Towards a better comprehension of reactive transport coupling experimental and numerical approaches

In this work we focus on further understanding reactive transport in carbonate rocks, in particular limestones characterized by a bimodal pore size distribution. To this end, we performed injection experiments with CO2-saturated water on a sample of Euville limestone and monitored the experiments with a medical CT scanner. Microscanner imaging was performed before and after alteration. Experiments showed that permeability increased by nearly two decades due to the alteration process. This increase could be attributed to the formation of a preferential dissolution path visualized on the CT images. Microscanner images show that preferential dissolution areas are characterized by the presence of numerous enlarged macropores. The preferential dissolution path created therefore retains a porous structure and does not correspond to a wormhole-type channel. To provide further knowledge of the small-scale physics of reactive transport, we performed Lattice-Boltzmann simulations of flow in a numerically generated model 2D porous medium having geometrical and topological features designed to approach Euville limestone. We showed that the fluid velocity increased in nearly percolating paths of macropores. Considering the experiments, this means that the CO2-saturated water starts to enter high-velocity zones earlier than low-velocity zones, inducing an earlier onset of the alteration process and a more pronounced local dissolution. However, numerical results showed that the alteration of non-connected macropores leads to an increase of permeability much smaller than the experimentally observed one. To explain this fact we used effective medium modelling that permits predicting the variation in permeability as a function of the fraction of macropores and consequently as a function of alteration. It proved that as long as there is no alteration-induced percolating path consisting of macropores, the increase in permeability is relatively low as shown by the Lattice-Boltzmann simulations. An increase in permeability of several orders of magnitude is only observed when the macroporosity is close to the percolation threshold. This fact is in accordance with the experimentally observed results

Algorithmes graphiques parallèles

La production d'algorithmes parallèles de synthèse d'images ceux-ci étant des algorithmes nouveaux ou des versions parallèles d'algorithmes séquentiels, est en étroite relation bilatérale avec l'architecture cible choisie. Noua présentons dans ce papier des versions parallèles d'algorithmes de tracé de segment et une version nouvelle d'un algorithme de remplissage et de traitement des surfaces visibles. Pour chaque algorithme; le parallélisme, ainsi que l'influence de l'architecture sur son utilisation, sont évalués

Synthese d'images et parallelismes : algorithmes et architectures

SIGLECNRS T 57249 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Observations qui montrent que l'activité du Soleil et les changements de ses pôles magnétiques sont liés aux mouvement du centre de gravité de son système planétaire

Only a lot of observations that show that all Sun activities and its magnetic pole fields flip is linked by the center of mass of its planetary systemSun cycles like used nowadays seem to obey some sort of rules. In this work I present only a lot of observations that show that all its activity and its magnetic pole fields flip is linked by the center of mass of its planetary system and permit a precised defined cycle. It's only observations that have to be grounded by mathematical and physical more deeper examinations that could conduct to the simple and incredible fact, in a real concordance way to the Musica Universalis, that the sun is like a dynamo supply by the center of mass of its own planetary system

Development of a Versatile Mechanical Testing Device for In Situ Synchrotron Tomography and Diffraction Experiments

International audienceA new mechanical stage to perform in situ 3D imaging using synchrotron X-ray tomography is presented. Pairing control and acquisition allows the running of high quality continuous mechanical tests to study damage and fracture in any kind of structural materials. The modular design make this device very versatile with the possibility to use many specimen geometries and load ranges up to 5 kN, and switch within minutes from tomography to X-ray diffraction configurations. Examples of successful experiments to study the damage mechanisms with a technical polymer material are give

In situ 4D mechanical testing of structural materials: The data challenge

International audienceThis papers presents recent progress with materials investigations via in situ mechanical testing at the synchrotron, so called 4D experiments. More automated and more integrated stress rigs now allow to produce new kind of data sets to study deformation and fracture of structural materials. Two recent examples are presented, one with a polymer material and another one with a polycrystalline metallic alloy. Challenges with data organisation and storage and automatic analysis are discussed in the view of the upgrade of the main synchrotron sources which will greatly increase the number and size of the future data sets

Towards a better comprehension of reactive transport coupling experimental and numerical approaches

