The TOGI (Troll Oseberg Gas Injection) production system is extraordinary in many respects. It features production of gas from a five well template located in 305 metres of water depth in the Troll East province. Unprocessed gas is transported in a inch pipeline to Oseberg where it is injected in the reservoir in order to enhance oil recovery Production Control and Monitoring is performed from the Obseberg Field centre. All installations utilized in the normal production mode are located on the seabed.
The Production Control Systems (PCS) features several new items, Eg:
Communication signals superimposed on power circuits
In-situ acoustic sand detector.
Control and monitoring of methanol injected into five wells from a common header
Acoustic leakage detection
A remote operated tool capable of making up 12 electrical bridges in a single dive
Remote operated control pod running tool with novel features
In addition, the Intervention Control System (ICS) is configured as a hybrid system (direct hydraulic and electrohydraulic multiplex) featuring computerised operator interface. Such intervention techniques are not new to the subsea industry, but experience is limited to a few installations which are rather dissimilar in design.
A general description of the PCS and ICS is given in OTC 5950 (1989). The purpose of the present paper is to expand on OTC 5950 for three selected topics though to be of interest to SUT participants.
The power and communication system developed for TOGI consists of 12 systems which are nearly physically identical. There are two system pr. well such that each pod is wired as if it were a single satellite (There are two different designs of conductive couplers to reduce design level common mode failure). This approach would be considered conservative by most people, and indeed it was intended as such. Limited confidence in both conductive and inductive couplers for a 31 bar ambient is one of the reasons for this conservativism. Design of electrical systems is also influenced by the overall design strategy for TOGI which aims at keeping the Manifold Piping Module (MPM) entirely free of active components due to its size and inherent difficult maintenance. The latter principle applies to all subsystems including the PCS. Thus, active distribution systems with key component retrievable only with the MPM were avoided.
It is recognized that the present system has some serious operational disadvantages, e.g. the somewhat cumbersome pull-in of the service line and connection of electrical bridges. These disadvantages were accepted as the price to be paid for achievement of objective referred above.
A complete rationale for selection of system architecture is given in OTC 5950 (1989), the purpose of this section of the present paper is to given a report of system performance as-built, prior to deployment.
Fig 1 is a simplified diagram of one circuit. It consists of a 60 hz power system and a communication system operating on an 1800 hz carrier. The following items may be identified on the diagram