Numerical Simulation of Pollutant Transport in Fractured Vuggy Porous Karstic Aquifers

This paper begins with presenting a mathematical model for contaminant transport in the fractured vuggy porous media of a species of contaminant (PCP). Two phases are numerically simulated for a process of contaminant and clean water infiltrated in the fractured vuggy porous media by coupling mixed finite element (MFE) method and finite volume method (FVM), both of which are locally conservative, to approximate the model. A hybrid mixed finite element (HMFE) method is applied to approximate the velocity field for the model. The convection and diffusion terms are approached by FVM and the standard MFE, respectively. The pressure distribution and temporary evolution of the concentration profiles are obtained for two phases. The average effluent concentration on the outflow boundary is obtained at different time and shows some different features from the matrix porous media. The temporal multiscale phenomena of the effluent concentration on the outlet are observed. The results show how the different distribution of the vugs and the fractures impacts on the contaminant transport and the effluent concentration on the outlet. This paper sheds light on certain features of karstic groundwater are obtained

SIMULACIJA SANACIJE VODONOSNIKA SLABOPROPUSNIH LEĆA FENOMENOM POVRATNE DIFUZIJE

Fluid flow in a dual permeable medium (DPM) is essential in solute transport in mining and aquifer studies. In this paper, water flushing into a contaminated DPM containing fine-grained lenses with different geometries was investigated with the Lattice Boltzmann Method (LBM). The LBM model used in this study was D2Q9 with a relaxation time of 1, a cohesion value of 3 for a fluid density of 1 (mu.Lu-3). The saturated fluid in the DPM was a contaminant that usually stays in low permeable lenses and after flushing, it is leaked into the porous medium by a second fluid (water). This phenomenon is predominant when the displacing fluid has a lower concentration than the contaminated fluid. Diffusion and advection are the main mechanisms that control fluid flow in the porous medium. The results of the simulations showed: (1) advection controlled solute transport through the flushing phase, and back-diffusion occurred after the change in phase; (2) the lenses’ geometry influenced the fluid flow pattern and the remediation process. As a result, aquifer remediation strategies based on the lenses’ geometry and their permeability can help us select the appropriate environmental protection.Protjecanje fluida kroz medije s dvostrukom propusnošću bitno je kod proučavanja transporta otopljene tvari u rudarstvu ili kroz vodonosnik. U ovome radu, s pomoću metode Boltzmannove rešetke, istraženo je ispiranje vodom medija dvostruke propusnosti koji sadržava sitnozrnate leće različite geometrije. Metoda Boltzmannove rešetke u ovome istraživanju uključivala je korištenje modela D2Q9 s vremenom otpuštanja 1 te vrijednošću kohezije 3 za fluid gustoće 1 (mu. Lu-3). Medij dvostruke propusnosti zasićen je fluidom koji je ujedno predstavljao i zagađivač koji se obično zadržavao u slabopropusnim lećama iz kojih se širio nakon ispiranja poroznoga medija sekundarnim fluidom (vodom). Ova je pojava prevladavajuća u slučaju kada istiskujući fluid ima manju koncentraciju od kontaminiranoga fluida, a difuzija i advekcija dva su osnovna mehanizma koja kontroliraju tok fluida kroz šupljikavu sredinu. Rezultati simulacije pokazuju da: (1) advekcija kontrolira transport otopljene tvari tijekom faze ispiranja, dok se povratna difuzija odvija nakon promjene u fazi; (2) geometrija leća utječe na oblik toka i proces sanacije. Rezultat je strategija sanacije vodonosnika bazirana na geometriji i propusnosti leća koja može pomoći u zaštiti okoliša

Particle straining in vuggy porous media

Formation damage is the loss of inherent permeability of porous media and is of vital importance in petroleum engineering. One important mechanism of formation damage is particulate straining, where suspended solid particles jam the flow pathways and reduce its flow capability. Most studies of particulate transport have been performed in porous media of uniform pore size, such as sandstones and sandpacks. Carbonates often contain large openings, called vugs, which can affect the flow and transport properties (particle straining) of the porous medium. In this study, particle straining experiments are performed on multiple configurations of synthetic vuggy media. A novel method is introduced to generate synthetic vuggy glass bead cores: glass beads, with dissolvable inclusions, are sintered in the presence of air in a muffle furnace and later dissolved with a core flood. Smaller-sized glass beads are injected at multiple flow rate and injection concentrations and changes in porosity, permeability, vug size, and particle effluent volume are monitored using continuous pressure measurements and computed tomography scanning. The results are combined with quasi-2D streamline simulations to understand the particle deposition patterns in these vuggy media. Furthermore, spontaneous imbibition experiments are conducted on multiple configurations of these synthetic vuggy media and capillary rise is measured. Rudimentary vug-pore flow models are generated, and solved for spontaneous imbibition using a computational fluid dynamics solver, to better explain the behavior observed in the experiments. The results can be summarized as follows: (i) particles penetrate and deposit at a deeper depth when a vug is present; (ii) the particles deposit on the vug-matrix boundary and result in a smaller and smoother vug; (iii) the maximum change in the vug is observed at the bottom of the vug; and (iv) more particle deposition occurs in the matrix around the vug. The high permeability vugs cause flow convergence, which increases the particle-particle and particle-matrix interaction, and results in an increased number of particles dropping out of the flow stream. Each vug has a sphere of influence within which it will affect the particle flow pathway; if the sphere of influence of two vugs overlap, the particle will be affected by both the vugs, with the dominance depending on the separation between the particle and the vug. The results suggest that for the vug conditions studied, the vugs in series focus the flow and increase the depth of particle deposition and the total volume of particles deposited in the core. The vugs in parallel acts independently as separate vugs, with their separation greater than their individual sphere of influence, and do not dictate the deposition of injected particles. In future, this study can be carried forward by conducting experiments inside a CT machine, to enable time-lapse particle deposition maps, on proxy vuggy media or real rocks. Coupled with real-time porosity, permeability, and possibly resistivity measurements, new near-wellbore interpretative models can be envisioned for improved formation evaluation of vuggy carbonatesPetroleum and Geosystems Engineerin

Automatski generator mreže kontrolnih volumena za diskretizaciju sintetičke mikrostrukture

Radom je razvijen automatski generator mreže u svrhu diskretizacije materijala sa unutarnjim granicama. Razvijeni generator mreže generira trokutne konačne volumene. Od korisnika se zahtjeva definiranje funkcije udaljenosti i funkcije veličine. Primjenjeni algoritam temelji se na spregu Delaunayjeve triangulacije i mehaničke analogije. Izrađena su proširenja u vidu generiranja poligonalnih domena i domena sa unutarnjim granicama. Dobiveni rezultati pokazuju pouzdanost metode