Fraction Of Pores Research Articles

Melamine degradation to bioregenerate granular activated carbon

The industrial chemical melamine is often detected in surface water used for drinking water production, due to its wide application and insufficient removal in conventional wastewater treatment plants. Melamine can be removed from water by adsorption onto granular activated carbon (GAC), nevertheless, GAC needs periodic reactivation in costly and energy intense processes. As an alternative method, GAC can also be regenerated using biomass capable of degrading melamine in a process called bioregeneration. We assessed melamine biodegradation in batch experiments in fully oxic and anoxic, as well as in alternating oxic and anoxic conditions. Additionally, we studied the effect of an additional carbon source on the biodegradation. The most favourable conditions for melamine biodegradation were applied to bioregenerate GAC loaded with melamine. We demonstrate that melamine can be biodegraded in either oxic or anoxic conditions and that melamine degrading biomass can restore at least 28% of the original GAC adsorption capacity. Furthermore, our results indicate that bioregeneration occurs mainly in the largest pore fraction of GAC, impacting adsorption kinetics. Overall, we show that bioregeneration has a large potential for restoring GAC adsorption capacity in industrial wastewater.

Effective medium modeling of pressure effects on the joint elastic and electrical properties of sandstones

Subsurface rocks are subjected to different stress states, and as such, physical properties of rocks including elastic modulus and electrical resistivity are stress-dependent. Joint modeling of the stress-dependence of elastic and electrical properties is important for interpreting coincident elastic and electrical measurements. We present a modeling approach for the pressure-dependence of the joint elastic and electrical properties in brine-saturated sandstones, that links both properties to the same microstructure. This approach combines the differential effective medium (DEM) and the self-consistent approximation (SCA) with the dual-porosity concept to model the pressure-dependence of P-wave velocity and electrical resistivity simultaneously measured in four sandstone samples. There is good agreement between model results and laboratory experimental results for both the elastic and electrical properties. The model parameters optimized to fit the data are: constant stiff and “soft” (or compliant) aspect ratios; a fixed critical porosity; and pressure-dependent stiff and soft porosities. These model-derived pressure-dependent porosities correlate with the observed velocity and resistivity pressure-sensitivity of the rocks, for example, the higher the initial volume fraction of compliant pores, the higher the P-wave velocity pressure sensitivity. The results show that the pressure-dependence of the P-wave velocity and electrical resistivity can be jointly modeled satisfactorily using the dual-porosity concept, where the pore space is simplified to contain a single set of stiff and soft pores.

Bulk modulus for fluid-saturated rocks at high frequency: modification of squirt flow model proposed by Mavko & Jizba

SUMMARYThe squirt flow model, proposed by Mavko & Jizba, has been widely used in explaining the frequency-related modulus and velocity dispersion between ultrasonic and seismic measurements. In this model, the saturated bulk modulus at high frequency is obtained by taking the so-called unrelaxed frame bulk modulus into Biot's or Gassmann's formula. When using Gassmann's formula, the mineral bulk modulus is taken as matrix bulk modulus. However, the soft pores (cracks) in rocks have a weakening effect on the matrix bulk modulus. The saturated bulk modulus at high frequency calculated with mineral bulk modulus as matrix bulk modulus is higher than the real values. To overcome this shortcoming we propose a modified matrix bulk modulus based on the Betti–Rayleigh reciprocity theorem and non-interaction approximation. This modification takes the weakening effect of soft pores (cracks) into consideration and allows calculating the correct saturated bulk modulus at high frequency under different soft-pore fractions (the ratio of soft porosity to total porosity) or crack densities. We also propose an alternative expression of the modified matrix bulk modulus, which can be directly obtained from laboratory measurements. The numerical results show that the saturated bulk modulus at high frequency using the original matrix bulk modulus (i.e. mineral bulk modulus) is approximated to that using the modified one only for rocks containing a small amount of soft-pore fraction. However, as the soft-pore fraction becomes substantial, using the original bulk matrix modulus is not applicable, but the modified one is still applicable. Furthermore, the results of the modified squirt flow model show good consistency with published numerical and experimental data. The proposed modification extends the applicable range of soft-pore fraction (crack density) of the previous model, and has potential applications in media having a relatively substantial fraction of soft pores or almost only soft pores, such as granite, basalt and thermally cracked glasses.

