Balmoral: Conception to Production

ABSTRACT Sun was faced with the challenge of commercially developing Balmoral, a small reservoir located in a water depth of 460 ft on Block 16/21a of the UK sector in the North Sea. All options were examined and Sun finally chose a subsea development with a Floating Production Vessel located over a central template. The success of this method of development could lead the way to the development of other marginal fields in the North Sea and in many other parts of the world. It could also lead to a more cost effective way to develop reservoirs in much deeper waters. INTRODUCTION The Balmoral Field is situated 140 miles off the North East coast of Scotland in Block 16/21a. The Balmoral group with North Sea Sun Oil (NSSO) as operator discovered the field in 1975. Seven years later in 1982 the decision to develop the field was taken. Crude oil was to be collected from 13 subsea production wells and processed on the world's first purpose built Floating Production Vessel before being exported through a 14" diameter pipeline to the Brae/Forties pipeline and then onto the Cruden Bay receiving station in Scotland. INITIAL STUDIES Knowing that this was a marginal development NSSO was faced with the cha11enge of exactly what type of cost effective facilities should be used. Reservoir management had indicated that the maximum recoverable reserves were 67.5MMSTB of oil with a gravity of 39.90° API and a GOR of 366 SCF/STB with no significant sulphur or CO2 It was expected to produce at a peak production rate of 35,000 BOPD for approximately three years before commencing its decline. Oil recovery would be improved by maintaining reservoir pressure with water injection and by introducing gas lift in the production wells to sustain flowing capacities. Gas re-injection wou1d not be possible. Additiona1 allowances would have to be made for other prospective reservoirs close by. A study was carried out to compare the costs of a platform versus a floating system based on recoverab1e reserves of 50, 65 and 100 MMBBLS for a floater and 65,80,100,120 and 150 MMBBLS for a platform. The study's conclusions were that for the equivalent recoverable reserves a platform was 40% more costly than a floater. PRODUCTION FACILITIES The "Basis of Design" stated that the process system must be designed for the following (Information available in full paper) The produced fluids were to be directed via a riser system from the subsea template to the process facilities on the FPV. On-board manifolding was to be provided to allow strong or weak wells to be directed to the first or second stage separator. In addition to gas lift, gas was also to be used for power generation with the remainder being flared as there was no existing gas export 1ine adjacent to Balmoral and a newline was not justifiable for the quantity of gas available.