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Mineral precipitation can drastically alter a reservoir’s ability to transmit mass and energy during various engineering/natural subsurface processes, such as geothermal energy extraction and geological carbon dioxide sequestration. However, it is still challenging to explain the relationships among permeability, porosity, and precipitation patterns in reservoirs, particularly in fracture-dominated reservoirs. Here, we investigate the pore-scale behavior of single-species mineral precipitation reactions in a fractured porous medium, using a phase field lattice-Boltzmann method. Parallel to the main flow direction, the medium is divided into two halves, one with a low-permeability matrix and one with a high-permeability matrix. Each matrix contains one flow-through and one dead-end fracture. A wide range of species diffusivity and reaction rates is explored to cover regimes from advection- to diffusion-dominated, and from transport- to reaction-limited. By employing the ratio of the Damkohler (Da) and the Peclet (Pe) number, four distinct precipitation patterns can be identified, namely (1) no precipitation (Da/Pe 100), (3) fracture isolation (1 1), and (4) diffusive precipitation (1 < Da/Pe

Transport processes in porous media have been traditionally studied through the parameterization of macroscale properties, by means of volume-averaging or upscaling methods over a representative elementary volume. The possibility of upscaling results from pore-scale simulations, to obtain volume-averaging properties useful for practical purpose, can enhance the understanding of transport effects that manifest at larger scales. Several studies have been carried out to investigate the impact of the geometric properties of porous media on transport processes for solute species. However, the range of pore-scale geometric properties, which can be investigated, is usually limited to the number of samples acquired from microcomputed tomography images of real porous media. The present study takes advantage of synthetic porous medium generation to propose a systematic analysis of the relationships between geometric features of the porous media and transport processes through direct simulations of fluid flow and advection-diffusion of a non-reactive solute. Numerical simulations are performed with the lattice Boltzmann method on synthetic media generated with a geostatistically based approach. Our findings suggest that the advective transport is primarily affected by the specific surface area and the mean curvature of the porous medium, while the effective diffusion coefficient scales as the inverse of the tortuosity squared. Finally, the possibility of estimating the hydrodynamic dispersion coefficient knowing only the geometric properties of porous media and the applied pressure gradient has been tested, within the range of tested porous media, against advection-diffusion simulations at low Reynolds (, Geofluids, 11 (6), ISSN:1468-8115, ISSN:1468-8123

Biochar was tested as an active capping material for oil spill contaminated sediment and its performance was compared to activated carbon and organoclay. Polydimethyilsiloxane fibers were used as passive samplers to evaluate the vertical porewater concentration of selected polycyclic aromatic hydrocarbons through the sea-sediment and the capping layer (1 cm resolution). Experiments were carried out on the laboratory scale using 7.5 cm (∼500 g) of contaminated sea-sediment that were capped with 3 cm (∼150 g) of capping materials. The porewater concentrations of the polycyclic aromatic hydrocarbons were compared using a reactive-diffusion model. Biochar showed a greater capping efficiency than activated carbon and organoclay. For example, anthracene porewater concentrations in the first centimetre of capping material, after 1 month, were reduced by 69%, 56% and 99% respectively for activated carbon, organoclay and biochar. The porewater concentrations were used to model the long term (≥12 months) behaviour of various cap configurations with a numerical simulations. Biochar can be considered a cost-effective alternative to the more consolidated sorbent materials.

Phase separation of formation fluids in the subsurface introduces hydrodynamic perturbations which are critical for mass and energy transport of geofluids. Here, we present pore-scale lattice-Boltzmann simulations to investigate the hydrodynamical response of a porous system to the emergence of non-wetting droplets under background hydraulic gradients. A wide parameter space of capillary number and fluid saturation is explored to characterize the droplet evolution, the droplet size and shape distribution, and the capillary-clogging patterns. We find that clogging is favored by high capillary stress; nonetheless, clogging occurs at high non-wetting saturation (larger than 0.3), denoting the importance of convective transport on droplet growth and permeability. Moreover, droplets are more sheared at low capillary number; however, solid matrix plays a key role on droplet’s volume-to-surface ratio., Geofluids, 2019, ISSN:1468-8115, ISSN:1468-8123

In this paper, we describe a lattice Boltzmann model to simulate chemical reactions taking place at the interface between two immiscible fluids. The phase-field approach is used to identify the interface and its orientation, the concentration of reactant at the interface is then calculated iteratively to impose the correct reactive flux condition. The main advantages of the model is that interfaces are considered part of the bulk dynamics with the corrective reactive flux introduced as a source/sink term in the collision step, and, as a consequence, the model’s implementation and performance is independent of the interface geometry and orientation. Results obtained with the proposed model are compared to analytical solution for three different benchmark tests (stationary flat boundary, moving flat boundary and dissolving droplet). We find an excellent agreement between analytical and numerical solutions in all cases. Finally, we present a simulation coupling the Shan Chen multiphase model and the interface reactive model to simulate the dissolution of a collection of immiscible droplets with different sizes rising by buoyancy in a stagnant fluid.

The retention of contaminants in the finest and less-conductive regions of natural aquifer is known to strongly affect the decontamination of polluted aquifers. In fact, contaminant transfer from low to high mobility regions at the back end of a contaminant plume (i.e. back diffusion) is responsible for the long-term release of contaminants during remediation operation. In this paper, we perform pore-scale calculations for the transport of contaminant through heterogeneous porous media composed of low and high mobility regions with two objectives: (i) study the effect of permeability contrast and solute transport conditions on the exchange of solutes between mobile and immobile regions and (ii) estimate the mass of contaminants sequestered in low mobility regions based on concentration breakthrough curves.

Co.S.Mo (Contamination Screening Model) è un modello speditivo che ha l'obiettivo di simulare il trasporto di inquinanti in acque sotterranee in relazione ad eventi di sversamento accidentale al suolo per la definizione di scenari di emergenza. Lo scopo è quello di valutare i tempi di arrivo e la concentrazione di inquinanti in corrispondenza di punti di prelievo idropotabile. Il modello, utilizza la soluzione analitica monodimensionale dell'equazione del trasporto advettivo e dispersivo proposta da Domenico (1987) [3] per simulare il trasporto verticale attraverso la zona non satura e orizzontale nella zona satura. L'uso del software risulta estremamente semplice grazie ad una interfaccia intuitiva per l'inserimento dei parametri e per la lettura dei risultati. Co.S.Mo, è basato su ipotesi semplificative, ed è stato validato mediante confronto con modelli numerici consolidati (CHEMFLO [2] per la zona non satura e MODFLOW/MT3D per quella satura). Questo lavoro si inserisce nell'ambito di un Intesa Operativa tra l'Istituto di Ricerca sulle Acque (IRSA-CNR) e la Protezione Civile.