Combinatorial structural-analytical models for the prediction of the mechanical behaviour of isotropic porous pure metals

This work provides insight on the prediction of the mechanical behaviour of isotropic porous pure metals using empirical and structural-analytical models and proposes two new combinatorial structural-analytical models for the estimation of the mechanical properties. Porous metals such as foams are advanced engineering materials and therefore the prediction of their properties for their optimisation is beneficial. Nevertheless, the estimation of their mechanical behaviour generally relies on semi-empirical models, which are limited to specific materials (i.e. type of metal + type of internal structure + individual property) and for which empirical constants need to be determined. Among the available structural-analytical models, which were developed to estimate mathematically equivalent thermophysical properties, the Symmetric and Interconnected Skeleton Structural (SISS) model gives the best prediction over a broad range of volume fraction of pores (i.e. 0.4–1.0) but always significantly overestimates the elongation to failure. This study presents the derivation of new combinatorial structural-analytical models that are able to rapidly and accurately predict the Young modulus plus ultimate tensile strength and the elongation to failure, respectively, across the entire range of volume fraction of pores. These models have physical bases, are not time- and computing-intensive (thus rapid and low cost), and have reasonable accuracy for materials whose microstructure is uncertain.

Numerical analysis of the effective properties of inhomogeneously polarized porous piezoelectric ceramics with ni-doped pore walls taking into account the influence of volume fractions of metal and pores

The paper considers a porous piezoelectric composite with metal layers deposited on the interface between the piezoelectric and vacuum phases. Such metal layers can be added technologically to improve the mechanical and electromechanical properties of the composite. To find the effective moduli, we designed a simple representative cubic volume of a unit cell consisting of a piezoelectric matrix with a compound spherical pore in its center. In turn, the compound pore includes the pore itself and a hollow metal sphere on its surface. The composite's three phases were all modeled as piezoelectric materials. The conducting interface layer was modeled as a piezoelectric material with very high dielectric constants, small piezoelectric moduli, and elastic properties of the employed metal, while the vacuum pore was modeled as a piezoelectric material with marginal moduli. The mathematical formulation of boundary value homogenization problems with full contact conditions on the interface boundaries, based on the Hill energy criterion, was described. By solving nine boundary value problems of electroelasticity with different boundary conditions for displacements and electric potential by the finite element method, a complete set of effective moduli of the piezoelectric composite is determined. The importance of considering the inhomogeneous polarization due to the presence of pores and metallic inclusions was discussed. An approximate method was proposed for determining the inhomogeneous polarization field in a piezoceramic matrix, based on a preliminary solution of the electrostatic problem for dielectrics and locating the element coordinate systems rotated along the polarization vector. The paper describes the results of computational experiments for a piezocomposite consisting of PZT-5H piezoceramic matrix, pores, and nickel layers on the pore surfaces. Comparisons between the effective properties of this composite with different volume fractions of metal and the conventional porous piezocomposite were provided, depending on the porosity and taking into account the inhomogeneous polarization. Significant differences were observed for some piezomoduli and dielectric constants, which are promising for various practical applications of the considered composites in piezoactuators using the phenomenon of the transverse piezoelectric effect.

Flexural behaviour of hybrid fibre reinforced concrete beams made with various packing factors and fine to total aggregate ratio

The objective of this study is to investigate the flexural behavior of M30 grade PSCC, GFRSCC, SFRSCC and HFRSCC beams made with PF=1.12 and s/a=0.53 and PF=1.14 and s/a=0.57 to understand the effect of copper slag as partial replacement of fine aggregate on its deflection characteristics and cracking behaviour. The yield and ultimate load taken by HFRSCC beams made with optimum PF and s/a ratios are higher than the conventional RCC beam elements. The deflections at centre at failure in HFRSCC beams made with optimum PF and s/a ratios were more than that of conventional beams. This shows improvement in ductility of HFRSCC beams. First crack formation was delayed in M30 grade HFRSCC beams due to dense micro structure with low pore fraction and reduced pore size due to which fatigue strength is increased which in turn increases the time taken for first crack occurrence and thereby increasing the load carrying capacity. The deflection at the mid span decreased in HFRSCC beams which shows that the flexural stiffness of the elements increases thereby reducing the structural member’s deformability, increasing strength and hence controlling deflection.

