Effective Pore Space Research Articles

Pore Chemistry and Architecture Control in Anionic Functional Ultramicroporous Materials for Record Dense Packing of Xenon.

Adsorptive separation of Xe and Kr is an industrially promising but challenging process because of their identical shape and similar physicochemical properties. Herein, we demonstrate a strategy through rationally designing the linkers of anionic functional ultramicroporous materials (FUMs) to finely regulate the pore chemistry and architecture, which creates unique stepped channels incorporating dense polar nanotraps to generate a larger effective pore space and enables dense packing of Xe. A new hydrolytically stable FUM (ZUL-530) was prepared, which for the first time achieves a Xe packing density exceeding the liquid Xe density at atmospheric conditions in metal-organic frameworks (MOFs) (based on experimental data), resulting in both excellent Xe uptake (2.55 mmol g-1 at 0.2 bar) and high IAST selectivity (20.5). GCMC and DFT-D calculations reveal the essential role of the stepped traps in the dense packing of Xe. Breakthrough experiments demonstrate remarkable productivities of both high-purity Kr (6.70 mmol g-1) and Xe (1.78 mmol g-1) for the Xe/Kr (20:80) mixture. In a model nuclear industry exhaust gas, ZUL-530 exhibits a top-class Xe dynamic capacity (28.8 mmol kg-1) for trace Xe, which proves it is one of the best candidates for Xe/Kr separation.

Impact of CO2 sequestration on pressure systems in saline aquifer: Simulation of differential pressure evolution in the caprock-reservoir

CO2 sequestration in the saline aquifer is one of the most promising means of geological sequestration, and the realization of safe CO2 sequestration without leakage is the common goal of sequestration projects. Mature continental sedimentary basins typically have a long drilling and production history, and several wellbores inevitably penetrate the saline aquifer. These wellbores have been identified as risky locations for CO2 leakage. Scale-up CO2 injection can cause large-scale perturbations to the saline aquifer pressure system, affecting the sealing integrity of wells within the sequestration site. Considering that differential pressure is a key driver of wellbore leakage, this paper establishes and validates a three-dimensional cap-reservoir model to simulate the evolution of the differential pressure between the cap-reservoir due to CO2 sequestration. The simulation results show significant differences in the magnitude and rate of pressure buildup in the cap and reservoir during injection and in the rate of overpressure dissipation after stopping injection. These differences caused the dynamic evolution of the interlayer pressure difference. They formed peaks in the injection and stopping stages, and the peak in the injection stage was higher than in the stopping stage. The peak decreases as an exponential function with increasing distance from the injection well. In the constant rate injection mode, the peak rises linearly with increasing injection rate, and the effect of injection temperature on the peak can be neglected. A sensitivity analysis of reservoir hydrogeological parameters was done. From the perspective of controlling differential pressure, an ideal saline aquifer should be characterized by deep burial, low salinity, high permeability, and large effective pore space. This study is significant for CO2 sequestration site optimization and CO2 leakage risk control.

Effect of Water on Effective Pore Structures for Medium-Rank Coal: Based on the Prefreezing Nitrogen Adsorption-Desorption Experiment.

Water is ubiquitous in coal reservoirs, and its distribution can have a remarkable influence on the effective pore space of methane. This study conducted the combination experiments of moisture equilibrium and prefreezing nitrogen adsorption-desorption to explore the adsorption behavior of water in coal pores and thus to reveal the distribution characteristics of water in pores with different scales as well as the influence of water on pore structures. The results showed that the adsorption mechanism of water vapor undergoes a transition from monolayer to multilayer to condensation with the increase in relative humidity (RH). The occurrence characteristics of adsorbed water in coal pores are controlled by the RH and pore size. When the RH is increased from 0 to 98%, the nitrogen adsorption capacity, specific surface area, and effective pore volume of the samples were all decreased significantly due to the different adsorption modes of water, which is more significant in pores with d < 10 nm. Additionally, the relative pressure corresponding to the branching position of the nitrogen adsorption-desorption curve will be changed with the increase in moisture content. Based on this, it is calculated that the adsorbed water will change the smoothness of the pore wall and the complexity of the pore structure.

