ENIGMA ITN is an Innovative Training Network funded by the European Commission.
ENIGMA ITN ( European training Network for in situ imaGing of dynaMic processes in heterogeneous subsurfAce environments) aims at training a new generation of young researchers in the development of innovative methods for imaging process dynamics in subsurface hydrosystems, in order to enhance understanding and predictive modelling capacities and to transfer these innovations to the economic sector.
The 15 young PhD students trained within the network contribute to develop the spatial representation of subsurface heterogeneity, fluxes, chemical reactions and microbial activity, through the integration of data and approaches from geophysics, hydrology, soil physics, and biochemistry. The network ENIGMA gathers 21 partners (15 academic and 6 industrial) from 8 European countries. Each of the 15 PhD students conducts the research work in 2 or 3 institutions, in collaboration with the industrial partners.
AGU Fall Meeting is the largest international Earth and space science meeting in the world (more than 25 000 attendees in 2019). After two dynamic meetings in New Orleans and Washington, D.C., AGU meeting returned last December to the Moscone Center in San Francisco to celebrate the past and inspire the future during this Centennial event.
Here are the testimonials of 6 ENIGMA ITN European PhD students: having the luck to receive feedback from other scientists and students, providing a different point of view concerning a specific study, and exchange ideas about an original topic is tremendously enriching for their research and for their experience as young researchers. Let’s hear them out!
“I enjoyed having the chance of meeting and talking with various researchers and big names that we usually can only meet through their publications and citations,” expressed Guilherme Nogueira, PhD student at the Helmholtz Centre for Environmental Research in Leipzig and part of the EU-funded project ENIGMA ITN, as he returned from the AGU Fall Meeting 2019. The conference of the American Geosphysical Union celebrated its centennial this year. In a digital age, such events contribute to spread the feeling of a scientific community across the world, by bringing people together beyond papers. They offer fellows opportunities to discuss their work and beyond, establishing personal connections across labs. It helps create the germs of future scientific collaborations. Although time-consuming and not so eco-friendly, participating gives in a condensed way the feedback, the network and opportunity that help one’s research path.
of participating in conferences is the same as the core spirit of the ENIGMA
ITN project they are part of. ENIGMA ITN is a EU-funded project (ITN – Innovative
Training Network) training 15 PhD students on innovative methods for imaging
process dynamics in subsurface hydrosystems. Developing a dynamic spatial
representation of groundwater systems requires numerous expertise, data and
methods from not only hydrology, but also geophysics, soil physics and
biochemistry. The PhD students make the most of their research project through lab
visits – the secondments – within the project network, regular network meeting
and a common training program.
It was Jorge’s, one of the ENIGMA fellows based at the University of Liège, first time in such a large conference. He presented his last results on deep modelling for better imaging the subsurface: “When imaging the subsurface we can only put sensors on the surface or in a limited number of wells. The sparsity of such observations prevents us from directly obtaining a sharp image. In order to get such an image we can use additional information such as the expected spatial structure of geological materials, e.g. channels, lenses, dikes, etc. Constraining imaging methods to display these realistic patterns is, however, not straightforward. Our research uses recently developed deep generative models to constrain an efficient imaging method to display such realistic patterns.”
San Francisco gave him the opportunity to replace his work in a greater
perspective. “I really enjoyed the chance of putting my research in context
with all other areas in the Earth sciences” he said. “I saw a lot of nice
applications of machine learning and data-driven models in multiple areas
different than my own (such as surface hydrology and seismology) of which I was
not really aware of but that were insightful for my current research.”
This year, AGU celebrated its centennial by hosting special sessions on the history of geosciences. It was highly appreciated by Jorge: “I found the one on near surface geophysics to be quite insightful. It was a very nice summary of the development of different geophysical methods, covering both the instrumentation side and the processing and modeling side. In addition, the talks were given by recognized scholars that greatly contributed to such development.” Lara attended the same special session calling it a “unique opportunity”: “We got a past, present and future view on the different methods from well-known scientists in the area.” Affiliated to CNRS and based at Geosciences Rennes, she is working on monitoring spatio-temporal water redistribution in the subsurface with seismic methods. She presented the results of a time-lapse field experiment where the applicability of seismic and electrical methods was tested to monitor water saturation changes in the near-surface unsaturated zone. “There is growing interest in understanding unsaturated zone processes as they have control over water availability, contaminant transport, and geotechnical matters, and these methods can be applied in a non-intrusive way (i.e. without digging a borehole) to provide subsurface information”.
