Dynamic Pore Research Articles

Calculation of pore diameters in zeolites

Pore diameters of zeolites are calculated using a new freely available software tool which identifies rings based on the crystallographic notation of atoms. In addition, an automated algorithm allows to extract information from molecular dynamics outputs so that dynamic pore diameters are calculated and compared to an experimental reference. This is useful in order to identify different rings along a given channel as well as for the calculation and analysis of ring deformations due to framework dynamics and sorbate diffusion.

Evaluation of foam generated with the hydrocarbon solvent for extra-heavy oil recovery from fractured porous media: Pore-scale visualization

Aqueous based foam injection has gained interest for conventional oil recovery in recent times. Foam can control the mobility ratio and improve the sweep efficiency in oil reservoirs over gas flooding. However, due to the high viscosity of the oil, its application in heavy oil reservoirs is challenging. Moreover, the oil-wet nature of carbonate reservoirs makes it difficult for aqueous based foam to efficiently remove the heavy oil. On the other hand, hydrocarbon solvents have been used for decreasing the heavy oil viscosity and increase its recovery by diffusion and mixing mechanisms. However, the low rate of diffusion/dispersion, inadequate sweep efficiently and asphaltene precipitation, especially in heterogeneous reservoirs, are the major challenges during solvent injection. In this paper, hydrocarbon solvent based foam (SBF) as an alternative to solvent flooding is explored for heavy oil recovery from a fractured porous media.Hydrocarbon solvent-based CO2 foam was used to increase sweep efficiency during heavy oil recovery. The foam was generated with the help of a fluorosurfactant in a hydrocarbon solvent. Static bulk performances of foam were analyzed at different concentrations of surfactant. Surface tension measurements were also performed to study the adsorption of surfactant into the liquid-gas interface and its effect on foamability and foam stability. A specially designed fractured micromodel (oil wet, representing fractured carbonate reservoirs) was used to visualize the pore-scale phenomena during solvent based foam injection. For the first time, extra heavy oil with a viscosity of about 30,000 cp has been used in this study for pore scale visualization. A high-quality camera was utilized to capture images/movies.According to static experiments, although the value of the surface tension of hydrocarbon solvent was initially low, the addition of surfactant slightly decreased the surface tension further improving the foam stability. However, the mechanisms involved in foamability and foam stability of non-aqueous based foam are more complicated than water based foam and cannot be discussed solely based on surface tension and bulk analysis. In addition, dynamic pore scale observation through this study revealed that solvent based foam can significantly contribute to heavy oil recovery with different mechanisms. At the initial stage, solvent diffuses and mixes with viscous oil and reduce the viscosity. Later, foam bubbles improve the sweep efficiency by diverting the solvent toward the untouched part of the porous media. Foam bubbles partially blocked the larger pores in matrix/swept-area increasing the contact of solvent and heavy oil, providing better mixing. Therefore, oil is swept much faster and more efficiently from the grain in oil-wet porous media compared to that of conventional solvent flooding.

The X-Ray Micro-Tomography Backed by Molecular Dynamics Simulations in the Analysis of Shock-Induced Damage in Ductile Materials

We have studied spallation in single crystal of metals under shock at very high strain rate. Our work has been devoted to understanding, and predicting the dynamic ductile damage processes of nucleation, growth and coalescence of voids in these extreme conditions of impact. Recovered sample only indicates final state of damage. Molecular Dynamics calculations are predicting the phenomenon over time. However we need experimental results to validate and improve simulations and models. X-ray tomography analyses are appropriate to extract pore volume distributions. Our study on ductile materials allowed us to conclude that experimental analyses exhibit two power laws attributed to growth and coalescence regimes. Moreover power law is scale invariance so it is possible to compare experiment (macroscopic) to calculation (microscopic). We show that there are good correlations between experimental and Molecular Dynamics pore volume distribution. Thanks X-ray microtomographies findings we progress in understanding the phenomenon of dynamic damage.

