The borehole source SBS42 generates compressional waves (P) in water filled boreholes. The seismic signals are highly repeatable. Energy released by the IPG5000 discharges through a coaxial cable terminated by two adjacent spark electrodes. The spark discharge vaporizes water by a high-pressure plasma. This generates vapour bubbles which expand and collapse, thereby generating high-frequency seismic waves.
The hydrophone string BHC4 is used to receive P-waves in water filled boreholes. The BHC4 consists of a downhole cable containing a Kevlar tension string and a number of moulded hydrophones at pre-defined intervals. Each hydrophone consists of a sensor with a pre-amplification board. The electronic boards are powered from the surface by a bank of rechargeable AA cells. The cable is terminated by a connector to the seismograph.
The Impulse Generator IPG5000 (formerly named IPG1005) is the high voltage supply to the seismic borehole sources BIS-SH and SBS42. The energy is stored in a large capacitor bank which discharges through a mechanical switch.
The IPG5000 is controlled by a Remote Control Unit (RCU). The RCU allows the user to start the seismic survey by a single or continuous shot release. The repetition rate is freely selectable under continuous operation. The RCU is connected to the seismograph to send an accurate trigger signal.
The borehole source BIS-SH generates horizontally polarized shear waves (SH) and compressional waves (P). The seismic signals are highly repeatable. The source works in dry or water filled boreholes and can be used in vertical or horizontal boreholes.
Energy released by the IPG5000 discharges through a system of electromagnetical coils adjacent to a copper plate. If the plate is rejected a mechanical impact to the borehole wall is generated. The borehole source is coupled to the borehole wall by a pneumatic clamping system (inflatable bladder). The orientation of the source is controlled from surface by a torsionally stiff hose.
The Multistation Borehole Acquisition System (MBAS) is a digital three-component geophone string used to receive P- and S-waves in dry or water filled boreholes. Up to ten individual stations with tri-axial sensors can be connected. The stations are aligned to ensure that all horizontal sensors are oriented in same direction. The system can be oriented from the surface by a torsionally stiff hose. Each station is clamped to the borehole wall by two pneumatic cylinders. An external trigger can be plugged into the USB interface on surface which is connected to a laptop. The operation is entirely controlled by the acquisition software. A separate seismograph is not required.
Mama Ngina Street: Vedic House, 2nd Floor – North Wing. Nairobi, Kenya