presentation considered that e.g. temperature has an underestimated
potential for hydrogeological questions about subsurface transport. Most of the
time questions related to groundwater quality and quantity aspect deal with
head and concentration neglect possible derived information from dynamic
process imaging (e.g. temporary changes of viscosity by a variation of the
temperature). Thus, my presentation had the goal to highlight, that temperature
and dissolved gas injections (e.g. tracer tests) promising opportunities for
different aquifer systems worldwide and that added information, e.g. about the
matrix diffusion, can be imaged and derived. As global scientific outcome I
showed that hot and cold water injections offer the possibility to quantify
dynamic aquifer changes, as both tracers influence the dynamic viscosity. This
seems me to be one way to increase the robustness of predictions. One general
outcome of my presentation was, that knowledge from different sites (Belgium
and India) is transferrable and we can learn equally from the both sites
Following his oral presentation, he was pleased that “a scientist I didn’t know before came some time after my oral presentation in another session to me personally to speak shortly about my presented work. For me it was a reward, indicating that the science I do has a small impact. This motivated me strongly to continue my work as well as to increase the impact of my results by advancing my methodologies much more”.
For Justine, from Itasca Consultants (France) and based within Geosciences Rennes, presenting her work really helped to broaden her point of view.
“I presented a poster of the results of my first experiment in the Äspö Hard Rock Laboratory, Sweden. This experiment consisted to image the fractures in the subsurface in a tunnel situated at 410 m of depth with Ground Penetrating Radar (GPR). With this method, we could know the number, the localization and the orientation of the fractures with sub-millimeter aperture (and very low flow of water) in a block of rock of 3.4 m x 12.0 m dimension. We then build a statistical model deduced from outcrop data (fracture traces seen on tunnel walls). By combining the field data with the statistical fracture model of the tunnel, we can estimate the GPR detectability in terms of fracture sizes and orientations in a very low permeable crystalline rock. This experiment is only the first part of my research. The next experiment consisted to image the connectivity between fractures and the preferential pathways of groundwater (by GPR monitoring during tracer tests). The general objective of this work is to use the GPR information to reduce uncertainties of current fracture models. These models can be used (with additional studies) to define if a site is suitable or not for deep disposal nuclear waste.
of my poster allows to have valuable discussions from people (academic and
industrial researchers & students), outside of my labs. Getting a fresh
look about at my research allows me to take a step back and gain insights for
new perspectives. If I feel stuck in a task, it is better to take a step back
in order to broaden my point of view to be able to enrich it in a more
“detached way”. In addition, I really liked my scientific session (about
fractures) because it allows me to meet a lot of people working on the same
subject. It was also the occasion to meet people from Itasca Consulting Group,
Inc (the headquarter in Minneapolis) and SKB, the companies that I work for.”
Guilherme agrees with Richard and Justine: “Having the chance of receiving feedback from other scientists and students, providing a different point of view concerning a study, and exchange ideas about a topic is tremendously enriching for the research and for our experience as ESR.”
Guilherme presented a
poster on the results of field tests carried out to acquire in-situ and
accurate spatial and temporal variations of groundwater travel-times and oxygen
consumption rates around the interface of a stream and its adjacent aquifer in
center Germany. “By combining field experiments, high-frequency measurements,
and numerical modelling we highlighted the influences and links of surface
variations and its impacts in the subsurface flow and reaction dynamics. It
helps us improve our understanding of the relations between water temperature, river
stage and aquifer heterogeneity and their impact on the development of reactive
zones shaping surface and groundwater quality. We
demonstrated that changes in reaction processes have a greater relevance in the
development of such zones since local transport processes are less affected by
short and seasonal fluctuations of river dynamics. Furthermore, we showed that
higher turnover potentials are related to zones with slightly lower hydraulic
conductivity, probably linked to accumulation of organic matter of different
sources at the interface of different aquifer materials.”
Besides, he engaged in larger discussions: “I also took part in a workshop about the Critical Zone, where I could specifically get involved with other scientists that have their main focus in a similar area as we research. With that, I could see how (and how to) our interests and open questions are aligned in a specific context/topic, improve the network, and discuss/come up with common questions and ideas for developing the field and the Critical Zone community.”
The conference helped others develop a sharper vision of their field. Satoshi, from Jülich Research Centre (Germany) develops new methods to image minerals in the subsurface: “My presentation was associated to the development of electrical method for detecting calcite, which is one of the minerals, in subsurface. We showed the results from newly developed laboratory setup that allowed us to visualize calcite precipitation process in 2D porous media as well as measure electric properties with spectral induced polarization method. Thanks for this setup, we could better understand how calcite precipitation process changes the measured electric signals. It can be used to remediate, control groundwater flow and stabilize the soil.“ He linked his work directly with other developments in the field: “The feedback for my experimental work which pointed out what is the major issue in my experiment and what other people in my research field are thinking about right now. I had gut feeling about the way how my research field will develop and about the area where other people are not really focusing on. “
On a more
personal level, Satoshi was also pleased to have time to catch-up with former
colleagues from Japan. Lara did the same. “I got to meet again and catch up with US-based researchers I had met last
year. I think it is important to seize these opportunities from early on and
build international relationships that can lead to collaborations.” she said.
