PhD on faster alteration of rocks in active faults? Insight from experimental and numerical simulations, with application to geothermal energy (M/F)

13 Apr 2024
Job Information

Organisation/Company

CNRS

Department

Institut des sciences de la Terre

Research Field

Geosciences
Astronomy
Environmental science

Researcher Profile

First Stage Researcher (R1)

Country

France

Application Deadline

3 May 2024 - 23:59 (UTC)

Type of Contract

Temporary

Job Status

Full-time

Hours Per Week

35

Offer Starting Date

1 Oct 2024

Is the job funded through the EU Research Framework Programme?

Not funded by an EU programme

Is the Job related to staff position within a Research Infrastructure?

No

Offer Description

The Centre national de la recherche scientifique is one of the world's leading research institutions. To meet the major challenges of today and tomorrow, its scientists explore life, matter, the Universe and the workings of human society. Internationally recognized for the excellence of its scientific work, the CNRS is a benchmark in the world of research and development, as well as for the general public.
The thesis will be carried out within the ISTerre laboratory.
ISTerre is a joint research unit of Université Grenoble Alpes, CNRS, USMB, IRD and Université Gustave Eiffel, located at 1381 rue de la Piscine 38400 Saint-Martin d'Hères, on the Bourget du Lac science campus. It is part of the Observatoire des Sciences de l'Univers de Grenoble (OSUG) and the PAGE research cluster of the Université Grenoble Alpes (UGA). It employs around 300 people and has an average annual budget of €7 million. It is organized around 9 research and service teams, with the scientific objective of studying the physics and chemistry of planet Earth, with a particular focus on coupling observations of natural objects with experimentation and modeling of the associated complex processes. ISTerre also carries out solid Earth observation missions, and hosts and maintains national fleets of geophysical instruments, as well as a data center.
The thesis will be carried out within the Faults Team, which is made up of 25 people: researchers and teacher-researchers, post-docs, PhD students...
The PhD student will be co-tutored by the two PhD advisers, in their responsive fields of expertise (experiments for ML Doan and numerical modelling for FV Donzé).
The PhD student will be benefit from the extensive training proposed by the Université Grenoble-Alpes (at least, 120h of training). The progress of the PhD student will be screened every year by an independent committee to ensure the PhD research advances smoothly. The PhD student will have the opportunity to present his research to the ANR AlterAction interdisciplinary network of academic researchers and geothermal R&D staff, all working on the alteration processes in active faults.
The doctoral school will be STEP - Sciences de la Terre de l'Environnement et des Planètes (Earth, Environmental and Planetary Sciences).

The project focuses on the process of maturation of active faults in the upper crust by chemical alteration of their fault walls, and on the feedback between alteration and tectonic activity. This topic is at the center of the AlterAction ANR project (https://anr -
alteraction.osug.fr/), gathering 20 scientists from four institutions, supported by geothermal companies, and funded for 42 months
(2024-2027).
The main research hypothesis is that fault activity induces new fractures that enhance fluid-rock interactions and the associated fault zone alteration. This feedback forcing would accelerate the maturation of active faults by creating clay gouges that weaken the fault and decrease its core permeability over time. Such a process could also deteriorate the flow properties in Enhanced Geothermal Reservoirs, such as Alsace, which is also a place of active tectonics. Therefore, a better understanding of the coupling between damage and alteration in active faults and reservoirs is required.
Our focus is on granitoid rocks, which are the lithology of both the Rhine Valley geothermal reservoirs and the wall rocks of the Nojima fault responsible for the 1995 Kobe earthquake in Japan. The PhD student will have access to samples from both sides. Dynamic loading will pulverize granitoid rocks from both study sites, which enhances their permeability (Doan & Gary, 2009). This facilitates the laboratory alteration of centimetric samples, as shown by preliminary experiments (Denys, 2021). Experiments and numerical simulations can then be used to test the main research hypothesis.
The study to be undertaken by the PhD laureate is twofold:
1.Experimental investigation of the influence of deviatoric stress on rock alteration Several monthlong experiments at various deviatoric stresses will be conducted on the newly upgraded triaxial percolation cells of the ISTerre laboratory, on which preliminary alteration experiments were successful. Stress, strain, permeability, and fluid geochemistry wil be recorded during the experiments. X-ray CT scans will quantify the changes in the fracture network induced by fluid percolation. A possible extension of the experiments may be performed at the European Synchrotron Research Facility (ESRF), for which a CHRONOS proposal was submitted to perform time-lapse X-ray imaging of the sample during the alteration experiments.
2.Numerical simulations of the alteration and deformation of rocks subjected to deviatoric stress when percolated with reactive fluids. The simulations will be validated by reproducing the experimental results. Modelling will be used to upscale the experimental results to natural faults and geothermal reservoirs to reproduce the increase in damage and alteration when approaching the fault core, as observed along faults.
The PhD student will benefit from the research network of the AlterAction ANR Project. Especially, he/she will strongly collaborate with another PhD student from Montpellier University, who is in charge of quantifying damage and alteration along the Nojima fault zone, using samples from the GSJ-Hirabayashi samples from mineralogical observations and petrophysical measurements.
Although the PhD topic is dedicated to fundamental research, the PhD student will have the opportunity to interact with representatives of the geothermal companies that expressed their interest in the project at the time of its submission.