Experimental Study on the Pore Pressure of the Silty Soil Around Tunnel Under Subway Loading

Based on the global digital system, by fully considering the factors of the pore pressure, such as the frequency, the dynamic stress amplitude, the consolidation ratio as well as the overconsolidation ratio, the dynamic triaxial test was conducted to study the dynamic pore pressure of the silty soil around the tunnel of the Guoquan Road station of line No. 10 subway in Shanghai, and the change law of the pore pressure influenced by each factor was obtained. The results show that the logarithmic curve is adopted to describe the relationship between the pore pressure and the vibration times. Besides, the model parameters are determined with the regression analysis. The results offer some valuable references to the design subway tunnel.

Study of Adsorption and Desorption Performances of Zr-Based Metal-Organic Frameworks Using Paper Spray Mass Spectrometry.

The dynamic pore systems and high surface areas of flexible metal–organic framework materials make them excellent candidates to be used in different kinds of adsorption processes. However, the adsorption and desorption behaviors of therapeutic drugs on metal–organic frameworks in solution are not fully developed. Here, we systematically investigated the adsorption and desorption behaviors of a typical therapeutic drug, verapamil, over several Zr-based metal–organic frameworks [e.g., Zr-FUM, UiO-66(Zr), UiO-66(Zr)-NH2 and UiO-66(Zr)-2COOH] as well as ZrO2 in an acetonitrile solution by using paper spray mass spectrometry. In contrast to other materials, UiO-66(Zr)-2COOH demonstrated a superior adsorption performance to verapamil due to their strong acid-base and/or hydrogen-bond interactions, and the adsorption process fitted well with the pseudo-second-order kinetic model. As verapamil-adsorbed materials were used for desorption experiments, ZrO2 demonstrated the most favorable desorption performance, whereas UiO-66(Zr)-2COOH yielded the poorest desorption capability. These Zr-based materials had also been coated at the surface with filter papers for the analysis of various drugs and proteins in the process of paper spray mass spectrometry. The results demonstrated that among the studied materials, ZrO2-coated paper gave the most favorable desorption performance as a pure drug solution, whereas the paper from UiO-66(Zr) demonstrated the optimal capability in the analyses of therapeutic drugs in a complex matrix (e.g., blood) and a protein (e.g., myoglobin).

Dynamic pore-scale network model (PNM) of water imbibition in porous media

A dynamic pore-scale network model is presented which simulates 2-phase oil/water displacement during water imbibition by explicitly modelling intra-pore dynamic bulk and film flows using a simple local model. A new dynamic switching parameter, λ, is proposed within this model which is able to simulate the competition between local capillary forces and viscous forces over a very wide range of flow conditions. This quantity (λ) determines the primary pore filling mechanism during imbibition; i.e. whether the dominant force is (i) piston-like displacement under viscous forces, (ii) film swelling/collapse and snap-off due to capillary forces, or (iii) some intermediate local combination of both mechanisms.A series of 2D dynamic pore network simulations is presented which shows that the λ-model can satisfactorily reproduce and explain different filling regimes of water imbibition over a wide range of capillary numbers (Ca) and viscosity ratios (M). These imbibition regimes are more complex than those presented under drainage by (Lenormand et al. (1983)), since they are determined by a wider group of control parameters. Our simulations show that there is a coupling between viscous and capillary forces that is much less important in drainage. The effects of viscosity ratio during imbibition are apparent even under conditions of very slow flow (low Ca)–displacements that would normally be expected to be completely capillary dominated. This occurs as a result of the wetting films having a much greater relative mobility in the higher M cases (e.g. M = 10) thus leading to a higher level of film swelling/snap-off, resulting in local oil cluster bypassing and trapping, and hence a poorer oil recovery. This deeper coupled viscous mechanism is the underlying reason why the microscopic displacement efficiency is lower for higher M cases in water imbibition processes.Additional results are presented from the dynamic model on the corresponding effluent fractional flows (fw) and global pressure drops (ΔP) as functions of capillary number and viscosity ratio. These results indicate that unsteady-state (USS) relatively permeabilities in imbibition should be inherently rate dependent.

