Seabed intervention

For more than 60 years, Jan De Nul Group has executed international dredging projects from start to finish, making it the ideal partner to execute offshore dredging services for the oil & gas industry, and for the offshore renewable energy market. Excavating trenches for submarine pipelines, backfilling trenches to protect pipelines, dredging subsea excavations for wellhead protection, and realizing shore approaches, including possible installation of a cofferdam and pipe pulling, aren’t holding any secrets for Jan De Nul Group.

To execute these dredging services the Group can rely on 28 Trailing Suction Hopper Dredgers with a hopper capacity varying from 2,320 m³ to 46,000 m³. These types of dredgers use a dynamic tracking system which allows the drag head to follow a predefined trench at low tolerances, resulting in minimum quantities being trenched at a lesser cost. The hoppers are able to dredge up to 155 m deep. For backfilling of trenches with sand and gravel, the dredge pipe can be used as a fall pipe.

To tackle the hardest and most difficult soil conditions during shore approach dredging, Jan De Nul Group can rely on 14 Cutter Suction Dredgers with a total installed diesel power varying up to 27,240 kW.  

The suitable equipment will be selected or can be adapted to meet the client’s demands.

Canada, Provision of White Rose Wellhead Excavation (SWRX)

Jan De Nul Group executed wellhead protection excavation for Husky Energy on the White Rose Project in Canada. The project was located approximately 200...

Jan De Nul Group executed wellhead protection excavation for Husky Energy on the White Rose Project in Canada. The project was located approximately 200 nautical miles south east of Newfoundland on the Grand Banks of the Atlantic Ocean. The excavations provide wellhead protection against iceberg scouring. Jan De Nul Group mobilized its Trailing Suction Hopper Dredger Vasco da Gama in 2003, at that time the world’s largest Hopper Dredger, to execute the first campaign. With a 9 m depth and dimensions of 50 X 60 m, this central excavation was the largest to be excavated. In 2012, Jan De Nul Group performed similar excavations with the current largest Trailing Suction Hopper Dredger in the world, Cristóbal Colón, equipped with two suction pipes for 155 m water depth.

Key figures
Country

Canada

Client's name

Husky Oil Operations Limited

Contractor's role

Main Contractor

Technical specs
Equipment

Trailing Suction Hopper Dredger Cristóbal Colón equipped in long configuration with two suction pipes capable of dredging up to 155 m water depth

Scope

Excavation of South White Rose Extension Glory Hole:
Water depth: 120.5 m LAT
Floor: 80 m x 45 m (depth 10.5 m)

Soil

Overlying sand layer with occasional sandstone hardpan on top of hard clay layer of up to 350 kPa and more, presence of glacial till, interbedding of numerous large to very large boulders (with largest dimension up to 4m)
and large clusters of boulders

Volume

102,627 m³ net design volume

Dredging depth

10.5 m deep i.e. up to 131 m LAT

Saudi Arabia, Manifa Field Causeway and Island Construction Project

The Manifa Field Causeway and Island Construction Project, covering a total area the size of Manhattan, is by far one of the most prestigious projects ever...

The Manifa Field Causeway and Island Construction Project, covering a total area the size of Manhattan, is by far one of the most prestigious projects ever realized in Saudi Arabia. The location on the east coast was complex where the shallow waters made it impossible to use common offshore oil drilling platforms to gain access. The solution was to reclaim an island at each drill site. Over a period of three years, 25 oil drilling and production islands each with space for ten drilling wells, and two water injection islands were designed and built. To connect these islands the contract included the design and construction of 41 km length of causeways, including fourteen bridges.

Key figures
Country

SAUDI ARABIA

Client's name

Saudi Arabian Oil Company (for IK contract)
Aramco Overseas Company B.V. (for OOK contract)

Contractor's role

Main Contractor

Period
February 4, 2007 to April 30, 2013

Papua New Guinea, PNG LNG EPC2 Offshore Pipeline Project

The PNG LNG Project was an integrated development that included gas production from operating fields in the Southern Highlands and Western Provinces of Papua...

The PNG LNG Project was an integrated development that included gas production from operating fields in the Southern Highlands and Western Provinces of Papua New Guinea. To build these facilities the installation of a 407 km long offshore pipeline was required. Jan De Nul Group was in charge of the 3 km trenching works at the landfall at Caution Bay, as well as the 52 km trenching works up to the landfall at the Omati River, located approximately 24 km up river from the Gulf of Papua. 

Key figures
Country

Papua New Guinea

Client's name

ExxonMobil / Esso Highlands Ltd

Contractor's role

Subcontractor to Saipem

Period
June 18, 2013

Sweden, Karehamn Wind Park

For the Karehamn offshore wind farm in the Swedish part of the Baltic Sea, 16 foundations were required for the 3 MW turbines. Jan De Nul Group was awarded the...

For the Karehamn offshore wind farm in the Swedish part of the Baltic Sea, 16 foundations were required for the 3 MW turbines. Jan De Nul Group was awarded the design, construction and installation of these foundations.

All foundations were constructed on top of two large barges in the port of Zeebrugge (Belgium) in over a period of only 5 months. Because of the varying water depths in the Baltic Sea, the height of the cylindrical part had to be uniquely designed. The height of the elements ranges from 15 to 25 m with the heaviest element weighing approximately 1,940 tons.

The seabed had been prepared before installation of the foundations.
The first half a meter of the seabed was removed.  In order to provide an even cushion layer for the foundations, a gravel layer was installed. To level the cushion layer, a levelling system has been developed by means of a levelling beam installed on the Cutter Suction Dredger Vesalius. This allowed for gravel bed foundation to be levelled within the design tolerances of 45 mm.