Pore distribution of compacted Ca-montmorillonite using NMR relaxometry and cryoporometry: Comparison with Na-montmorillonite

Abstract This study investigated the pore distributions in water-saturated Ca-montmorillonite using 1H nuclear magnetic resonance (NMR) measurements for various dry densities (0.8–1.6 g/cm 3 ) and porewater salinity conditions (deionized water, 0.1 and 1 M CaCl2) at a temperature range of 233–303 K. The volume fractions of the interlayer pore and the non-interlayer pore in the compacted Ca-montmorillonite were quantified by NMR relaxometry. At a lower Ca-montmorillonite density (0.8 g/cm 3 ), the volume fraction of the 3-HL-dominated interlayer pore was close to 20%, while that of the non-interlayer pore was higher ( > 80%) than that in Na-montmorillonite. For the higher density (1.4 g/cm 3 ), the volume fraction of the interlayer pore in both Ca- and Na-montmorillonite seemed to be more than 90% close to the total porosity. This comparison showed that the main factor affecting the pore distribution in the compacted Ca- and Na-montmorillonite is density. Meanwhile, the effect of the porewater salinity is relatively smaller. The effect of the interlayer cations is also relatively smaller at the higher density. The established method based on NMR relaxometry is expected to provide structural parameters for a realistic modeling of mass transport in water-saturated compacted clay.

Powder reuse and its contribution to porosity in additive manufacturing of Ti6Al4V

Powder reuse has become a central issue in the pursuit to industrialize metal Additive Manufacturing (AM). Furthermore, build porosity is a critical concern to component reliability and damage tolerance of the metal. However, the contributions of powder reuse to metal porosity has received very limited attention. In this study, the porosity resulting from Powder Bed Fusion-Electron Beam Melting (PBF-EB) AM of Ti6Al4V was characterized over a series of 30 build cycles (consisting of ~ 480 h cumulative build time) using X-ray Micro Computed Tomography (μCT). Investigated were the volume fraction of pores (i.e. the porosity), as well as the pore size, shape, and spatial distribution. The most prevalent pores identified were: i) those originating from the gas atomized powder, and ii) those caused by incomplete fusion of the melt pool. Although there was a minor reduction in the pore size distribution with powder reuse, the overall average volumetric porosity was 0.10 ± 0.02% and there was no significant change with increasing reuse. An inverse relationship between pore diameter and sphericity was found, with large pores posing greater effective stress concentration. Whereas the greatest pore density was located at the transition between the contour and melt beams, approximately 0.5–1.0 mm adjacent to the surface of parts, the largest pores were located within the interior hatching region. Hence, despite progressive deformation of the particles and an increase in oxidation, there was no discernable change in metal porosity with powder reuse in PBF-EB AM of Ti6Al4V.

Preparation of graphene-based aerogels by Pickering emulsion method and their performance

Pickering emulsion were used as soft template for the preparation of two different kinds of graphene-based aerogels (graphene aerogels, named AGAs and graphene/polyvinyl alcohol (PVA) aerogels, named BGAs) in this work. The Pickering emulsions show good control effect on the pore sizes, density and porosity of the two kinds of graphene-based aerogels. The increase of the oil/water ratio in the emulsion can leads to increase of pore size and porosity and decrease of density of AGAs and BGAs. And the increase of agitation speed during the emulsion preparation leads to the decrease of the pore sizes of AGAs and BGAs, while shows slight influence on the porosity and density of the materials. Volume filling behavior was found when AGAs and BGAs adsorbing organics, so it is considered that high porosity and high open pore fraction in the aerogels will favor the adsorption capacity on organics.

An integrated microporosity model of 3D X-ray micro-tomography and directional solidification simulations for Ni-based single crystal superalloys

The shrinkage microporosity formed during the directional solidification of Ni-based single crystal superalloys can significantly reduce the fatigue life of turbine blades, which may lead to a catastrophic flight accident due to the failure of aeroengines. We developed an integrated mesoscale model, which combined the shrinkage pressure drop from dendritic growth using cellular automaton method and X-ray microtomography characterization for Ni-based single crystal superalloys. The critical shrinkage pressure drop was derived from the simulation and compared to the empirical functions and experimental measurements. It was found that the pressure drop was so critical for predicting the microporosity accurately, and its relationship with the pore size and fraction was established via direct comparison to X-ray tomography. Using this integrated model, the pore size, percentage, and distribution as a function of directional solidification conditions can be successfully simulated. The model can predict small pores at the roots of the secondary dendrite arms in the early stage of solidification, and the large ones in the interdendritic liquid at the late stage of solidification. Therefore, this proposed approach has demonstrated to predict not only the influence of the processing conditions such as withdrawal rate on pore volume fraction, but also the root cause of pore size distributions.

