Recent OES Post Trenching Projects

The following is a brief description of the most recent post trenching projects successfully completed by OES.

2012     GHANA EARLY PHASE INFRASTRUCTURE PROJECT, WEST AFRICA
2012     HADERA GAS PIPELINE PROJECT, ISRAEL
2012     AYER CHAWAN BASIN PIPELINE DIVERSION PROJECT, SINGAPORE
2011-2012     SHIPBUILDING 'BORNEO PRINCESS', INDONESIA
2010     ANGOLA LNG PROJECT, ANGOLA
2008     KURNELL TO BUNNERONG CABLE INSTALLATION PROJECT, AUSTRALIA
2008     UJUNG PANGKAH PROJECT, INDONESIA
2007     VISCAS WANDO PROJECT, KOREA
2007     IOCL – PARADIP TERMINAL, INDIA
2007     ONGC – GRID CONNECTIVITY PROJECT, INDIA
2007     SOUTH SUMATRA / WEST JAVA PROJECT , INDONESIA
2007     TURKEY GREECE PIPELINE PROJECT, TURKEY
2006     TOREADOR PROJECT, TURKEY
May 2005     PTT THIRD TRANSMISSION PROJECT, THAILAND
Mar 2006     TOWNGAS TWIN PIPELINES PROJECT, HONG KONG
Nov 2005     TNC PROJECT, BRASIL
Apr 2005     GAPL SPM Pipeline Project, India. 2005
Sep 2003 - 2004     NUBI RIVER CROSSING, TOTAL INDONESIE, INDONESIA
Jul 2003     SHELL GOLDENEYE AND BRITISH GAS ATLANTIC CROMARTY SHORE CROSSINGS,VOACZ, SCOTLAND
Jun 2003     DF1-1 PROJECT, COOEC, CHINA
Aug 2003     GUANABARA BAY, PETROBRAS, BRAZIL
Aug 2002     ESSO PIPELINE, BASS STRAIT, AUSTRALIA, ALLSEAS
Jul 2002     DUKE ENERGY PIPELINE, BASS STRAIT, AUSTRALIA, ALLSEAS
May 2001     PETROBRAS MARLIN SUL/ RONCADOR SHORE CROSSING, BRASIL
May 2001     CABOT PIPELINES PROJECT, MALAYSIA, CABOT
Aug 2000     CANTARELL NITROGEN PROJECT, MEXICO, GLOBAL OFFSHORE
Jan 2000     TUNU 6, INDONESIA, PTK, TOTAL INDONESIE
Jan 2000     PETROBRAS MARLIN SUL/RONCADOR, BRAZIL
Sep 1999     PECIKO 42” NS RIVER CROSSINGS, PTK, TOTAL INDONESIE
Aug 1999     16” NS PIPELINE REPAIR REBURIAL, PTK, TOTAL INDONESIE
Jun 1999     PECIKO 24” NS SHORE CROSSING, SAIPEM/ PTK, TOTAL INDONESI
Apr 1999     SHELL TERMINAL LANKA, GEOCEAN, SRI LANKA
Apr 1999     ESSO BLACKBACK, BASS STRAIT, CSO, AUSTRALIA
May 1998     EFFLUENT OUTFALL PROJECT, PUNJ LLOYD Ltd, DAHEJ, INDIA
May 1998     PINGHU PROJECT, SAIPEM/EMC JV, CHINA
Oct 1997     SABAH GAS PIPELINE, SABAH, SMIT INTERNATIONAL, MALAYSIA
Jun 1997     LANGKAWI ISLAND WATER SUPPLY PIPELINE, IPCO-ASAL, MALAYSIA
Apr 1997     ONGC HRG HX/HY PIPELINES, BRESWATER MARINE CONTRACTING BV, INDIA
Mar 1997     ONGC, B173-A WELL PLATFORM PIPELINE, INDIA, LARSEN & TOUBRO
Jan 1996     ARAMCO, JIZAN PROJECT, SAUDI ARABIA, McDermott - ETPM East Inc.
1995     ONGC, SBHT GAS PIPELINE SHORE CROSSING, UMBRAT BEACH, INDIA
1993     BONGKOT GAS PIPELINE, THAILAND, STOLT COMEX SEAWAY
      OTHER PROJECTS