International audienceIn this work we focus on further understanding reactive transport in carbonate rocks, in particular limestones characterized by a bimodal pore size distribution. To this end, we performed injection experiments with CO 2 -saturated water on a sample of Euville limestone and monitored the experiments with a medical CT scanner. Microscanner imaging was performed before and after alteration. Experiments showed that permeability increased by nearly two decades due to the alteration process. This increase could be attributed to the formation of a preferential dissolution path visualized on the CT images. Microscanner images show that preferential dissolution areas are characterized by the presence of numerous enlarged macropores. The preferential dissolution path created therefore retains a porous structure and does not correspond to a wormhole-type channel. To provide further knowledge of the small-scale physics of reactive transport, we performed Lattice-Boltzmann simulations of flow in a numerically generated model 2D porous medium having geometrical and topological features designed to approach Euville limestone. We showed that the fluid velocity increased in nearly percolating paths of macropores. Considering the experiments, this means that the CO 2 -saturated water starts to enter high-velocity zones earlier than low-velocity zones, inducing an earlier onset of the alteration process and a more pronounced local dissolution. However, numerical results showed that the alteration of non-connected macropores leads to an increase of permeability much smaller than the experimentally observed one. To explain this fact we used effective medium modelling that permits predicting the variation in permeability as a function of the fraction of macropores and consequently as a function of alteration. It proved that as long as there is no alteration-induced percolating path consisting of macropores, the increase in permeability is relatively low as shown by the Lattice-Boltzmann simulations. An increase in permeability of several orders of magnitude is only observed when the macroporosity is close to the percolation threshold. This fact is in accordance with the experimentally observed results

Morphology and Distribution Structure Characterization of Methane Hydrate Formed in the Presence of Amphiphilic Antiagglomerant Additive

International audienceWe investigate the impact of commercial amphiphilic anti-agglomerant additive (AA) on hydrate crystals morphology, size and dispersion in organic phases, by using optical imaging and Raman spectroscopy. To better reproduce the conditions during oil and gas offshore production, methane hydrates were formed from saline water (5 g/L NaCl) in the presence of AA additive at various concentrations (aqueous solutions of 5 and 7 % wt), by using Ketrul211® condensate phase (corresponding to a petroleum cut of C12-C14 carbon distribution), under a constant subcooling of 8.5 ± 0.5 K and 70 bar. Two systems have been studied: water-AA/methane and water-AA/ketrul211®/methane. By optical imaging observation, the presence of AA additives leads to polygonal periodic crystals (with size ranging from ca. 1 to 10 µm) for the water-AA/methane system, and perpendicular needle crystals (with size close to 10 µm) for the water-AA/ketrul211®/methane system. In the absence of AA additive, no polygonal or needle crystals morphology has been observed. With the help of Raman imaging, the methane hydrate distribution has been investigated at a micrometer scale: the formation of methane hydrates aggregates is revealed inside the ketrul211® bulk phase matrix

Microsecond time-resolved x-ray diffraction for the investigation of fatigue behavior during ultrasonic fatigue loading

International audienceA new method based on time-resolved X-ray diffraction is proposed in order to measure the elastic strain and stress during ultrasonic fatigue loading experiments. Pure Cu was chosen as an example material for the experiments using a 20 kHz ultrasonic fatigue machine mounted on the six-circle diffractometer available at the DiffAbs beamline on the SOLEIL synchrotron facility in France. A two-dimensional hybrid pixel X-ray detector (XPAD3.2) was triggered by the strain gage signal in a synchronous data acquisition scheme (pump-probe-like). The method enables studying loading cycles with a period of 50 µs, achieving a temporal resolution of 1 µs. This allows a precise reconstruction of the diffraction patterns during the loading cycles. From the diffraction patterns, the position of the peaks, their shifts and their respective broadening can be deduced. The diffraction peak shift allows the elastic lattice strain to be estimated with a resolution of ∼10 -5. Stress is calculated by the self-consistent scale-transition model through which the elastic response of the material is estimated. The amplitudes of the cyclic stresses range from 40 to 120 MPa and vary linearly with respect to the displacement applied by the ultrasonic machine. Moreover, the experimental results highlight an increase of the diffraction peak broadening with the number of applied cycles

Revealing the role of microstructure architecture on strength and ductility of Ni microwires by in-situ synchrotron X-ray diffraction

Deformation mechanisms of cold drawn and electropolished nickel microwires are studied by performing in-situ monotonous and cyclic tensile tests under synchrotron radiation. X-ray diffraction tests allow probing elastic strains in the different grain families and establishing a link with the deformation mechanisms taking place within the microwires. The measurements were carried out on several microwires with diameters ranging from as-drawn 100 mu m down to 40 mu m thinned down by electropolishing. The as-drawn wires exhibit a core-shell microstructure with <111> fiber texture dominant in core and heterogeneous dual fiber texture <111> and <100> in the shell. Reduction of specimen size by electropolishing results in a higher yield stress and tensile strength along with reduced ductility. In-situ XRD analysis revealed that these differences are linked to the global variation in microstructure induced by shell removal with electropolishing, which in turn affects the load sharing abilities of grain families. This study thus proposes a new way to increase ductility and retain strength in nickel microwires across different diameters by tuning the microstructure architecture