The critical role of pore size on depth-dependent microbial cell counts in sediments

Cell counts decrease with sediment depth. Typical explanations consider limiting factors such as water availability and chemistry, carbon source, nutrients, energy and temperature, and overlook the role of pore size. Our analyses consider sediment self-compaction, the evolution of pore size with depth, and the probability of pores larger than the microbial size to compute the volume fraction of life-compatible pores. We evaluate cell counts vs. depth profiles gathered at 116 sites worldwide. Results confirm the critical role of pore size on cell counts in the subsurface and explain much of the data spread (from ~ 9 orders of magnitude range in cell counts to ~ 2 orders). Cells colonize pores often forming dense biofilms, thus, cell counts in pores are orders of magnitude higher than in the water column. Similar arguments apply to rocks.

Prediction of hot tearing susceptibility of direct chill casting of AA6111 alloys via finite element simulations

Abstract To predict hot tearing susceptibility (HTS) during solidification and improve the quality of Al alloy castings, constitutive equations for AA6111 alloys were developed using a direct finite element (FE) method. A hot tearing model was established for direct chill (DC) casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion. By applying this model to real manufacture processes, the effects of casting speed, bottom cooling, secondary cooling, and geometric variations on the HTS were revealed. The results show that the HTS of the billet increases as the speed and billet radius increase, while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases. This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation, which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.

Parametric Modeling Study of PEM Fuel Cell with Platinum Group Metal -Free Cathode Catalyst Layer

Polymer electrolyte fuel cells offer zero-emissions energy conversion but are commercially limited by cost and durability. Stack cost can be reduced by using platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR). PGM-free catalysts have lower volumetric activity relative to PGM catalysts and consequently require thicker catalyst layers. Thicker catalyst layers result in increased oxygen transport resistance and flooding in the cathode, which must be considered to accurately model PGM-free fuel cells and quantify the distinct transport resistance. For this purpose, we have developed a well validated model to elucidate relative contributions to oxygen transport resistance. This two-phase, transient, non-isothermal, channel-to-channel model contains cathode catalyst layer morphology informed by plasma-focused ion beam (P-FIB) SEM. Furthermore, the model includes agglomerate treatment of volumetrically active catalyst primary particles coated by ionomer. The structure of the agglomerate model is well suited for describing the catalyst layers containing metal organic framework (MOF) derived metal-nitrogen-carbon catalysts that are roughly spherical and volumetrically active for ORR. The MOF-derived Fe-N-C catalyst used in this study’s experiments contains atomically dispersed active sites and uniform, tunable primary particle size. In this presentation, we will report on our investigation of the performance sensitivity to a wide variety of operating conditions and MEA design specificiation, including cell temperature, gas pressures, cathode thickness, hydrophobic pore fractions and wettability, catalyst primary particle size, ionomer content, and ionomer equivalent weight. Non-dimensional characteristic parameter analysis on the model results is used to distinguish the transition between proton conductivity limited and oxygen transport limited performance, and indicate critical values that affect the the through plane ultilization of the catalyst. This information and studies on the impact of active site density help us set catalyst-specific targets for meeting fuel cell performance goals. With highly active PGM-free catalysts, we can model the impact of parameter changes on transport with experimental validation.DOE ACKNOWLEDGEMENTThis material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office (FCTO) under award number DE-EE0008076. The authors gratefully acknowledge research support from the Electrocatalysis Consortium (ElectroCat), established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under contract number DEEE0008076.

A study on design and properties of woven-nonwoven multi-layered hybrid geotextiles

The area of forests continues decreasing while the water/soil loss becomes worse. In these complicated environments, mechanical properties, stability, high modulus and low elongation of geotextiles are required. On a premise of the acquisition of good mechanical properties and the improvement in the deformation and puncture resistance of nonwoven fabric, woven/nonwoven hybrid geotextiles are designed and made with needle punch processing technology in this study. The test results indicate that the mechanical properties of hybrid geotextiles are improved significantly when the areal density of nylon fabrics is increased. In particular, with the areal density of 400 g/m2, hybrid geotextiles exhibit the maximal mechanical properties and puncture resistance. Moreover, the pore fraction of hybrid geotextiles decreases as a result of a rise in the areal density of nylon top/bottom layers. The use of a 3 D mesh fabric as the interlayer provides the needle punched composite geotextiles with the highest tensile resistance, puncture resistance. The composite geotextiles are treated with acid and alkali to simulate the corrosion under natural conditions of stabilized soil. The resultant geotextile has good mechanical properties and acid/alkali degradation resistance. This allows the hybrid geotextiles to stabilize water and soil conservation in complicated conditions.