2012 GHANA EARLY PHASE INFRASTRUCTURE PROJECT, WEST AFRICA

EPC contract awarded to OES by Micoperi for the project which includes the shore approach installation and the post lay trenching works on the 12” Jubilee Gas Export pipeline. (Current)

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2012 HADERA GAS PIPELINE PROJECT, ISRAEL

Post trenching and Backfill of 8.2 KM X 20" NS concrete coated pipeline in Israel for Hadera Gas Pipeline project using the OES trenching machine “White Jaguar” and backfill sled “John Cat”. The operations are carried out using a DPDSV in up to75m water depths using the OES clump weight system.

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2012 AYER CHAWAN BASIN PIPELINE DIVERSION PROJECT, SINGAPORE

World's first, De-burial of a 48" Pipeline from 8m below the seabed in silty sands overlying very hard clays. OES High pressure Jetting system is used to perform the de-burial and the pipeline floated and towed to shore for disposal. OES 'Bengal Tiger' trenching machine with Overboard Dump system is used to create a wide and deep trench.

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2011-2012 SHIPBUILDING 'BORNEO PRINCESS', INDONESIA

Design and construction of OES 'Borneo Princess' a leisure/work vessel at OES marine base in Balikpapan Indonesia. This boat is 24m long and 9 m Beam and catamaran hull with options of a 160' Sail Mast or a 10t crane. The boat is also equipped with 2 X 450 HP Main engines and 12 people?s accommodation. The designs were done by OES and approved by ABS.

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2010 ANGOLA LNG PROJECT, ANGOLA

Trenching three pipelines which were 18", 22" and 24" 1m TOP below the seabed. The soils consisted of Cemented sand and soft rock. The OES innovative rock trenching machine OES 'Tiger Shark' was used for this project and the scope of work successfully completed operating this system off a DP vessel. OES provided all of the Jetting pumps including hydraulic power packs, mechanical trencher 'Tiger Shark', Heave compensator, onsite operation, supervision and engineering.

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2008 KURNELL TO BUNNERONG CABLE INSTALLATION PROJECT, AUSTRALIA

EPC contract for laying 2 x 132 KVA feeder systems comprised of 6 x 5.5” power cables and 2 x fibre optic cables across Botany Bay including the directional drilling of 7 shore approaches through rock in Sydney for Energy Australia (currently in progress).

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2008 UJUNG PANGKAH PROJECT, INDONESIA

Turnkey post trenching of 1 x 18” and 1 x 20” world’s first live gas pipeline trenching using the OES catamaran barge ‘Buaya Besar’ and OES ultra shallow water trenching system.

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2007 VISCAS WANDO PROJECT, KOREA

Hae Chun with Equipment design /trenching for VISCAS –Wando of 2 x 5” Submarine cables with articulated pipe coverings in Korea.2007.

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2007 IOCL – PARADIP TERMINAL, INDIA

EPC contract for the engineering, procurement, construction procedures associated with a 48” N.S. pipeline PLEM, SBM, installation including laying 3 km of 14” N.S. effluent pipeline.

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2007 ONGC – GRID CONNECTIVITY PROJECT, INDIA

Consortium partnership with Naftogaz for an EPC contract to design and install 52 offshore Oil and Gas platform electrical substations, subsea risers, platform structural extensions and lay 26 subsea cables.

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2007 SOUTH SUMATRA / WEST JAVA PROJECT , INDONESIA

Post-trenched 15km of 32” pipeline in very hard soils using OES high pressure system.

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2007 TURKEY GREECE PIPELINE PROJECT, TURKEY

18 kms of 2” fibre optic cable laying/trenching, pipeline span stabilization, trenching 6 kms and shore approach installation of 36” pipeline in the Marmara Sea.

