Methodology and technique of 2D CDP Seismic Acquisition with towed streamer
Seismic data acquisition will be carried out with the use of ION DigiStreamer system, which includes onboard recording system and seismic streamer. Length of seismic streamer active part will be 7000m (max. 8000m), which will provide for fold coverage of 140 (max. 80) with channel spacing 12.5 meters and shotpoint interval 25 meters. Nominal streamer depth is from 6 to 15 m. Streamer control, depth and position control will be implemented using depth controllers installed along the streamers with interval 300 m.
Seismic data arriving to the onboard system in digitized form are recorded on IBM 3590/3592 magnetic medium (or HD) in SEG-D format.
Air guns array will be used as a source of elastic vibrations. Source array is composed of 2 sub-arrays 9 guns each, on 15m base. Source firing time is initiated by navigation system, and shot pulses are formed by LongShot controller providing automatic timing correction for each gun, their time characteristics analysis, and identification of spontaneous and skipped shot points with printout of statistics of the whole emitting system.
Prior to survey commencement and further on, a full set of tests as provided by equipment manufacturer will be carried out on a monthly basis, at intervals not more than 35 days. The tests will be recorded on magnetic tape and analyzed onboard. During the entire period of survey, the status of recording equipment will be controlled by daily tests prescribed by the manufacturer.
Background noise will be recorded prior to the start and upon completion of each line, followed by analysis in order to define root-mean square noise level for each record. In the course of line acquisition, control gathers with all channels and time marks will be produced at intervals of 100 shotpoints. Single trace display for the near channel will be produced for each line.
In the course of field works, seismic data pre-processing will be performed by onboard processing system PROMax for operative quality control of acquired data.
Average planned speed of line acquisition - 4.5 knots - provide for good performance and acceptable noise level for the towed equipment.
Positioning of the vessel and towed equipment will be performed by two independent navigation systems with the use of GPS and GLONASS satellites.
Recording system DigiSTREAMER
|
2DType Manufacturer Recording form Sampling interval HF filter Analogue LF filter Recording devices Storage media Display system plotter |
DigiSTREAMER 2D ION USA SEG-D (rev.2) 8058 32-bit IEEE 0.5,1, 2, 4 ms 2 Hz , 6 dB/octave 103-824 Hz , 256 dB/octave RAID-system,24 Tbyte; IBM 3592 data storage IBM 3592 cartridges OYO GS-624-24” |
Streamer DigiSTREAMER
|
Type Manufacturer Length of the streamer active part Length of cable (Lead-In) Number of channels Length of active section Diameter of active section Type of filler Operational depth (export section type) Survival depth Streamer working temperature Streamer storage temperature Hydrophone group interval Type of hydrophones Teledyne Number of hydrophones in group Groups of hydrophones Group sensitivity Seismic winch Maximum capacity |
DigiSTREAMER ION (USA) 7000 m (max 8 000 m) 350 m 560 (max 640 at length 8 000 m) v 99.7 m 53 mm +/- 3 mm (5,3 cm) Solid state (patent, unliquid gel) 30 m max (98 ft) 300 m (984 ft) from -5 to +30°C (from 23 to 86°F) from -20 to +60°C (from -4 to 140°F) 12,5 m (8 groups per section) T-2BXE 8 In-line layout with distribution for noise control 19 V/bar to 8 000 m(ODIM A/S, Norway) |
Devices of the streamer’s depth and positioning
Type of depth control devices:
|
- Without course indicator - With course indicator Manufacturer Interface of data exchange with the seismic streamer Fixed direction indicator - Accuracy Depth sensors accuracy |
DigiBird 5010/5010-2 Exportable Compass Bird 5011E/5011E-2 ION (USA)
Serial FSK, 26 kHz, 2 400 bit/sec DigiCOURSE Model 321 Magnetic Compass +-0,5 ° +-0,15 meters |
Energy source system
|
Type of source points Manufacturer Number of pressure lines Number of sources in each line Length of the lines Distance between the Lines Conducting wire length Total volume of cameras Controller type Temporary permit Winches High pressure compressors Type
|
Sleeve Gun SG-IIB ION, USA 2 9 15 m 7 – 10 m 600 ft 2 860 cubic inch LongShot (Real Time Systems Inc., USA) 0,1 msec 2 basic and 4 auxiliary (ODIM A/S, Norway) 3 pcs. Sauer WP-6442 (209 bar (2000 psi), 500 cu m/h) (Germany) |
Navigation seismic complex (at the additional request)
|
Type Manufacturer |
ORCA-2D ION Concept Systems Limited (USA) |