Marine Scotland

Oil and Gas Pipeline Survey

October 23, 2018 by No Comments

Survey: MRV Scotia 1518S

Duration: 18 –  24 October 2018

Equipment: Day grabs; TV drop frame with lasers; armoured cable; SVP; swathe multibeam echosounder system; EK 60; CTD; VMADCP and time lapse cameras.

Objectives:

  1. To assess the hydrographic influences on the aggregation of fish around surface laid oil and gas pipelines.
  1. To assess the handling and performance of a benthic time lapse camera.

 

Procedure:

MRV Scotia will depart from Aberdeen Harbour at 08:00 on 18 October and after all drills have been performed the vessel will proceed to the agreed survey start point.  The nature of the survey work will be heavily dependent on the prevailing weather conditions encountered.  The survey techniques are no different to previous surveys conducted by MSS using MRV Scotia.  The proposed survey is based on two parts:

  • The deployment and recovery of time lapse camera for the duration of the survey; and
  • The collection of fisheries acoustic data over 24 hour periods from a pipeline station.

Time Lapse Camera: The time lapse cameras will be placed on the seabed at the beginning of the survey at Station 9.  On completion of the survey, the cameras will be recovered on board the vessel.

EK60, CTD and VM-ADCP: The collection of fisheries acoustic data will involve two parallel transects 1 to 2 km in length running perpendicular to a pipeline (Figure 1).  Survey speeds during when collecting EK60 and VM-ADCP data will be 8 knots and 4 knots respectively.  Each survey will be conducted on different days.

During the collection of VM-ADCP data, CTD measurements will be made every 4 hours at the ends and centre point of a transect.  Water samples will also be collected to enable the calibration of the fluorescence detector on the CTD.  While transiting between CTD stations the EK60 will be switched off and the VM-ADCP used to collect water column current data.  The pipelines of interest are annotated in Figure 1.

Multibeam and Seabed Video footage: A sound velocity profile (SVP) will be collected 500 m outside of the survey location.  On completion of the SVP, MRV Scotia will complete a multibeam swathe along the length of the targeted pipeline. Survey speed will be 4 knots.  The output will be checked for any anomalous features that could interact with other survey equipment.  If features are identified MRV Scotia will relocate in the immediate area and repeat the multibeam swathe along the pipeline until a suitable length of pipeline is identified.

The multibeam data will be assessed to identify changes in the seabed substrate.  The substrates will be ground-truthed using a drop-frame camera.  The drop-frame will be deployed 500 m from the pipeline off the stern of the vessel using an armoured cable.  The drop-frame will be kept at 1.5 m above the seabed/pipeline and towed using the vessel’s bow thrusters at a speed of 1 knot or less (0.5 m per second) on a course perpendicular to the pipeline.  Video capability on the drop-frame will be forward looking and vertically mounted. It will also have a transponder enabling its position to be monitored and recorded.  The maximum time spent transecting the pipeline will be less than 5 seconds.

Multibeam transects will be run parallel and perpendicular to the pipeline to collect backscatter water column data for assessing the dimensions of fish aggregations.

On completion of the survey work, MRV Scotia will return to Aberdeen Harbour for unloading on 24 October.

Figure 1 showing a schematic diagram of the survey design for collecting fisheries acoustic data, VM-ADCP data and CTD data over a 24 hour period.

Figure 2 shows the stations 4 and 9 that will be surveyed during survey 1518S

Further Information:


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