GFA

Borehole 3D Geophone

Borehole 3D Geophone Mod. GFA 50/100 is designed for seismic borehole testing according to ASTM D7400-08 (downhole) and ASTM D4428 (crosshole). It is based on 3x high-sensitivity sensor elements (nat.freq.10 Hz - 1 vertical and 2 horizontal sensors), oriented according to a triad of orthogonal Cartesian axes XYZ. Supplied with a cleat assembly to sustain its weight at the requested depth (GFA cable is graduated in meters), this borehole geophone has a pneumatic-mechanical clamping system with lateral lever and spacer block. Simply connect the pump to the GFA panel to operate: pumping air at a pressure of 2-3 bar, you will achieve excellent sensor coupling to the borehole wall (diameter between 50 and 110mm for use with the standard spacers). GFA is lightweight and easy to transport; the anodised aluminium casing makes it suitable for use on-site and easy to maintain. Moreover, two GFA can be connected one under the other by means of a special spacer accessory. Available in two versions: GFA-50 with 50m of cable and GFA-100 with 100m of cable.

Cable reel with 50 m cable
Models
Methodologies

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HOW IT WORKS?

GFA

Simply connect the pump to the GFA panel to operate: pumping air at a pressure of 2-3 bar, you will achieve excellent sensor coupling to the borehole wall (diameter between 50 and 110mm for use with the standard spacer).

Moreover, two GFA units can be connected one under the other by means of a special spacer accessory (see “Standard Test Methods for Downhole Seismic Testing” - ASTM D7400-08)

 standard equipment includes:

  • Cable reel with probe (GFA-50 with 50m cable, GFA-100 with 100m cable)
  • Nose piece for drilling muds
  • Manual Pump
  • Cleat Assembly
  • Connecting cable for seismograph
 

GFA ACCESSORIES

Spacer accessory to connect two GFA units - vertical distance between sensors = 1m

TECHNICAL SPECIFICATIONS
GFA
Number of geophones
3 geophones with nat.freq. 10Hz+/-5% (1 vert.+ 2 horiz.),
high sensitivity (100V/m/sec +/-5%) 
Cable length
50m or 100m, graduation in meters, mounted on cable reel with probe support
Probe dimensions
Ø51mm, length 570mm (anodised aluminium case)
Borehole diameter 
Min. 55mm, max. 110mm (with standard spacer block; larger diameters upon request)
Cable reel dimensions
540x400x250mm
Weight
GFA-50: <12kg; GFA-100: <17kg
Seismograph connection
Standard: Cannon type NK2721C (GEA24, 16SN-U-P) or Souriau (GEA3, Anteo). Other adapters available upon request
Technical specifications subject to change without notice
Number of geophones
3 geophones with nat.freq. 10Hz+/-5% (1 vert.+ 2 horiz.),
high sensitivity (100V/m/sec +/-5%)
Cable length
50m or 100m, graduation in meters, mounted on cable reel with probe support
Probe dimensions
Ø51mm, length 570mm (anodised aluminium case)
Borehole diameter
Min. 55mm, max. 110mm (with standard spacer block; larger diameters upon request)
Cable reel dimensions
540x400x250mm
Weight
GFA-50: <12kg; GFA-100: <17kg
Seismograph connection
Standard: Cannon type NK2721C (GEA24, 16SN-U-P) or Souriau (GEA3, Anteo). Other adapters available upon request
Technical specifications subject to change without notice