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TOREADOR PROJECT, TURKEY

  • 12km of 1 x 12” Shore Approach
  • 1m TOP
  • Sandy Soils
  • Near shore to 60 meter water depth in Black Sea, Turkey utilizing a moored ship.
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PTT THIRD TRANSMISSION PROJECT, THAILAND

  • 70 km of 1 x 42” NS
    Plus pre-lay
    span rectification
    (dredging)
  • 1m TOP/2.3m TD
  • Hard clay to 300 kPa
  • Used two DP vessels, high pressure, new machine design, backfill sled, 70 km

PTT Third Transmission Project – Thailand, 2006 Turnkey EPC contract for the trenching of 70 km of 42” NS pipeline to 1 meter TOP using two DP vessels, a high pressure spread and new backfill sled machine design in hard clays up to 300 kPa. Included pre-lay span rectification (dredging).

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TOWNGAS TWIN PIPELINES PROJECT, HONG KONG

  • 2 x 18” NS Twin 50 kms
  • 3m TOP/3.6m TD
  • Soft Clays
  • Two Pipelines trenched together 300mm apart.

Towngas Twin Pipelines Project – Hong Kong, 2006 EPC contract for the “world’s first” trenching of two 18” NS twin pipelines together, 300 mm apart in soft clays to 3 meters TOP

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TNC PROJECT, BRASIL

  • 2 x 16” NS
    1 x 12”NS
  • 1.2 m TOP
    1.8m TD.
  • Sands, Soft clays and very Hard Clays
  • Shore approach installation and HDD Exit stress rectification, trenching and backfill.

Petrobras – TNC Project – Brasil, 2005 EPC contract for shore approach installation the trenching of two 16” and one 12” NS pipelines in sands, soft clays and very hard clays to 1.2 metres TOP. Also included HDD exit stress rectification and back fill.

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GAPL SPM Pipeline Project, India. 2005

  • 1 x 48” NS
  • 1m TOP
  • Soft Clays, Sections with very hard shelly clays
  • 6m tidal range and strong currents

Adani Port - GAPL SPM Pipeline Project – India, 2005 EPC contract for the trenching one 48” NS pipeline in soft clays (some sections with very hard shelly clays) to 1 meter TOP in 6 meter tidal range and strong currents.

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NUBI RIVER CROSSING, TOTAL INDONESIE, INDONESIA

This project consisted of completing the trenching not able to be done by others on the river bank approaches on both sides of the Nubi River. The OES trenching machine was used to dig down 4 meters in the sandy/silty soils at the HDD exit to the pipeline, uncover it and then trench it down to the required TOP and within the stringent out of vertical straightness tolerances. OES used its catamaran trenching barge “Buaya Besar” which was able to access the very shallow areas at high tide and perform the difficult trenching work. The trenching was successfully completed within schedule in September 2003. OES provided the complete trenching, marine, diving and survey spreads.

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SHELL GOLDENEYE AND BRITISH GAS ATLANTIC CROMARTY SHORE CROSSINGS, VOACZ, SCOTLAND.

This project was successfully completed in July 2003. The trenching was considered complex due to both pipelines carrying piggybacks, the potentially harsh environment north of Aberdeen, the difficult soils consisting of sands, hard clays, rocks and cobbles up to 200mm in size and that previous jetting work by others on pipelines in the area were not very successful. A large amount of detailed planning went into the project. The 18”/6” and 20”/4” piggybacks were fitted in a special sheath designed specifically for the OES bi-directional “Sumatran Tiger” trenching machine to roll on. OES provided both low and high pressure jet pumps up to 1,000 psi) to accommodate the soils. Van Oord ACZ provided the “Manta” barge which was excellent for the harsh environment. Both pipelines were trenched in the first section to 2 meters TOP and to 1 meter TOP in the second section. Of note was that the trenching was diverless.

The work was a huge success with the trenching being completed well ahead of schedule. This was mainly due to the excellent equipment preparation and performance and teamwork of OES and Van Oord ACZ.

