Up to recent time, underground has been investigated mainly for its non-renewable natural resources neglecting its huge potential for storage and geothermal capability. A full energetic transition from traditional hydrocarbon resources to carbon free energy needs smart and safe underground use. In addition to being a source of geothermal energy, the subsurface is a vast 3D space that can be used in a carefully planned way for the management of carbon-free energies through the geological storage of CO2 and various other forms of energy vectors (e.g., H2, heat, compressed air).
For a safe and efficient exploitation of all natural resources (e.g., geothermal energy, hydrocarbon, minerals) or underground storage, one critical effort is to identify, characterize, and monitor natural clayey cap rock overlying a target (resource reservoir or storage volume), which plays an essential role in risk reduction (e.g., water table contamination, substances upward leakage) due to their low permeability. Characterization of clayey rocks is thus a key issue in this context. Focusing on this geological formation allows reducing a great part of geotechnologies issues.
The identification, characterization, and monitoring of the mineralogy and permeability of the clayey rocks is classically done using boreholes geological, geochemical and geophysical measurements. Despite having a high accuracy, boreholes measurements are invasive and can only bring punctual information at high cost. Surface-based geophysical tools, and especially electrical and electromagnetic (EM) methods (i.e. electric and/or magnetic field measurements), can provide additional information between boreholes at a significantly lower cost and repeatable in time. Interpretation of EM measurements is usually performed using only the direct current (DC) electrical resistivity, which yields to equivalency, sensitivity, and spatial resolution problems. These problems limit the method ability to identify different compartments and therefore generate interpretation difficulties. Using EM measurements and complex resistivity will improve the reliability and accuracy of the interpretation. But, this improvement requires high level of instrumental, theoretical and modeling developments at different scales, in particular for clayey rocks, as these rocks have a typical complex electrical signature associated with their strong surface electrical properties which is function of the clay mineralogy.
The main objective of the project is to improve the characterization of the complex and frequency dependence of electrical properties of different clays minerals and mixtures. For that purpose, we intend to closely combine measurements, modeling and inversion tools at different scales (from nano to pluri-m) in parallel to instrumental development. This work will require the development of upscaling procedures, from the mineral/water interface (nano/micrometric) to the field scale (decametric to kilometric). Laboratory experiments using Spectral Induced Polarization (SIP) and multi-scale simulations will be conducted in order to validate the upscaling relationships developed theoretically. These models will be included in an existing inversion code in order to characterize the complex electrical conductivity (chargeability) more precisely after inversion.
In parallel, we aim at improving the reliability of EM imaging at depth based on Controlled Source EM (CSEM) by resolving the surface heterogeneities “static” effects which often deteriorates the imaging capabilities deeper. We will develop a new prototype of EM Induction device (EMI) in order to image densely over large zone the shallow earth (from deca to hectometers). This project will help to push further the use of geophysical methods for the characterization of clayey cap rocks.
Monsieur Jean-Francois Girard (Institut de Physique du Globe de Strasbourg)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
IPGS Institut de Physique du Globe de Strasbourg
METIS Milieux Environnementaux, Transferts et Interactions dans les hydrosystèmes et les Sols
IC2MP Institut de Chimie des Milieux et des Matériaux de Poitiers
BRGM Bureau de recherches géologiques et minières
IRIS IRIS INSTRUMENTS
Help of the ANR 670,024 euros
Beginning and duration of the scientific project: January 2018 - 48 Months