Operating Experience with Navion Munin FPSO at the Lufeng Field

Abstract

1.0 ABSTRACT This paper describes the operational experiences gained from oil production from the Lufeng 22-1 Field in the South China Sea with the Floating Production Storage and Offloading (FPSO) vessel "Navion Munin". Station keeping of Navion Munin is provided by the novel Submerged Turret Production (STP) concept, which has an internal turret diameter of 2,7 m. The paper also addresses the experiences from actual disconnection operations during typhoon conditions. The paper further reviews the experiences gained so far with respect to start-up and operation of the process facilities including fulfillment of functional requirements, regularity, weather sensitivity, mooring and offloading. 2.0 INTRODUCTION 2.1 Field Arrangement Lufeng 22-1 is a small oil field located remote from existing infrastructure in the Pearl River Mouth basin in 333 meter of water approximately 265 km Southeast of Hong Kong in the South China Sea. See figure 1 - Lufeng 22-1 Location. The field, owned by Statoil (75%) and CNOOC (25%), was discovered in 1986 and two further appraisal wells were drilled in 1989. The field was developed with five horizontal wells with horizontal section lengths between 480 and 2040 meters. The field was marginal with considerable uncertainties in the reservoir production parameters. The anticipated costs of a conventional stand-alone development did not make the field economically viable and an alternative model was therefore required. The oil reserves to be recovered were initially estimated to be ca. 30 mmSTB. By 15 February 2002, when the field most likely will be shut down, 27,8 mm STB will have been recovered. The environmental conditions in the South China Sea also contributed to the difficulties experienced by potential field developments in the area. Typhoons are frequent and the area is affected by solitons (subsurface waves generated by tidal variations). The Lufeng 22-1 Field was developed by the FPSO "Navion Munin" of the multipurpose shuttle tanker (MST) type. The Lufeng Development Company (LDC) provides the FPSO facilities on day rate lease for a fixed period of 2 years plus optional extensions. See figure 2 - Field Development Arrangement. 2.2 Subsea The Lufeng 22-1 Field is developed with five subsea horizontal production wells drilled through a 5-slot template on the seabed. The reservoir properties of the Lufeng field dictated that artificial lift was required after a very short time to maintain an acceptable production rate. Subsea booster pumps were selected as intervention and replacement facilities could be installed onboard the FPSO. Each subsea booster pump is rated at 400 kW, maximum fluid capacity is 25.000 bbl per day and maximum differential pressure generated by the booster pumps is 45 bar. All tooling and one spare cartridge for the booster pump are installed on the FPSO where retrieval and replacement can be done within one day using an ROV, the ship's motion-compensated aft crane and conventional guide wire arrangement. See figure 3 - Light Intervention. The subsea system is designed to use diverless technology. The wells are designed to minimize intervention over the life of the field.