The development of a three phase metering system for installation on seabed templates at or near subsea wellheads is described. The Subsea Metering System (SMS) design measurement accuracies are +/− 5%. Its design pressure is 3640 psi. The design provides passive, self-regulation of the SMS over its operating range of 3000 to 18000 blpd at volumetric gas fractions of 10 to 90% and watercuts from 0 to 90%. The SMS considerably reduces capital costs of subsea field developments as it eliminates the need for (1) a separate test line from the subsea wellhead template to the platform and (2) test separator equipment on the platform.

Bulk gas and liquid separation is achieved via a unique separator concept which enables the volumetric rate of each to be measured. Commercially available vortex meters may be used to determine the bulk gas flow rate while a proprietary constriction meter is used to determine the bulk liquid rate. The watercut is measured by a Texaco Microwave Watercut Monitor1. The watercut monitor is capable of accurately determining the water fraction of oil and water emulsions and/or mixtures from 0 to 100% regardless of which fraction is continuous. A nuclear densitometer enables the amount of gas entrained in the bulk liquid stream to be determined so appropriate corrections can be made to the gas, oil and water rates.

The performance of the SMS as determined from topside tests on Texaco's Tartan Alpha Platform in the North Sea is presented in comparison with standard test separator equipment. The schedule for completing the topside tests and fitting the SMS to the Highlander Template is reviewed.

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