Statistical Effective Diffusivity Estimation in Porous Media Using an Integrated On-site Imaging Workflow for Synchrotron Users

Transport in porous media plays an essential role for many physical, engineering, biological and environmental processes. Novel synchrotron imaging techniques and image-based models have enabled more robust quantification of geometric structures that influence transport through the pore space. However, image-based modelling is computationally expensive, and end users often require, while conducting imaging campaign, fast and agile bulk-scale effective parameter estimates that account for the pore-scale details. In this manuscript we enhance a pre-existing image-based model solver known as OpenImpala to estimate bulk-scale effective transport parameters. In particular, the boundary conditions and equations in OpenImpala were modified in order to estimate the effective diffusivity in an imaged system/geometry via a formal multi-scale homogenisation expansion. Estimates of effective pore space diffusivity were generated for a range of elementary volume sizes to estimate when the effective diffusivity values begin to converge to a single value. Results from OpenImpala were validated against a commercial finite element method package COMSOL Multiphysics (abbreviated as COMSOL). Results showed that the effective diffusivity values determined with OpenImpala were similar to those estimated by COMSOL. Tests on larger domains comparing a full image-based model to a homogenised (geometrically uniform) domain that used the effective diffusivity parameters showed differences below 2 % error, thus verifying the accuracy of the effective diffusivity estimates. Finally, we compared OpenImpala’s parallel computing speeds to COMSOL. OpenImpala consistently ran simulations within fractions of minutes, which was two orders of magnitude faster than COMSOL providing identical supercomputing specifications. In conclusion, we demonstrated OpenImpala’s utility as part of an on-site tomography processing pipeline allowing for fast and agile assessment of porous media processes and to guide imaging campaigns while they are happening at synchrotron beamlines.

Gas transport in organic-rich nanoporous media with nonequilibrium sorption kinetics

We present a mathematical model for one-dimensional gas transport in organic-rich nanoporous media subject to nonequilibrium sorption. The model is developed from two governing equations to simulate Knudsen diffusion and viscous flow in the free phase, and surface diffusion in the sorbed phase. The pore space is shared between the free and sorbed phases by defining concentration-dependent free- and sorbed-phase volume fractions. The governing equations are coupled through a source/sink term described by a kinetic sorption model. The impact of the reduced effective pore space and sorption on free-phase mass transfer is characterized by defining effective diffusion coefficients. The governing equations are numerically solved based on the finite element method. The model is utilized to analyze the temporal and spatial concentration data obtained using X-ray micro-CT scans from two experiments, including Krypton transport into a coal sample and Xenon uptake into a shale sample. The proposed model closely reproduces total concentration profiles in both experiments, and captures the concentration peak in Xe-shale system due to the significant nonequilibrium sorption and slower process of reaching equilibrium. The modeling results show that surface diffusion dominates the total mass transport in Xe-shale system with higher adsorption affinity. In Kr-coal system with lower adsorption affinity, the sorbed phase contributes significantly to the total mass transport mainly at high pressures. In addition, the sorbed phase can occupy up to 30% of pore space, which reduces the free-phase diffusion coefficient by 40% in Xe-shale and 80% in Kr-coal. Accordingly, neglecting the sorbed-phase volume in nanoporous media may overestimate the effective free-phase diffusion coefficient. This study shows the significance of the nonequilibrium adsorption for gas transport in nanoporous media.

Effect of Water Saturation on Gas-Accessible Effective Pore Space in Gas Shales

Abstract The existence and content of water will certainly affect the effective pore space of shales and therefore is a key point for the evaluation of in-situ gas content and gas flow capacity of shale reservoirs. In order to reasonably evaluate the gas storage and flow capacities of water-bearing shale reservoirs, the effect of water on the effective pore space of shales needs to be understood. In this study, the Upper Permian Longtan shale in the southeastern Sichuan Basin, China, was selected as an example to conduct nuclear magnetic resonance cryoporometry (NMRC) measurements under different water saturation levels. The gas-accessible effective pore spaces in shales under different water saturation levels were quantified, and the effect of water saturation on gas-accessible effective pore space in shales was investigated. The results show that water plays an important role in the gas-accessible effective pore space of shales. When the Longtan shale increases from a dry state to a water saturation of 65%, 75%, and 90%, the gas-accessible effective pore volume decreases by 35%-60% (average 46.3%), 50%-70% (average 58.8%), and 65%-82% (average 75.8%), respectively. Water has an effect on the gas-accessible effective pore space regardless of pore size, and the effect is the strongest in the 4-100 nm range, which may be mainly due to the high content of clay minerals in the Longtan shale. Our studies are of important theoretical significance and application prospects for accurately evaluating the gas-accessible effective pore space of gas shales under actual geological conditions.