Representative Elementary Volume (REV) in spatio-temporal domain: A method to find REV for dynamic pores

One of the potential risks associated with subsurface storage of CO2 is the seepage of CO2 through existing faults and fractures. There have been a number of studies devoted to this topic. Some of these studies show that geochemistry, especially mineralization, plays an important role in rendering the faults as conduits for CO2 movement while others show that mineralization due to CO2 injection can result in seep migration and flow diversion. Therefore, understanding the changes in reservoir properties due to pore alterations is important to ensure safe long term CO2 storage in the subsurface. We study the changes in the Representative Elementary Volume (REV) of a rock due to reactive kinetics over a time, using a statistical approach and pore-scale CO2-rock interactiondata. The goal of this study is to obtain the REV of a rock property that accounts for pore-scale changes over time due to reactive kinetics, and we call this as spatiotemporal REV. Scale-up results suggest that the REV changes with time when CO2-rock interaction is considered. It is hypothesized that the alteration in pore structure introduces more heterogeneity in the rock, and because of this the magnitude of REV increases. It is possible that these noticeable changes in REV at pore-scale may have an impact when analyzed at the reservoir scale.

Damage mechanism of stabilizing piles suffered from liquefaction based on dynamic numeric analyses

A large deformation from liquefaction in saturated subgrade may lead to the instability of slope and the damage of the reinforcement measures. Firstly, in order to evaluate the damage mechanism of stabilizing piles suffered from the saturated subgrade liquefaction, this paper perform a dynamic centrifuge modelling test using a kind of stabilizing concrete model pile to study the dynamic water pore pressure, landslide of slope and dynamic crack of the stabilizing pile. Secondly, the breaking damage mechanism of the stabilizing pile is discussed under the condition of a large liquefaction deformation by means of the dynamic consolidation finite element method. The study shows that the large deformation of the reinforced slope caused by the liquefaction leads to a decrease in the earth pressure in front of the stabilizing pile and an increase in the earth pressure behind the stabilizing pile. These comprehensive effects result in a significant increase in the dynamic excess bending moment of the stabilizing pile, and eventually, the total static and dynamic bending moment of the stabilizing piles exceeds the ultimate bending moment and leads to the breaking damage of the piles.

Pore to pore validation of pore network modelling against micromodel experiment results

Pore network modelling (PNM) has been widely used to study the multiphase flow and transport in porous media. Although a number of recent papers discussed the PNM validation on core-scale parameters such as permeability, relative permeability and capillary pressure; quantitative predictive potential of PNM on pore by pore basis has rarely been studied. The aim of this paper is to present a direct comparison between PNM simulations and corresponding micro-model experiments at the same scale and the same geometry. A number of well-defined and constrained two-phase flow in porous medium experimental scenarios were utilized to validate the physics solving part in PNM (filling rules, capillary and viscous pressure). This work validates that a dynamic pore network flow solver can predict two-phase flow displacements for these experiments for drainage situations at both pore and plug scales. A glass-etched micro-model is used to quantify the accuracy of a dynamic PNM solver on pore and core levels. Two-phase drainage micro fluidic experiments at different flow conditions are performed on micro-models. PNM simulations are performed on the same pattern and flow conditions as used in micro-model experiments. The two-phase distribution extracted from experiment images is registered onto rsults of PNM simulations for direct pore to pore comparison. Pore-scale matching level is found at around 75 % for all three test cases. The matching level of core-scale parameters such as S w c and oil-phase permeability varies from case to case; the relative error to micro-model experiment measurements varies from 15 to 60 %. Possible reasons leading to discrepancies on core-scale parameters are discussed: missing considerations during validation of the combination of uncertainty in both simulator input parameters and experiments are seen as the principal factors.