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DF1-1 PROJECT, COOEC, CHINA

The 22” NS DF1-1 pipeline trenching was performed in water depths ranging from 10 to 72 meters. Part of the work was from a derrick barge in shallow water and the rest from the DP vessel “Fu Lai”. The OES proprietary clump weight system was used for the deeper waters from the DP vessel. The soils were very hard and the trenching concentrated on some 30 groups of spans requiring correction. Once again the trenching was done diverless and ROV free. The trenching was successfully completed in June 2003. OES provided the complete trenching spread.

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GUANABARA BAY, PETROBRAS, BRAZIL

OES has developed a Minimum Pipeline Risk Trenching System (MPRTS) for Petrobras in Guanabara Bay, Brazil, which was used to successfully trench four worlds first zigzag pipelines. The 18” zigzag pipelines are shallow water oil lines laid in a zigzag pattern with 10 degree radius bends to reduce thermal growth and upheaval buckling. They were trenched to 1 meter TOP.

Previous damage to existing oil lines by others and consequential environmental damage has promoted Petrobras to adopt a new upheaval proof pipeline design and also have OES design and operate an MPRTS. The MPRTS consists of a small 25 metre length light draft catamaran barge, “Grand Jacare” owned by OES, that moors to the pipeline fore and aft does not normally use anchors or anchor handling vessels which propose significant risks to existing pipelines.

The OES “White Jaguar” machine was used with some minor modifications to rollers to allow it to negotiate the many 10 degree bends. OES provided the complete trenching, marine spreads and shallow water pipeline tow & tie-in assistance.

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ESSO PIPELINE, BASS STRAIT, AUSTRALIA, ALLSEAS

OES has successfully completed trenching the Esso 11.8 km 14” NS pipeline to 0.5m TOP. The work also includes trenching the HDD exit down to depth. The work was performed from the DP Vessel “Searanger”. Soils are mainly sand though there are sections of cemented sands, calcarenite and coral. The trenching work was completed ahead of the scheduled trenching time.

OES provided the complete trenching spread, trenching supervisors and operators/ mechanics. The same diverless system was used for the Duke project below.

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DUKE ENERGY PIPELINE, BASS STRAIT, AUSTRALIA, ALLSEAS

OES has successfully completed the trenching the Duke Energy 3.5 km 14” NS pipeline to 0.6m TOP. The work also included trenching the HDD exit down to depth. The work was completed from the DP Vessel “Searanger”. A minimum of two passes was required due to pipeline trenching stress requirements. The soils were mainly sand though in a few locations, cemented sands and coral were encountered. Even though the trenching spread was not set up for the harder soils, two additional passes on these short sections achieved the required trench depth. The trenching work was completed ahead of the scheduled trenching time.

OES provided the complete trenching spread, trenching supervisors and operators/ mechanics. This project was the world’s first diverless, ROV free deployment, trenching by jetting machine. Acoustic scanners were used to locate the pipeline and place the machine.

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PETROBRAS MARLIN SUL/ RONCADOR SHORE CROSSING, BRASIL

The project was successfully completed in May 2001 and consisted of trenching the 20” pipeline shore crossing to 2.3 metres TOP (3 metres trench depth). The scope included the shore approach installation and trenching up to 40 metres up the beach above the waterline in rough seas of up to 4 metres breaking on the shore.

During the planning stage, Petrobras reviewed various options to trench or stabilize the inshore works and shore crossing, but no European or American contractor would take on the project as a lump sum. The option to directionally drill a second pipeline adjacent to the first out through the surf zone and then do a subsea tie-in to the existing line was seriously considered. In previous years, cofferdam methods of construction had failed in heavy seas. The technical feasibility was in doubt and the cost would have been an order of magnitude greater than post trenching.

OES responded to the challenge and provided a lump sum turnkey price. The site environment was very difficult being isolated, very exposed to the Atlantic Ocean with large swells up to 4 metres that could quickly blow up, very mobile sands (active beach) and 8 metre high sand dunes onshore.

