The goal of you PhD project is to better understand how fractures zones change the productivity of reservoirs. Can you explain some the challenges you are exploring in your research ?
The hot water that’s exploited through deep geothermal wells [in Alsace] circulates in fracture zones within granite. My goal is to develop quick and economically viable tools, adapted to industry needs, to characterise the permeability of these fracture zones. For this, I have rock samples taken from geothermal wells and geophysical data from well logs. I am studying three sites with a total of seven wells, including four deep wells at Soultz-sous-Forêts, which are already well documented, two wells at Rittershoffen, and one well in Illkirch. These wells represent a wealth of data, which are interesting.
How do you do it ?
On on hand, I am interested in the characterisation of clay minerals due to hydrothermal alteration in rocks. In collaboration with the University of Poitiers, I am using the short-wave infrared method (SWIR), which is still a relatively unused tool in geothermal research. This methods makes is possible to identify illite, which is the main mineral resulting from hydrothermal alteration in the granite reservoirs of the Rhine graben. In this way, we are able to quantify and locate illite down the borehole, which makes it possible to measure the extent and intensity of the alteration in the fracture zones intersecting these wells. The method is very fast: the analysis of a sample takes less than a second, as opposed to 30 to 40 minutes using other methods like X-ray diffraction. I have been able to process around 3000 samples. This has given me a global view of hydrothermal alteration in the wells.
However, this method needs to be calibrated because the measurements are very dependent on the geology of the granite. This is a real challenge for the Illkirch well, which has not yet been studied. This is the goal for the coming months.
What is the second part of your thesis, which will keep you occupied in the months to come ?
The second part consists of studying the electrical logs acquired in three wells at Soultz-sous-Forêts, Rittershoffen, and Illkirch. The purchase of software – funded by the LabEx G-eau-thermie Profonde – will allow us to model the response of the tools.
How did you find out about this subject ?
This project is the natural continuation of my University of Strasbourg Master’s of geology internship with ÉS-Géothermie in 2017. Interested in geothermal energy, I enrolled in EOST’s geothermal course, during which I was able to visit geothermal sites and meet ÉS’ professionals. During my internship, I studied rock samples from the geothermal wells to characterise their mineralogy and assess the alteration of the granite. I enjoyed this a lot and wated to investigate further. With my supervisors Albert Genter (ÉS) and Jean-François Girard (IPGS), we submitted a CIFRE (Industrial Conventions of training through Research)thesis proposal to eh National Research and Technology Agency (ANRT) for funding.
How does this PhD framework work ?
I am employed by ÉS for three years to carry out my thesis, for which I spend 70% of my time with the company. ÉS receives a grant from the ANRT and finances the laboratories with which I work: the IPGS of Strasbourg and the University of Poitiers.
Why are you interested in geothermal energy ?
Geothermal energy, in addition to being a very important new source of energy for the energy transition, is also very stimulating on a scientific level: being able to study fracture zones, develop new methods and have a large amount of data . It is also stimulating to work on the industrial side where we see the activity and the drilling day by day.
« Approche de la perméabilité des réservoirs géothermiques profonds fracturés (socle). Étude des altérations hydrothermales (argiles) et des logs électriques des forages géothermiques d’Alsace » CIFRE thesis 2017-2020, directed by Jean-François Girard (Université de Strasbourg) and Patricia Patrier (Université de Poitiers), supervised by Albert Genter (ÉS).