3D IP and Resistivity Surveys

INTRODUCTION

For complex geological areas that do not have linear chargeability and resistivity trends, 3D surveys are recommended. Generally, the IP array is distributed in such a way that orthogonal dipoles are measured with an offset pole-dipole survey pattern (White 2001).

Purpose of the survey

The offset pole-dipole survey layout was historically designed for resistivity and IP surveys targeting mineral deposits at depths of several hundred meters. The setup alternates current and potential electrodes in separate lines, with large electrode spacings (50-200 meters) covering areas of several square kilometers. To increase depth of investigation, some surveys use potential lines farther from the current lines, occasionally leading to low potential signals, negative apparent resistivity values, and challenges in data inversion when large resistivity contrasts exist.

Vector IP/Resistivity Surveys

Vector IP/Resistivity surveys share a similar field layout to traditional surveys but stand out through an innovative approach to data processing. By transforming dipole measurements into vectors—a method at the forefront of geophysical research—we’re able to extract more detailed subsurface information.

This technique can be applied to historical datasets with orthogonal dipole configurations (such as offset pole-dipole or other arrays) or incorporated into new survey designs optimized for vector IP. The resulting vectors carry both amplitude and directional information, leading to significantly enhanced resolution both laterally and at depth.

As Loke (2024) notes:
“Not surprisingly, including the direction component in the dataset improved the resolution of the inverse model compared to using the amplitude component alone.”

These advanced surveys have been increasingly popular among our clients, offering a powerful tool for more accurate subsurface imaging.

Bibliography

White, R.M.S., Collins, S., Denne, R., Hee, R., Brown, P., 2001, A new survey design for 3D IP inversion modelling at Copper Hill, Exploration Geophysics, 32, 152 – 155

Loke, M.H., Wilkinson, P.B., Gance, J., Malet, P-B,.Truffert, C. and Leite, O., 2022b. Measurement and inversion strategies for 3-D resistivity surveys with vector arrays. Geophysical Prospecting, 70, 578-592.