Biofilms in porous media: development of macroscopic transport equations via volume averaging with closure for local mass equilibrium conditions

In this work, we upscale a pore-scale description of mass transport in a porous medium containing biofilm to develop the relevant Darcy-scale equations. We begin with the pore-scale descriptions of mass transport, interphase mass transfer, and biologically-mediated reactions; these processes are then upscaled using the method of volume averaging to obtain the macroscale mass balance equations. We focus on the case of local mass equilibrium conditions where the averaged concentrations in the fluid and biological phases can be assumed to be proportional and for which a one-equation macroscopic model may be developed. We predict the effective dispersion tensor by a closure scheme that is solved for the cases of both simple and complex unit cells. The domain of validity of the approach is clearly identified, both theoretically and numerically, and unitless groupings indicating the domain of validity are reported

Pore-scale modelling of biofilm activity in the underground storage of hydrogen

The storage of hydrogen in the subsurface to compensate fluctuations in energy demand and supply is considered an important part of future energy strategies. It has been observed that, within the period of storage, there is a partial conversion of hydrogen in the presence of carbon dioxide to methane. This has been attributed to the activity of microorganisms (archaea and bacteria) indigenous to the storage site. The talk will look at pore-scale phenomena including the interplay of different microbes (methanogens, acetogens, and acetotrophs) within a biofilm at the gas—water interface, the growth and decay of the multi-species biofilm, and the diffusion, consumption, and production of the dissolved gases. A numerical model with interface tracking, based on a volume-of-fluid method, is proposed for investigating these effects. The aim of the study is the description and quantification of the dominant processes which determine the amount of biomass such a reservoir can support and the rate at which the microorganisms produce methane as a contribution to explaining the observed field-scale phenomenon

A domain decomposition approach to finite-epsilon homogenization of scalar transport in porous media

Modeling scalar transport by advection and diffusion in multiscale porous structures is a challenging problem, particularly in the preasymptotic regimes when non-Fickian effects are prominent. Mathematically, one of the main difficulties is to obtain macroscale models from the homogenization of conservation equations at microscale when epsilon, the ratio of characteristic lengthscales between the micro- and macroscale, is not extremely small compared to unity. Here, we propose the basis of a mathematical framework to do so. The focal idea is to decompose the spatial domain at pore-scale into a set of N subdomains to capture characteristic times associated with exchanges between these subdomains. At macroscale, the corresponding representation consists of a system of N coupled partial differential equations describing the transport of the spatially averaged scalar variable within each subdomain. Besides constructing the framework, we also compare numerically the results of our models to a complete resolution of the problem at the pore-scale, which shows great promises for capturing preasymptotic regimes, non-Fickian transport, and going toward finite-epsilon homogenization

A coupled, pore-scale model for methanogenic microbial activity in underground hydrogen storage.

Underground hydrogen storage (UHS) as a means of energy storage is an efficient way of compensating for seasonal fluctuations in the availability of energy. One important factor which influences this technology is the activity of methanogenic microorganisms capable of utilising hydrogen and carbon dioxide for metabolism and leading to a change in the stored gas composition. A coupled, pore-scale model is presented which aids in the investigation of the mechanisms that govern the conversion of hydrogen to methane, i.e. advective hydrogen flow, its diffusion into microbial biofilms of multiple species, and its consumption within these biofilms. The model assumes that spherical grains are coated by a film of residual water and treats the biofilm development within each film in a quasi one-dimensional manner. A sample simulation using the presented model illustrates the biofilm growth process in these films as well as the competition between three different microbial species: methanogens, acetogens, and acetotrophs

Homogenization via formal multiscale asymptotics and volume averaging: How do the two techniques compare?

A wide variety of techniques have been developed to homogenize transport equations in multiscale and multiphase systems. This has yielded a rich and diverse field, but has also resulted in the emergence of isolated scientific communities and disconnected bodies of literature. Here, our goal is to bridge the gap between formal multiscale asymptotics and the volume averaging theory. We illustrate the methodologies via a simple example application describing a parabolic transport problem and, in so doing, compare their respective advantages/disadvantages from a practical point of view. This paper is also intended as a pedagogical guide and may be viewed as a tutorial for graduate students as we provide historical context, detail subtle points with great care, and reference many fundamental works

Relations between C9orf72 expansion size in blood, age at onset, age at collection and transmission across generations in patients and presymptomatic carriers

A (GGGGCC) n repeat expansion in C9orf72 gene is the major cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). The relations between the repeats size and the age at disease onset (AO) or the clinical phenotype (FTD vs. ALS) were investigated in 125 FTD, ALS, and presymptomatic carriers. Positive correlations were found between repeats number and the AO (p < 10 e−4 ) but our results suggested that the association was mainly driven by age at collection (p < 10 e−4 ). A weaker association was observed with clinical presentation (p = 0.02), which became nonsignificant after adjustment for the age at collection in each group. Importantly, repeats number variably expanded or contracted over time in carriers with multiple blood samples, as well as through generations in parent-offspring pairs, conversely to what occurs in several expansion diseases with anticipation at the molecular level. Finally, this study establishes that measure of repeats number in lymphocytes is not a reliable biomarker predictive of the AO or disease outcome in C9orf72 long expansion carriers

Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: a cross-sectional study.

We aimed to accurately estimate the frequency of a hexanucleotide repeat expansion in C9orf72 that has been associated with a large proportion of cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD)

Dissolution des roches carbonatées par injection d'acide

Les traitements d'acidification sont généralement utilisés pour stimuler l'injection et/ou la productivité des puits dans les formations de carbonates. Cependant, de nombreux traitements ne produisent pas les résultats attendus en terme de gain de productivité à cause de la mauvaise modélisation autour du puits des mécanismes physiques intervenant durant le processus d'injection acide. La nature instable du phénomène de dissolution en milieu poreux entraîne la formation de canaux fortement conductifs appelés wormholes, qui sont difficiles à modéliser quantitativement. Un modèle de dissolution à l'échelle de Darcy est proposé comprenant une équation de Darcy-Brinkman, pour la partie écoulement couplée avec un modèle de dissolution en non-équilibre local. Un simulateur numérique 3D a été développé pour résoudre ce système d'équations en utilisant une méthode de pas fractionnaire et des schémas TVD. Les résultats sont présentés sur des configurations 2D et 3D aussi bien pour des systèmes homogènes qu'hétérogènes. Les résultats numériques sont discutés d'un point de vue qualitatif et quantitatif par rapport à la littérature et comparés aux résultats expérimentaux. Les expériences ont été réalisées sur un massif de sel quasi 2D dans lequel on a injecté une solution d'eau salée sous saturée. Les instabilités de dissolution, le développement des canaux et la propagation des wormholes ont été enregistrés à l'aide d'une caméra vidéo. En se basant sur les résultats 2D, la possibilité d'une description du phénomène à l'échelle de la section, c'est-à-dire en effectuant des moyennes sur des sections du domaine, a été explorée. Plusieurs approches sont utilisées, tels que les modèles à une équation, où le milieu considéré incorpore la physique du wormhole et la matrice poreuse environnante, et les modèles à deux équations pour lesquels les wormholes sont traités séparément. Les implications théoriques sont discutées en se basant sur les résultats numériques.TOULOUSE-ENSEEIHT (315552331) / SudocSudocFranceF