Penguin Wet Gas Measurement

摘要

The Penguin cluster is a formation of five different reservoirs located in the UK sector of the North Sea. It is produced via a 65km subsea tie-back to the Brent Charlie platform; the world’s third longest tie-back. The cluster is made up of five different reservoirs, each with significantly different gas to oil ratios. The gas volume fraction (GVF) of the arriving fluids is in the region of 85 to 95% and thus was considered to be too high for accurate (+-5%) measurement of the gas and oil phases using a multiphase meter (MPM) and too low for a wet gas meter. Due to the length of the tie-back a Severe Slug Suppression Device (S~3) was installed on the platform topsides. The S~3 in effect acts as a partial separator and thus the opportunity was taken to use this device to partially separate the fluids and hence move the MPM in to a more favourable operating environment. Consequently a 14 inch Solartron ISA Dualstream II (DS II) wet gas meter was installed on the wet gas outlet of the S~3 and a Framo Vx multiphase meter on the gassy liquid outlet. The outlet of these meters is then recombined prior to being routed either to the production or test separator. Prior to the production separator the Penguin fluids are commingled with the Brent fluids. As Brent pays Petroleum Revenue Tax and Penguin does not, there is a requirement for the metering to achieve an accuracy of +-5% on gas and oil. Following start-up it was observed that the readings from the DS II wet gas meter were out with the manufacturers specifications of +-5% for gas and +-10% for liquids. The meter was operating at a pressure of 35bar and Lockhart-Martinelli (LM) values of up to 0.5. Based on the information available it was concluded that the correction algorithms required for the Penguin meter differed significantly from those obtained with the previous much smaller 6 inch research meters (and on which the Penguin meter correlations had been based). With a nominal pipe size of 14 inches, Penguin was by far the largest DS II meter Solartron ISA had manufactured, and unfortunately, at the time of manufacture there was no test facility that was realistically capable of testing the meter on wet gas. However, with the commissioning of the enhanced Statoil K-Lab wet gas test facility, it was decided that the best method to ascertain the cause of the flow meter discrepancy was to manufacture a second identical meter and to test it across as much of the operating range of the Penguin meter as possible. This paper discusses the performance of the DS II meter immediately after first oil, the changes and onshore testing required to meet the specification, and the actual offshore testing of the new algorithms.