Future Trends in Subsea Control Systems
Devraj Sonavane
Associate Director, Application Engineering Services
Aker Solutions

Ameya Tipnis
Deputy Manager - Controls, Application Engineering Services
Aker Solutions

Subsea production system (SPS) technology is constantly facing challenges to be able to go deeper, be at more remote locations and handle harsher production fluids. This coupled with the advancement in subsea processing and compression technology is driving fast-track technology development in various SPS building blocks.

Subsea production system (SPS) technology is constantly facing challenges to be able to go deeper, be at more remote locations and handle harsher production fluids. This coupled with the advancement in subsea processing and compression technology is driving fast-track technology development in various SPS building blocks. Subsea control systems, one of the most important SPS building blocks, are not isolated from this wave of change. The focus of the latest developments in this area is to enable: (1) installation of more instrumentation to monitor the condition of the system, (2) higher electrical power to power the equipment at the sea bed, and (3) increase of data transmission capacity and speed. These will be supported by digitalization, which drives integration of data, hardware, disciplines, value chains, industries, business models and people.

The ar ticle will provide an over view of the future trends in subsea control systems, developed to address the challenges of the ever dynamic subsea industry.

1 . Use of Simulation Tools (Digital Twins):
There is a growing interest in simulation technology which can help analyze the technically complex and diverse system of subsea production. An operator training simulator(OTS) takes care of the gap between theoretical training and hands-on practice. A dynamic simulation tool allows virtual testing and analysis of components through state-of-the-art software programs.

The major benefits of simulation software are:

Operator Training:
Simulation can improve trainees’ skills and allow them to undertake high -risk activities or procedural tasks and learn from error within a safe environment without dangerous implications. This reduces risks involved in start-up and shutdown activities.

Improved Product Design and Development:
By simulating the process and control systems, the operator has the ability to test the configuration and logic programmed for the plant. This provides the ability to test control strategies and identify potential design flaws that may lead to downtime and production loss.

Increased Safety:
It provides the ability to test both safety and process interlocks. This reduces the risk before commissioning by allowing users to gain familiarity and build process and operational competencies before deploying to offshore locations.

Capture Knowledge for the Future:
As the knowledge base utilized for the simulation grows, the skillsets of the operators using it can be extended accordingly.

2. All Electric Systems:
The high cost of deep water installations has increased the reliability demands of subsea control systems. Fields in deep water or requiring a long step-out severely limit the practicality of electro-hydraulic control systems. As a result, the subsea industry has been working on the development of an allelectric control system for many years. Electrical control of subsea valves is of growing importance in advanced boosting or separation systems. Electrical actuators are already used to operate subsea valves for controlling process fluid. The allelectric system will enable cost savings for both topsides and umbilicals. It will also create oppor tunities for fur ther cost reduction and a more flexible SPS in comparison with conventional electrohydraulic systems.

Key drivers for exploring electrification of subsea production system include: Reduced Cost - Simplified umbilicals, reduction in subsea hardware and equipment required on the topside.

Lower Operating Expenses - Better predictive maintenance, hydraulic fluid is not required

Reduced Environmental Impact - No release of hydraulic fluid to the sea, no high pressure equipment required on the topside

Enabling digitalization - Ability to monitor functionality and conditions

Higher Flexibility - Easy tie -backs, plug and play integration of control systems

3. Faster Subsea Communication:
The links to topsides from a subsea installation can be communication bottlenecks when utilizing dedicated shielded twisted pairs or coaxial conductors, or power conductors for combined power and signal (CPS). Typically with this setup, data transmission rates have been low and transmission per formance is becoming insufficient to cater to the ever -increasing demand for subsea data. A high bandwidth communication link is now a critical enabler for the continued development of subsea controls. A fiber optic link fulfils all the requirements for subsea communication.

Generally a fiber optic link goes from the subsea gateway to the topside umbilical termination unit (TUTU) to the first communication node subsea, usually the subsea routing module.

