Trenching and backfilling for Vega Pleyade pipeline
Client: Total, France
Tierra del Fuego is located in the extreme South of Argentina at a latitude of 54 degrees South. Climate conditions are harsh, with persistent strong winds also during summer. To connect a new offshore gas production facility in the Vega Pleyade Gas Field, client has ordered to install a 24" pipeline from the platform to the existing Rio Cullen treatment facility. For the landfall and the shallow waters a trench of 2 meters depth is dredged before installation of the pipe (pretrenching). Soil conditions encountered are predominantly moraine, partly covered with recent deposits of sand and gravel. An abundance of boulders is identified on multibeam and side scan sonar surveys. For backfill of the trench and pipeline coverage various options are studied.
Due to the high costs related to delay of the pipelaying operation a risk assessment of the installation works is performed to identify the critical path and the potential delays. One of the delay risks are the moraine soil conditions (with possibly weak rock) in combination with the presence of large boulders, that might lead to low productivity of the dredging works. To anticipate on this uncertainty the dredging works are moved forward in the overall construction schedule, resulting in a larger float and therefore reduction of the risk to delay the pipe installation works.
During negotiations Client is advised with dredging related expertise (working methods, conditions, pricing schedules) aiming for a clear division of responsibilities and sufficient guarantees to meet project milestones. Also procedures are prepared for use of the site supervision team witnessing the works.
Detailed Description of Actual Services Provided by Blue Pelican Associates:
appraisal of the geophysical and geotechnical investigation
review of contractor proposal
critical path analysis and the introduction of float