Detection of a geological barrier by electrical resistivity tomography using buried electrodes

Electrical Resistivity Tomography (ERT) methods have been applied within a disturbed till complex to assist in the detection of a geological barrier on a waste deposit site. Crossborehole, single-borehole and hole-to-surface direct current (DC) electrical measurements were performed. For this studies electrodes were fixed to the well-tubes at a distance of 0.5 m to each other during casing installation. Sets of pole-pole data were aquired and inverted using a SIRT-algorithm to produce resistivity images. Due to the spacing of the electrodes the achieved image resolution and depth of investigation of these techniques are between typical values of surface surveys and logging measurements. Additionally single-borehole measurements were evaluated yielding synthetic electrical logs, simulating Laterlog 7, short norm al and long normal logging tooI measurements, respectivily. The cross-borehole and single-borehole inversion results as well as the computed synthetic logs show clear resistivity contrasts between different types of unconsolidated sediments. Resistivity changes obtained from the ERT-methods image the geological structure. In comparision with surface measurements, well logging and drilling results it helps to find a consistent modell of the geological barrier.