OES incorporated several new innovations into its tried and proven operating methodology. The bi-directional “White Jaguar” trenching machine was used to trench in towards and away from the beach, lowering the pipeline on successive passes. The active sands and waves resulted in almost immediate trench backfill and at times only the top third of the trenching machine was visible above the sand during trenching operations. The good team effort of all involved resulted in the crossing being generally completed within schedule and to the required trench depth.

OES provided the complete Shore Pull assistance, trenching spread, trenching supervisors and operators/mechanics and assisted with the marine, diving and survey spread operations. Back to the top

CABOT PIPELINES PROJECT, MALAYSIA, CABOT

This project consisted of trenching two parallel pipelines (20” and 10” of between 3 and 11 metres separation) to 1.5 metre, 0.75 metre and 0.5 metre TOP at different locations along their 6.5 km route from shore to an SBM. The pipelines had been in operation for two years but had significant stability problems and spanning that was not resolved via alternative stabilization methods. The decision was made to post trench between tanker off-loadings, thus creating a fixed working window. Soils varied along the route between sand and hard clays to 80 kPa undrained shear stress, water depths ranged from 6 to 35 metres and currents up to 5 knots. Previous stabilization work including sand and grout bags, gravel and other items had to be removed as part of the scope. Even though on day rates due to the difficulties involved, the project has been achieved in record time and less than the envisioned schedule. Of note is the team effort of all involved. The project was successfully completed in December 2000.

OES provided the trenching spread, trenching supervisors and operators/ mechanics.

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CANTARELL NITROGEN PROJECT, MEXICO, GLOBAL OFFSHORE

This project consisted of trenching two 48” NS and one 42” NS pipelines to one metre TOP in sands in shallow waters from the shore out to the 6.5 km mark in the Gulf of Mexico and was successfully completed on schedule in August 2000.

The original pre-dredging was only partially successful. OES was called in when other systems proposed to rectify the problem were deemed not suitable. This was especially so for sled based machines which could not handle the very close proximity of the pipelines (spaced only approximately 2 metres apart) and which had difficulty spanning the very wide “V” shaped trench required in sands.

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TUNU 6, INDONESIA, PTK, TOTAL INDONESIE

This project consisted of the trenching of two 24” NS, one 20” NS and four 8”+1” (piggyback) NS pipelines associated with the new Tunu 6 field and was completed in early 2000.

Most pipelines were to be trenched to a 2.0 metres minimum cover with extra cover to 2.5 metres required at the drill rig crossing locations.

The Tunu 6 pipelines were all trenched without any major problems. The Tunu 6 pipes are world’s first pipelines to be trenched to such a very stringent out of vertical alignment tolerance (for some pipelines, 12cm over 50 metres) in an effort by Total to eliminate upheaval buckling which has caused many high temperature pipelines in the area to push up out of the seabed. OES achieved the tolerances required and apart from working in the shallow water inter-tidal areas in which there was a lot of waiting for high tide, progress went very well.

OES provided the expertise, subsea trenching spread including the “Arabian Leopard”, and “Tasmanian Tiger” trenching machines, including all pumps, ancillary equipment and supervisory personnel.

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PETROBRAS MARLIN SUL/RONCADOR, BRAZIL

This project was successfully completed in January 2000 and consisted of the post trenching of 20 kilometres of 20” NS pipeline to 1 metre cover, from near the shoreline out to 20 metre water depth. The area is characterized by very mobile loose sands and a very active wave climate with 3 to 4 metre swells and regular 35 knot winds.

The pipeline was trenched off a DP vessel. The trenching machine used is the innovative lead keel bi-directional “White Jaguar” which is capable of trenching towards shore or away from shore.

OES scope of work included the supply of the trenching spread, trenching supervisors and operators/mechanics.

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PECIKO 42” NS RIVER CROSSINGS, PTK, TOTAL INDONESIE

This project was successfully completed in September 1999.

