Draping High-Resolution Magnetic Mapping in the Northern Vosges and Rhine Graben (France) Using a Three-Component Fluxgate Magnetometer Mounted on Small Unmanned Aerial Vehicles.
Abstract
The exploration for new energy resources such as geothermal energy substantially relies on the identification of the structures that make up faulted and fractured reservoirs. The objective of the DONUTS project is to establish a set of methods for the quantitative interpretation of geophysical data to describe the geological characteristics of these reservoirs.
One of the study-site of the DONUTS project is in the French Upper Rhine Graben and Northern Vosges. In this region, fault zones and associated fracturing systems at the roof of the magmatic and/or metamorphic basement of the basin are a key target for geothermal drilling projects aiming at electricity production. However, due to the depth of the targets (more than 2 km) and the absence of seismic markers in the granitic and metamorphic basement, only the main faults with large throws (more than 100 m) are identified by geophysical interpretation. The secondary structures that are significant flow conduits in this system have typically a smaller throw and a few kilometers length. The geophysical methods commonly used for exploration do not have sufficient resolution to recognize these structures. Aeromagnetic surveys with very small UAVs (under 3 kg) enable a cost-effective and high-resolution study in the Rhine Graben. A 3-component fluxgate magnetometer is mounted on two types of UAVs to acquire draping magnetic data over a 40 km² area with a 50-m line-spacing and height above the ground. This technology also allows for surveying in mountainous and/or forested regions where it is difficult or impossible to acquire geophysical data on the ground. With this survey approach, magnetic data has a constant height above the ground, which minimizes the distance-to-sources variations effects but amplifies the amplitude of magnetic-terrain anomalies. This becomes especially relevant closer to the ground and if spectral potential-methods transforms such as reduction-to-the-pole are to be used. To solve the difficulty of variable altitude data, computation techniques based on the equivalent-source layer are proposed. They allow to compute potential-field transforms on a horizontal plane of fixed altitude. In addition, the magnetizations obtained at different depths below ground are linked to the geological maps.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMNS012..06M
- Keywords:
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- 0920 Gravity methods;
- EXPLORATION GEOPHYSICS;
- 0925 Magnetic and electrical methods;
- EXPLORATION GEOPHYSICS;
- 0935 Seismic methods;
- EXPLORATION GEOPHYSICS;
- 0999 General or miscellaneous;
- EXPLORATION GEOPHYSICS