Abstract

An important new initiative to clean up the seabed has resulted in a major project to decommission and remove redundant subsea wells. The subsea well decommissioning project was instigated by BP Exploration to fulfill its commitments and obligations under various license agreements. When exploration wells are no longer required for further appraisal or development, the requirement is to remove all subsea wellhead equipment and clear the seabed. This paper will describe first the organisation and execution of the project. It will then look at the experience gained and how it challenges the current well suspension philosophy.

Introduction

The joint BP Exploration and Coflexip Stena Offshore (CSO) project was tasked to remove redundant suspended subsea exploration and appraisal wells in the United Kingdom (UK) sector of the North Sea. The principles of the project were safety, recognition of the environment and efficiency, both operational and financial.

Looking at the number of wells to be removed, a single project team was charged with the safe and efficient decommissioning of these suspended wells. The first tranche of the work covered some 24 wells and makes it the largest single programme of its kind ever carried out in the North Sea. The purpose of this paper is to outline the key steps taken to achieve the aims of this project.

Within the project CSO were selected as the lead contractor using the established light well intervention vessel the CSO Seawell. With this vessel the project could offer BP a total package producing savings and efficiency with a combined programme. As part of the project scope, an extensive amount of well engineering had to be completed to ensure the safe and correct abandonment of all the wells. This resulted in the project team having to complete a critical review and analysis of the condition of a large number of different suspension designs.

The Challenge

In the UK, there is considerable pressure on the Government from Fishing and other marine related organisations for a clear sea bed. All subsea wells, if they are not held for a development, must therefore be removed.

There are around 400 suspended subsea Exploration and Appraisal (E&A) wells in the UK Continental Shelf (UKCS), of which BP is responsible for 72. To meet the challenge, BP inaugurated the subsea well decommissioning project. The decision to remove the wells sends a powerful message to Environmental and Fishing organisations and the UK Government of BP's commitment to both fulfill its obligations and to provide a seabed clear of such obstructions.

The wells have to be decommissioned and abandoned in accordance with legislative requirements, BP policy and UK Offshore Operators Association (UKOOA) guidelines (Reference 1). Typically, these require the permanent plugging of a well by, if possible, two laterally extensive, tested barriers. The wellhead must then be removed at least 10 ft below the seabed and all debris removed, for a 70 m radius around the location. All the wellheads and debris must be returned to shore and would normally be sent for scrap steel recycling. In the case of this project each field group had the option to refurbish wellheads if considered economic.

This opened a challenge to the project team on the issue of plugging policy and the approach to temporary well suspensions. The design of well suspension will have a direct effect on final abandonment and this needs to be considered.

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