Snorre TLP Configuration and Analysis Technology
Authors: Almeland I-B. , Gaul T.R. , Pettersen D.J. , Vogel H. 
Published: October 2008

This paper gives a summary of the structural design of the Snorre Tension Leg Platform (TLP) and presents the final platform configuration. The most important parameters and requirements governing TLP configuration are presented. Key aspects of the sizing process and final geometry are summarized and finally an outline of the analysis methodology is provided. The selection of a TLP configuration is an interative process rather than the result of one particular exercise.

DESIGN CONSIDERATIONS

As the Snorre TLP is the first one in Norwegian waters and third one ever to be installed, it was of particular importance to establish a well founded base for the design at an early stage. Most of this work was initiated and completed in the 1985 - 87 timeframe 1,2.

The key factors accounted for in the structural design basis of the Snorre TLP are:Regulatory RequirementsEnvironmental CriteriaSafety ConsiderationsFunctional RequirementsFabrication AspectsInstallation Considerations

Regulatory Requirements

Considering that the Snorre TLP was the first one in the Norwegian sector and no design practice was yet established, considerable work effort was necessary to establish the basis for structural design of the TLP. The overall objective was to ensure compliance and correct interpretation of the regulatory requirements, and establish Saga Petroleum's overall philosophy for safe and economical use of available resources. The study work during the feasibility and conceptual design phases covered all areas of the design and helped to test and further develop the structural basis. Most important to the configuration and analysis work were areas such as hydrodynamic loads, load cases, response analysis, calculation of stress, analysis methods and procedures.

Norwegian Petroleum Directorate (NPD) was kept informed on a regular basis so as to ensure consistency with NPD regulations and the interpretation thereof.

Environmental Criteria

Based on the environmental data from nearby fields and site-specific measurements, the environmental criteria for the Snorre Field was established. The main wave and wind data are based on about 7 years of Statfjord field measurements. Current measurements were taken at Snorre over a two year period. To ensure a complete and consistent basis for the design, design criteria for the Gullfaks and Oseberg fields were also evaluated and compared.

Safety Considerations

The main safety consideration influencing structural design of the Snorre TLP deck was the objective to separate hazardous and non-hazardous areas. This resulted in a topside layout consistent with those on other on large production platforms on the Norwegian continental shelf (separated living quarters, utilities-, drillings-/wellbay- and process- areas). (See Fig. 1.)

Another safety consideration affecting the deck layout was escape route philosophy. The objective was to provide straight escape routes to the east and west ends of the platform where the marshalling and lifeboat facilities would be located. The goal was to keep the distance from any working area to any escape route to 15 m or less.

From early safety studies the need to design for accidental flooding was identified.