Numerical modeling of regional stress distributions for geothermal exploration

International audienceAny high-enthalpy unconventional geothermal projectcan be jeopardized by the uncertainty on the presence of the geothermal resource at depth. Indeed, for the majority of such projects the geothermal resource is deeply seated and, with the drilling costs increasing accordingly, must be located as precisely as possible to increase the chance of their economic viability. In order to reduce the " geological risk " , i.e. the chance to poorly locate the geothermal resource, a maximum amount of information must be gathered prior to any drilling of exploration and/or operational well. Cross-interpretation from multiple disciplines (e.g., geophysics, hydrology, geomechanics. . .) should improve locating the geothermal resource and so the position of exploration wells ; this is the objective of the Euro-pean project IMAGE (grant agreement No. 608553), under which the work presented here was carried out. As far as geomechanics is concerned, in situ stresses can have a great impact on the presence of a geothermal resource since they condition both the regime within the rock mass, and the state of the major fault zones (and hence, the possible flow paths). In this work, we propose a geomechanical model to assess the stress distribution at the regional scale (characteristic length of 100 kilometers). Since they have a substantial impact on the stress distributions and on the possible creation of regional flow paths, the major fault zones are explicitly taken into account. The Distinct Element Method is used, where the medium is modeled as fully deformable blocks representing the rock mass interacting through mechanically active joints depicting the fault zones. The first step of the study is to build the model geometry based on geological and geophysical evidences. Geophysical and structural geology results help positioning the major fault zones in the first place. Then, outcrop observations, structural models and site-specific geological knowledge give information on the fault zones family sets and their priority rule. In the second step, the physical model must be established, including constitutive equations for the rock mass and the fault zones, initial state and boundary conditions. At such large scales, physical laws and parameters are difficult to assess and must be constrained by sensitivity analysis. In the last step of the study, the results can be interpreted to highlight areas where the mechanical conditions favor the presence of a geothermal resource. The DEM enables accounting for the strong stress redistributions inherent to highly-segmented geometries, and to the dilational opening of fault zones under shearing. A 130x150 square-kilometers region within the Upper Rhine Graben is used as a case-study to illustrate the building and interpretation of a regional stress model

Numerical assessment of the near-wellbore rock matrix permeability gain due to thermal stimulation

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Adapted numerical modelling strategy developed to support EGS deployment.

International audienceThe exploitation of Enhanced/Engineered Geothermal Systems (EGS), for electricity and/or heat production, is a promising way to increase the amount of renewable energies contribution in the energetic mix in Europe. In regard to the required production characteristics (production temperature and flowrate) for the economical viability of EGS, the favourable targeted geological systems are deep and fractured. In order to reduce the risks and the prohibitive costs linked to the depth of such geothermal systems, numerical modelling is a useful tool to understand such deep fractured systems and to help in the construction and in the management of the deep infrastructures (wells architecture, stimulation of wells, implementation of adapted network of wells). Nevertheless, this forces to a change of paradigm in comparison to « classical » reservoir modelling based on mechanics of continuum media. Indeed 3D Discrete Fracture Network (DFN) approach looks fairly adapted to catch the mechanical and hydraulic phenomena in the fractured rock mass around wells and to understand the global systems in the network of wells. The conceptualisation of the fractured rock mass is a crucial step for such DFN models not only for the geometry but also to constrain the constitutive behaviour of singularities (fault zones, fractures etc.), depending on the tectonic context. We present some results illustrating how DFNs can be used to study the EGS behaviour at several scales

Flp and Cre expressed from Flp–2A–Cre and Flp–IRES–Cre transcription units mediate the highest level of dual recombinase-mediated cassette exchange