Thematics : Earth Sciences / Geothermal energy and Fault Mechanics / Fluid-rock interaction
Alteration in active faults:
Active faults are tectonic objects of great societal interest. There are the loci of devastating earthquakes. They are also preferential pathways for fluid flow (Bense et al., 2013), a key factor for georessources, by controlling the genesis of mineral deposits or by allowing the circulation of geothermal fluids.
Large active faults tend to differ from younger fresh faults. They are the loci of the greatest earthquakes, but they creep often (Kaduri et al., 2017). The damage zone thickness tends to saturate with large displacement (Savage & Brodsky, 2011). Deep scientific drilling in large active faults shows systematically a differentiated fault gouge, surrounded by a halo of fracturing and alteration (Fujimoto et al, 2001). Despite its importance for fault evolution, the process of alteration in large active faults is still not well understood.
Recent progresses have been made in the characterization of alteration, stemming from the extensive study of enhanced geothermal systems (EGS) by combining borehole logging and petrophysical properties on cuttings. Fluid percolation at high temperature activates hydrothermal reactions, changing reservoir properties, as seen from granitoids forming EGS reservoirs in the Rhine Valley (Vidal et al., 2018). But this description of alteration remains static. Alteration products will plug the newly created EGS reservoir fracture network (Bartier et al., 2008) and reduce its geothermal efficiency. Hence, quantifying the alteration dynamics allows assessing the longevity of EGS reservoirs.
The kinetics and thermodynamics of granitoid alteration reactions may be quantified in autoclaves. It remains difficult to scale up such results to core or reservoir scales, as it does not fully describe the progressive interplay between fracture network flow and fluid-rock interactions. To the opposite, dynamic flow-through experiments performed on pre-fractured or porous medium in percolation cells (Luquot & Gouze, 2009) provide key data for this upscaling. However, they are difficult to perform in low-permeability formation, like in granitoids. Pre-loading samples with Split Hopkinson Pressure Bars can generate intense fracturing, especially in granitoids (Doan and Gary, 2009; Aben et al., 2016), because of its high-strain rate loading, reminiscent of co-seismic loading in faults. In the triaxial percolation cells of ISTerre, it was possible to reproduce post-damage cementing after several months of calcite rich fluid circulation
(Luquot and Gouze, 2009; Aben et al, 2017). Recent experiments on the same percolation cells showed that a strong alteration could be also induced within a pulverized granite sample after 3 months of percolation of CO2-rich fluid at 180°C (Denys, 2021). The multi-centimetric samples also exhibited significant creep, as observed in some active faults.
Nojima fault (Japan):
After the devastating Mw 7.3 Nanbu-Kobe earthquake of 1995, a 750 m deep borehole was drilled to the Nojima fault core at 625 m. Continuous coring and borehole logging showed the granodiorite protolith experienced several stages of alteration (Ohtani et al., 2000):(1) a pre-faulting alteration at T sup to 270°C generating pervasive chloritization, (2) a fault-related alteration that deposited laumontite (Ca-rich zeolite) and smectite at Tsup to 150°C at the bottom 300 m (i.e. a 30m thick zone, given the well trajectory) and (3) recent deposition of calcite and siderite, that heals the fault after earthquakes (Boullier, 2011). We aim at characterizing and reproducing this second stage of alteration, concomitant with the maturation of the fault.
Soultz-sous-Forêt geothermal plant (Alsace, France):
The Soultz-sous-Forêt EGS test site focused geothermal research in France in the early 2000s. It drilled monzogranitic rocks down to ~5km. EGS reservoir encompasses extensively altered rocks rather than fresh work. A mineralogic (Bartier et al., 2008) and petrophysical description (Sausse et al., 2006) provides a detailed static description of alteration, mainly due to the deposition of illite, which reduces permeability, and some tosudite rich in lithium (Li). The exact phasing of alteration is not well understood, and seems to occur in addition to deposition of carbonates. It is key to understand not only the current alteration, but also its evolution with fluid circulation associated to EGS exploitation. Yet, no dynamic alteration study has been performed on the Soultz-sous-Forêt rocks, where commercial extraction of Li is undertaken. Quantifying fluid-rock interaction will help to understand how alteration can modify the hydraulic properties of the reservoir and how alteration can enrich flowing fluids in Li during EGS exploitation.
Ojective: by testing the effect of increasing deviatoric stress, the influence of the mechanical loading onto the alteration process should be determined and quantified.
Objectives for promoting the doctoral student's research work:
At least 2 articles are expected to come out of this PhD : one about the experimental results (confirming or not the main scientific hypothesis), and one about the numerical modeling (extending the feedback to large scale evolution of EGS fractures and active faults). There's no confidentiality problems related to the PhD.

