Positioning accuracy is determined with the aid of onboard special global positioning system DGPS and integral navigational system Trigger Fish. Independent bottom-cable positioning control is done by Sonardyne positioning system.
The XZone Marsh Line 2C (SI Technology, Russia) or SeaRay®-100 / 4C (Sercel, France) systems are used to record data, each comprises onboard central recording system and a digital bottom-cable. In both systems receivers’ power supply and data exchange is performed across-the-wire from the onboard recorder.
In 2011 XZone system was thoroughly tested by “VERIF-I” (Great Britain). In bottom cables XZone Marsh Line various receiver modules aimed at recording of different components of wave field from 2C (hydrophone+geophone) to 4C (three-component XYZ geophone and hydrophone) can be used, the onshore component of the receiver unit FlyLander, which in any configuration can be connected with the offshore component of the system.
In SeaRay®-100 bottom cable there are used 4C receiver modules, which include omnidirectional MEMS accelerometers+hydrophone, registration can also be done at the adjoining land.
2D2C and 2D4C OBC survey
OBC works are usually performed using conventional two-vessel or multi-vessel technology shooting along successively deployed CMP shooting lines.
Satellite navigation system is used to control shooting. CMP and recording system synchronization is provided via the radio channel.
As soon as each spread is shot the bottom-cable is towed to the profiled distance to provide the designed CMP fold of coverage.
As it is a cycled process, shooting is performed until full profiling is done.
3D2Ñand 3D4C OÂÑ survey.
3D operations are carried out by special paddle vehicles, three or four of which are used for the streamer deployment and its set-up, whereas one or two ones are used as elastic signal sources.
To excite oscillation special shallow-water mud-resistant source arrays Malysh (total volume of 490-800 inches3) are used.
The specially designed by Norwegian company PGS Exploration groups of air sources GGun, MiniGGun (total volume 600-1200 in 3) are used as sources of elastic signal in shallow water areas.
3D operations are performed by means of four or 4-8 deployed in parallel streamers 100-400 m apart from each other.
Deployment template is shot cross-line by one or two sources (flip-flop mode).
Quality Management and control
When shallow water acquisition is in process, party Chief (supplied with satellite phone), QC team and Supervisor shall be onboard the base vessel to support the field team. QC staff is equipped with development and QC systems: MESA professional, ProMax, SPW Field, Focus. |