Recombinase-mediated cassette exchange (RMCE) is a powerful tool for unidirectional integration of DNA fragments of interest into a pre-determined genome locale. In this report, we examined how the efficiency of dual RMCE catalyzed by Flp and Cre depends on the nature of transcription units that express the recombinases. The following recombinase transcription units were analyzed: (i) Flp and Cre genes expressed as individual transcription units located on different vectors, (ii) Flp and Cre genes expressed as individual transcription units located on the same vector, (iii) Flp and Cre genes expressed from a single promoter and separated by internal ribosome entry sequence and (iv) Flp and Cre coding sequences separated by the 2A peptide and expressed as a single gene. We found that the highest level of dual RMCE (35–45% of the transfected cells) can be achieved when Flp and Cre recombinases are expressed as Flp–2A–Cre and Flp–IRES–Cre transcription units. In contrast, the lowest level of dual RMCE (∼1% of the transfected cells) is achieved when Flp and Cre are expressed as individual transcription units. The analysis shows that it is the relative Flp–to–Cre ratio that critically affects the efficiency of dual RMCE. Our results will be helpful for maximizing the efficiency of dual RMCE aimed to engineer and re-engineer genomes

The mitochondrial genome of the pathogenic yeast Candida subhashii: GC-rich linear DNA with a protein covalently attached to the 5′ termini

As a part of our initiative aimed at a large-scale comparative analysis of fungal mitochondrial genomes, we determined the complete DNA sequence of the mitochondrial genome of the yeast Candida subhashii and found that it exhibits a number of peculiar features. First, the mitochondrial genome is represented by linear dsDNA molecules of uniform length (29 795 bp), with an unusually high content of guanine and cytosine residues (52.7 %). Second, the coding sequences lack introns; thus, the genome has a relatively compact organization. Third, the termini of the linear molecules consist of long inverted repeats and seem to contain a protein covalently bound to terminal nucleotides at the 5′ ends. This architecture resembles the telomeres in a number of linear viral and plasmid DNA genomes classified as invertrons, in which the terminal proteins serve as specific primers for the initiation of DNA synthesis. Finally, although the mitochondrial genome of C. subhashii contains essentially the same set of genes as other closely related pathogenic Candida species, we identified additional ORFs encoding two homologues of the family B protein-priming DNA polymerases and an unknown protein. The terminal structures and the genes for DNA polymerases are reminiscent of linear mitochondrial plasmids, indicating that this genome architecture might have emerged from fortuitous recombination between an ancestral, presumably circular, mitochondrial genome and an invertron-like element

Modélisations couplées Hydro-Mécaniques en milieux poreux partiellent saturés : application à la ventilation de galeries profondes

During the last decades, the study of coupling phenomena became more and more important in Geomechanics and Civil Engineering. Radioactive wastes repository in deep geological formation is a perfect illustration of this kind of problems. Indeed, due to numerous stakes, all acting phenomena must be considered in order to determine the first fonctionnality of the repository structure: the full safety confining of radioactive wastes. During the building period of the repository structures, the excavation and the ventilation of galleries induce solicitation of the surrounding rock mass. The abject of this work is to characterize the importance .and the nature of this solicitation. It's fundamental to determine the phenomena kinetics (progression of the drying front induced by ventilation, the extent of the perturbated zone) and the strengh of induced couplings (stresses in front of gallery, damage). The aim of all this considerations is to evaluate the eventual modifications of the rock and its confining abilities. The theoretical approach is the Mechanics of Porous Media defined by Coussy (1995), which leads to a formalism at the macroscopic scale and allows to determine the evolutions of the rock, considered as partially saturated porous medium (three-phases medium). The aim of the different models presented in this work is to describe the fluids transfers in the rock mass and to take into account constitutive aspects of the mechanical behavior of the rock (damage, plasticity).Durant les dernières décennies, l'étude des phénomènes couplés a pris une importance considérable dans de nombreux problèmes de la Géomécanique et du Génie Civil. Le stockage des déchets radioactifs en formations géologiques profondes est une parfaite illustration de ce genre de problème. En effet du fait des nombreux enjeux, il va être nécessaire de prendre en compte tous les phénomènes intervenant, afin de pouvoir tirer des conclusions sur la fonctionnalité première de la structure de stockage à savoir: le confinement en toute sûreté des déchets radioactifs. Durant la phase de construction des structures de stockage, le creusement et la ventilation des galeries vont solliciter le massif rocheux environnant. L'objet de ce travail est de caractériser l'importance et la nature de cette sollicitation. Il est notamment primordial de déterminer la cinétique des phénomènes (progression du front de séchage induit par la ventilation, étendue de la zone perturbée) et la forces des couplages induits (contraintes en paroi des galeries, endommagement, etc.). Toutes ces considérations ont pour but d'évaluer les modifications éventuelles de la roche et ainsi ses capacités de confinement. L'approche théorique retenue est celle de la Mécanique des Milieux Poreux définie par Coussy (1995) permettant, grâce à un formalisme à l'échelle macroscopique, de déterminer les évolutions de la roche en tant que milieu poreux partiellement saturé (formé d'une phase solide, d'une phase liquide et d'une phase gazeuse). Les différents modèles présentés dans ce travail ont pour objectif de traduire au mieux les transferts de fluides au sein du massif rocheux mais également les aspects constitutifs liés au comportement mécanique de la roche (endommagement, plasticité)

