Successful transient EM survey in the North Sea at 100 m water depth

Centrica Energy (formerly Venture) selected a self installing and re-usable platform concept (SIP) to develop their F3FA gas field in the Northern Part of the Dutch sector of the North Sea. On 6 February 2009 and following an initial FEED study, the contract was awarded to Heerema Fabrication Group (Main Contractor and Fabricator), in partnership with Iv-Oil & Gas (Designer and Procurer of process equipment) and SPT Offshore (Installation Contractor and Foundation Designer). The platform weighed in total 8,800 ton, including a 4,000 ton deck and 4,800 ton substructure including the suction pile foundation. The water depth at the F3FA site is 41m and the bottom of the cellar deck is located at 20m above LAT. The platform has an overall dimension of 63m × 45m footprint and protrudes some 90m above the seabed (excluding vent stack). The platform concept consists basically of a deck of 5 levels supported by 4 unbraced legs (3.25m outside diameter × 77m long) and founded on 4 huge suction piles (15m outside diameter × 13m deep). The platform is transported and installed using a large flat top barge (BOA 35 measuring 124m long × 31.5m wide × 8m high) and 3 tug boats (75, 90 and 183 ton bollard pull) for the tow from HFG’s yard in Vlissingen to the F3FA site in the Dutch sector of the North Sea. The leg lowering and deck lifting was achieved using 12× 900 ton strand jacks. The suction pile foundation was installed using 4× suction pumps. During the detailed design stage of the project, the concept design was subject to several elementary changes in the structural design. This had to do with the severe environment, the increased deck weight and water depth compared to the earlier utilisation of the concept. Fatigue and transport and installation issues had a significant impact on several key structural design elements. This complicated the deck-leg connections and several members in the truss deck. The deck leg connection was amended from a simple clamp connection in to a superbolt and sleeve connection at the top deck and a clamped and grouted connection at the cellar deck. In order to improve the stiffness of the legs, leg stiffening frames were placed on top of the suction piles. Due to the limited and slow roll & pitch response of the platform whilst on the BOA barge during tow, high seafastening forces were predicted. These high seafastening forces were transferred in to the barge using pinned seafastening arms. Water depth limitations and the additional leg stiffening frames necessitated to use a fairly high grillage structure of 6.5m high. All these items changed the deck construction towards a method obstructing completion of non-structural disciplines and changed the inshore mating operation of the substructure with that topside towards a complex lifting and fitting campaign. Despite these elementary design changes and some rigorous changes in the planning of the various activities, the contract schedule was achieved in time. The above efforts had an obvious effect on the managerial issues towards the project. It required a doubling of the manning levels and engineering issues of in some cases R&D nature. Despite all these challenges and complications, the platform left Vlissingen well ahead of time, on 18 August 2010, to set sail for the F3FA site. Upon arrival in the field, the weather deteriorated severely and the tow was forced to seek shelter in Rotterdam. Just before arrival in Rotterdam severe waves were encountered up to 6–7m maximum. Upon inspection in Rotterdam, the design proved to be resilient as no signs of damage were observed. Following 10 days waiting on weather the platform was towed to the field for the second time. Installation and lifting the deck to the top elevation was achieved within a record time of 2 days and 4 hours. Thereafter the platform hook-up team continued to work on the platform including completing the deck leg connections, such as installation of superbolts at the top deck level and clamp shells, rubber pads and grout at the cellar deck level. Further hook-up work consisted of hooking up the life support systems before arrival of the drill rig on 14th October 2010. The drilling of the first well was completed early January 2011 and first gas was introduced in to the pipeline system since week 4 of 2011.

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A Spatial Analysis of the Potentials for Offshore Wind Farm Locations in the North Sea Region: Challenges and Opportunities

ISPRS International Journal of Geo-Information ◽

10.3390/ijgi9020096 ◽

2020 ◽

Vol 9 (2) ◽

pp. 96 ◽

Cited By ~ 1

Author(s):

Gusatu ◽

Yamu ◽

Zuidema ◽

Faaij

Keyword(s):