Numerical Modeling of Chloride Transport in Concrete under Cyclic Exposure to Chloride.

Concrete structures under cyclic exposure to chlorides entail a higher risk of embedded steel corrosion along with accelerated ionic ingress from the environment. This study proposes a coupled transport model considering moisture and chloride distribution in concrete to investigate the influence of a cyclic exposure condition on chloride penetration. In this model, pore size distribution to quantify the effective pore space for moisture and chloride mobilizations was determined to establish the governing equation for chloride transport through non-saturated concrete. From the simulation results, the rate of chloride penetration increases with decreasing ambient humidity levels due to the enhanced chloride convection. Finally, the coupled transport model was verified by comparing in-situ data, showing reasonable correlations with 0.83 and 0.93 of determinant coefficients for 22 and 44 years of exposure, respectively, while those obtained from LIFE 365 were much lower.

Ionic Liquid/Non-Ionic Surfactant Mixtures as Versatile, Non-Volatile Electrolytes: Double-Layer Capacitance and Conductivity

Ionic liquids (ILs) are being increasingly used as processing aids to formulate electrode/electrolyte composites where the electrolyte acts as a template, defining the effective electrolyte-filled pore space between 2D materials such as graphene and MXenes. This is often facilitated with non-ionic surfactants. However, little is currently known about how these surfactants impact double-layer formation and ionic conductivity. Herein, we measure these properties for two commonly used non-ionic surfactants, P123 and Triton X-100 (TX-100) mixed with the IL, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI). A significant increase in the minimum capacitance is observed at 40 wt% surfactant by up to 88% and 102% for P123 and TX-100, respectively. On the other hand, the higher viscosity of the mixtures, lowers the ionic conductivity from 8.5 mS cm−1 (neat IL) to 1 mS cm−1 (40 wt% surfactant). Despite the significantly higher viscosity of P123/IL mixtures compared to TX-100/IL, both electrolyte series show the same reduction in ionic conductivity with respect to concentration. Pulse field gradient nuclear magnetic resonance was also used to show that for both electrolyte series, the diffusion coefficients follow a similar trend.

Using clay microporosity to improve formation evaluation in potential residual oil zones: Cypress Sandstone, Illinois Basin

Clay microporosity in sandstones can cause erroneously high water saturation calculations if not properly accounted for and reduces effective pore space when evaluating a formation. We conducted a petrographic study to characterize and quantify the clay mineral microporosity of the fluvial facies of the Mississippian Cypress Sandstone in the Illinois Basin. This data helped achieve more accurate saturation calculations through core and well log analyses in potential Cypress residual oil zones. Petrographic thin sections were analyzed by scanning electron microscopy with backscatter imaging and energy dispersive X-ray spectroscopy. Clay mineral species identified included pore-filling kaolinite books, blocks, and vermicules; chlorite clusters; illite mats; illite-smectite webs; grain-coating inherited chlorite rims; and pore-bridging illite hairs. Volume percentages of microporosity particular to clay mineral species were determined by image analysis. Average microporosity values in kaolinite, chlorite, illite, and illite-smectite were 41%, 57%, 67%, and 65%, respectively. Effective clay mineral volumes, including microporosity, showed a >2-fold increase over estimates determined by X-ray diffraction, constituting an average volume of 4%. Comparing these volumes with gamma-ray log estimates proved Stieber’s work to predict clay volume most accurately. Clay volumes were used as input parameters in the dual-water method for determining water saturation, resulting in greater residual oil saturations than those predicted from Archie’s equation. Accounting for clay microporosity in helium porosimetry measurements of total porosity resulted in an ~11% decrease to effective porosity. Results from this research improve estimates of water saturation and porosity and highlight the importance of studying microscale mineralogical properties during reservoir characterization.