Returning to Leipzig,
Guilherme feels motivated to continue his work: “From the conference I brought
back feedback and ideas I received to complement and implement in what is to
come from my research – fruitful discussions supported me to see strong and
weak points in the study we are carrying out to answer out research questions.
Furthermore, I also personally brought the good scientific energy and mood that
is around the week conference, motivating any scientist and attendee to seek
and question always for more in any field of science. I enjoyed a lot to see
how many and much of science and research is going on around the globe (and
outside it) in what concerns geosciences as a whole!”
Richard keeps in mind what he saw at AGU: “It was
visible, that data science related tools have already a very good
practicability (e.g. applying data mining techniques on surface data imaged by
satellites) but are still rarely in use for real large-scale cases in the
subsurface. This highlighted me clearly, that by applying new innovative
subsurface imaging techniques always recent developed data science applications
are worth to consider as well as that the transfer from local to large scale is
important and must be as realistic as possible.”
Back in Rennes, Lara
concludes: “It was
pleasing to see the research of my fellow [ENIGMA] PhD students and the
progress we have made. AGU can also be rather overwhelming, you find people doing very good
science and it is great getting to talk to them, however that can also make you
feel a bit conscious about your own work. I still try to use those moments as
motivation.” She finishes with wise words: “As I am in the last year of the PhD
the main thing I take with me is to not get lost in the details.” We wish her
and the others luck for the final PhD stretch!
Event: AGU Fall Meeting 2019, San Francisco (USA) Poster by Justine Molron, Niklas Linde, Ludovic Baron, Jan-Olof Selroos, Caroline Darcel, Philippe Davy
The identification of (open) fractures in the subsurface is critical for evaluating potential routes for contaminant transport from deep disposal sites. Ground Penetrating Radar (GPR) is suitable for this task and its detection capacity depends on fracture characteristics (orientation, aperture and size) and on the dielectrical and electrical contrast between the fluid or material filling the fractures and the surrounding bedrock.
A GPR experiment was performed in the Äspö Hard Rock Laboratory (Sweden) in a tunnel located 410 m below the sea level with a length of 20 m long, a width of 4 m and a height of 4.5 m. The geological formations are fractured granite, diorite and granodiorite with negligible matrix permeability and very low transmissive fractures (10E-9 to 10E-10 m2/s for most permeable zones).
We used 160 MHz, 450 MHz and 750 MHz antennas, pulled along the clean and flat tunnel floor along parallel lines separated by 0.10 m for 160 MHz and by 0.05 m for 450 and 750 MHz antennas. This measurement set-up and antenna choices allow for a 3D identification of fractures from GPR diffractions and reflections, with different image resolutions and investigation depths reaching 10m, 8m and 5m for 160, 450 and 750 MHz, respectively.
Based on the data, we identify 15 reflections that could correspond to larger fractures with dimensions of 2 to 5 m. We compare the GPR-inferred fractures with the corelogging of three 9.5 m deep boreholes that were drilled after the GPR campaign. The strong GPR reflections in the borehole area largely correspond to the depth and orientation to the fractures identified by the Optical Televiewer (OPTV) data.
Additionally, pumping and injection tests in each borehole showed that the GPR-inferred fractures are situated in the most permeable regions. The occurrence of GPR fractures was then compared with a statistical description of the fracture network built from the intersection of boreholes and 2D trace maps from tunnel walls. Given the average size of the GPR-inferred fractures, we demonstrate that they are overall consistent with the expected fracture density below the tunnel.
Event: AGU Fall Meeting 2019, San Francisco (USA) Poster by Behzad Pouladi, Niklas Linde, Olivier Bour, Laurent Longuevergne
Subsurface characterization often relies on inversion of either pressure or tracer data. Unless data from many pumping and observation wells are available, the inversion process only resolves smooth low-resolution images of subsurface properties, which leads to less accurate subsurface ﬂow and reactive transport predictions. Furthermore, tracer tomography can be very challenging and convergence to a global minimum is difficult. Active-distributed temperature sensing technology opens up the prospect of replacing tracer test data with estimates of subsurface groundwater flux .
