These are two of the most common electrical methods. They measure parameters associated with voltages induced in the ground by direct application of current. Resistivity gives information on ground bulk resistivity while IP gives ground impedance or capacitance.
Recent Advanced Geosciences resistivity survey & developments include multi pole-dipole arrays for greater resolution. Data products typically include contoured color-image pseudo-section profiles and contoured shaded color image plan maps of several parameters.
Multi-Pole-Dipole for 3D IP Inversion Modelling
The development of 3D IP inversion software has led to the requirement for more readings with depth. To increase the signal strength at greater n values, pole-dipole and two receivers are applied. CGG has specialized in the acquisition of this innovative IP exploration method.
Downhole IP
Logging of the resistivity and IP values down a borehole is an important part of an exploration program involving surface IP, applied in base-metal exploration, particularly for lead-zinc bodies and also for nickel and copper. As these in-situ geo-electrical characteristics determine the surface IP responses, knowledge of them enables a better understanding of the surface data and guides any future exploration program. When drilling an IP anomaly, it is necessary to determine if the source of the surface IP anomaly has been intersected. Further, by using wider electrode spacing, a near miss can be detected where the main IP body is a few or tens of meters away from the drill hole.
Applications
Mineral exploration: detection of disseminated sulphide ore bodies by their resistivity and/or IP anomalies. Both as surface method and as downhole IP.
Groundwater investigation: aquifers can be detected as resistivity anomalies.
Stratigraphy mapping: differing soil and/or rock types may have different inherent resistivity.
Geotechnical: soil or rock resistivity is important in many geotechnical projects.
Environmental: IP methods can assist in the assessment of the acid generating potential of waste rock and tailings from mine operations. Resistivity can be used to map contamination plumes.
Equipment
CGG operates both time and frequency domain IP equipment. A variety of transmitters and receivers are available to suit all operating requirements and environments.
