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All electric technology unlocking stranded assets

By  Craig Ferguson and Zahid Hasan, Forsys Subsea Monday, 01 August 2016 13:45
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Forsys Subsea’s Craig Ferguson and Zahid Hasan discuss a new integrated approach to how system designs and installation methods converge in a new generation of subsea architecture.

Images from Forsys Subsea.

The dramatic drop in oil prices has renewed interest in innovation and technologies that enable safe, environmentally responsible and cost effective development solutions. As increasing complexity of deepwater subsea projects has driven the industry away from standardization, we believe that early engagement, greater collaboration and a focus on technology are the key to making oil economically viable at US$50/bbl.

The total subsea EPCI scope to include SPS, SURF and installation will typically vary between 35-40% of total CAPEX, which is where the integrated EPCI model with a focus on technology can make the most impact. In the Asia Pacific region, operators are seeking technology solutions that allow them to unlock stranded developments that contain recoverable reserves in existing assets.

These are economically and technologically constrained by considerable tieback distances and host facilities with limited topsides expansion capacity. Fully all-electric subsea architectures combined with electrical heating for hydrate and wax mitigation and surveillance and data management services can significantly reduce the development cost of these marginal subsea tiebacks.

Additionally, they allow for lower operational expenditure through enhanced diagnostics and feedback from the subsea system. The objective of the stranded asset studies is to evaluate, through Forsys Subsea’s integrated approach, the use of all-electric technologies to the extent that not only will the hydraulic conduits in the subsea umbilical be suppressed but also any chemical injection lines can be eliminated.

This could be achieved through compact high voltage DC power transmission cables with integrated fiber optics, leaving only a small volume of required chemicals for injection that subsea storage technology could enable.

The cost rationale.

Integrated approach

For many years, the subsea industry has predominantly used conventional electro-hydraulic control systems for the operating of subsea valves and for the distribution of power and communication signals to subsea sensors. This means that all valve movement is performed hydraulically through the distribution of hydraulic fluid through umbilicals and flying leads to subsea actuators.

Current state-of-the-art technology already allows for simpler and lighter subsea equipment with all-electric subsea production control systems, which most significantly reduce cost through the removal of hydraulic actuators, compensation and tubing throughout the entire field (thus reducing structure size, umbilical diameter and topsides footprint).

All-electric actuation easily detects the health of the device and introduces the possibility to self-test and enable better condition and performance monitoring. Further, electric actuators can be replaced without interruption of production (except for those on safety critical Fail Safe Closed valves) and can be significantly smaller for large and high-pressure valves (7in and 20 KSI).

One case study conducted by Forsys Subsea in Asia Pacific demonstrated that the dry weight of an all-electric subsea manifold with eActuators reduced by 15% compared to the conventional electro-hydraulic design of a similar manifold. Similarly, the weight of a subsea tree with G4 actuators to allow Fail Safe Close functionality reduced by 5% compared to a similar electro-hydraulic subsea tree (only in the case when an electric downhole safety valve is selected as well).

Further, the removal of all associated hydraulic controls components simplified the testing and eliminated the potential of ingress of water into the hydraulic circuit. From an HSE perspective, the risk of leakage of hydraulic fluid is completely reduced through all-electric actuation systems. The all-electric umbilical has a smaller cross section that allows for the manufacture and spooling of longer continuous lengths.

As the overall umbilical weight is reduced, a smaller vessel can be used for installation, lowering the total installed cost for the stranded asset cases. Electrically-Trace-Heated Pipe in Pipe (ETH-PIP) technology realizes a single flowline solution with heat tracing cables and optical fiber in a reeled PIP annulus, allowing the client to heat the flowline to prevent or remediate fluid blockages to maximize uptime with simpler preservation operations.

In Technip’s ETH-PIP, electrical power is supplied from a single topsides power source either via a power umbilical or an integrated production bundle (IPB) to the connection termination assembly, located at the closest end of the ETH-PIP. Electrically heated pipelines have become a well-established technology to prevent hydrate and wax plugging in long subsea tiebacks.

As a next step, a dedicated high voltage DC power system with integrated fiber optic communication could replace conventional power and signal distribution, completely eliminating the need for a separately installed umbilical, offering significant architecture optimization and reduction of total installed cost. DC power is the preferred solution for longer subsea tiebacks, with higher transmission capacity and with fewer conductors than AC power systems.

The service chemicals could be distributed from subsea chemical storage systems installed as close as possible to the delivery point at the subsea tree or manifold, which would negate the need for topsides mounted infrastructure and interfaces. Using these designs developed in the concept stage, Forsys Subsea can monitor and assess the entire subsea system integrating life of field well surveillance, monitoring, data interpretation and advisory services.

This is particularly powerful with all-electric solutions and heated pipe technology. Precise control of the power, together with fluid temperature monitoring all along the flowline with optical fibers, offer a high flexibility of operation management and will provide information to help accelerate decision time in the production phase.

Key benefits

An integrated approach.

Fully all-electric subsea architectures combined with heated pipe technology, integrated high voltage DC power and fiber optic distribution, subsea chemical storage and life-of-field monitoring services can significantly reduce the total installed cost.

It improves HSE with no pressurized equipment and reduced emission to the environment; reduces cost through the removal of hydraulic infrastructure subsea and elimination of the umbilical with a separated power cable; and improves operational efficiency with heating technology for higher uptime, and better condition and performance monitoring.

Technology benefits include less sensitivity to water depth and long distances; faster and more accurate choke and valve operation; ROV retrievable actuators and distribution for late field life installations; and the enhancement of subsea storage to economic viability.

This unique combination drives a new step change approach to how system designs and installation methods converge in a new generation of subsea architecture. Forsys Subsea has applied this thinking to realize double digit percentage reductions to the total installed cost for marginal subsea tiebacks to constrained host facilities in mid-to-deepwater subsea environments in the Asia Pacific region.

Craig Ferguson
has been in the oil and gas industry for nine years and has held offshore installation, design, project, subsea system and field development engineering roles in the US, Africa, UK and Singapore. He is presently the business integration and planning manager for Asia Pacific with Forsys Subsea in Singapore. Ferguson holds a Bachelor of Science in Petroleum Engineering.

Zahid Hasan
has been in the oil and gas industry for 12 years and has held structural engineering and subsea system engineering roles in Singapore and Australia. He is presently a lead field development engineer with Forsys Subsea in Perth, Australia. Hasan holds a Master of Engineering.

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