Abstract

Oil and gas exploration in South China Sea is entering into medium and deep water depth where flexible riser is becoming economically competitive and technically accessible for floating production. An 8 inch production riser has been designed for one of the existing field in the targeted area. This paper presents all aspects of the design of the 8 inch production riser from design requirements and material selection, layer design, cross-section validation to physical properties including axial, rotational and bending stiffness.

Theoretical methodology for design of layers and cross sections is presented and compared with available numerical tools. The design of the polymer layers focuses on chemical and physical properties, the design of the carcass layers considers the crushing capacity by taking into initial deflection into account. The design of the tensile and pressure armor wires considers both capacity and fatigue.

Introduction

CNOOC Research Institute (CNOOC RI) intends to develop offshore flexible riser technology with targeting application area in South China Sea where the water depth ranging from several hundred meters to a couple of thousand meters. This paper demonstrates the design methodology for all layers which are essential for a typical production riser. Design of flexible riser cross section is based on the requirements of the anticipated application of the riser considering as a minimum the following factors: water depth, service life, pressure/temperature and internal fluid contents and environmental operational conditions.

The design follows primarily the requirements set by API 17J. The flexible riser is expected to meet at least the following overall requirements according to the Specifications:

  • The flexible riser shall be capable of withstanding all design loads and load combinations

  • The flexible riser shall have sufficient service life to perform its function, particularly the load bearing metallic layers

  • The material used for manufacturing the flexible riser shall be compatible with the exposed environment

  • The material used for the flexible riser shall withstand the corrosive environment to which it will be exposed

  • The flexible riser shall provide a tight conduit to prevent fluid Leakage

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