Microfabric Evaluation of Lime-Treated Clays by Mercury Intrusion Porosimetry and Environment Scanning Electron Microscopy

This study investigates the microstructure of lime-treated clayey soils using mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) analyses. Parameters that were varied include lime percent (3, 6, 9%), curing duration (7, 28 days and 1 year), soil pulverization level and mellowing period (1 and 24 h). All samples were compacted at optimum water contents using standard Proctor compaction energy. The 34 MIP and several ESEM analyses conducted on these samples showed that lime content and curing duration had significant impact on the resulting microstructure. MIP results, presented as mercury intrusion curves, total porosity values and pore size distribution histograms revealed that lime stabilization changed the microfabric of clayey soils through a dynamic pore refinement process. Although increases in pore sizes and porosities were observed in the short term (up to 28 days), after a curing period of 1 year, considerable decreases in pore sizes and porosities were noted. A novel “Pore Size Amplification Factor”, (PSAF) was calculated to determine the amplification and/or deamplification of different pore size ranges compared to the untreated soil. ESEM analyses confirmed that while the addition of lime to clayey soils initially increased pore size within the microstructure, over time, as the pores became partially or even completely blocked, the pore sizes reduced. Pores of different sizes and cementation within and on the particles were visible. ESEM findings also showed that pore shapes were not always circular as is assumed in MIP analyses. The results of this study add valuable insight into the time related changes in the microfabric of lime-treated soils.

Analysis of Vehicle-Force-Induced Dynamic Pore Pressure in Saturated Pavement With LSPM Drainage Base

Abstract Dynamic pore pressure caused by moving-vehicle forces may cause damage in asphalt pavement. However, few field data of dynamic pore pressure are available. This research aimed to study the time histories of dynamic stress and dynamic pore pressure in the drainage base of large stone porous asphalt mixes (LSPM) under moving-vehicle forces. To this end, heat-resistant dynamic stress and pore-pressure sensors were developed and used to measure the dynamic stresses and pore pressures in the field. A numerical fluid-solid coupling simulation method was used to analyze the response of pavement under moving wheel forces. Numerical simulation results matched well with in situ test data. The time histories of dynamic pore pressure in the pavement are quantitatively analyzed, and the hydraulic mechanism of moisture-induced damage is verified. This study provides a theoretical guide for pavement design.

Numerical-analytical study on effect of three-phase poroelastic medium model parameters on dynamic displacements and porous pressures response

The problem of loading on a one-dimensional partially saturated poroelastic rod is considered. A mathematical model of a partially saturated porous medium based on the Bio model was used. Solid skeleton displacements and pore pressures of fillers are chosen as basic functions defining wave process. A mathematical model of the boundary-value problem of the dynamic theory of poroelasticity is considrered in Laplace domain. The solution in time domain is obtained using the stepping method of numerical inversion of the Laplace transform. Dynamic displacement responses and pore pressures are presented for different values of the parameters of the poroelastic material model.

LEAP-GWU-2015: Centrifuge and numerical modelling of slope liquefaction at the University of Cambridge

As part of the LEAP-GWU-2015 exercise, a dynamic centrifuge test was conducted at the University of Cambridge on a 5° slope of medium dense Ottawa F-65 sand. The model preparation and saturation details are presented in this paper. This paper presents the experimental data recorded during small and large magnitude sinusoidal ground motions. After the experiment, numerical simulations of the experiment were performed using the finite element code Swandyne. The results from these numerical analyses are compared with the centrifuge test data and the deformations observed during the post-test investigations. The numerical analyses replicated many of the salient features of the test, such as the overall generation of excess pore pressures and attenuation of accelerations in the liquefying ground. More subtle results, such as the de-liquefaction shocks and the asymmetric response due to differences in upslope and downslope accelerations were less well captured in terms of the expected spikes in the dynamic excess pore pressures and accelerations. Overall, the combination of centrifuge testing and numerical analysis were found to complement each other well.