With the gravel bed installed and levelled, the Heavy Lift Vessel Rambiz lifted the foundations off the barges and installed the foundation to within 30 cm of the theoretical position.

After installation, they were ballasted so they could withstand the forces of waves and currents and carry the actual wind turbine. 

The shaft of the foundation was filled with magnadense crushed iron ore. The other compartments were filled with crushed iron ore, and finally a layer of heavy quarry stone was placed as a top capping layer in order to provide scour protection.

Stones of up to 130 kg were placed in the ballast caissons by means of the inclined fall pipe of the vessel Simon Stevin positioned in DP2 mode. To prevent the gravel bedding layer from being washed away, an anti-scour quarry stone layer was installed around the external edge of each foundation.

Key figures
Country

Sweden

Client's name

E.ON Vind Sverige AB

Contractor's role

EPC Contractor

Period
September 7, 2011 to April 21, 2013
Technical specs
Scope

Engineering, procurement, construction and offshore installation of 16 concrete gravity based foundations for Vestas V112 wind turbinegenerators. The foundations were poured on barges after which they were installed. The seabed had been excavated and a gravel bed been installed. Subsequently these foundations are protected from seabed erosion by means of scour protection. Heavy fill ballast such as iron ore is installed in the shaft and ballast bins. Appurtenances (J-tubes, ladders, handrails, etc) were included in the design.

Soil

Clay and sand overlaying bedrock

Volume

10,000 m³ of reinforced concrete
2,000 ton weight of GBF
5,000 m³ of seabed excavation works and gravel bed
7,000 m³ of scour protection outside GBF
50,000 ton heavy ballast fill, includes 25,000 ton iron ore based fill

Dredging depth

8 m – 21 m

Equipment

Multipurpose spudpontoon DN109, Levelling vessel Vesalius, HLV Rambiz, Transport barge DN143 (DWT 24,000 tonnes), Transport barge DN120 (DWT 10,000 tonnes),
4 Towercranes (Civil Works), 2 Mobile cranes (Civil Works)
Truck mixers & concrete pumps (Civil Works)

UK, Langeled Pipeline Project

To meet the growing energy requirements of the United Kingdom a new offshore pipeline from Norway’s gas-rich fields to the eastern coast of the UK was laid. The...

To meet the growing energy requirements of the United Kingdom a new offshore pipeline from Norway’s gas-rich fields to the eastern coast of the UK was laid. The 44inch diameter pipeline crosses 1,200 km, making it the longest offshore pipeline ever built. Jan De Nul Group executed the shore approach and landfall works and was responsible for the offshore dredging and rock placement. The offshore trench, some 20 km long and 1.5 to 2 m deep, was excavated using the Cutter Suction Dredger J.F.J. De Nul in boulder clay. The backfilling of the trench was performed using the Trailing Suction Hopper Dredger Filippo Brunelleschi, which also carried out the pre-sweeping of the offshore sand dunes.

Key figures
Country

United Kingdom

Client's name

Statoil S.A. on behalf of Norsk Hydro as operator

Contractor's role

Main Contractor

Period
August 1, 2004 to February 28, 2006
Technical specs
Scope

Civil Works: Microtunnelling and pipeline installation
Dredging Works: Dredging, backfilling and pre-sweeping

Soil

Civil Works: Hard clay
Dredging Works: Hard clay and boulders

Dry (earth) works

Onshore pipeline installation

Volume

Civil Works: Microtunnel: 380 m; Cofferdam: 220 m
Dredging Works: Volume dredged: 880,000 m³; Volume pre-sweeping: 250,000 m³; Volume rock-dumping: 37,000

Dredging depth

25 m with CSD and 70 m for pre-sweeping

Equipment

J.F.J. De Nul
Filippo Brunelleschi
Civil Works Equipment

Norway - France, Norfra Pipeline Installation Project

In the 90s Norway and France entered into an agreement to transport natural gas from...

In the 90s Norway and France entered into an agreement to transport natural gas from Draupner to Dunkirk. As a result, the NorFra transportation system was planned. This 42 inch diameter, 835 km long, high pressure natural gas pipeline was laid from the Draupner E platform in the Norwegian Continental Shelf to the Northern coast of France. Four separate dredging packages were tendered for this project and a combined contract was awarded to Jan De Nul Group. The total dredging scope involved offshore pre-sweeping of sand dunes on the seabed over a distance of 230 km, pre-trenching in stiff clay at the location of the crossing of the Westhinder Shipping Lane, and dredging, backfilling and civil works related to the shore approach, beach crossing and pipe pull at Dunkirk.

Key figures
Country

Norway - France

Client's name

Statoil for a Consortium including Statoil, Norsk, Hydro, Saga Petroleum, Esso, Mobil, Total, Elf, Agip, Shell, Neste Petroleum and Conoco

Contractor's role

Main Contractor (Part JDN: 100%)

Technical specs
Equipment

TSHD Gerardus Mercator, TSHD Galilei 2000, TSHD Amerigo Vespucci, TSHD Cristoforo Colombo, CSD Marco Polo with TSHDs Niña & Pinta

Soil

Sand, clay, gravel

Volume

2,000,000 m³ land fall dredging and 5,000,000 m³ presweeping

Scope

Cofferdam installation: Length 520 m and width 6 m
Presweeping in the offshore sector
Landfall at Dunkirk (dredging, backfilling, civil works)
Dry (earth) works
Landfall cofferdam installation: length 520 m, width 6 m

Dredging depth

0 to 45 m