TOGI Subsea Station: Technical Overview
Authors: Varvin K. 
Published: October 2008

The TOGI gas is produced from one subsea production station installed at 303 meter water depth in the Troll field. Initially 4 wells with a peak capacity of 3.25 Sm3/day will deliver the required quantities of gas to the Oseberg field.

The TOGI subsea station has been designed for diverless installation and maintenance, and it is controlled from the Oseberg field over a distance of 48km.

This paper describes the TOGI Subsea Station layout and design philosophies. Experiences from the development of prototypes and from fabrication, testing and installation of the complete system are subsequently presented. Finally some ideas for future use of the TOGI technology are discussed.

INTRODUCTION

The decision taken in June 1986 to design, fabricate and install a unique subsea gas production system in the Troll field, represented at that time a major challenge for Norsk Hydro. Ideas, as listed below should then be transformed to prototypes and tested out in 303m water depth on live gas wells:Remote control and monitoring of subsea wells over a 48km distance with no surface support on the Troll field.Designing a subsea station where all active components are built into independently retrievable modules.Strict reliability requirements for all equipment permanently installed.All fluid supply to the subsea station through two hydraulic lines and one hydrate/corrosion inhibitor line. For special well kill purposes a kill hub installed within the manifold should be used, eliminating the need for a 48km kill line. Pressure bleed off by gas venting to the sea.Running of all the tools needed during installation/well completion operations by one common electrohydraulic intervention control system.All installations, including the pull-in and connection of a 20" pipeline to be performed without divers, only by assistance from tools and ROVIS remotely controlled from surface. This paper is one in a series of six which are presented at the OTC 1991.

SYSTEM LAY OUT AND DESIGN PHILOSOPHIES

Fig. 1 shows the TOGI P & ID. This drawing describes the system architecture in addition to the piping, valves and instrumentation. All connections between modules are made up by stroking the hubs horizontally after a retrievable seal plate has been landed in between the hubs. The seal plate is hanging in a hinged clamp. The retrievable modules sitting inside the 6 slot template structure that is piled to the sea bottom are the following:X-mas trees with individually retrievable control pods.Manifold module with production isolation valves (6"), gas header, chemical and hydraulic distribution headers with isolation valves, centrally located kill hub and cables for electrical distribution.Pig module with 12" and 20" isolation valves and with a hub for pig launcher connection. All the isolation valves are ROV operated. The chemical injection lines are routed via the control pods where an injection orifice with differential pressure measurement is included. For leak testing gas is vented through an orifice on the X-mas tree to the sea and pressure sensors in the production and annulus bores monitor any pressure build up.