Deployment of Multiphase Pumps on a North Sea Field

Abstract

During the past years, the Oil and Gas industry has invested a lot of resources in the development of the multiphase technology (flow modelling, multiphase production equipment, fluid-related effects). The POSEIDON programme aimed at developing multiphase pumping based on the rotodynamic helico-axial design. This technology has been qualified with two tests on onshore fields. After an extensive comparison with conventional alternatives involving separation, compression, pumping, additional pipeline, it has been decided to install a multiphase boosting station on the offshore DUNBAR field in the North Sea. This paper will present a summary of the qualification tests, the Dunbar field case, the comparison between several export alternatives, the reasons for the selection, the export system over 22 km, the multiphase boosting station (two 4.5MW units) and installation related issues. Field experience after more than a year of operation will be discussed. INTRODUCTION For a period of time, multiphase technology focused only on flow modelling. Later, it was deemed likely that multiphase transport capabilities could be extended if technology could be developed to increase the transportation distances (horizontal as vertical as well). It was also estimated that such a scheme would be more reliable and easier to operate if the fluid-related effects (such as hydrates, waxes, mineral deposits, etc...) could be better controlled. In the frame of this vision, as early as mid-85, TOTALFINAELF has undertaken an extensive programme of development of multiphase technology components such as multiphase pumping and multiphase metering. Several twin-screw pumps were tested in different fields with encouraging results. But the extension of the capabilities in terms of flow rate immediately demanded a new concept. By mid 85, TOTALFINAELF in association with IFP (Institut Français du Pétrole) and Statoil launched the POSEIDON programme. This initiative aimed at developing the rotodynamic helico-axial pumping concept. This concept has been qualified, it is presently deployed in onshore or topsides applications as well as in deep offshore conditions. The largest individual capacity per pumping unit is in operation on the North Sea Offshore field of Dunbar. This paper delivers a summary of the qualification campaign which took place on several operated fields, and presents the case of DUNBAR operated in a higher pressure and flowrates domain as compared to the initially anticipated applications. The POSEIDON research and development programme received the financial support from the EU in the frame of the THERMIE Programme. SOME LESSONS FROM THE PAST FIELD TESTS A first prototype has been tested onshore in Tunisia. This first prototype had the following main mechanical features and design specifications. Main mechanical features:Casing design pressure: 5000psiIsostatic and subcritical shaft including 13 impellers (8×250 mmØ and 5×232 mm Ø)Bearings: hydrodynamic and thrust bearingMechanical seals: single and compensatedLubrication: incorporated and autonomousBuffer tank of 4.5 m3 Main design specifications:Suction total (gas+liquid) flowrates: 200m3/hSuction pressure: 40 barDifferential pressure: 40 barSuction GLR: 10Speed: from 3000 to 6000 rpmElectrical driver power: 500 KW On the field, the pump was tested in the following conditions:Suction total flowrates: 140–260 m3/hSuction pressure: 8–15 barDifferential pressure. 5–15 bar (max: 23 bar)

Experimental Investigation on Transient Pressure Characteristics in a Helico-Axial Multiphase Pump

“…Falcimaigne et al [10] has discussed the achievements and perspectives of helico-axial technology of IFP (Institute of Petrole France) in Priobskoye and Topacio fields. Some other applications of helico-axial pump such as core component in multiphase transportation systems have also been reported [11][12][13][14]. The performance tests and applications prove that the helico-axial pumps could do well at liquid-gas two-phase pumping work.…”

“…The pressure range has two main determinants: the dimensionless head of the last stage, and the fluctuation amplitude of the pump. The dimensionless head H could be defined as Equation (12), which shows the pumping ratio of the stages in the whole pump:…”

Multiphase Pumping: Achievements and Perspectives

“…The Dunbar case, largest in power offshore, was recently presented in detail, including the field experience after two years of operation (Leporcher et al, 2001). The two other recent applications are briefly described hereunder.…”