Study on nano-alumina in concrete

Nano-materials in concrete helps in effective utilization pore space occupation leading to minimal etrringate formation which in-turn improving overall durability and improved performance of concrete on long-term. The present study aims at experimental investigation on Nano-alumina in concrete, its optimizations and its effects in concrete overall strength. Nano-alumina has been added to the concrete mix proportions of 1%, 2%, 3% and 4%.Totally108 cubes, cylinders and prism were casted for the grades of M30 and M40 of concrete and their respective compressive strength, spilt tensile strength and flexural strength has been analyzed by experimental investigation. The distribution of ultra-sonifcated, nano-alumnia in concrete has been analyzed by means of Scanning Electron Microscopic image patterns. Based on the experimental study Nano-alumina with 1% has showed better distribution along the matrix of concrete and also efficient in terms of improved compressive strength, split tensile strength and flexural.

A Retardation Factor Considering Solute Transfer Between Mobile and Immobile Water in Porous Media

In advective-dispersive simulations of aquifers, retardation factors using linear adsorption isotherms are commonly employed to represent the adsorption-desorption process for solutes in soil. In particular, the retardation factors that use entire pore space (total porosity) or effective pore space (effective porosity) are widely used. Although another retardation factor that describes solute transfer between mobile and immobile water in porous media has been developed, characteristics of the model have not been examined extensively. This retardation factor retains the ease of use and characteristics of the first two models; for example, its breakthrough curve is similar to those generated by models that employ total porosity for aquifers in which groundwater flow is fast and solute transport by advection and mechanical dispersion is predominant, as well as models that employ effective porosity for aquifers in which groundwater flow is slow, solute transport by molecular diffusion is predominant, and a large amount of adsorption-desorption occurs. It is therefore expected that when performing advective-dispersive simulations of aquifers with complex structures (e.g., aquifers in which sand and clay layers alternate), the reproducibility of the simulation results will be improved by using the retardation factor of this latter model, which considers solute transfer between mobile and immobile water.

Quantifying Fluid‐Wettable Effective Pore Space in the Utica and Bakken Oil Shale Formations

AbstractCombined (ultra‐) small angle neutron scattering measurements [(U)SANS] and a contrast matching technique were employed to quantify the porosity and pore size distribution from 1 nm to 10 μm and to differentiate accessible (open) pores and inaccessible (closed) pores with respect to organophilic and hydrophilic fluids for two Utica and two Bakken shale samples. The results indicate that around 40–70% of the pores in the Utica oil shales (mixed carbonate mudstone) are accessible to oil, and 34–37% of the pore surfaces are water‐wet. In contrast, the Bakken oil shales (mixed siliceous mudstone and carbonate/siliceous mudstone), which have high total organic carbon contents, have a higher proportion of isolated pore space that is not preferentially wet by oil or water, with less than 36% of the pores accessible to both fluids. In addition, for both formations, pores less than 3 nm in diameter are not oil accessible (organic matter related) but water accessible (clay tactoids related).

Fines migration and permeability decline during reservoir depletion coupled with clay swelling due to low-salinity water injection: An analytical study

Fines migration is crucial for reservoir permeability, involving both fine particle detachment and re-deposition along the flow channels. Fines migration behavior can either promote or obstruct fluid flow within the reservoir and is crucial for productivity optimization that needs fundamental understanding. The present work focuses on the contributions from effective stress build-up due to reservoir depletion and decreases in brine salinity from low-salinity water injection. Particle detachment is studied analytically by using the critical retention concentration function modified with stress and salinity dependents. Increase in formation effective stress leads to deformations within the reservoir configurations due to micro-cracks and reduced pore dimensions. Decreased size of the travelling channels promotes particle detachment, while the critical retention concentration decreases. A sensitivity study reveals that, under influence of effective stress, particle size and fluid velocity are dominant parameters controlling the fines migration by influencing the particle detaching forces. With decreasing brine salinity (e.g. via low-salinity water injection), clay particles that are attached on the pore surface increasingly swell, leading to reduction in effective pore space and flow channel. Decreased pore space directly obstructs travelling of suspended particles and fluids which results in permeability decline. Initial clay particle size is found to be a critical factor controlling particle detachment behavior. Small initial particle sizes are not likely to detach from the pore surface as a result of weak detaching forces, hence the analysis finds the critical retention concentration unchanged resulting in negligible permeability decline as a function of brine salinity. Considering both effects, effective stress and brine salinity, stress-dependent effects dominate salinity-dependent effects at low effective stress while the two contribute equally at high effective stress. Permeability decline is also determined from analytical results of the fine particle critical retention concentration, which emphasizes the roles of effective stress and brine salinity on the flow in reservoir porous media.

