Technology boosts subsea reliability

As high energy costs drive the need for increased productivity, subsea surveillance advances allow real-time viewing of what exactly is going on beneath the surface

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By  O&GME Staff Published  May 2, 2006

Technology|~|technology-200.gif|~||~|Rcent technological advances in surveillance and monitoring systems for subsea oil and gas production facilities are enabling enhanced recovery of hydrocarbons, improved production rates and lower operating and capital costs. As the analysis of subsea operations has become more advanced, so has the need for more accurate surveillance and monitoring techniques to create a real-time picture of just what is going on beneath the surface.

Proper surveillance systems are vital for any subsea control system to work properly. The greater the monitoring capacity of any installation, the lower the risk of having to intervene below the surface — which is more often than not expensive and can be hazardous. Ensuring a reliable, accurate flow of live data from under the sea surface enables a constant monitoring at base of both production process and the performance of the infrastructure under the water.

Recent technological advances include multiphase flow metering, fibre optic sensors, and intelligent well control devices — all known as ‘smart field’ technologies. These are proving particularly useful when it comes to narrowing the gap in production costs between the historically more expensive subsea process and onshore below surface oil and gas production.

They are also helping increase the financial viability of marginal fields —through enhanced oil recovery.
This new technology is also helping one of the largest and most challenging offshore developments in the world — Ormen Lange — the 70 million cubic metre per day offshore gas field being developed in Norwegian waters (Ormen Lange partners: Hydro, 18.0728%; Shell, 17.0375%; Petoro, 36.4750%; Statoil, 10.8441%; Dong, 10.3420%; ExxonMobil; 7.2286%) and due to start production in October next year.
Bertmand Trond, principal engineer, at Hydro Oil & Energy Projects, says there are several new aspects in surveillance and monitoring that are being introduced in the project. “There are a lot of challenges [with Ormen Lange] so we have a fibre-optic point-to-point system dedicated to each electronic module on each well.” He added, “These modules can also intercommunicate on a local network — and that’s a new development.

We also have electronic communication. We use transformers on the umbilical termination head in order to maintain low voltage and that contributes to reliability.”

Another new feature is an acoustic leak detection system designed to address leaks of synthetic oil, which, Trond says, can in Hydro’s experience cause reliability issues with subsea operations. “It’s sending information on leaks as well as just listening out for them and it’s technology that’s been used by the [Norwegian] navy. We also have wet gas monitoring for each well to measure the water content of the gas and there’s a dosage valve on each well adjusted according to water the measurements being taken.”

The complexity of new subsea production facilities means new systems are constantly being developed, says Tim Whitaker, programme manager systems and technology at Norway’s Aker Kvaerner.

“These systems often have a high intrinsic value, are critical to field operation and also to high retrieval and maintenance costs. A typical example is a subsea pump for water injection or for production pressure boosting,” he said.

In 2005, Aker Kvaerner, installed a marinised multiphase pump in the North Sea for CNR International.

Whitaker comments: “Monitoring the condition of key pump components from a remote location is essential for effective maintenance and intervention planning. As an integral part of the subsea multiphase pump, a system for monitoring bearing vibration levels and motor winding temperature has been deployed. This system reports vibration and temperature levels every few seconds back to the surface for analysis. If the vibration or temperature levels change in comparison with the historical data, this could indicate that it is necessary to change the operational parameters of the pump to guarantee its lifespan to the next planned maintenance window. By extending maintenance intervals to permit scheduled use of vessels, there are larger Opex savings.”

Many subsea production facilities now have permanent surveillance systems in place not only for the infrastructure but also for reservoir management, which means improved recovery rates. Geospace Engineering Resources International — a unit of OYO Geospace — has installed the world’s largest permanent deepwater seismic recording system for BP at its North Sea Valhall Field. This is expected to add 60 million barrels of recoverable reserves to the field, accelerate field production rates, and significantly reduce future field development costs through fewer dry holes and less support services.

Meanwhile, Schlumberger has developed a subsea system infrastructure that enables surveillance and control of subsea fields from the reservoir to the client office. This system is designed to: improve the productivity of subsea wells; increase the reliability, accuracy, and availability of data acquisition and provide a remote subsea network that is flexible, expandable, and highly adaptable.

This Subsea Monitoring & Control (SMC) system creates a distributed network between the surface, subsea, and subsurface reservoir instrumentation. Schlumberger says that the increase in data availability through advanced surveillance systems, such as the SMC platform, allows innovative ways to monitor subsea systems and production operations from the sandface to the host facilities.

The oil service giant says: “This enables productivity optimisation through closed-loop actions based on accurate real-time information. When real-time data acquired from subsea monitoring systems is combined with modeled and historical data, expert analysis- — as part of productivity optimisation services — provides the operator with a more detailed analysis of production and system performance. This enables interventions and remedial production operations to be planned more efficiently, thereby reducing downtime, production loss, and operating expenses.”

Schlumberger currently has 16 systems in production for two projects in the UK North Sea, and has proposals under evaluation to deploy these systems in the Gulf of Mexico, West Africa and Australia. The initial implementation for advanced subsea boosting and seawater injection applications has highlighted the benefits of an open, transparent, and versatile high-speed subsea area network.

It adds: “As these technologies become more proven through additional trials and installations, the responsibility to assess the cost versus benefit, and be more aggressive towards the adoption of subsea reservoir and production surveillance systems, shifts to the subsea operating community.” Such system productivity solutions are optimally considered at the front-end engineering and design stage, and are included in future project tenders that can benefit from independent surveillance options. These projects show that a production control system with an open architecture for subsea surveillance and control can help operators, Schlumberger said.

All these technological advances in surveillance and monitoring practice are now making subsea operations as reliable as surface operations — and also leading to the creation of the intelligent well.
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