Particle and pore dynamics under column leaching of goethitic and saprolitic nickel laterite agglomerates

In an agglomerated particle heap leach process, the pore network structure within the agglomerates and the particle bed is a critical determinant of efficient lixiviant flow. During the leaching period a degree of slumping can occur, changing the structure of the inter-particle void spaces and the porosity of the particle bed. The ability to characterise the agglomerate pore network structure and measure its changes over the leach period is essential for the understanding and improvement of lixiviant flow and the ultimate performance of the heap. Three dimensional (3D) non-destructive X-ray micro-tomography (XMT) offers a great opportunity to provide detailed spatially resolved structural information of these multiphase particulate systems. The aims of this paper are to compare and contrast the dynamic pore network structure of saprolitic (SAP) and goethitic (G) Ni laterite mineral agglomerate beds undergoing acid leaching by periodic scanning with XMT, as well as to extract quantitative porosity information from this data and correlate it with/to other measures of bed stability, specifically mass loss and particle bed slump. The resulting XMT analyses were able to reliably discriminate between solid and gas phases, enabling the estimation of porosity from the segmented images which in turn agreed well with the measured mass loss and slump. The SAP particle bed has consistently higher porosity and leach stability compared to the G particle bed and this is consistent with the higher HL processability of SAP ores compared to G ores observed in other studies.

New insights into cochlear sound encoding.

The inner ear uses specialized synapses to indefatigably transmit sound information from hair cells to spiral ganglion neurons at high rates with submillisecond precision. The emerging view is that hair cell synapses achieve their demanding function by employing an unconventional presynaptic molecular composition. Hair cell active zones hold the synaptic ribbon, an electron-dense projection made primarily of RIBEYE, which tethers a halo of synaptic vesicles and is thought to enable a large readily releasable pool of vesicles and to contribute to its rapid replenishment. Another important presynaptic player is otoferlin, coded by a deafness gene, which assumes a multi-faceted role in vesicular exocytosis and, when disrupted, causes auditory synaptopathy. A functional peculiarity of hair cell synapses is the massive heterogeneity in the sizes and shapes of excitatory postsynaptic currents. Currently, there is controversy as to whether this reflects multiquantal release with a variable extent of synchronization or uniquantal release through a dynamic fusion pore. Another important question in the field has been the precise mechanisms of coupling presynaptic Ca 2+ channels and vesicular Ca 2+ sensors. This commentary provides an update on the current understanding of sound encoding in the cochlea with a focus on presynaptic mechanisms.

Viral infection: HIV uses a 'molecular iris' to control capsid access.

This study shows that dynamic pores in the capsid of HIV allow the import of substrates for reverse transcription, thereby shielding the reaction from the host cytosol.

HIV-1 uses dynamic capsid pores to import nucleotides and fuel encapsidated DNA synthesis.

During the early stages of infection, the HIV-1 capsid protects viral components from cytosolic sensors, such as cGAS, and nucleases, such as TREX, while allowing access to nucleotides for efficient reverse transcription1. Here we show that each capsid hexamer has a size-selective pore bounded by a ring of six arginine residues and a ‘molecular iris’ formed by the N-terminal β-hairpin. The arginine ring creates a strongly positively charged channel that recruits the four nucleotides with on-rates that near diffusion limits. Progressive removal of pore arginines results in a dose-dependent and concomitant decrease in nucleotide affinity, reverse transcription and infectivity. This positively charged channel is universally conserved in lentiviral capsids despite the fact that it is strongly destabilising without nucleotides to counteract charge repulsion. We also describe a channel inhibitor, hexacarboxybenzene, which competes for nucleotide binding and efficiently blocks encapsidated reverse transcription demonstrating the tractability of the pore as a novel drug target.