Two crossings of 1.3 km (Sanga Sanga) and 0.8 km (Dondang) were post trenched. The minimum top of pipe was 2.5 metres which, combined with the 48” OD concrete coated pipe, gave trench depth of 3.8 metres - water depths ranged to 15 metres CD.

The permanent pipeline stress profile in conjunction with the irregular river bed profile resulted in some areas of the 1.3 km Sanga Sanga crossing to be trenched to 5 metres top of pipe (6.3 metres trench depth) - an extraordinary achievement considering the 3 to 4 knot tidal currents, zero visibility and extensive debris including trees up to 1m diameter caught under the pipe. The Sanga Sanga river is used by ocean-going vessels which restricted the trenching operations. Trenching to 7.8 m trench depth is considered to be a world’s first.

Both rivers were trenched simultaneously due to schedule requirements. OES provided two trenching spreads, trenching supervisors and operators/mechanics.

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16” NS PIPELINE REPAIR REBURIAL, PTK, TOTAL INDONESIE

This project involved the replacement and reburial of a section of pipeline that had risen above the seabed and sea level due to upheaval buckling.

The OES spread was used to retrench the pipeline to 2 metres top of pipe over approximately 600 metres with controlled transitions up to the original 1 metre top of pipe existing pipeline.

The replacement pipe section, being longer than the original, was re-laid in a partial loop. The OES trenching machine readily handled the curved pipeline section.

This project was successfully completed in August 1999. OES scope of work included the supply of the trenching spread, trenching supervisors and operators/mechanics

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Peciko 24” NS SHORE CROSSING, SAIPEM/ PTK, TOTAL INDONESIE

This project was successfully completed in June 1999.

The project involved the post trenching of two parallel 24” NS concrete coated pipelines of approximately 5.6 metres top of pipe out to water depths of minus 13 metres CD to 2.5m TOP. Soils ranged from sandy clays to soft clays. Unique to this project was trenching through 0.5 km of a previously unknown old dead coral bed in the inter-tidal zone. The coral was mainly in small football-sized lumps that were readily removed by the trenching machine’s eductor system. Littoral drift was high, resulting in significant trench backfill between passes. The OES trenching machine removed the backfill whilst making the new trench.

OES scope of work included the supply of the trenching spread, trenching supervisors and operators/mechanics.

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SHELL TERMINAL LANKA, GEOCEAN, SRI LANKA

This project was successfully completed in April 1999 and consisted of the post trenching of 3 kilometres of 10” NS pipeline from a Single Buoy Mooring (SBM) to shore. The OES “Tasmanian Tiger” was used.

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ESSO BLACKBACK, BASS STRAIT, CSO, AUSTRALIA

This project consisted of the development and operation of an innovative deep water trenching sled -the “Tiger Prawn II” - capable of trenching a flexible flow line with rigid “piggy back” control line attached to 1 meter cover in very loose sands and silts in 100 to 400 metre water depths off a DP vessel.

OES was approached and given 8 weeks to design, build and test a system. OES accepted the challenge. The pipeline could not be trenched with OES lead keel equipment which rolls on the pipeline because of the “piggy back” configuration, and so a sled concept was used.

The OES “Tiger Prawn I” (TPI) sled which was designed for cables and flexible flow lines could not be used as the Blackback umbilical was too rigid and could not be deflected in the TPI deflector shroud. A new wider sled then was necessary that treated the umbilical like a rigid pipeline, in that all the soils under the pipeline needed to be excavated.

Normal surface-supplied water from pumps located on the ship could not be used as the water depths were too deep, which would create excessive water pressure drop in the hoses in addition to extensive current loadings on the hoses. Submersible pumps were then decided on, and stainless steel bore hole pumps which had a proven track record were used. Electric motor drivers were considered, but hydraulic drive was opted for on the basis of cost, maintenance and safety. In addition, OES owns the largest hydraulic power pack (350 kw) in Australia which was used to power their “Mad Max” machine.

Water eductors for sand removal were used which although not energy efficient are used quite successfully on all the other shallow to moderate water depth OES trenchers.

