"FPSO+Subsea" mode is a typical offshore oil field development mode. This mode is suitable for deep water developments where other types of facilities such as jacket platforms or TLPs are either not economically viable or technically feasible comparing to subsea systems. This mode is widely used in Brazil's deep water developments. Jacket platforms + FPSO or Subea tie backs have been the major development mode in South China Sea in the past (Yue,2013;Mao and Yang 2016). CNOOC recently developed its Liuhua16-2 oil field located in South China Sea by this FPSO+Subsea mode. Due to the complexity of the environment and the large scale subsea systems with three oil fields and a total of 26 subsea wells, we had faced a lot of challenges during the development such as complex FPSO turret, long distance subsea tie backs, flow assurance, pipelines and umbilicals interferences under special South China Sea soliton currents etc.
The Liuhua16-2 oil field development is comprised of three oil fields namely Liuhua16-2, Liuhua 20-2 and Liuhua21-2. The three developments were discovered one after another from 2010 through 2015. The three fields are located in South China Sea with water depth around 420m. they are located in a triangle layout with the far most fields about 30km apart from each other. During the course of the discovery various development concepts were studied. including re-development of the existing Liuhua11-1 oil field with the new Liuhua16-2 prospects with TLPs. Due to the TLP technology has never been exercised in China, there is a question of the suitability of TLP application at the typhoon and soliton prone South China Sea(Mao,2014). With the discovery of all three oil fields, CNOOC finally decided to develop all of the three together with FPSO+subsea mode. This development mode is more favorable due to CNOOC had long experience of FPSO operations as well as subsea production systems (Li and Ji,2016; Li and He,2016; Mao,2014; Liu and Mao,2015). Both are technically proven and economically appealing. However, during the design and project execution phase, multi technical issues were encountered such as the world record long distance power supply by direct variable frequency drive, the 17 dynamic flexibles and umbilicals interferences in the water column due to complex soliton current, the high gas oil ratio challenges to flow assurance, the complex turret system ever built in China etc. Due to the criticality of the facilities, a comprehensive monitoring system was installed to the FPSO and mooring to collect environmental data, FPSO motion as well as mooring line angles. This article is intended to share the major challenges as well as solutions we adopted. The project was successful which achieved first oil in Sept. 2020. Fig. 1 is a field general layout overview.
