The economics of oil and gas production in the North Sea are now leading the industry towards increasing use of subsea technology for the development of the smaller fields. The Buchan field, located some 150 kms NE of Aberdeen in 120 m of water, and with estimated recoverable reserves of the order of 50 million barrels, typifies the North Sea "marginal field". This paper describes the drilling and completion phases of Buchan development, and is presented as a companion paper to Geological aspects of the drilling Buchan field. The paper highlights the methods by which the potential hazards of drilling the highly-overpressured reservoir were overcome, outlines the evolution and implementation of the well completion methods adopted, and discusses problems encountered and lessons learned.
Owing to the uncertainty about the performance of the tight and fractured reservoir and the low figure of recoverable reserves Buchan is a truly marginal field. The projection is that it will produce 50 million barrels over a period 5 years but the range of possible recoveries is wide and financial in the venture high. In the light of this risk any development scheme had to incur minimum expenditure and provide production at the earliest possible date. The scheme adopted, subsea completions with a floating production platform and tanker export, meets these criteria. Figure 1 shows the production system: oil is produced from seven subsea wells, (a central cluster of five at a template and two satellite wells) through a subsea manifold at the template and individual risers, to a semisubmersible production vessel. Degassed crude is then pumpted down the production vessel. Degassed crude is then pumpted down the manifold again through the 12 in. riser and out along the seabed for export via a CALM loading buoy.