Another feature of TPII was combination ballast tank/sled skids that could be deballasted with pressurized air to reduce sled weight and seabed friction. A subsea pressure gauge panel monitored sled/umbilical interaction loads, pump pressures and sled inclination. This was monitored by a simple video camera and relayed to the surface. A work class ROV was used for hydraulic operation of depth of cut, deballasting operation and trench and sled inspection.

Some of the soils encountered were very soft silts with a very shallow angle of repose and were found to slough into the trench immediately after passage of the sled skids caused by released pressure on the seabed and consequent liquefaction of the seabed. The sled skids also interfered with the removal of the soils by the jets as sand built up on the inside of the skids.

What OES learned on the project was:

  • the concept of hydraulic-driven subsea pumps for deep water is very effective;
  • there are even more problems with jet sleds in sands for rigid pipeline than OES already understood;
  • the soil eduction system can be increased 100% capacity by the use of double volute/double intake centrifugal pumps instead of the inefficient water eduction;
  • combined with the existing OES lead keel system, the addition of a) and c) above will yield a very good deep water rigid pipeline trenching system.
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EFFLUENT OUTFALL PROJECT, PUNJ LLOYD Ltd, DAHEJ, INDIA

This project was successfully completed in May 1998.

The project involved post trenching the IPCL Effluent Outfall in Dahej, India. The 20" NS pipeline was post trenched to 2.2 ms trench depth across the intertidal zone. Water depths ranged from 0-15 m LAT. The tidal range was 10 m with the barge high and dry at low water. Currents were estimated to be up to 11 knots perpendicular to the pipeline. Soils consisted of cohesionless sands.

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PINGHU PROJECT, SAIPEM/EMC JV, CHINA

This project was successfully completed in May 1998. OES was called in to post trench after extensive efforts were expended attempting to pre-trench.

The project involved the post trenching of two shore crossings, being 1.1 km of 14" NS and 2.6 km of 10" NS pipelines. Currents were up to 6.8 knots perpendicular to the pipelines, the water depths ranged from 0-15 metre LAT and the trench depth was 3 m. Soils ranged from cohesionless sands through to stiff clays. The operating environment was extremely difficult. The trenching machine had to dig down to expose the pipeline at the beginning of each pass. The success of the project was due to the ability of the OES machine to operate in strong currents, evacuate the trench and to clear littoral drift infill whilst making new trench at the same time on each pass. OES scope of work included the supply of the trenching spread, trenching supervisors and operators/mechanics.

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SABAH GAS PIPELINE, SABAH, SMIT INTERNATIONAL, MALAYSIA

This project was successfully completed in October 1997. OES was called in to post trench after the previous contractor was unsuccessful.

The project required the post trenching of 1.6 km of 16" NS pipeline in sands (cohesionless soils) in the surf zone. The trenching machine had to dig down approximately 4 m to expose the pipeline at the required starting point. Currents ranged from 5-6 knots in 0.3-15 metre water depths. Trench depths of 3.5 m were required. At points, the trench width at the seabed reached 20 metres. Success of the project was largely attributed to the OES eductor system that deposited sand far away from the trench and prevented rapid infill. OES scope of work included the supply of a trenching spread, trenching supervisors and operators/mechanics. The project was completed within schedule and budget to the satisfaction of the Client.

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LANGKAWI ISLAND WATER SUPPLY PIPELINE, IPCO-ASAL, MALAYSIA

This project was successfully completed in June 1997.

The project involved the installation of a 35 km long subsea potable water pipeline between Langkawi Island and the Malaysian mainland, with two shore crossings. The steel pipeline is 28" NS with an external concrete weight coat and internal concrete lining. The total length to be post trenched was 10 km, comprising of 5 km at each end. The minimum required cover was 1 m (ie a 1.9 m trench depth). As required by the client, OES's scope of work included the supply of a trenching spread, a barge spread, a diving spread and all trenching and diving personnel. The barge was a catamaran type suitable for very shallow waters. The project was completed within schedule and budget to the satisfaction of the Client.

