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Subsea Control System

The Challenge

Build a user-friendly, flexible, robust, easy-to-maintain Subsea control system within time and cost constraints. These Subsea Control systems monitor and control valves in multiple oil wells.

The Solution

Infodat 's robust and user-friendly solution is built using two computing systems. A HMI application - Topside Control Unit (TCU) software - runs on a Compact PCI system operating on Windows XP platform. The HMI application was developed using LabVIEW with Datalogging and Supervisory Control (DSC) module. A second system running on LabVIEW RT runs on a Compact FieldPoint system. The Compact FieldPoint software functions as a watchdog unit and holds the Hydraulic Power Unit (HPU) in a stable state in the event of a MSCU failure. It also acts an interface to the HPU, using the commands from the TCU to control the HPU valves.

System Design

The Topside Control Unit (TCU) software is a LabVIEW executable using Data Logging and Supervisory Control (DSC) module features. The TCU controls Hydraulic Power Unit valves via the Compact FP module, and the Subsea valves through an SEM (Subsea Electronic Module). The TCU sends Valve operation commands to the SEM through an Active-X Interface. These commands are interpreted by a proprietary Active-X Server, which in turn controls the SEMs through a serial RS-232 interface.

The TCU enables the operators to control the Xmas trees (of valves) and wells via the HMI. The TCU also monitors the Hydraulic Power Unit, Emergency Shutdown (ESD) System and Process Shutdown (PSD) System.

Security

Security is an important system requirement since it is unattended for long periods of time. While the system provides a great deal of flexibility to reconfigure it, access to the TCU system also needed to be limited to three classes of users - Operator, Supervisor, and Engineer. Logon access for each class of user is restricted via password protection. An access log is maintained for each Logon attempt. Using LabVIEW DSC module to build the system makes it easy to design such layered security.

User Configurable Parameters

The TCU supports multiple wells with each well supporting various hydraulic valves (single actuator, double actuator etc), which can be easily configured. The TCU lets users switch between SEM controlled valves and directly controlled valves seamlessly. This flexibility drastically reduces the time taken to bring a new well online or in replacing field equipment.

On the HMI, the setup and configuration of valves on each well can be viewed individually. A user with the correct access privileges can change valve parameters including alarm limits and alarm priority. He can also suspend the alarming for maintenance.

A Historical Trending screen displays an interactive chart that plots past data retrieved from the historical database. The displays can be customized to show data for a given time span and range. In addition, the current alarms and the alarm log can also be viewed.

Software Health and Watchdogs

The HMI application and the Compact Field Point unit constantly communicate over an Ethernet every 250 milliseconds. If TCU fails to communicate, the cFP holds the current state of HPU valves. It also executes a predefined shutdown sequence in case of a shutdown signal trip and TCU crash. This protects against computer crashes and network problems.

Rugged, Easy-to-Maintain Control System

In summary, a rugged, robust and easy-to-maintain control system for Subsea Valve control was installed at our customer system. The new system provides a flexible, easy-to-use and more intuitive user interface. The LabVIEW-based software is easy to modify, and the state-of-the-art National Instruments hardware is inexpensive and easy to maintain. By developing the system using LabVIEW, Infodat reduced software development time by more than a factor of ten as compared to the time taken to develop a similar PLC based system.