For an area where no previous knowledge of jack-up penetration / sub-bottom information is available the location must be cored, this may be done by a coring vessel prior to rig arrival or from the rig upon positioning at the location.
1. independent leg jack-up rigs
A) Location
Area, block name or number, Latitude, Longitude.
B) Bathymetry
A Bathymetric survey of location covering at least one square kilometre with line spacing not exceeding 100 metres with interlines at 25 metres close to location to determine levelness of the seabed. If the location is in an uncharted area, a larger area may be required. Indication should be made regarding which reference port was selected to measure the depths and which tidal prediction data was used.
C) Seabed Hazards
A side scan sonar survey carried out over the same area as the Bathymetric survey. In some cases, a magnetometer survey is necessary to locate potential embedded objects. For platform locations, a diver's / RCV survey covering 2 to 3 times the area of the rig be carried out around the area to search for potential hazardous construction debris and for footprints of previous jack-up activity which may hinder proper positioning of the rig.
D) Sub-Bottom Profile
A survey covering the same area as the Bathymetric survey should be carried out using boomer or sparker type equipment to establish sub-bottom anomalies that might endanger the safe support of the unit or the drilling program.
E) Soil Sample And Analysis
In areas where data or type and nature of underlying soils are scarce or in areas where "punchthrough" situations are prevalent, soil coring and analysis will be required. The core should be cut deep enough to go beyond the expected penetration and a leg penetration curve should be computed after relevant information, such as footing shape and bearing area as well as weight per footing at maximum preload, should be given to the survey company conducting the soil investigation.
2. Mat Supported Jack-Up Rigs
The requirements are similar to those for independant leg jack-up rigs, with particular emphasis on the interlining at 25 metres as mentioned in B as seabed levelness is most important. Coring is not necessary for this type of rig. However, bottom probing by divers may be required in harder bottoms to assess that the skirt will not be damaged. In softer bottoms a magnetometer survey is necessary to assure that there are no hazards embedded which may damage the mat (wrecks, lost anchors etc.......).
3. Floaters (Semis, Drillships, Tenders)
Most companies carry out a similar Site Hazard Survey for floaters or jack-up rigs. Bathymetry of an area encompassing the proposed anchor pattern is necessary as well as a Seabed Features Survey for hazards over the same area and a sub-bottom profile to detect in depth anomalies which may affect the drilling program.