ABSTRACT

This paper provides an overview of the Zinc Electro-hydraulic Multiplex Control System, which provides for monitoring and control of 10 subsea wells and the subsea manifold functions as well as control and safety monitoring hardware for all Zinc process equipment located on the Alabaster platform A description of the system architecture, together with a discussion of the design requirements, is provided, with an emphasis on the subsea template based hardware

INTRODUCTION

Zinc1 is a subsea production system, installed in 1,460 ft of water, for development of the Mississippi Canyon 354 Field in the Gulf of Mexico The subsea template is linked to Exxon's Alabaster platform, located in Mississippi Canyon Block 397 approximately 6 miles west of Zinc's location, via separate electrical and hydraulic control umbilicals

The Zinc Subsea Production Control System is characterised by a number of significant design features

  • All subsea control system components located on a self-contained control skid which is integrated into the production manifold

  • Control and safety monitoring of all platform-based Zinc process equipment integrated with the subsea production control system

  • Guidewire installed subsea system components using a vessel of opportunity

  • Subsea intervention/maintenance by a work class 'ROV of opportunity'

The control system architecture is implemented as an Electro-Hydraulic Multiplexed system with dual electric and hydraulic supplies consolidated into Subsea Control Pods (SCP's) for Xmas trees and mainfold functions Each mterchangeable SCP, however, provides control and monitoring functions for either two trees, or one tree plus the Zinc subsea production manifold AH subsea hydraulic and chemical supplies are routed from the umbilical end terminations to the tree and manifold functions via fully welded hard piped tubing assemblies with metal-to-metal, self-sealing couplings being used at all disconnection points. Electrical connections between the incoming umbilical and distribution network to individual Control Pods are via ROV manipulator-deployed inductive connector assemblies The entire template electrical distribution network with its supporting framework is recoverable using a simple Running Tool

Equipment designed for the Alabaster platform follows industry standard practice, the operator's control console is dual redundant, hot standby with full colour graphic displays In addition, significant integration of the control and safety monitoring of the associated Zinc process equipment has been achieved

SYSTEM OPERATING PHILOSOPHY

The Zinc Subsea Control System is an electro-hydraulic multiplexed system with Subsea Control Pods capable of controlling the tree valves on up to ten wells, plus the mainfold pigging valves, and the chemical injection system The control system also includes the capability to monitor/control Zinc-related Alabaster platform facilities via the Zinc Control Console (ZCC) The control system interfaces directly to the platform's existing safety/shutdown systems and automatically implements the various levels of both Emergency Shutdown and Process Safety Shutdown detected either by the platform's systems or the safety related topsides and operational subsea sensors which exist within the control system itself

The Control System's subsea multiplexing is performed via the Subsea Control Pod, which is commanded by the Zinc Control Console Each Control Pod is capable of operating two trees, or one tree and the manifold

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