Innovative Solutions Enable Production Start of China’s First Marginal Subsea-Tieback Oil Field
Liuhua4-1 (LH4-1) oil field is located 215 km southeast of Hong Kong in the South China Sea. The field was first discovered in 1987, but because of economic and technical challenges, it was not until 2012 that the development of this field became a reality. The 300-m-water-depth oil field was successfully tied back to an existing oil field [Liuhua11-1 (LH11-1)] through subsea pipeline, power cable, and multiplex control umbilical. The project executions included disconnection, life extension, and reconnection to the existing oilfield floating-production system (FPS). It was also China’s first tieback subsea development project. To develop this marginal oil field, a number of technical challenges were overcome through a series of new technologies, and their successful development and implementation.
The LH4-1 oil field is located in the Pearl River mouth basin at central rising Block 29/04. It is 11 km northwest of the LH11-1 FPS (Zuan et al. 2013). The confirmed geophysical reserves are approximately 3.0×107 m3, and the water depth ranges from 260 to 310 m. The field facility is designed for 20 years of service life, with 15 years of field economical life.
The oil field uses a set of subsea production systems through subsea tieback to the existing LH11-1 oil field. The subsea-production systems comprise eight subsea horizontal wells, each completed with a downhole dual-electrical-submersible-pump (ESP) artificial lift system. One of the wells is a multilateral well with a smart completion. Seabed equipment includes eight subsea horizontal trees rated for 5,000 psi and a central production manifold. Individual wells are commingled to the production manifold through 6-in. vertical jumpers. The outlet of the production manifold is connected to the subsea pipeline through an 18-in. vertical jumper. The fluid is then pumped through an 11.7-km 18×22-in. pipe-in-pipe subsea pipeline system with inline pipeline-end terminations (PLETs) on either end. A bridging manifold is installed on the subsea side of LH11-1. The function of the bridging manifold is to receive fluid from the LH4-1 pipeline and existing LH11-1 subsea-production system. The mixed fluid is then transported through two LH11-1 existing subsea flexible flowlines to the floating production, storage, and offloading (FPSO) system Nanhai Shengli for processing and storage.
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