Donan Field Decommissioning Project

Abstract

Abstract. The Donan Field was located in UKCS blocks 15/20a and 15/20b. BP Exploration operated the field on behalf of Britoil, Conoco, OMV and Croft. Field production from two subsea wells began in April 1992 via the Oil Production Vessel (OPV) Seillean. In 1997 the field reached the limit of economic production.BP Exploration successfully agreed a field decommissioning programme with the DTI. It was carried out in February 1998, using a light well intervention vessel, CSO Seawell, to abandon the wells and remove the subsea infrastructure. The abandonment of the Donan field was carried out safely and with no harm to the environment. It was not delivered within its original budget, but still represented significant saving over other abandonment options. It provided substantial learning for BP Amoco, which is now incorporated into the organisation for future operations. Introduction. The Donan Field was located in UKCS blocks 15/20a and 15/20b, in 141 metres of water, approximately 200km northeast of Aberdeen. The field was discovered in 1987. BP Exploration operated the field on behalf of Britoil, Conoco, OMV and Croft. Field production from two subsea wells began in April 1992 via the Oil Production Vessel (OPV) Seillean1. This was the original single well oil production system (SWOPS) vessel which had produced the Cyrus field. In 1997 the field reached the limit of economical production and it was shut in for decommissioning. In total the field produced 15.3 million barrels of oil. This paper is a factual account of the approach taken by BP Exploration to remove the field facilities. It addresses gaining UK government approval for the operation; the well preparation by OPV Seillean; the project organisation and the decommissioning techniques used. It also reviews the subsequent environmental surveys. In particular, it reviews the problems encountered during the operations and how these were overcome. Legislative Background. The decommissioning or abandonment of producing fields in the UKCS is controlled by the Department of Trade & Industry (DTI). The process is governed, principally, by Section 1(1) (Abandonment of Offshore Installations) of the Petroleum Act 1987, revised in 1998. This requires Operators to seek permission from the DTI for both Cessation of Production (COP) and abandonment of the installation / field. The former is justified on economic grounds. The latter requires Operators to demonstrate that they have an abandonment solution which is consistent with international obligations and it has proper regard for the environment, risks to personnel, other users of the sea and cost considerations. At the time of this project the British Government had not ratified the OSPAR agreement concerning offshore installations. However, since this was a simple sub sea installation, BP Exploration made the presumption of complete removal of all equipment. Operators are required to solicit the views of all interested parties before finalising the abandonment plan. The DTI will solicit the views of any other government departments. This consultation process has to be open and transparent and as a consequence can be fairly protracted.