Requirements

Research Field

Geosciences

Education Level

Master Degree or equivalent

Research Field

Astronomy

Education Level

Master Degree or equivalent

Research Field

Environmental science

Education Level

Master Degree or equivalent

Languages

FRENCH

Level

Basic

Research Field

Geosciences

Years of Research Experience

None

Research Field

Astronomy

Years of Research Experience

None

Research Field

Environmental science

Years of Research Experience

None

Additional Information
Additional comments

Candidates must hold a Master's degree in Earth Sciences, Mechanics or Inorganic Chemistry.
The following skills are expected:
good knowledge of rock mechanics and an appetite for experimental work.
Previous experience in numerical modeling is required.
As there will be strong interaction with the many researchers involved in the ANR project, with a variety of expertise, the candidate must be open-minded and willing to communicate his results.
- Planned collaborations:
The PhD student will benefit from the research network of the AlterAction ANR Project. Especially, he/she will strongly collaborate with another PhD student from Montpellier University, who is in charge of quantifying damage and alteration along the Nojima fault zone, using samples from the GSJ-Hirabayashi samples from mineralogical observations and petrophysical measurements.
Although the PhD topic is dedicated to fundamental research, the PhD student will have the opportunity to interact with representatives of the geothermal companies that expressed their interest in the project at the time of its submission.
- International opening:
The PhD will focus on a Japanese fault, and collaboration has begun with Japanese researchers. Also, the Rhine Valley extends into Germany, where geothermal energy is also getting developed. So there is an international opening, in addition to the wide opening between the French community.

Website for additional job details

https://emploi.cnrs.fr/Offres/Doctorant/UMR5275-FABCAR-091/Default.aspx

Work Location(s)

Number of offers available

1

Company/Institute

Institut des sciences de la Terre

Country

France

City

ST MARTIN D HERES

Geofield

Where to apply

Website

https://emploi.cnrs.fr/Candidat/Offre/UMR5275-FABCAR-091/Candidater.aspx

Contact

City

ST MARTIN D HERES

Website

http://isterre.fr/

STATUS: EXPIRED