Publications Scientifiques et Média

Petrophysical properties in faulted basement rocks: Insights from outcropping analogues on the West European Rift shoulders.

Abstract

In continental extension settings like the West European Rift, the main target for high-temperature geothermal drillings is the fault zones in basement rocks of the grabens. However, the reservoir properties of these structures remain almost unknown during the predrilling resource evaluations. This study shows the petrophysical evolution in fault zones on three outcropping areas at the basins’ shoulders. We highlight three petrographical groups with different petrophysical evolution in the fault zones: granites and granodiorites, metamorphic rocks with schistosity, and massive metamorphic or magmatic facies. It provides a first estimation of their reservoir properties that can be used for dual-porosity modeling.

Lionel Bertrand, Y. Géraud, M. Diraison

On the use of aeromagnetism for geological interpretation : 2. A case study on structural and lithological features in the Northern Vosges.

Abstract

In many grabens of the West European Rift System, several drilling projects are targeting fluid conductive faults to produce electricity with geothermal energy. In order to reach the adequate temperatures, the targeted faults are located in the basement rocks or at the basement/cover interface. Unfortunately, the basement rock facies and structural data useful for reservoir modeling are often poorly constrained because of the lack of boreholes deeper than 2,000 m and seismic information on the deep subsurface. With the aim to outline the basement structure in the Upper Rhine Graben, two aeromagnetic surveys were conducted where the basement outcrops in the Northern Vosges, with different flight parameters and types of magnetometers. An interpolator using equivalent sources for gridding these two surveys is described by Gavazzi et al. (2020). Here, we describe the geological interpretation of these surveys. We demonstrate the consistency between the total magnetic field intensity and the outcropping lithological units organized in ENE-WSW subvertical bands. In detail, three main blocks were delineated, separated by N-S faults linked to the graben formation and ENE-WSW-inherited Hercynian faults. The latter faults, together with more local NE-SW and NW-SE faults, compartmentalize the N-S-oriented basement rocks. This is relevant for geothermal prospection where the N-S faults are the main targets because fluid flow through other fault systems is deemed restricted. With a focus on the interface between the Northern Vosges and the Upper Rhine Graben, we also demonstrate considerable segmentation on the main graben boundary faults.

Lionel Bertrand, Bruno Gavazzi, J. Mercier de Lépinay, M. Diraison, Y. Géraud, M. Munschy

On the use of aeromagnetism for geological interpretation: 1. Comparison of scalar and vector magnetometers for aeromagnetic surveys and an equivalent source interpolator for combining, gridding, and transforming fixed altitude and draping data sets.

Abstract

Airborne magnetic surveys are common in geosciences. High-precision surveys are usually performed at a low altitude, draping the topography, using scalar absolute magnetometers and active compensation systems to correct the disturbances generated by the carrier. Another solution is to measure the total magnetic intensity using vector magnetometers, which allows compensation for aircraft fields to be calculated directly, without compensation systems. This study uses data of an industrial airborne survey and of a vector magnetometer survey with a small overlapping area in the Vosges (France) to compare both data sets and shows that both solutions provide results of the same overall precision. This paper also addresses the issue of combining fixed altitude and draped level data sets as well as topographic effect management by proposing an equivalent source interpolator based on a set of simple dipole sources. A synthetic case shows that the equivalent source interpolator allows to compute grids of the magnetic anomaly as well as potential field transforms from a draped data set with an error level a few orders of magnitude lower than could be obtained with minimum curvature, a classically applied interpolator. The interpolator is also tested on a case study in the Vosges massif of which geological interpretation is presented in Bertrand et al. (2020). The results confirm the observations made on the synthetic case and show that the equivalent source interpolator is more tolerant to navigation errors (altitude) than minimum curvature and allows more rigorous computation of potential field transforms of draped data sets.

Bruno Gavazzi, Lionel Bertrand, M. Munschy, J. Mercier de Lépinay, M. Diraison, Y. Géraud

Aerial magnetic mapping with an unmanned aerial vehicle and a fluxgate magnetometer: a new method for rapid mapping and upscaling from the field to regional scale.

