The Balmoral development constituted one of the largest subsea facilities at its time of commissioning in 1986 and included a purpose built floating production vessel (FPV). Experience gained over seven years in the operation of pipelines, risers, subsea controls, downhole pressure monitoring systems and other equipment are presented in this paper.
The Balmoral field (Block 16/21) is located in the UK sector of the North Sea, some 140 miles NE of Aberdeen in a water depth of 145 metres. The field was discovered in 1975 and development drilling began in 1984 with production commencing in November 1986. The Balmoral facilities (fig 1) comprise the world's first purpose built floating production vessel (FPV) moored over a large subsea template accommodating ten subsea production wells, three manifolds and major components of the electrohydraulic control system. The FPV and template are connected by a system of flexible risers and a dynamic riser control umbilical.
Ten template productions and nine satellite wells (three production, six water injection) tied back to the template were included in the initial project. At the time of commissioning, Balmoral was one of the largest subsea complexes in the North sea. Since then, three further Sun operated satellite developments have been linked into the Balmoral facilities Glamis (1989), Blair (1989) and Stirling (1993). Although Blair is now abandoned, the complex as a whole has included seventeen production and seven water injection wells. The inbuilt flexibility in the original Balmoral topside and subsea facilities has enabled these other fields to be included with relative ease and potential still exists for future tie-ins. In seven years of operation, Sun has gained invaluable experience in operating a floating/subsea complex, some of which have been detailed previously (ref 1-7).
The Balmoral reservoir located approximately 7000 R below sea level was initially judged to have a STO11P of between 187 and 299 MMSTB of which 67 million were recoverable. These figures were based on the results of appraisal drilling and a 2-Dimensional seismic survey. By 1992, it was apparent that the reservoir was over performing and a reservoir simulation model indicated a revised STO11P of Up to 2S6 MMSTB with recoverable barrels of 100 million.
In 1992, a 3-Dimensional seismic survey was conducted and the exercise has confirmed the recoverables at the revised figure of 100 million, but reduced the potential variation of STO11P to between 173 and 210 MMSTB.
Recoverable reserves were raised by over 30% with the accuracy much improved so allowing better technical and financial assessment of field life and potential for future in-till wells.
The Glamis field, located approximately 7 km south east of Balmoral, has proved to be a source of additional production and revenue. Coming on stream in 1989, this Jurassic accumulation was estimated to possess 17 MMSTB, since revised upwards to 21 MMSTB. An additional benefit is that the high GOR (1037 scf/stb) of the crude provided gas for the gas lifting of Balmoral wells which were experiencing decline in flow rate due to increased water cuts.
