Alwyn Area: A Case History in Improved Business Performance

Abstract

Abstract The Alwyn North field, situated in the UK sector of the Northern North Sea, came on stream in late 1987. Development used classic North Sea technology. Plateau production was originally forecast to last no more than four years for oil, and seven years for gas. Over the past three years Alwyn North has been developed into an integrated area operation with the start-up of the adjacent minimum-facilities Dunbar field and the sub-sea development of the Ellon field. The Dunbar field has made full use of new technology, including Tender Assisted Drilling, a lightweight jacket and multiphase export. Substitution terms incorporated within the gas sales contract allowed movement into new emerging UK gas markets. Increased reserves have been identified by the application of 3D-seismic and the further appraisal of new (and old) reservoir compartments. Increased productivity has been achieved through debottlenecking of the process plant and by drilling long reach horizontal wells. Increased cost effectiveness has been delivered by a "continuous improvement" campaign resulting in OpEx reductions and increases in oil and gas sales. A further phase of developments is now in preparation. On Alwyn North an infill drilling campaign is scheduled to follow the interpretation of the newly acquired second 3D survey, and a miscible gas injection scheme is currently being studied. On Dunbar the installation of multiphase pumps will sustain export potential and further sub-sea developments will be phased in. An autonomous power supply and acoustic communication scheme is under review to improve economics of long distance tie-backs. Initial Development of Alwyn North The Alwyn North field, developed jointly by Total Oil Marine plc (33.3% - operator) and Elf Exploration UK PLC (66.7%) was originally discovered in 1975. Development consent was given in 1982 on the basis of initial recoverable reserves of 385 Mboe (200 Mbbls of oil and 26.6 Gm' of gas) with a production plateau of four years for oil, seven years for gas, followed by a progressive decline through to 1998. A series of discoveries had been made in an area to the south of Alwyn North, but they were considered uneconomic to develop at that time. The field is situated in the northern sector of the North Sea, 140 kms to the east of the Shetland Islands and 465 kms north-east of Aberdeen, in close proximity to the Brent and Ninian fields (Fig 1). There are two main reservoirs. The Brent oil reservoir at 3,100 metres is hghly compartmentalised into panels, each supported by water injection. A total of ten oil wells and seven water injectors were drilled. The Statfjord gas reservoir, slightly deeper at 3,400 metres, was developed by twelve wells using natural depletion (Fig 2).