There are numerous advantages of using a fiber optic link, which include: Extremely High Bandwidth:
No other cable-based data transmission medium offers the bandwidth that fiber does.

Longer Distance:
In fiber optic transmission, optical cables are capable of providing low power loss, which enables signals to be transmitted for a longer distance.

Safe and Reliable:
Fiber optic cables are tolerant of seawater ingress, unlike conventional electrical conductors.

Resistance to Electromagnetic Interference:
Fiber has a very low rate of bit error, as a result of fiber being so resistant to elec tromagnetic interference. Fiber optic transmission is virtually noise free.

Easy to Accommodate Increasing Subsea Equipment:
With the use of fiber optic cable, new equipment can be added to the existing cable infrastructure.

4. Condition Monitoring and Use of Data:
Condition monitoring (CM) is the process of monitoring the parameters of machinery condition in order to identify significant changes indicative of a developing fault. There are three main approaches to maintenance - reactive, periodic, and predictive. Predictive maintenance is preferred for high value equipment as this uses the actual condition of an asset to determine the potential for failure. CM is a major component of predictive maintenance. The ability to detect damage at an early stage can reduce the costs and down -time associated with repair of critical damage. The use of condition monitoring allows maintenance to be scheduled or other actions to be taken to prevent damage and avoid its consequences. Condition monitoring has a unique benefit in that conditions that would shorten the normal lifespan of a piece of equipment can be addressed before they develop into a major failure.

CM data acquisition is performed by the use of fixed sensors or measurement devices permanently mounted to the monitored machine. An increase in computing power of the available electronics and decreasing costs enables the analysis of this enormous volume of data collected by the sensors and provides meaningful reports for condition monitoring. The data collection at the transducer involves signal conditioning, filtering, sampling and digital signal processing.

The key advantages of condition monitoring are:
  • Gives early warning of potential failure: When parameters to be monitored are well selected and properly analyzed, this gives warning of potential failure well in advance. The information gained can be used effectively for maintenance planning purposes.
  • Gives information about the nature of the failure: When there is a failure in the system, CM can be used for a root cause analysis. The rate of sampling and access to maintenance history on the machine may have an influence on the quality of the final decisions made.
  • Allows management of failure: Identification of a failure does not necessarily mean that immediate maintenance action is needed. CM can be used to plan maintenance action.
  • Evaluates corrective action: Immediately after a system has been repaired it should be subject to condition monitoring testing. This will potentially identify assembly or installation faults that may lead to early failure.
  • Use for performance optimization: CM enables the understanding of bottlenecks or backlogs in the production stream which can assist in optimization of the assets involved.

5. Subsea Internet of Things (SIoT):
The term SIoT is inherited from the term Internet of Things (IoT). SIoT is a network of smart sensors and smart devices used to provide operational intelligence such as performance, condition and diagnostic information. Unlike IoT, SIoT focuses on subsea communication through the water and the water-air boundary. SIoT systems are based on smart, wireless devices incorporating radio and hybrid technologies. SIoT systems incorporate standard sensors including temperature, pressure, flow, vibration, corrosion and video. Processed information is shared between nearby wireless sensor nodes. SIoT systems can be used for environmental monitoring, oil and gas production control and optimization and subsea asset integrity management .

There is also a recent increase of interest in the integration of IoT and cloud computing. Subsea cloud computing provides an efficient means for SIoT systems to manage large data sets. It is an adaption of cloud computing frameworks to meet the needs of the underwater environment.

Faster implementation of next-generation subsea controls systems will certainly benefit the customer as well as the industry overall. Training simulators will enhance operator efficiency by giving them the training required them to make correct decisions. All- electric systems will create opportunities for cost reduction and a more flexible SPS in comparison with conventional electrohydraulic systems. Fiber optic communication provides the high bandwidth required to cater to the increased demand of subsea data. Condition monitoring systems lead to optimization of systems and production .

It may be concluded that high performance control systems enabled by advanced technology ensure a prolonged life of field, reduced capital and operating expenditure, increased productivity, reliability and safety.