Influence of corn residue biochar on water retention and penetration resistance in a calcareous sandy loam soil

Biochar can be potentially used as an amendment to beneficially enhance the physicochemical qualities of agricultural soils. In this study the effects of corn (Zea mays L. cv. Maxima) residue and its biochar on the soil–water characteristic curve (SWCC), the soil penetration resistance curve (SPRC, penetration resistance versus matric suction), plant available water (PAW) content, least limiting water range (LLWR) and integral water capacity (IWC) were examined in greenhouse experiments. Indices of soil physical quality and hard-setting (soil compaction during the drying processes) behavior were also measured. Pots (5 kg) were filled with a calcareous sandy loam mixed with raw corn residue or its biochars at rates of 1, 2, and 4 percent (w/w). Low and high temperature biochars, produced by slow pyrolysis process at 350 and 650 °C were evaluated. Both biochar amendments significantly ameliorated soil physical properties such as bulk density, total porosity, water retention and penetration resistance (Q) compared to the un-amended soil. Pore size distribution was significantly altered in favor of a greater fraction of wider pores (i.e. macro and mesoporosity) in the biochar amended soils. The lowest Q value was observed for the unmodified corn residue at a 4% application rate (CR 4%) in all of the matric suctions. The increase in Q with drying was attributed to Q’s strong relationship with the effective stress which originated from the matric suction. The hard-setting indices inferred from the SWCC and SPRC and shown by the slope of power model b (0.709), ΔQ (3.31 MPa), ΔQ/Q3000 (1.98), hard-setting index related to structural pores, H1 (789 hPa) and hard-setting index proposed by Dexter (2004b), HDexter (1163 hPa), were more pronounced in the untreated compared to the treated soils. Overall the changes in soil available water (SAW) for plants following biochar application was compared using three different indices, PAW, LLWR and IWC. Applying biochar could increase soil water availability such that PAW increased from 0.100 in the control to 0.156 cm3 cm−3 in BC-650 4%, LLWR100 increased from 0.079 in CR1% to 0.122% cm3 cm−3 in BC-350 2% and IWC increased from 0.072 in the control to 0.166 cm3 cm−3 in CR4%. The positive correlations between PAW, LLWR and IWC with soil physical quality indices like S1 and S2 (slopes of SWCC at first and second inflection points, related to structural and matrix pores, respectively) indicated these quantities were a potentially useful tool for evaluating soil physical quality.

Pore-Scale Investigation of the Effect of Micro-Porous Layer on Water Transport in Proton Exchange Membrane Fuel Cell

A 3D lattice Boltzmann model is developed to simulate the pore-scale two-phase flow in the porous transport layer (PTL). The PTL, composed of the gas diffusion layer (GDL) and the micro porous layer (MPL), is stochastically reconstructed and validated by comparing the pore size distribution (PSD) with experimental data. This work focuses on the effect of MPL on liquid water transport in terms of hydrophobicity, PSD and structure. It is found that more hydrophobic material and smaller pore size apply higher local capillary force against the water transport. Water can only break through the crack-free MPL under an extremely high inlet pressure (about 400 kPa). Under the real operating conditions of a fuel cell, the PTL with single GDL suffers flooding with a low fraction of dry pore. With the presence of cracked MPL, the fraction of dry pore increases significantly since a large amount of water is constrained in the electrode and only the rest flows into the GDL through the cracks, which can keep the membrane hydrated and avoid flooding. Finally, a systematically designed PTL is proposed with uniformly distributed perforations, which can automatically balance the water content and further optimize the proton conductivity and reactant transport, simultaneously.

Effect of Environmental Exposure on the Pore Structure and Transport Properties of Carbon Nanotube-Modified Mortars.

Τhe present study investigates the pore structure and transport properties of carbon nanotube-modified cementitious mortars after exposure to freeze-thaw cycles and immersion to sulfate ion solution (sulfate attack) and compares them to those of un-exposed mortars. The effect of parameters related to carbon nanotube content (within the range of 0.2–0.8 wt.%) and type of dispersant (superplasticizer/surfactant) are investigated. It is found that carbon nanotube inclusion results, overall, in a significant drop of the total porosity before exposure. Results demonstrate that environmental exposure leads to a reduction of the fraction of small diameter pores and a respective increase in capillary porosity for both dispersive agents compared to un-exposed specimens. Diffusion coefficients of nano-modified specimens are lower compared to those of un-modified mortars, both before exposure and after sulfate attack. In the case of freeze-thaw cycling, the diffusion coefficients were found to be higher in carbon nanotube-modified mortars when surfactants were used as dispersants, although with improved gas permeability values.