Abstract

Magnetic measurements with an unmanned aerial vehicle are ideal for filling the gap between ground and airborne magnetic surveying. However, to obtain accurate aeromagnetic data, the compensation of magnetic effects of the unmanned aerial vehicle is a challenge. Typically, scalar magnetometers are towed several metres under the unmanned aerial vehicle to minimize its magnetic field. In this study, a fluxgate three-component magnetometer is attached 42 cm in front of the unmanned aerial vehicle at the tip of a composite pipe. Using a scalar calibration, the sensor can be calibrated, and the permanent and induced magnetic fields of the unmanned aerial vehicle can be compensated. The contributions of the magnetic measurements at different altitudes to the unmanned aerial vehicle results were tested over an area of 1 km² in the Northern Vosges Mountains. The area is located in a hamlet surrounded by a forest where few geological outcrops are observed. Three magnetic surveys of the same area are obtained at different altitudes: 100, 30 and 1 m above the ground. The unmanned aerial vehicle magnetic data are compared with a helicopter aeromagnetic survey at 300 m above the ground and a ground magnetic survey using upward continuations of the maps to compare the results. The magnetic maps (300, 100, 30 and 1 m above the ground) show very different magnetic anomaly patterns (e.g. amplitude, shape, wavelength and orientation). The magnetic data at different altitudes improve the understanding of the geology from the local to more general scales.

P. Le Maire, Lionel Bertrand, M. Munschy, M. Diraison, Y. Géraud

Fluxgate three-component magnetometers for cost-effective ground, UAV and airborne magnetic surveys for industrial and academic geoscience applications and comparison with current industrial standards through case studies.

Abstract

In applied geophysics, magnetic methods are used in a wide range of industrial and academic applications with environmental, engineering or exploration components (e.g. military ordnance detection, pipe detection, archaeology, resources exploration, geological mapping). According to the type of application and the scale of the study, surveys can be conducted on the ground or airborne, each having its own industrial standard. In ground survey applications single component or scalar gradiometers are widely used. In airborne surveys the intensity of the magnetic field is measured with scalar magnetometers and the disturbances of the aircraft are compensated with real-time compensation units. This paper proposes another approach using the latest developments on the use of fluxgate three-component magnetometers. They have a light weight, a low power consumption, are rugged and allow a simple magnetic compensation of the carrier. They can provide a more precise and/or a more cost effective alternative to current measuring standards. They can also be mounted on UAVs to fill the gap in measurement capabilities between ground and airborne surveys, and therefore offer a new range of applications. A review of four case studies concerning archaeology, unexploded ordnance detection, lithology and structural geology studies is presented to illustrate the possibilities of application of such an approach and how it compares to current industrial standards in ground and airborne surveys.

Bruno Gavazzi, P. Le Maire, J. Mercier de Lépinay, P. Calou, M. Munschy

On the use of fluxgate 3-axis magnetometers in archaeology: application with a multi-sensor device on the site of Qasr ‘Allam in the Western desert of Egypt.

Abstract

Fluxgate 3-axis magnetometers are seldom used on archaeological sites due to their lack of precision. Nonetheless, they offer light weight, low power consumption and the ability of compensation of the magnetization of the prospecting device. This study proposes to use calibration and compensation processes developed for space research and aerial measurement to build a multi-sensor and georeferenced device to assess deep and shallow objects for large-scale archaeological investigations in Qasr ‘Allam, in a context of heavy sedimentary coverage and uneven surface. The use of the device on the site in combination with potential field transformations of the signal such as the double reduction to the pole and the vertical derivative reveal a vast irrigation system as well as a large religious facility. A comparison with gradiometric measurements shows a resolution as good at least for shallow sources. The precise positioning allows targeted excavations that validate the geophysical interpretations and offer new archaeological information. These discoveries give enough proof to the local authorities to define the area to be protected from the threatening progression of agricultural fields. Copyright © 2016 John Wiley & Sons, Ltd.

Bruno Gavazzi, R. Alkhatib-Alkontar, M. Munschy, F. Colin, and C. Duvette

Fluxgate vector magnetometers: A multisensor device for ground, UAV, and airborne magnetic surveys.

Abstract

Fluxgate magnetometers are quite uncommon in geophysics. Recent advances in calibration of the devices and their magnetic compensation ability led Institut de Physique du Globe de Strasbourg to develop instruments for magnetic measurements at different scales for a wide range of applications — from submetric measurements on the ground to aircraft-conducted acquisition by unmanned aerial vehicles (UAVs). A case study on the aerial military base BA112 shows the usefulness of the instruments for the detection of underground pipes, unexploded ordnance, and archaeological remains.

Bruno Gavazzi, P. Le Maire, M. Munschy, A. Dechamp

Colloque GEOFCAN

Détection d’une ancienne décharge en milieu difficile d’accès par approche conjointe de profils ERT et d’aéromagnétisme en drone

Résumé

Dans le cadre de la réhabilitation d’une ancienne décharge sur une surface fortement végétalisée, une cartographie magnétique par drone, complétée par des profils ERT, ont été déployés. Les mesures drones ont été faites à différentes élévations en fonction de la praticabilité pour s’assurer de capter les limites de ladite décharge. Les résultats drone mettent en évidence un ensemble contrastant fortement avec l’encaissant aux différentes échelles d’observation, ce qui a permis de délimiter une partie de la zone d’enfouissement. Les résultats ERT montrent une couche de terrain d’environ 2 m d’épaisseur, possiblement du remblai, reposant sur un terrain conducteur a priori lié aux déchets de plus de 10 m d’épaisseur. Les résultats des deux méthodes sont concordants et complémentaires, ce qui est prometteur pour l’étude de site à fortes contraintes d’accès.

