TOGI Deepwater Gas Cluster Control Systems

ABSTRACT Development of the TOGI Project entails installation of a five well gas cluster on the Troll Field which will produce gas for injection into the Oseberg reservoir for the purpose of recovery enhancement by pressure control. Unprocessed gas is transported 35 miles in a 20" pipeline from Troll to Oseberg. The template production will be remotely controlled and monitored from the Oseberg A-platform by means of a Multiplexed Electrohydraulic System which comprises such exceptional features as acoustic sand detectors on each Xmas Tree and acoustic leakage detection. A 24 core electrical cable and three stainless steel tubes connect the template control system with the control station at Oseberg A. The template at Troll is located in 305 meters (1000 ft.) of water and is a diverless design depending on remotely operated running tools for installation and maintenance. The workover control system is also a Multiplexed Electrohydraulic System utilizing computer control. It serves as a common facility for all the remotely operated running tools required for installation, pull-in and pigging operations. A comprehensive program of testing and quality enhancement is included in the TOGI Project. INTRODUCTION Fig. 01 illustrates the main elements of the TOGI Production System. A five well, (six slot) template located at the Troll Field in the Norwegian North sea is tied to the Oseberg B platform by a 20" line which will carry unprocessed gas, driven by the reservoir pressure. The TOGI Project is entirely commercial, it has no experimental objectives in its own right. Production regularity is required to be in order of magnitude 80%. A minimum of two wells must produce in order to ascertain liquid hold-up in the line. All control and certain monitoring functions are required operational in order to produce a well. TOGI requires more monitoring functions than most other field installations. This is basically due to the potential hazards associated with transportation of unprocessed well fluids over long distances. Fig. 02 shows the TOGI schedule. Fig 03 illustrates the TOGI modularization scheme. The major modules are the Manifold Module, the Pigging Module (deployed from a rig whenever needed), five Xmas Trees, production and service line pull-in ramps and connection areas. The entire top surface of the Template structure is covered by (retrievable) protective roofs. It has been a design objective to make the Manifold Module as simple as possible as this module is difficult to retrieve for maintenance. There are no active control or monitoring functions on this module, all isolation valves are ROV operated. In terms of control equipment it contains only piping/ wiring and connectors. REQUIREMENTS FOR CONTROL AND MONITORING Subsea active control functions required for TOGI Production are limited to on - off operation of 9 process valves located on each of the five Xmas Trees and two SCSSV's. All valves designed for infrequent operation are based on ROV intervention.