June 22, 2015

The Dipole-Dipole electrode configuration is ideal for detecting off-hole targets because the transmitter and receiver electrodes are always at the same distance apart as the configuration moves down the borehole.  This makes detecting anomalies easier because if there weren’t any, the resistivity profile would be flat in a uniform half-space.

 In one case, a borehole was augered to bedrock and the four (4) dipole-dipole stainless steel ‘pins’ attached to new IP-wire were lowered at 1-metre intervals.  A Phoenix 3 kW transmitter injected over 1 amp of current into the current electrodes and a Scintrex IPR12 receiver measured the voltage drops and time-domain IP response.  The pulse was at 2 seconds on and 2 seconds off.  The “a”-spacing was 3-metres for the first run and 5-metres for the second run.  The goal of the survey was to detect how long boiler room piles, located a few metres away, extend into the ground and whether they could extend into bedrock.  The IP response (spectral decay) was useful for detecting near surface interference caused by pipes and utilities.