In-situ experiments of gas/water fracturing : Geophysical Monitoring of initiation and propagation of fractures

5 to 6 months between January and July 2024

Predicting occurrence of hydraulically induced damage in geological systems constitutes a major challenge in subsurface engineering. An in situ experiment is being performed at the Tournemire site (Southern France) to evaluate under which conditions fractures could be initiated/propagated in a saturated, indurated clayey formation due to an increase of gas or water pressure. This fracturing field test will be conducted using three types of boreholes (each being 20 m long) : (i) one injection borehole ; (ii) eight boreholes dedicated to geophysical monitoring of the “dynamic” fracturing process ; (iii) height boreholes equipped with distributed fiber optic sensor cables and two boreholes equipped with strain gauges to record deformation and estimate the location of the fractures being opened, which will help constraining the geophysical survey. This network is used for two purposes : (1) long term monitoring of resistivity and induced polarization (IP) parameters before and after the stimulations (over a period of several years), and (2) self-potential monitoring just before, during, and shortly after the hydraulic stimulation.

The intern will be recruited to process data acquired during experiments conducted in 2022 with a special focus on resistivity and IP monitoring, and also to participate to new experiments consisting of gas injection. To summarize, the experiments should give elements about : (i) how the gas cracking pressure depends on both the kinetics of gas injection and gas dissolution/diffusion in argillite, which would give a practical method for controlling-guarantying the cap rock integrity e.g. in gas storage application ; (ii) how the self-sealing of cap rocks may occur after a possible cracking ; (iii) quantitative information about fracture propagation due to fluid overpressure, (iv) providing data of fracture initiation/propagation from a field test.

The processing of geophysical data will be two steps : 1) assessing the quality of experimental data and, 2) 3D time-lapse inversion of resistivity and IP to image the evolution of these two geophysical parameters during injection experiments.

Location : This full-time position will be mainly located at ISTERRE in Grenoble with potential missions to the Tournemire site (IRSN).

Student profile : The candidate must be a highly-motivated and self-directed person with a solid knowledge in geophysics. The successful candidate must have a strong background in computing and geophysics. The suitable candidate must be fluent in signal processing, production data interpretation, and inverse methods. Notably, the processing of geophysical data will be conducted with the pyGIMLi package (pygimli.org/).

Applicants should email their Curriculum Vitae to :
Gregory Bièvre (ISTerre) : gregory.bievre univ-grenoble-alpes.fr
Pierre Dick (IRSN) : pierre.dick irsn.fr
Mai-Linh Doan (ISTerre) : mai-linh.doan univ-grenoble-alpes.fr