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ONGC HRG HX/HY PIPELINES, BRESWATER MARINE CONTRACTING BV, INDIA

This project was successfully completed in April 1997.

Two 12" NS concrete coated pipelines (1 off 6 km & 1 off 6.9 km long) were post trenched by OES. The minimum depth of cover was 1.2 m (ie 1.9 m trench depth) for the required full lengths between three offshore platforms. The trenching works were performed from the DP vessel "Rockwater 2" in 48-65 m water depth. Thirteen pipeline crossings with twelve transitions were involved in this project. Average trenching speeds were slower than 26 km long, 6" NS concrete coated pipeline was trenched for the required full length between two offshore normal due to the high number of crossings, but when possible, rates of up to 3 km/day were achieved. Parts were done in a single pass and others, in harder soils, were done in two passes. OES's scope of work included the supply of a trenching spread, trenching supervisors and operators/mechanics. The project was completed within schedule and budget to the satisfaction of the Client.

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ONGC, B173-A WELL PLATFORM PIPELINE, INDIA, LARSEN & TOUBRO

This project was successfully completed in March 1997.

A 26 km long, 6” NS concrete coated pipeline was trenched for the required full length between two offshore platforms. The required pipeline depth of cover was 1.2 m (ie a trench depth of 1.5 m) which was achieved in a single pass. Trenching was performed from the DP vessel "Rockwater 2" in 48-55 m water depth. Three cable crossings were involved in this project. The maximum shear strength of the clays measured during trenching was 38 kPa. Average trenching speeds of 2-3 km per day were achieved. The longest trenched length made in one day was 4.05 km. OES's scope of supply was a trenching spread, trenching supervisors and operators/ mechanics. The project was completed within schedule and budget to the satisfaction of the Client.

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ARAMCO, JIZAN PROJECT, SAUDI ARABIA, McDermott - ETPM East Inc.

The project was successfully completed in late 1995/early 1996.

This project consisted of two 24" NS, 3.5 km long shore crossings, two 12" shore crossings and four SBM pipelines to 1.5 m cover. OES worked from the McDermott barge. The shore crossings involved the use of a pontoon barge which was pulled between the shore and the McDermott barge moored offshore. Multiple passes were used. OES scope of supply was the trenching spread, trenching supervisors and operators/mechanics. The project was completed within schedule and budget.

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ONGC, SBHT GAS PIPELINE SHORE CROSSING, UMBRAT BEACH, INDIA

This project was successfully completed in 1995.

The shore crossing consisted of post trenching a 42"NS (54" OD) with a concrete coating, to 4 m cover in sand and some hard clay. This was considered a "World's First" achievement. A flat bottom barge was used to allow trenching either side of high tides in a region where the tides ranged 8 metres. Multiple passes were used. OES scope of supply was the trenching spread, trenching supervisors and operators/mechanics. The project was completed within schedule and budget.

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BONGKOT GAS PIPELINE, THAILAND, STOLT COMEX SEAWAY

This project was successfully completed in 1993.

Thirty five kilometres of 30" concrete coated pipeline was trenched to 2 metre cover in a single pass. Soils varied in shear strength from 15-80 kPa. The water depth was 35 m. OES used a high pressure pump arrangement for this job. Trenching speeds of up to 3.8 km/day was achieved in softer soils with an average rate of 1.6 km/day. OES's scope of supply was the trenching spread, trenching supervisors and operators/mechanics. The project was completed within schedule and budget.

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OTHER PROJECTS

In addition to the above, OES personnel have performed trenching of over 70 pipelines with the following equipment:

  • HeereMac Deep Water Jet Machine, New Zealand.
  • OES Rock Trenching Machine, Australia.
  • Bond Petroleum Lenita Field Plough, Australia.
  • Woodside Offshore Petroleum Plough, Australia.
  • ETPM Deep Water Jet Sled, North Sea.
  • Martech Self-Propelled Jet Machine, USA.
  • Norman Industries Jet Machine 12' to 30", USA
  • Norman Industries Jet Machine 4" to 12", USA.
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