BGK 3/ 7: Borehole Geophone

The borehole geophone BGK3 is used to receive P- and S-waves in dry or water filled boreholes. The borehole geophone BGK3 consists of a tri-axial sensor whereas the BGK7 consists of six horizontal sensors, separated by 30° intervals, and one vertical sensor. The geophone is coupled to the borehole wall by a pneumatic clamping system (inflatable bladder). Air is supplied to the BGK3/7 through an electro-pneumatic hybrid cable with a Kevlar tension string. A magnetic compass shows azimuthal deviation to North and can be used to get the orientation of the geophone in the borehole. The cable is terminated by a connector to the seismograph.

The borehole geophone is pneumatically clamped to the borehole wall by means of a robust air bladder. A magnetic compass shows azimuthal deviation to North. Typical applications are VSP surveys, crosshole measurements and shear wave tomography.

Natural sensor frequency: 30 Hz (others on request)

Sensor arrangement: Tri-axial (BGK3) or 6 horizontal (30°)/1 vertical (BGK7)

Operational depth: Up to 100 m

Receiver length: 705 mm

Receiver diameter: 51 mm

Receiver weight:3 kg

Cable weight per meter: 145 g

Cable strength: 2150 N

Borehole diameter: 75 mm (or larger if spacers are used)

Clamping system: Inflatable bladder

Orientation: Magnetic compass (+/-2.5°)

Depth indicator: Cable marking every 2 m

Connector: To any seismograph

Storage: On drum