Here, the value of using estimated subsurface groundwater fluxes as a data source to reconstruct subsurface hydraulic properties is explored using a sequence of synthetic multivariate Gaussian aquifers with different measurement configurations. These results are compared to inversion of pressure data and joint inversion of the two data types with the inversions being based on the Principal Component Geostatistical Approach . Inversion of pressure data resulted in a smoothed reconstruction of aquifer heterogeneity capturing approximately high and low conductivity regions while ground water flux data inversion leads to higher-resolution estimates. This is reflected, for one of the considered examples, by a correlation coefficient that increases from 0.57 for the pressure data to 0.65 for the ground water flux data. The complimentary nature of the data sets is represented by a correlation coefficient that increases to 0.74 for the joint inversion of the two data types.To conclude, inversion of ground water flux whether individually or jointly with pressure data, can provide enhanced information about the heterogeneity of subsurface media compared with using pressure data alone.
Event: AGU Fall Meeting 2019, San Francisco (USA) Presentation by Lara Blazevic, Ludovic Bodet, Niklas Linde, Laurent Longuevergne, Sylvain Pasquet, Thomas Hermans, Damien Jougnot
Geophysical methods provide non-intrusive means to obtain subsurface information of relevance for agriculture, pollutant transport and critical zone processes. Electrical resistivity tomography (ERT) is routinely employed to derive water content and associated fluxes while seismic methods in hydrogeophysics have recently developed with the estimation of Poisson’s ratio from the combined use of P-wave traveltime tomography and surface-wave dispersion inversion. Here, we investigate the complementarity of such time-lapse approaches in a well-known and controlled context.
The Ploemeur Hydrological Observatory, located in Brittany (France), lies on a contact zone between granite and micaschists. The crystalline bedrock aquifer is an important source of drinking water for the nearby population and is monitored with numerous boreholes and experimental campaigns on site.
In September 2018, we carried out a two-day controlled and gradual infiltration experiment in soil overlaying the micaschists and performed eleven repeated electrical resistivity and active seismic acquisitions on two orthogonal lines crossing the 2.2×2.4 m2 infiltration area. In total, 3.3 m3 of water were injected. Adjacent to the infiltration area, time-domain reflectometry (TDR) sensors installed at different depths provided real time water content estimates during the experiment. They reveal that in the upper 0.25 m, the increases in water content may exceed 125%, and may increase by 25-50% even at 2 m depth. Our 2D and 3D time-lapse ERT inversions agree with these findings, in that we observe a decrease of up to 90% in electrical resistivity in the upper 1 m.
For the seismic data, we computed the differences in first arrival times with respect to the first reference acquisition by cross-correlating the traces and observed positive relative changes in traveltimes in the infiltration area going from 30-90%. The 2D time-lapse traveltime inversion shows a similar behavior as the ERT with P-wave velocities decreasing between 50-90% in the upper 1 m.
Our ultimate aim is to combine these results with S-wave velocities from surface-wave analyses and perform joint 3D time-lapse inversion of the dataset to better constrain water content and rock physics models in the vadose zone.
Event: AGU Fall Meeting 2019, San Francisco (USA) Presentation by Richard Hoffmann, Pascal Goderniaux, Alain Dassargues
Informative reference data for a realistic assessment of aquifer heterogeneity is a prerequisite for robust transport simulations. Structure-based imaging using salt or a dye as tracer with a known concentration and volume to observe transfer times, is a powerful hydrogeological tool in moderate heterogenous media. Solving then the advection-dispersion equation will explain most of the point to point transport behavior. But, once the aquifer heterogeneity is more complex, e.g. in a double porosity medium like chalk, matrix porosity linked to diffusion processes must be taken into consideration to avoid a biased interpretation of the tracer information. Thus, performing additional local process-based imaging using smart tracers as dissolved gas and hot or cold water, assists to explain the late-time tailing behaviors realistically.
Smart tracers were injected in a sub-horizontal fracture connecting
two adjacent wells to provide data about the complementary behaviors of
each tracer and to focus on matrix diffusion processes. One reference
data set is a 70 hours injection of hot water (∆T = + 40 °C)
complemented by two 10 minutes uranine pulse injections within an
inflatable double packer system isolating the sub-horizontal chalk
fracture of interest. The temperature signal arrives at a 7.55 m
distance with a delay of 12 hours compared to the first uranine
injection and shows a rebound after the injection stopped. Useful
reference data for further numerical modelling consists now in (a) local
fracture geometry information deduced from interpretation by analytical
solutions and, (b) matrix diffusion information.
Numerical modelling of those smart tracer experiments may question deterministic models for predictions and motivates for data-driven prediction tools like Monte-Carlo simulation procedures within a direct predictive framework. Distance based global sensitivity analysis (e.g. simultaneous variation of multiple input variables like diffusion coefficient, aperture and matrix storage) will be considered accounting for temperature related changes of viscosity and density. Key information about the most influencing parameters are main model outcomes, as local process understanding is very useful for possible future upscaling in regional models made of structure-based imaging.