The Challenges of Lufeng 22-1 Development

Abstract

1.0 ABSTRACT This paper describes the challenges involved with the development, design and fabrication of the FPSO and related facilities for the development of the Lufeng 22-1 field. The field will be developed using five subsea wells connected to the FPSO by two flexible flowline risers. The five horizontal wells will be drilled through single template and completed with subsea production trees mounted with electrically driven booster pumps, installed to provide the means of artificial lift. The FPSO is based on a multipurpose shuttle tanker (MST) fitted with a processing plant which has a capacity of 125,000 bpd of gross fluid volume, and 60,000 bpd of crude oil. The storage capacity of the vessel is 640.000 bbls. The individual well rates are expected to reach 25,000 bpd of fluid and 15,000 bpd of oil. The Lufeng crude oil is paraffinic, low sulphur with a high wax content. The API gravity is 31.1" and the pour point 43°C requiring the oil to be stored at elevated temperature above wax appearance temperature of 62°C. The mooring system is a Submerged Turret Production (STP) system which is disconnectable in extreme weather conditions. 2.0 INTRODUCTION 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. Extensive testing was performed on the appraisal wells with rates of up to 24,000 bpd achieved and approximately 1.6 mmbbls of oil produced. The tests confirmed the high porosity of the sandstone reservoir and indicated the need for horizontal well technology to delay water influx and maximise oil recovery. The field is being developed with five horizontal wells with horizontal section lengths between 480 and 1800 meters. The field is marginal with considerable uncertainties in the reservoir production parameters. The anticipated costs of a conventional stand alone development do not make the field economically viable and alternative model was therefore required. The oil reserves to be recovered are estimated to be ca. 30 mmbbls representing a recovery factor of approximately 25% of the original oil in place. The environmental conditions in the South China Sea also contribute 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 system chosen to develop the field is an FPSO based on the multipurpose shuttle tanker MST Munin. Facilities are provided on day rate lease. See figure 2 - Lufeng 22-1 Field Development Arrangement.