Subsea/Surface Systems

The Stingray generator was designed by Engineering Business to extract energy from water that flows due to tidal effects. As the sea level changes under the influence of the moon and sun, it gives rise to enormous bodies of moving water, which flow between landmasses and over undulations in the seabed to produce strong marine currents.

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William Furlow

Stingray harnesses energy from tides

The Stingray generator was designed by Engineering Business to extract energy from water that flows due to tidal effects. As the sea level changes under the influence of the moon and sun, it gives rise to enormous bodies of moving water, which flow between landmasses and over undulations in the seabed to produce strong marine currents. Tidal streams are a relatively condensed form of renewable energy and are accurately predictable. This is one of the key advantages of tidal stream power generation over other forms of renewable power. Its predictable nature provides the opportunity to market electricity under the current pool management regime without risk of under or over provision.

The flow of the tidal stream over the Stingray hydroplane causes an oscillating motion, which is used to directly operate hydraulic cylinders to produce a flow of oil. This can be used to drive a hydraulic motor, which in turn drives an electrical generator. A yaw mechanism ensures that the hydroplane is directly aligned with the flow of water throughout the ebb and flow of the tide.

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The Stingray converts tidal stream currents to generate power on the seabed.
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The Stingray is a seabed-mounted device situated typically in any water depth to 100 m and below the most damaging effects of waves. (There is a range of seabed mounting techniques, but the demonstrator will have a gravity base.)

Last year, with a grant from the UK government, EB was able to fast-track a commercial and technical feasibility study of the Stingray system. The three-month study included detailed mathematical, physical, and cost modeling of Stingray. At the end of November 2001, EB submitted a full report and made a presentation to the UK Department of Trade and Industry Water Power Technologies Advisory Panel (Waptap). Subsequently, the Waptap committee recommended support for the EB proposal to design, build, and install a 150-kw demonstrator.

EB installed the demonstrator last summer. The launch and recovery system for Stingray is based around a moored barge and will be used to deploy the generator in about 35 m water depth. During the initial phases of the project, EB tested the basic principles of the Stingrays operation with the device connected to the barge. The barge remained on site to allow recovery for inspection or modification as required.

As the test program progresses, EB plans to reconfigure the machine so that the generator will be connected to drives and a load bank on the barge by a small bundle of cables, so that the power generation of the Stingray can be accurately monitored.

Ultimately, EB hopes to install a subsea power cable from the landing point on the shore to the barge site. This will allow the removal of power generation and control equipment from the barge and installation in a suitable container on shore. EB may then operate the generator for up to 12 months prior to decommissioning.

Following a successful demonstration program, EB has plans to construct a 3-Mw pre-commercial tidal stream power station. This will incorporate the experience gained from the single 150-kw unit, and the farm would be connected to the local power distribution system.

Offshoot of UBD business addresses pipeline commissioning

Weatherford recently announced the formation of a targeted Pipeline & Specialty Services group within its Drilling & Intervention Services division. This was the result of several key acquisitions and the Blue Stream pipeline-commissioning contract, according to Don Galletly, senior vice president of corporate marketing for Weatherford.

The basis of the group sprang from Weath-erford's underbalanced drilling (UBD) capability and was accelerated as the company ramped up for the Blue Stream pipeline commissioning project between Russia and Turkey. Galletly explained that UBD uses the same types of compression equipment as pipeline commissioning. With the Blue Stream contract secured, Weatherford in a sense was able to finance the growth of its UBD fleet. The move to a dedicated pipeline services group gained momentum with a series of acquisitions, including Kopp, a pipeline commissioning company out of Germany, and International Nitrogen Services, which provides membrane technology for the production of nitrogen.

In 1999, through the purchase of Dailey International, Weatherford had established a 50% stake in INS, as well as expanding its UBD fleet. This year, Weatherford bought the remainder of INS and its unique technology, which is important because it allows the company to generate nitrogen on site rather than relying on bulky, cryogenically stored nitrogen services. Nitrogen is used in the commissioning process to dry the pipelines and in UBD operations to lighten the weight of the drilling media.

"There is a certain correlation between compression and nitrogen, and underbalanced and pipeline commissioning," Galletly said.

Weatherford also owns a compression fabrication facility in Singapore, which was used to fabricate the compression units needed both for pipeline commissioning and underbalanced services. This was critical in building the equipment required for Blue Stream. While this was a major project for Weatherford, Galletly said, "It is important for the company to look beyond Blue Stream towards a long-term involvement in pipeline services."

This is one of the drivers behind the formation of this new group. Galletly said the group will be able to exploit these pipeline commissioning capabilities across the globe, taking advantage of Weatherford's worldwide presence. Compression equipment has a relatively long life. The ability to provide equipment and services in two distinct markets, commissioning and UBD, ensures this equipment, and the people operating it, will be kept active and improve the company's returns.

KOP delivers tree

Kværner Oilfield Products recently delivered and installed a subsea tree and related produc-tion controls for Amerada Hess. The subsea tree will be used in 1,700-ft water depth at Garden Banks block 201 in the US Gulf of Mexico.

The 5-in. by 2-in. horizontal side valve tree is configured for smart well technology and includes five downhole hydraulic functions and one electrical function. The christmas tree features integral valves and twin parallel bore metal seals on the tubing hanger.

KOP is also supplying an EH MUX control system, including a subsea control pod and hydraulic and electric flying leads for Garden Banks block 201. Additionally, KOP will upgrade the master control station on the High Island block 373 platform. The control equipment design allows for future field expansion.

Multi-phase meter trials complete

Halliburton Energy Services has completed field trials in Algeria of its non-radioactive multiphase flow meter system. Called FastQ, this skid-mounted mobile system is capable of measuring the flow rates of oil, water, and gas continuously without any mixing or separating of fluids. The system uses the Flowsys Topflow meter.

The FastQ is used for exploration and prod-uction well testing, production monitoring, and allocation metering. Free of radioactive sources, it is environmentally friendly and safe to use. It has been successfully tested at independent flow test laboratories in Norway and the UK.

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