ESR N° 10: High resolution imaging of transport processes with GPR full-waveform inversion

Research Objectives

Dedicated full-waveform inversion approaches will therefore be developed for :

1. time-lapse crosshole measurements to image transport processes (gradients of local concentrations) in synthetic and field tracer tests (Krauthausen site) and
2. time-lapse single-hole and cross-hole measurements in fractured aquifers where the full-waveform phase and amplitude changes will be explored to estimate fracture thickness and filling material (Ploemeur site).

Tasks and methodology

1. Predict a field tracer test by applying a synthetic tracer test in a faithful heterogeneous aquifer model, use petrophysical relations to link hydrogeological to electromagnetic properties, and monitor the spatio-temporal spread of the plume using a GPR forward model.
2. Perform time-lapse cross-hole GPR-FWI of a field tracer experiment in Krauthausen test site, Germany.
3. Investigate tracer time-lapse GPR data that are reflected from fractures, and develop algorithms to extract characteristics of the aquifer.

Data and database

Data produced during the research project will be inserted on the TERENO database.

Dissemination and communication

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Oral presentation at the 2018 SEG Annual Meeting in Anaheim, CA :Time-Lapse Ground Penetrating Radar Full-Waveform Inversion to detect tracer plumes, A Numerical Study

Board member of the “RWTH Aachen SEG Student Chapter”.
More information on : https://rwthseg.wixsite.com/rwth-seg/board

Poster presented during the 4th Cargèse Summer School :Testing the potential of GPR-FWI to detect tracer plumes in time-lapse monitoring

Glossary

Ground penetrating radar (GPR) – a geophysical technique that uses high frequency electromagnetic waves with frequencies between 10 MHz-2 GHz. From the near-surface hydrogeological environment, the GPR response is influenced by the electrical properties: dielectric permittivity and electrical conductivity.

Petrophysical relations – models for transformation of measured geophysical properties (dielectric permittivity and electrical conductivity in GPR) to hydrogeological properties (e.g. porosity, hydraulic conductivity, salinity).

Cross-hole GPR – setup of radar waves traveling from a transmitter placed in a borehole to a receiver placed in another borehole several meters away.

Full-waveform inversion – Full-waveform inversion aims at revealing underground structures by searching for a dielectric permittivity and electrical conductivity distribution that explains the measured data. FWI uses the full waveform of the measured data and simulates more accurately the propagation of electromagnetic waves in the ground, and consequently improves considerably the spatial resolution compare to ray-based techniques.