The issue of improving monitoring and control of subsea completions while maintaining high reliability is critical due to accessibility and intervention costs. Hydraulic control of the downhole choke valves in multiple zones can be complex, and the situation is further complicated by the fact that traditionally different companies supply the downhole completion equipment and the tree control system at the wellhead. This can lead to less production data being available, reduced control functionality and valve control logic issues. Additional interfacing requirements also lead to an increase in costs for a project.
This paper details the design approach, application and advantages of a dedicated intelligent well completion (IWC) control system for subsea fields. It also reviews the methodology and issues related to the integration of the control system within an existing field development in the North Sea.
The proposed system has an electrohydraulic control module, provided by Schlumberger, mounted on a subsea production tree, which provides complete control and monitoring of the intelligent well independent from the tree control system. This approach allows the intelligent well subsea control system to be tailored specifically for the completion equipment and well type. It also provides additional protection to the tree control system from control line thermal expansion and the potential of leaks.
The subsea solution selected by the client aims to reduce the loading and project-specific customisation of the production critical tree control system. This will allow it to be standardised while still providing maximum performance and flexibility for monitoring and control of the well. This approach permits a single supplier, in this case Schlumberger, to manufacture and test the complete intelligent well control and surveillance system from surface to the subsea well prior to delivery and the site integration test (SIT). This reduces the overall project risk and avoids interface issues being detected late in the project phase.
Intelligent wells have been demonstrated to improve production in multi-zone wells through the use of active well management and the ability to monitor and change the well flow characteristics without intervention. These benefits, particulary the reduction in costly intervention, have lead to an increase in the number of intelligent wells installed subsea over the last few years. However, there are still a number of issues to solve to improve the overall operation and reliability of these systems.
The aim of this paper is to detail the drivers and benefits for a step change in the way in which subsea intelligent well systems are controlled and monitored today, and to profile a proposed method of implementation of such a system. This paper also covers the features and benefits gained from the use of a dedicated subsea intelligent well control solution and the experiences designing and delivering the system for a project in the North Sea.
System Philosophy Traditionally, subsea intelligent completions are controlled and monitored by the production subsea control module (SCM) mounted on the tree or manifold.