Wettability alteration implications on pore-scale multiphase flow in porous media using the lattice Boltzmann method

Multiphase flow in porous media is found in a variety of engineering problems, including in technologies focused on satisfying the energy needs of an expanding global population while minimizing the effects of human activity on climate change. The objective of this study is to provide a better understanding of the importance and interdependence of the wettability-altered fraction, the degree of wettability alteration, and the spatially-varying contact angle assignment in influencing the pore-scale and macroscale flow properties. In order to conduct this investigation and analyze the effects on the relative permeability curves and fluid configurations, the Shan-Chen multi-relaxation-time multicomponent lattice Boltzmann model with explicit forcing is utilized, and domains of increasing fractions of wettability-altered pores are generated. We find that the fraction altered, the degree of alteration, and the accurate contact angle assignment are all correlated, and play a role to varying extents in influencing the flow behavior and the resulting relative permeability curves. The fraction altered displays the strongest effect, and the effects of the degree of alteration and contact angle assignment become more significant when a larger fraction of the sample has undergone wettability alteration. A sample that has undergone fractional wettability alteration results in a larger resistance to the overall flow and more tortuous flow paths, at intermediate saturations, in comparison to a strongly water/oil wetting domain. In a high porosity domain that is becoming increasingly oil-wet, the degree of wettability alteration has a more pronounced effect on the flow behavior of the oil phase, whereas the flow of the water phase remains dictated by the large pore spaces and the regions of the domain that have not undergone wettability alteration until a significant fraction of the domain has been altered. Moreover, a spatially-varying contact angle assignment becomes more important for a system with a large distribution of contact angles. The results demonstrate the correlations between wettability alteration and pore geometry and highlight the need for an algorithm that captures the true time-dependent wettability state of a porous medium sample.

Quasi-static problems in the coupled linear theory of thermoporoelasticity

This article is concerned with the coupled linear quasi-static theory of thermoporoelasticity under local thermal equilibrium. The system of equations of this theory is based on the constitutive equations, Darcy’s law of the flow of a fluid through a porous medium, Fourie’s law of heat conduction, the equations of equilibrium, fluid mass conservation and heat transfer. The system of general governing equations is expressed in terms of the displacement vector field, the changes of the volume fraction of pores, the fluid pressure in pore network and temperature. The fundamental solution of the system of quasi-static equations in the considered theory is constructed and its basic properties are established. On the basis of Green’s formulas the uniqueness theorems for classical solutions of the internal and external boundary value problems (BVPs) are proved. Then, the surface and volume potentials are presented and their basic properties are given. Finally, the existence theorems for classical solutions of the BVPs are proved by means of the potential method (boundary integral equation method) and the theory of singular integral equations.

A Mechanistic Pore-Scale Analysis of the Low-Salinity Effect in Heterogeneously Wetted Porous Media

Low-salinity (LS) waterflooding has been a topic of substantial recent interest in the petroleum industry. Studies have shown that LS brine injection can increase oil production relative to high-salinity (HS) brine injection, but contradictory results have also been reported and a mechanistic explanation of these findings remains elusive. We have recently developed a pore-scale model of LS brine injection in uniformly wetted networks (Watson et al. in Transp Porous Med 118:201–223, 2017), and we extend this approach here to investigate the low-salinity effect (LSE) in heterogeneously wetted media. We couple a steady-state fluid displacement model to an innovative tracer algorithm and track the evolving salinity front as oil and HS brine are displaced from the network. The wettability of the pore structure is locally modified where water salinity falls below a critical threshold, and simulations show that this can have significant consequences for oil recovery. Our results demonstrate that, for heterogeneously wetted networks, the oil-wet (OW) pores are the only viable source of incremental oil by LS brine injection. Moreover, we show that a LS-induced increase in the displaced OW pore fraction is a necessary, but not sufficient, condition to guarantee additional oil production. Simulations further suggest that the initial OW pore fraction, the average network connectivity and the initial HS brine saturation are factors that can determine the extent of incremental oil recovery following LS brine injection. This study clearly highlights that the mechanisms of the LSE can be markedly different in uniformly wetted and in non-uniformly wetted porous media.