Hydrographic Surveys

When  moving into a new location the following  hydrographic surveys are required:

• seismic
• sidescan sonar
• water depth
• soil analysis.

These surveys are by arranged by the marine supervisor upon the Operations Engineer’s request and are carried out prior to moving a rig onto a new location, or siting a jacket.

Seismic Survey

An acceptable grid definition must be provided for example surveys over 1km2 lines of 1 000 m each (9 in each direction), 2 of them crossing the location plus 2 lines 50 m apart from location in each direction. (A total of 22 lines of 1 000 m each).

Each grid line to be surveyed with sparker boomer with adequate parameters.

Side Scan Sonar

Each grid line to be surveyed with side scan surveyor eventually to be modified according to equipment.

Water Depth

Echo sounding of location, 6/10 lines, 100 m apart 1 000 m each.

Soil Analysis

Minimum one core on location the coring depth to be decided upon on board soil testing results of upper layers. In case of anomalies within the limits of the jacking-up area, further coring should be carried out. The soil testing program should include onboard soil testing and onshore laboratory testing in accordance with normal practice approved by operation and contractor.

Diving Surveys

As well as the hydrographic surveys, a visual seabed survey is always required before moving a rig onto any location (new or old).

The rectangular area covered by a standard seabed survey is 300 ft wide by 400 ft long in a direction similar to the estimated final rig heading.  The marine supervisor shall organise visual seabed surveys.

Divers inspection of seabed on location not earlier than one week prior to jacking up operation. Final report of above surveys, should be made at least fourteen days prior to the rig going on location in order to obtain a certificate of approval.

As well as a standard diving survey, The marine supervisor will be requested to mark flowlines, subsea wellheads etc. at both new and old locations, as required. Immediately prior to a rig move (preferably within 24 hours), divers must check the top of the spudcans for debris and also reconfirm the amount of penetration.

Note: After drilling operations and the rig has been moved off location, a seabed scan shall be performed. Any debris located in the location vicinity shall be removed.