Multiphase Flow Metering - Operational Experience on Sub-sea Production Manifolds

Abstract

In the petroleum production area, multiphase meters are used to measure the produced fluids - natural gas, oil and water - at in-line flow conditions and without any need of separating the incoming phases. Thus, the Multiphase Flow Meters (MPFMs) offer the possibility of real-time, complete and continuous flow rate measurements. The oil industry has been supportive to the development of this technology and has mainly focusing its application on the offshore production, particularly at the sub-sea area. Several types of tests (e.g., performance, endurance and reliability) have been conducted worldwide and the usually acquired positive results have paved the way to several field applications. Thus, the in-line Multiphase Flow Metering Technology has had a continuous improvement and nowadays several petroleum companies are confidently incorporating this technology into their new designs. The demands associated to the sub-sea multiphase meter operation and its associated levels of reliability are particularly challenging. But, at deep sub-sea production the savings and operational benefits offered by this new technology could be quite significant. Thus, PETROBRAS among others, when considering the benefits of such application has focused its efforts on this technology and aimed its initial application to the sub-sea production. In the summer of 1997, Petrobras installed a multiphase meter in a sub-sea production manifold, at 450 meter of water depth (WD) and 5 km away from the host FPSO (Floating Production, Storage and Offloading) in the Albacora field. That was followed by a second sub-sea multiphase flow meter installed in the Marlim field at 950 meter of water depth (WD) and since then several others subsea manifolds with multiphase flow meters are under installation. This paper reports the long-term field operational experiences, and also gives an evaluation of the measurement performance, compared to the conventional test separator. The high level of development, already achieved by the multiphase flow metering technology, contributed to the PETROBRAS confidence in order to introduce a new generation of manifolds. Sub-sea manifolds can be a very attractive alternative to sub-sea layouts at deepwater fields. A drawback of the sub-sea wells production gathering is the individual well production management. The conventional production well tests when applied to sub-sea production manifolds require additional test flow lines and equipment, besides being time demanding and usually offering some operational problems, naturally, these drawbacks can be surpassed by the application of reliable multiphase flow metering. PETROBRAS is now installing the fourth generation of diverless sub-sea manifolds at Marimba East field. The main innovations are related to the metering system, where the well tests are based on multiphase and single-phase meters. In these manifolds the gas lift test line and production test line were eliminated, allowing significant cost savings. In addition, a multiphase meter will monitor continuously the well flow rates, while single-phase meters will similarly monitor the injection of lift gas. Introduction The main challenge for the next Campos Basin exploitation projects is to provide profitable and competitive solutions for ultra deepwater sub-sea oil fields.