Malta Survey activities Malta 19 September 2016 L. Facchin OGS National Institute of Oceanography and Experimental Geophysics
Offshore Multibeam (MBES) Sub bottom profiling (SBP: Chirp or Boomer) Multichannel reflection seismic (MCS) Onshore Refraction/reflection seismic Downhole seismic measurements
OLD Planned MCS lines (line spacing in map is 50m)
OFFSHORE Activities An area of about 12 Km 2 will be investigated. The acquisition is planned for a full bathymetric coverage to be performed by Multibeam Echo Sounder (MBES), a Sub Bottom Profiler (SBP) survey and Multi Channel Seismic (MCS) survey. The MBES coverage is depth dependant, and the line spacing will be decided in real time during the acquisition. The firs evaluation is: MBES 160 linear km; SBP 50 linear km; MCS survey line spacing 75-100 m.
Multi Beams Echo Sounder (MBES) Bathymetry
Offshore MBES data example
Swath bathymetry Multibeam Echo Sounder Manufacturer RESON Model Seabat 7125 Frequency Max ping rate 400 khz 50 Hz Number of beams 512 Max depth Depth resolution 175 m 6 mm In alternative a Seabat 8125 can be used. Is a High resolution system, with similar carachteristics and frequency.
Sub bottom profiling(sbp)
Planned SBP lines
Sub Bottom Profiler CHIRP Manufacturer EDGETECH Model 3100 Frequency Max penetration (Clay) Weight in air Weight in water Max depth rating of towfish 2-16 khz 70m 76 kg 32 kg 300 m In alternative a BOOMER system can be used. Is a High resolution system, with similar carachteristics.
Sub bottom profiling (SBP): data example
Offshore MBES and SBP Vessels: examples
Seismic survey The multi-channel seismic is a method for the subsoil exploration, the aim is resolving all the geological elements that characterize it. The choice of the acquisition parameters will be determined to have a compromise between resolution (for fully discriminate the reflectors) and penetration (to reach the targets depth).
Harmonic 30 G / 30 I Seismic equipment
The seismic source that will be used is a Sercel MINI GI gun. This choice allows to obtain a good compromise between frequency (vertical resolution) and energy (penetration). The higher the frequency the better the resolution is, but the penetration is limited. The high pressure compressed air to power the source will be provided by three portable compressors capable of producing about 700 liters/minute of air at a pressure of 230bar. The seismic cable has a short sensors distance, this feature allows to obtain a good horizontal resolution. The gun controller system allows shot timing synchronization for the two chambers (Generator and Injector) in a GI gun, or between different guns in a multiple guns array The levelling system is used to maintain the seismic cable at the target depth, for a better quality data result.
Seismic source The source consist of one mini GI-gun for a whole maximum volume of 60 cu.in (30 for generator and 30 for injector). The GI-gun can be operated in True GI, Harmonic, or air-gun mode. SOURCE Manufacturer SERCEL Model Mini GI GUN Configuration 30 G + 30 I (60 cu.in.) Mode True, Harmonic, air gun Array Composition 1 single mini GI-gun Total volume 60 cu. in. (0,98 l) Pressure 120 bar GEOMETRIC FEATURES
Seismic cable STREAMER Total lenght 300 m Total Channels 96 8x12 Sections The seismic cable is 300 m long, with channel interval of 3.125 m. The small diameter allows manual deployment and recovery of the streamer. Channel interval Diameter Section lenght Winch measures Total weight 3.125 m 41 mm 25 m 2m x 3m 5 tons
Seismic cable Manufacturer Geometrics Model Geoeel Number of channels 96 Group Interval 3.125 m Section Length 25 m Streamer length (12 sections) 300 m Hydrophones per Group 4 Hydrophones per Section 32 Hydrophone Type Benthos RDA Geopoint Group Sensitivity 9 V /bar Jacket Material Clear polyurethane Diameter 41 mm (1.6 in) Ballast fluid non-polluting silicone oil Weight 1.35 kg (3 lbs) /m Strain Member Vectran Streamer winch
Air delivery AIR COMPRESSOR Air delivery Speed Power supply Power Pressure Weight 235 l/min (8,3 c.f.m.) 1370 rpm Diesel 6,6 kw 230 bar 135 Kg The source will be supplied by three 8,3 c.f.m diesel compressors.
Recording system General features Manufacturer Model Geometrics GeoEel Digital Number of channels 96 A/D modules Channels per module 8 Sample Rates Programmable gains Record Length I/O Communications Bandwidth Resolution Dynamic Range Data Format 1/16 msec to 2 msec 0 db, 8 db, 18 db, 30 db, 42 db Up to 30,000 samples/trace 100Base TX Fast Ethernet DC to 8 khz 24 bits including sign 120 db SEG2, SEGD, SEGY Near trace monitor
Manufacturer Model Gun controller system Realt Time systems Sure Shot Number of guns 4 Gun types Bolt, Sleeve, G and G.I. Timing resolution 0.1 msec Predicted fire out 5 ms TTL high going Field Time Break Out Hydrophone signal Hydrophone signature Aim Point 16 bit D / A 25 75 msec after trigger BURST BUBBLE Generator only Fire pulse width 1-80 msec Example of bubble effect reduction; comparison between the sensor responses with only the Generator activated (top) and with both Generator and Injector activated (bottom). BURST Generator + Injector RITMARE - SAOS
Levelling system Manufacturer Model Operating Range Resolution Digicourse Digibird5010 0 to 122 m 0.15 m Number of birds 4 Power Supply 4 D cell Lithium batteries Bird deployment Real time monitoring Bird at sea RITMARE - SAOS
Seismic data example 200 ms 1000 ms Seismic line acquired in Thyrrenian sea in 2014. The seismic system is the same that will be used for Malta survey.
ONSHORE Activities Reflection seismic Refraction Seismic Downhole measurements
Reflection seismic
Refraction seismic
Downhole measurement