M. Nouveau, Bruno Gavazzi, J. Joly, A. Thaveau, Lionel Bertrand, F. Galluser

SEG Summit on Drone Geophysics

Going small: new application capabilities and perspectives using a few hundred grams magnetic kit integrated on a less than 1 kg drone

Abstract

This year we present the latest evolutions through the use of a magnetic kit that can be integrated on any small drone solution, and associated data processing. We review the limitations and differences with scalar magnetometer-based systems, and present new case studies using the kit on a DJI Mavik type drone (Figure 1) for survey performed at different elevation, fromm a few meters to 50 m agl. We present and discuss new applications capabilities or possibilities, notably for waste, pipes, and UXO detection, fractures assessment and resources exploration.

Bruno Gavazzi, Lionel Bertrand, Margaux Goupil, F. Galluser

SIM Dijon

Enerex, Solutions d’exploration du sous-sol : photogrammétrie, exploration magnétique

Lionel Bertrand

SEG Summit on Drone Geophysics

An integrated compact system with a takeof weight of 1kg for efficient and cost effective magnetic surveys: specifications, workfow and examples of application.

Abstract

We present such a system weighting around 1kg, allowing to produce up to 100 km of lines a day
with a precision of 1 to 2nT. Such a system is the result of previous work on the integration of
fluxgate measurements on diferent carriers (ground, air, see) and their magnetic compensation. A first prototype was presented on the previous summit on Drone Geophysics (2022). Its first
successful experimental fights, in the framework of an academic project for geothermal reservoir
exploration, showed its capacity to assess both deep basement and shallower fracture feld features form a 50m AGL survey. Since then, the technology readiness level has been improved and the first commercial fights have been performed. Such a solution require specifc processing steps and survey strategies to insure its efficiency, such as a compensation procedure taking into account more parameters than the more traditional median of profile removal.

Bruno Gavazzi, Lionel Bertrand, Margaux Goupil

Projet SARHAE. Le site archéologique des Rothenstaudenà Voellerdingen (67). Etude d’un habitat antique et de son environnement – Rapport d’opération 2024 : fouille, prospection géophysique, analyse des données LiDAR et paléo-environnement

CNRS; UMR 7044 – Archimède; Enerex; Direction Régionale des Affaires Culturelles du Grand Est – Service Régional de l’Archéologie – Site de Strasbourg; Université de Strasbourg – Investissements d’avenir; Communauté de Communes de l’Alsace Bossue; Commune de Voellerdingen; Société de Recherche Archéologique d’Alsace Bossue; INRAP; Université de Lorraine; UMR 7360 LIEC.

A. Nüsslein, H. Cicutta, D. Laurine, P. Duringer, Bruno Gavazzi, et al.

PEGGHy – Platform for Experimental Geophysics, Geotechnics and Hydrogeology of the Graduate School of Geological Engineering, Nancy, France

GEE 2025 – Geotechnical Engineering Education 2025 Nancy, France
International Conference “Charting the path toward the future” 2-4 July 2025
organized by TC306 – ISSMGE

J. Sausse, P. Cupillard, A. Abdallah, Y. Géraud, M. Diraison, C. Oltean, F. Golfier, O. Cuisinier

Projet SARHAE. Le site archéologique des Rothenstauden à Voellerdingen (67). Etude d’un habitat antique et de son environnement. Rapport d’opération 2023 : fouilles, prospection géophysique et analyse des données Lidar.

CNRS; UMR 7044; Société de Recherche Archéologique d’Alsace Bossue; Direction Régionale des Affaires Culturelles du Grand Est – Service Régional de l’Archéologie – Site de Strasbourg; Université de Strasbourg – Investissements d’avenir; Communauté de Communes de l’Alsace Bossue; Inrap; Enerex.

A. Nüsslein, H. Cicutta, Bruno Gavazzi, J. Thuault, A. Touvron

La campagne du printemps 2022 à Eridu, Irak du Sud

Chroniques d’Archimède 2022 | Territoires et Empires d’Orient

Ph. Quenet, A.-C. Rendu-Loisel

Géophysique magnétique , Villards d’Héria, rapport 5/8 2020.

S.R.A. Bourgogne Franche-Comté.

R. Grebot, Bruno Gavazzi, A. Quiquerez, H. Reiller