Introduction to Electrical Resistivity Tomography PDF

Electrical Resistivity Tomography Geotomography Outline Introduction Basic Theory Configuration Electrical Resistivity Method Induced Polarization Case Study Outline … (2) Cross-borehole Imaging Introduction Micro-Scale Field-Scale Interpretation Basic Theo...

Electrical Resistivity Tomography Geotomography Outline Introduction Basic Theory Configuration Electrical Resistivity Method Induced Polarization Case Study Outline … (2) Cross-borehole Imaging Introduction Micro-Scale Field-Scale Interpretation Basic Theory Basic Theory Configuration Resistivity of rocks, soil, and mineral Resistivity Model 1D (VES) 2D (ERT) Basic Theory of Inversion In other courses (Inversion) Recall the subject matter! Induced Polarization There are two more electrical based method closely related to the resistivity method, i.e., IP and SIP (complex resistivity). IP & SIP require more sensitive instrument. IP => mineral explorations, detect conductive minerals of very concentrations SIP => comparatively rare in commercial, popular in research subject IP & SIP use alternating currents (in frequency domain) Instrument Chargbility of porous medium Case Study To be continued.. Cross-borehole imaging One of the most severe limitations of 2-D imaging surveys carried out along the ground surface is the reduction in the resolution with depth. In theory, the only way to improve the resolution at depth is to place the sensors (i.e. the electrodes) closer to the structures of interest. This is not always possible, but when such boreholes are present, cross-borehole surveys can give more accurate results than is possible with surface surveys alone. Electrode configurations Two electrodes array – the pole-pole Three electrodes array – the pole-bipole Four electrodes array – the bipole-bipole Two electrodes array – the pole-pole Two electrodes array – the pole-pole Three electrodes array – the pole-bipole Four electrodes array – the bipole-bipole Single borehole surveys Single borehole surveys Reference Case Study (2-D field examples) Landslide – Cangkat Jering, Malysia Old Tar Works – UK Holes in clay layer - USA Time-lapse water infiltration survey – Nigeria Pumping test – UK Wenner Gamma array survey – Nigeria Mobile underwater surver – Belgium Floating electrodes survey – USA Oil Sands – Canada 3D – electrical imaging survey all geological structures are 3-D in nature a fully 3-D resistivity survey using a 3-D interpretation model should in theory give the most accurate results. Limitations: cost and time consuming (multi-channel) 3D-configuration Pole-pole array Pole-dipole array Dipole-dipole (Wenner and Schlumberger arrays) Case Study Hands-on