Offshore Construction Specialists (OCS)

    PIPELINE POST TRENCHING

    OCS maintains a robust inventory of  pipeline post trenching equipment and is continually upgrading. The key to efficient post trenching operations is to provide a well designed jet sled with an effective deployment and recovery system and efficiently deliver large volumes of  high pressure water and air.

    OCS has pipe riding and articulated pontoon jet sled configurations and has executed many pipeline post trenching projects.  All jetting componentry is designed, fabricated and operated by OCS. The most recent addition to inventory is a articulated pontoon sled capable of deployment in deep  (by ROV) or ultra shallow water.  This unit was deployed by two barges in moored configuration and a DP DSV (driven by Water depth and Contracting strategy) on the ENI Jangkrik pipeline much of it with a cover of  2.0 metre top of pipe. OCS clients have reported very positively on the performance of this jet sled.

    OCS also operates two pipe riding jet sleds and a portable A frame that can deploy the sleds independently without resorting to a separate crane.

    Key Equipment for a pipelie post trenching operation:

    • Effective deployment barge of DSV with efficient mooring system and handling crane
    • Jet sled configured specifically for the pipeline to be jetted.
    • Jet Sled deployment system.
    • High volume / pressure water distribution system.
    • High volume Air Distribution system.

    Trained personnel are also a key factor in operations.  All OCS key technicians are career employees qualified to operate all OCS strategic portable equipment.

    The newly built OCS utility barge is configured specifically for post trenching and includes built in piping for delivery of pressurised air and water to the sled along with an efficient centrally controlled mooring system and  sled deployment system.  Details of the barge are in a separate tab on this website.

    For third party marine equipment the OCS specific post trenching equipment spread can be set up on either moored or DP vessels. OCS personnel visit the vessel and design the most appropriate configuration for the most efficient performance.

    Average jetting pressures/volumes are in the range of 350 psi at 478 m3 per hour.  OCS has 3 jet pumps that deliver at this capacity giving a system capacity of over 1400 m3 per hour. The jet pumps are fed by high volume electric (1500 m3 per hour at 50 psi) and diesel (1500 m3 per hour at 50 psi) pumps to enhance pump efficiency.  In very hard materials higher pressures are possible by using smaller nozzle sizes and pumps of higher pressure capability.

    To manage the supply of water to the jet sled OCS has developed a unique bespoke design water distribution manifold that takes the water from the feed pumps and diverts it through the pressure pumps before sending the pressurised water to the jet sled. The manifold pipe work has been built into a 20 ft container frame work to enhance portability and ease of set up. The details of the equipment can be found in the equipment tab on this website.

    Spoil is removed from the cut trench by water eduction (using the high pressure water described above) and by air lifting.  For airlifting two 1080 cfm compressors are providing feeding a volume tank before being directed to the sled. In the case of the UB-01 which is equipped with 2 x 22 m3 volume tanks below deck for the air powered mooring winches the air supply is readily available.

    Our equipment is managed and operated by personnel who come from the same background as the main marine contractor.  We help the major marine contractor plan the work such that the post-trenching activity has the least impact on operations. We are proactive in highlighting potential issues and ensuring both parties win. OCS understands the importance of getting the job done safely and efficiently to minimise operational costs for all concerned.

    PIPE BURIAL EXPERIENCE

    OCS has undertaken numerous major post-trenching projects for different customers;

    • Jankrik for ENI. Burial of 42 km of 24” / 4” Piggy back to varying TOP from 0.5 metres to 2.0 metres using a pontoon articulated arm jet sled. Work from two moored vessels and DP vessel for two contractors (2016 / 2017).
    • Husky BD  ,  16" x 2.0 km, 2.0 metre TOP (2016)
    • Thai Binh for PVGAS, post trenching of 10km length of 12” pipeline for the gas distribution project, in ViThai Binh for PVGAS, post trenching of 10km length of 12” pipeline for the gas distribution project, in Vietnam. Main contractor is Sapura Kencana (Vietnam). Main contractor is Sapura Kencana.(2014)
    • Ketapang Petronas offshore Gresik in Surabaya, post trenching of 27km of 12” pipeline to 2m TOP (2013)
    • Pertamina EP MOL 12” Pipeline near Cirebon in Central Java Indonesial. (2013)
    • CSJV/Chevron Australia (DOMGAS 20" pipeline project) 2012, 20" CWC pipeline x 25km burial distance (in combination with intermittent rock bolting), 0.5/1.0m TOP cover. Karratha, Western Australia, Australia (2012)
    • HESS Indonesia (Ujung Pangkah Phase 1) 2010, 6" CWC, 12" CWC & 16" CWC pipelines x 5.500 km burial distance each line, 2.0m TOP cover. Nearshore north of Gresik/Surabaya, East Java, Indonesia(2009)
    • APD/Salamander (Serica Kambuna Development project) 2009/10, 14" CWC pipeline x 13.000 km burial distance, 2.0m TOP cover. Nearshore north of Medan, Sumatra, Indonesia (2008)

    Pipeline Post Trenching – Pre Qualification Document: Download