Reliable compressor control systems for subsea operation

As the quest for raw materials drives oil and gas companies further offshore, both risk and potential gains increase. At some point in offshore operations, it becomes nearly impossible to push oil and gas to the surface with the existing degree of natural pressure. Some hydrocarbons become non-recoverable due to the loss of pressure during production.

Moving production to the seabed, however, lowers the amount of pressure that is required to extract raw materials. It is estimated that the use of subsea innovation could allow oil and gas companies to recover almost 20 percent more from producing fields.

Additionally, capital expenditure could decrease between 30 to 40 percent, and overall operating costs could drop by nearly 50 percent due to decreased topside staff and supplies. As subsea facilities feed directly to onshore production facilities, the need for fewer personnel and elimination of topside structures also reduces risk. Further, exploration can be expanded into smaller, deeper fields and into harsher environments, helping companies access the resources needed to meet worldwide demand.

In particular, there are many pilot subsea technology projects focusing on the advancement of compressor controls. However, that is only the beginning. The potential exists for future applications to range from gas separation and high-integrity pressure protection system control to water disposal.

Requirements for control systems

To stand up in the intense conditions of a subsea system, oil and gas companies have many requirements for their control systems. To protect compressors from pressure surges, for example, closed-loop controllers are typically implemented. The controller also needs to meet additional environmental qualifications for use at extreme depths.

Similarly, the control system should leverage a standard programming environment so users can select machinery and components from multiple sources that have all been tested in advance to hold up under extremely harsh conditions. Additionally, reliable control system generally features: simplex, redundant or triple modular redundancy levels; online reconfiguration without requiring a process shutdown; IEC-16508 compliance, IEC-61131 compliance and Safety Integrity Level (SIL) certification; and remote monitoring of the system.

(Read more in the Sept/Oct issue of Turbomachinery International)