ABSTRACT

Lufeng 15-1 platform locates in South China Sea. The average water depth at the platform site is 286m, and there are large sand waves distributed in latticed and crescent shape. The uneven seabed topography introduces great challenges to jacket on-bottom design. In order to avoid seabed treatment, the platform is relocated 180m to the southwest of the original location. The mudmats are designed below jacket bottom framing to adapt to sand waves profile. The jacket was successfully installed using accurate positioning and monitoring system, which provides reference for the design and installation of deep water jackets under complex seabed topography.

INTRODUCTION

Lufeng oilfields are located in the Pearl River Mouth Basin, South China Sea, about 256km southeast of Hong Kong. LF15-1 jacket had been installed in April 2022. Up to now, it is the deepest and largest jacket ever installed in Asia. As shown in Fig. 1, the jacket is configured with 8 legs and 12 skirt piles with 102 inch diameter. The jacket structure measures 42m by 18m at top and 95m by 95m at bottom framing. There are a total of 13 horizontal framing plans. Four rectangular mudmats hang below the jacket bottom framing near the four corner legs through vertical columns and diagonal braces.

The jacket launch weight is about 30200 metric tons. It is transported and launched by barge HYSY229. Two 50m long sponsons are added to the "T" shaped barge to provide enough stability during launch. Heavy lifting vessel LANJING is utilized for jacket upending and lowering operation as well as pile installation.

This paper mainly focuses on the survey and monitoring results of sand waves at the LF15-1 platform site and the measures adopted in LF15-1 jacket on-bottom design. At last, the options for dealing with uneven seabed are discussed which should provide some useful information for other projects in the future.

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