull-based campaign has reduced vessel day rates and personnel costs by a substantial margin. To maximize the saving potential for rigless abandonment technologies and equipment, however, require collaboration between the operator and service provider.

The SWC latches and recovers all common 18.75-in. bore wellhead suspension systems. The system offers mechanical, abrasive, or explosive severance tools for plug-and-abandonment (P&A) campaigns and a small re-entry mandrel seal assembly for intervention. Deployment can range from vertically or horizontally rigged orienttions, and operations are limited by the remotely operated vehicle (ROV) limitations.

This paper presents four Phase III campaigns in the North Sea continental shelf as case studies. Each has unique challenges. Monohull vessels were used in the first 3 wells and the final campaign was run from a mobile offshore drilling unit (MODU)—this final approach brough rigless technology to a rig to further enhance operational capability.