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Publisher Offshore Technology Conference LanguageEnglish
Document ID 6628-MSDOI  More information10.4043/6628-MS
Content TypeConference Paper
TitleDesign of Gas and Oil Riser Installations for Offshore Platforms
AuthorsJ.W.A. Coker, Statoil A/S
Source

Offshore Technology Conference, 6 May-9 May 1991, Houston, Texas
ISBN978-1-61399-087-2
Copyright1991. Offshore Technology Conference
PreviewABSTRACT

The Piper Alpha (ref. Ocean Industry Jan 1991) accident has focused attention on the design of riser installations offshore. As shown in this incident two major factors must be considered when designing riser installations. These are:
  • to reduce the possibility of a dangerous event on a platform affecting the risers

  • to reduce the consequences to an acceptable level if a riser failure occurs.
There are many ways to design the installation so that the safety is at an acceptable level but this can be very dependant on the type of platform and function. The riser installation could, for example, be different if a concrete substructure is used instead of a jacket substructure.

This paper will indicate the various riser schemes used on installation today, outline the riser installation philosophy adapted for the latest Statoil designed platform and discuss how further installations can be designed to ensure acceptable safety at minimum investment cost.

INTRODUCTION

The risk associated with offshore installations for the production of oil and gas can, in principle be, divided into various risk areas. Different criteria can be used for the risk to personnel, the environment, or the risk to the capital investment. The risk can also be divided into the risk from design accidental events and residual events. The design accidental events are scenarios that the installation is designed to survive with acceptable damage to the personnel protection systems or/and the investment. The residual events are scenarios where it is likely the installation will suffer major damage or total loss.

The installation and equipment should therefore be designed such that the probability of the residual event is as remote as possible, within reasonable financial and practical considerations. The acceptance criteria must be decided on a company to company basis.

From the various studies carried out, which are backed up by the statistical data, the indication is that two types of platform (onboard) incidents can result in total loss of the installation. These are loss of control over the production wells and failure of the gas or oil risers. Both these type of events could lead to large releases of hydrocarbons over a long period of time.

The arrangement and design of the risers is therefore an very important parameter that must be considered during the design of offshore installations. With careful design it is possible to reduce the probability and consequence of a riser failure to a minimum, and to ensure the incident is contained into one area of the installation, at least for the time to allow safe evacuation of personnel.

RISER INSTALLATIONS ON EXISTING INSTALLATIONS IN THE NORTH SEA

Most of the early installations in the North Sea used a steel jacket design where the riser(s) was clamped to one of the main legs (ref. figure 1). The location of the riser was often decided by the arrangement of the process or metering systems.
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