The Green Canyon Block 29 development project is a deepwater multiwell system which utilizes a subsea template, a free-standing riser and a floating production facility (Fig. 1). Each of these features has an impact on the design of the Production and Workover Control Systems for the subsea production equipment (template and satellite trees). In addition to these considerations the design philosophy required that all active components of the system must be retrievable independently. This paper describes some of the key features of these unique control systems, as well as a brief account of the integration testing and installation.
The production control system is designed for operation in water depths from 1500 ft to 3500 ft (457 m to 1967 m). It is a diverless system, installed by means of guidelines. The maximum offset distance of a satellite well is 40,000 ft (12,192 m) and the combined total offset distance of all satellite wells is 170,000 ft (51,816 m).
The system is designed so that the control modules can be installed and retrieved independently of one another. This greatly simplifies offshore operations since there is no need to retrieve any of the electrohydraulic production control modules in order to retrieve the distribution or accumulator modules. The system is designed so that the outer twelve well bays on the template can be completed either on the template or alternatively tied into satellite wells by means of flowline connect ion modules. This feature provides the operator with an added degree of flexibility when developing the field. A hydraulic fluid flushing system is provided so that the operator can monitor the condition of the hydraulic fluid and replace it as necessary.
The system also incorporates a surface production safety system which monitors sensors in the process equipment and can implement varying degrees of process shutdown if the quantities being monitored go outside their prescribed 1imits.
The primary function of the production control system is to monitor and control the operation of up to 220 subsea valves on as many as 24 subsea wells.
The system is also designed to inject any of four chemica1s into each subsea well (e. g., for corrosion prevention), and to control the four subsea gate valves which isolate the gas and oil export lines from the subsea template to the shallow water platform. Finally, it also controls the surface production safety system, which monitors inputs from the process equipment and can implement up to eleven automatic shutdown sequences.
The first major design consideration was selection of the type of system to be used since the system is designed to operate up to 220 subsea valves, the number and volume of hydraulic pathways precluded the use of an all-hydraulic system, and led to the choice of a multiplexed electrohydraulic system for the tree functions. However, direct hydraulic control was retained for downhole safety valves, and piloted hydraulic control for the export line isolation valves.
