Abstract

In order to select a suitable foundation for large central manifold in LingShui17-2 deep-water gas field, on the basis of analysis of bearing capacity of subsea production system foundation and installation capacity of installation resources, this paper compares two major deep-water foundation solution - mudmat foundation and suction pile foundation. The adaptability of these two kinds of foundation for LS17-2 gas field were demonstrated, suction pile foundation was selected after the key factors such as the possible uncertainty, installation resource capacity and geological conditions were considered.

Introduction

Lingshui 17-2 deep-water gas field which has huge natural gas reserve is the first independently developed deep water gas field in China. Lingshui 17-2 gas field group is located in the northern part of the Qiongdongnan Basin in the western continental shelf of the northern South China Sea, with water depth of 1220m to 1560m. Lingshui 17-2 gas field and reserved gas field are included in this gas group. Lingshui 17-2 gas field can be divided into two parts: east block and west block. And four large central manifolds which design water depth is 1700m and design life is 30 years are located in these two blocks. During the design process of central manifold, the foundation type selection is very significant. It will affect the investment of project and the security of whole gas field.

Foundation of Subsea Production System

As the support structure, the main function of subsea foundation is effectively transfer all the loads from subsea system to the seabed and ensure the subsea system can be stabilized at the design location to satisfied to the function requirement. The foundation selection of subsea system shall be influenced by load property, structure characteristic, soil condition of seabed, installation resource capability and proposal, etc. So to obtain the economical and reasonable foundation design proposal for subsea system, the comparison and selection with soil data, bearing capacity of foundation and installation resource, etc. is necessary. For deep water subsea production system, mudmat foundation is the preferred alternative because of the simple and reliable structural style and installation easily. When the mudmat foundation can't achieve the design propose effectively, suction pile foundation with the strong bearing capacity and flexible installation can be used in deep water subsea production system development. The design and calculation method were noted in the standard API RP 2A, API RP 2GEO, DNVGL-RP-E303, ISO19901-4.

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