Protected Areas ◽

North Sea ◽

Water Depth ◽

Wind Farm ◽

Wind Farms ◽

Offshore Wind ◽

Offshore Wind Farms ◽

The North ◽

Challenges And Opportunities ◽

The North Sea

Over the last decade, the accelerated transition towards cleaner means of producing energy has been clearly prioritised by the European Union through large-scale planned deployment of wind farms in the North Sea. From a spatial planning perspective, this has not been a straight-forward process, due to substantial spatial conflicts with the traditional users of the sea, especially with fisheries and protected areas. In this article, we examine the availability of offshore space for wind farm deployment, from a transnational perspective, while taking into account different options for the management of the maritime area through four scenarios. We applied a mixed-method approach, combining expert knowledge and document analysis with the spatial visualisation of existing and future maritime spatial claims. Our calculations clearly indicate a low availability of suitable locations for offshore wind in the proximity of the shore and in shallow waters, even when considering its multi-use with fisheries and protected areas. However, the areas within 100 km from shore and with a water depth above –120 m attract greater opportunities for both single use (only offshore wind farms) and multi-use (mainly with fisheries), from an integrated planning perspective. On the other hand, the decrease of energy targets combined with sectoral planning result in clear limitations to suitable areas for offshore wind farms, indicating the necessity to consider areas with a water depth below –120 m and further than 100 km from shore. Therefore, despite the increased costs of maintenance and design adaptation, the multi-use of space can be a solution for more sustainable, stakeholder-engaged and cost-effective options in the energy deployment process. This paper identifies potential pathways, as well as challenges and opportunities for future offshore space management with the aim of achieving the 2050 renewable energy targets.

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Objective Analysis of Corrosion Pits in Offshore Wind Structures Using Image Processing

Energies ◽

10.3390/en14175428 ◽

2021 ◽

Vol 14 (17) ◽

pp. 5428

Author(s):

Waseem Khodabux ◽

Feargal Brennan

Keyword(s):

Image Processing ◽

North Sea ◽

Water Depth ◽

Pitting Corrosion ◽

Offshore Wind ◽

Real Field ◽

Deterministic Models ◽

The North ◽

The North Sea ◽

Pit Depth

Corrosion in the marine environment is a complex mechanism. One of the most damaging forms of corrosion is pitting corrosion, which is difficult to design and inspect against. In the North Sea, multiple offshore wind structures have been deployed that are corroding from the inside out. One of the most notable corrosion mechanisms observed is pitting corrosion. This study addresses the lack of information both in the literature and the industry standards on the pitting corrosion profile for water depth from coupons deployed in the North Sea. Image processing was therefore conducted to extract the characteristics of the pit, which were defined as pit major length, minor length, area, aspect ratio, and count. The pit depth was measured using a pit gauge and the maximum pit depth was found to be 1.05 mm over 111 days of exposure. The goal of this paper is to provide both deterministic models and a statistical model of pit characteristics for water depth that can be used by wind farm operators and researchers to inform and simulate pits on structures based on the results of a real field experiment. As such, these models highlight the importance of adequate corrosion protection.

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Profiling Corrosion Rates for Offshore Wind Turbines with Depth in the North Sea

Energies ◽

10.3390/en13102518 ◽

2020 ◽

Vol 13 (10) ◽

pp. 2518

Author(s):

Waseem Khodabux ◽

Paul Causon ◽

Feargal Brennan

Keyword(s):

Corrosion Rate ◽

Field Experiment ◽

North Sea ◽

Water Depth ◽

Wind Farm ◽

Sea Water ◽

Offshore Wind ◽

Corrosion Condition ◽

The North ◽

The North Sea

Corrosion in the marine environment is a complex and expensive form of damage. It is commonly studied by the deployment of coupons that reflect the marine corrosion a structure will experience, thus allowing design and maintenance prevention strategies to be developed accordingly. This study stems from the lack of information in the literature regarding the profiling of corrosion with respect to marine depth in the North Sea where important wind farm developments have been undertaken. To address such issue a field experiment has been designed and carried out in the vicinity of the Westermost Rough Windfarm in the North Sea. The field experiment consists of deploying steel S355 coupons below the tidal area and capturing the effects of corrosion, the mass loss from which the corrosion rate is derived and the chemical products that makes up the rust with water depth. The study involves proper planning and logistics to ensure that the field experiment survives the rough conditions of the North Sea for a duration of 111 days. A high corrosion rate of 0.83 mm/year has been observed in this experiment. This paper goes into the details of the deployment blueprint employed and the analyses of the coupons to provide a conclusive observation and modelling of corrosion with respect to water depth under free or open sea water corrosion condition.

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