For suction pile designed with pile top remains elevated above the mudline, the seal integrity of the suction pile would affect the pile bearing capacity performance. Drawing from the experience of a deepwater project i.e. Liuhua 29-1 located offshore South China Sea, the criticality of seal integrity was demonstrated. Efforts made in improving the design and testing of the suction plug-port assembly, and overcoming the challenges during subsea handling are shared in this paper. The purpose of this paper is to raise awareness of several important consideration for better design, testing and subsea handling of the suction plug-port assembly. Recommendations are included for practical reference.
Suction pile for common applications e.g. acting as foundation for offshore wind turbine (Byrne and Houlsby, 2003) or anchor system (Andersen et al., 2005) is usually designed to have the pile fully penetrated such that the base of the pile top plate is in full contact with the mudline. For cases where full contact cannot be achieved or intendedly elevated above the mudline, grouting would be applied to ensure gap is fully filled (OWA, 2019). On the other hand, for supporting subsea structures, the suction pile is not uncommonly designed with pile top remains elevated above the mudline without grouting applied. The latter design was applied to the Liuhua 29-1 (LH29-1) deepwater project.
The LH29-1 deepwater gas field is located offshore South China Sea with water depth ranging from 680 to 1200 m. The subsea production system consists of a subsea manifold connected to seven subsea trees and control system through a network of flexible flowlines, umbilicals and flying leads, and tied in to the existing Liuhua 34-2 production system via an infield flowline. The subsea manifold with a submerged weight of approximately 162 MT was supported by an 11-m long suction pile with an outer diameter of 7.6 m and wall thickness of 32 mm. Figure 1 shows the interface arrangement of the subsea manifold and the suction pile.