4-D imaging of sub-second dynamics in pore-scale processes using real-time synchrotron X-ray tomography

Abstract. A variable volume flow cell has been integrated with state-of-the-art ultra-high-speed synchrotron X-ray tomography imaging. The combination allows the first real-time (sub-second) capture of dynamic pore (micron)-scale fluid transport processes in 4-D (3-D + time). With 3-D data volumes acquired at up to 20 Hz, we perform in situ experiments that capture high-frequency pore-scale dynamics in 5–25 mm diameter samples with voxel (3-D equivalent of a pixel) resolutions of 2.5 to 3.8 µm. The data are free from motion artefacts and can be spatially registered or collected in the same orientation, making them suitable for detailed quantitative analysis of the dynamic fluid distribution pathways and processes. The methods presented here are capable of capturing a wide range of high-frequency nonequilibrium pore-scale processes including wetting, dilution, mixing, and reaction phenomena, without sacrificing significant spatial resolution. As well as fast streaming (continuous acquisition) at 20 Hz, they also allow larger-scale and longer-term experimental runs to be sampled intermittently at lower frequency (time-lapse imaging), benefiting from fast image acquisition rates to prevent motion blur in highly dynamic systems. This marks a major technical breakthrough for quantification of high-frequency pore-scale processes: processes that are critical for developing and validating more accurate multiscale flow models through spatially and temporally heterogeneous pore networks.

Spectral‐induced polarization measurements on sieved sands and the relationship to permeability

AbstractLaboratory measurements of the permeability and spectral‐induced polarization (SIP) response of samples consisting of unconsolidated sands typical of those found in New Zealand aquifers have been made. After correction of measured formation factors to allow for the fact that some were measured at only one fluid conductivity, predictions of permeability from the grain size (d) of the samples are found to agree well with measured values of permeability. The Cole‐Cole time constant (derived from the SIP measurements) is found, as expected, to depend upon d2, but can be affected by the inclusion of smaller grains in the sample. Measurements made on samples comprising of mixtures of grain sizes show that inclusion in a sample of even 10% of smaller grains can significantly reduce both the Cole‐Cole time constant (τCC) and the permeability, and support theoretical derivation of how the permeability of a mixture of grain sizes varies with the content of the mixture. Proposed relationships for using τCC as a predictor for permeability are tested and found to be crucially dependent on the assumed relationship between the dynamic pore radius and grain size. The inclusion of a multiplicative constant to take account of numerical approximations results in good predictions for the permeability of the samples in this study. It seems unlikely, however, that there is a single global expression for predicting permeability from SIP data for all samples.

Understanding the Role of Water Phase Continuity on the Relationship Between Drainage Rate and Apparent Residual Saturation: A Dynamic Network Model Study

When water drains from a porous medium, a small quantity of residual water typically remains trapped in the medium. The residual water saturation, $$S_{\mathrm{wr}}$$ , is a measure of the ratio of the volume of residual water to the volume of voids in the porous medium. While conventional multiphase flow concepts suggest that $$S_{\mathrm{wr}}$$ has a single value that is a property of the fluids and medium, significant evidence exists that $$S_{\mathrm{wr}}$$ may actually have a dynamic component, exhibiting different observed values when drainage takes place at different rates. Previous work by the authors used experimental measurements to explore this phenomenon. The work described here further explores the phenomenon through the use of a dynamic pore network model specifically designed to study the effects of changing fluid continuity in porous media resulting from dynamic drainage. The model is based on cylindrical pore throats and volumeless pore bodies. The relatively simple structure of the model makes it well suited to the purposes of the work, in that it provides a mechanism to simulate the effect of fluid continuity on drainage from a spatially random porous medium defined by a minimal number of parameters. Results suggest that the phenomenon may occur as a result of pore-scale preferential flow causing desaturation of the porous medium at the water-wet boundary. Significant sensitivity is observed to both porous medium configuration and resistance to water flow across the water-wet boundary.