| Title | NEAR-SURFACE GEOTHERMAL MAPPING – TESTING THE tTEM GEOPHYSICAL TECHNIQUE IN THE ROTORUA GEOTHERMAL FIELD |
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| Authors | R. Reeves, J. Pedersen, T. Brakenrig, P. Maurya, R. Kraghede, F. Christenson, L. McGovern and B. Moorhead |
| Year | 2021 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Rotorua geothermal Field, tTEM, Geophysics, permeability, resistivity, geothermal mapping |
| Abstract | The towed transient electromagnetic (tTEM) geophysical technique enables high-resolution near-surface resistivity measurements to be collected in a timely manner, resulting in a better understanding of the near surface (approx. top 100 m). The tTEM system in development by Aarhus University is tested in the Rotorua Geothermal Field, New Zealand. The aims of the work are to test the equipment in a low-resistivity environment where abrupt changes in resistivity may occur over short distances and to better define subsurface areas of geothermal activity and provide insights into the permeability structure between the groundwater aquifers and geothermal surface features. tTEM data collected from two sites show that the tTEM method can successfully define shallow resistivity targets and provide insights into the near-surface permeability structure. Areas of low resistivity correlate well with mapped geothermal surface features and suggest that subsurface areas of geothermal influence are larger than what is seen at the surface. A large amount of the tTEM data collected in part of the study had to be discarded because they were of poor quality – probably affected by cultural effects such as electric power lines and buried objects. However, the poor data was largely constrained to one part of the study area, so a good resistivity model could be generated in other parts of the study area and achieve the projects aims. |