Modélisations couplées Hydro-Mécaniques en milieux poreux partiellent saturés (application à la ventilation de galeries profondes)

Durant les dernières décennies, l'étude des phénomènes couplés a pris une importance considérable dans de nombreux problèmes de la Géomécanique et du Génie Civil. Le stockage des déchets radioactifs en formations géologiques profondes est une parfaite illustration de ce genre de problème. En effet du fait des nombreux enjeux, il va être nécessaire de prendre en compte tous les phénomènes intervenant, afin de pouvoir tirer des conclusions sur la fonctionnalité première de la structure de stockage à savoir: le confinement en toute sûreté des déchets radioactifs. Durant la phase de construction des structures de stockage, le creusement et la ventilation des galeries vont solliciter le massif rocheux environnant. L'objet de ce travail est de caractériser l'importance et la nature de cette sollicitation. Il est notamment primordial de déterminer la cinétique des phénomènes (progression du front de séchage induit par la ventilation, étendue de la zone perturbée) et la forces des couplages induits (contraintes en paroi des galeries, endommagement, etc.). Toutes ces considérations ont pour but d'évaluer les modifications éventuelles de la roche et ainsi ses capacités de confinement. L'approche théorique retenue est celle de la Mécanique des Milieux Poreux définie par Coussy (1995) permettant, grâce à un formalisme à l'échelle macroscopique, de déterminer les évolutions de la roche en tant que milieu poreux partiellement saturé (formé d'une phase solide, d'une phase liquide et d'une phase gazeuse). Les différents modèles présentés dans ce travail ont pour objectif de traduire au mieux les transferts de fluides au sein du massif rocheux mais également les aspects constitutifs liés au comportement mécanique de la roche (endommagement, plasticité).NANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Impact of faults and their mechanical properties on the regional stress field

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The Fission Yeast Crb2/Chk1 Pathway Coordinates the DNA Damage and Spindle Checkpoint in Response to Replication Stress Induced by Topoisomerase I Inhibitor

Living organisms experience constant threats that challenge their genome stability. The DNA damage checkpoint pathway coordinates cell cycle progression with DNA repair when DNA is damaged, thus ensuring faithful transmission of the genome. The spindle assembly checkpoint inhibits chromosome segregation until all chromosomes are properly attached to the spindle, ensuring accurate partition of the genetic material. Both the DNA damage and spindle checkpoint pathways participate in genome integrity. However, no clear connection between these two pathways has been described. Here, we analyze mutants in the BRCT domains of fission yeast Crb2, which mediates Chk1 activation, and provide evidence for a novel function of the Chk1 pathway. When the Crb2 mutants experience damaged replication forks upon inhibition of the religation activity of topoisomerase I, the Chk1 DNA damage pathway induces sustained activation of the spindle checkpoint, which in turn delays metaphase-to-anaphase transition in a Mad2-dependent fashion. This new pathway enhances cell survival and genome stability when cells undergo replicative stress in the absence of a proficient G(2)/M DNA damage checkpoint