The Drilling Engineering for Subsea Development Wells

Abstract

Abstract Twelve subsea development wells have been drilled in block 9/13 in the North Sea. The early completions were of exploration or appraisal wells, later wells were planned for development. The experience has led to a drilling engineering strategy for planning all wells to ensure that the maximum benefit from each well can be achieved. This involves: grouping the wells together to minimise surface locations and flowline routes; designing all wells to be suitable for a subsea completion; and specifying a rig that can be used for all phases of a subsea development. Introduction Since well 9/13a - 1 discovered the Beryl field in block 9/13, 215 miles (346km) north-east of Aberdeen, forty two more subsea wells have been drilled in the block, of which twelve have been completed. The early wells were for the appraisal of the original discoveries and exploration in other areas of the block. The success of the discovery resulted in the installation of two combined drilling and production platforms. The Beryl 'A', a three legged concrete platform with storage capacity in the base for more than 1bn bbls of oil, was installed in 1976. In 1983 the Beryl 'B', a steel jacket was installed with an oil export line to the 'A' platform. Oil export from the block has always been by tanker loading from a Single Point Mooring. In 1986 the Ness field was discovered by well 9/13a - 28 and the field came on stream with a subsea development in 1987 (Figure 1). From the very first well, the possibility of re-using the exploration and appraisal wells for subsea production via the platform facilities was always an option and wells which had identified significant hydrocarbon potential were suspended, pending completion. The first subsea well to be drilled as a development well was 9/13a-20. Since then several more subsea development wells have been drilled. This pattern of subsea developments using the process and export facilities of a platform is common to oil production from the North Sea.