Quantifying fluid-wettable effective pore space in the Utica and Bakken oil shale Formations

Quantifying fluid-wettable effective pore space in the Utica and Bakken oil shale Formations

THE BASIC LAWS OF THE CONCEPT OF PORE SPACE CONNECTEDNESS FOR PETROPHYSICAL MODELING OF RESERVOIR PROPERTIES OF TERRIGENOUS OIL ROCKS

The paper presents mathematical patterns that allow petrophysical modeling of the basic static and dynamic filtration-capacitive properties of rocks. The considered generalized laws are a mathematical expression of the concept of connected pore space and are obtained on the basis of a general model of effective pore space, based on the results of computer modeling of 3D percolation gratings.

Hydrate growth in quartzitic sands and implication of pore fractal characteristics to hydraulic, mechanical, and electrical properties of hydrate-bearing sediments

Gas hydrate pore habits significantly impact the pore-scale structure within hydrate-bearing sediments, and thus, play a central role in the physical property evolution. Characterization and quantification of the effective pore space within hydrate-bearing sediments at different hydrate saturations have not been well offered. This study performs random simulations of hydrate nucleation and growth in quartzitic sands to understand effects of hydrate saturation and hydrate pore habits on fractal characteristics of the effective pore space. Normalized pore-size fractal dimension and normalized maximal pore diameter are characterized and found to decrease with increasing hydrate saturation. In order to predict hydrate saturation dependent pore fractal characteristics, theoretical and empirical models are proposed and further extended to give implications to hydraulic, mechanical, and electrical properties of hydrate-bearing sediments during hydrate dissociation. Implications include that hydrate dissociation facilitates the absolute permeability and the electrical conductivity, and enhances first and then reduces the saturation exponent of Archie's law; hydrate dissociation also lowers the capillary pressure, and this promotes relative permeability to gas but inhibits relative permeability to water even the water saturation remains as a constant; shear strength of unsaturated hydrate-bearing sediments drops down due to the decreasing capillary pressure as hydrate dissociation. These implications all meet with conclusions in previous literatures.

Implementation of Dynamic Neutron Radiography and Integrated X-Ray and Neutron Tomography in Porous Carbonate Reservoir Rocks

The textural and geometrical properties of the pore networks (i.e. such as pore size distribution, pore shape, connectivity and tortuosity) provides a primary control on the fluid storage and migration of geofluids within porous carbonate reservoirs. These properties are highly variable because of primary depositional conditions, diagenetic processes and deformation. This issue represents an important challenge for the characterization and exploitation plan in this type of reservoirs. In this study, the complementary properties of neutrons and X-ray experiments are carried out to better understand the effects of pore network properties on the hydraulic behavior of porous carbonates. Neutrons have unique properties and are particularly suitable for this study due to the sensitivity of neutrons to hydrogen-based fluids. The used methodology combines dynamic neutron radiography (NR), integrated X-ray and neutron tomography (XCT, NCT), and computational fluid dynamics simulations (lattice-Boltzmann method) of porous carbonate reservoir analogues from central and southern Italy. Dynamic 2D NR images provide information regarding the fluid transport and the wetting front dynamics related to the effect of heterogeneities (e.g. fractures and deformation bands) at the microscale. The combination of NCT (dry and wet samples) and XCT (dry), generates more information regarding the effective pore space contribution to fluid flow. The fluid flow simulations generate information about the connected pore network and the permeability evaluated rock sample at saturated condition.

Fractal analysis of the pore structure for clay bound water and potential gas storage in shales based on NMR and N2 gas adsorption

Abstract Fractal dimension (D) is a critical parameter to estimate the heterogeneity of complex pore structure in shale gas reservoirs. To quantify the fractal dimension of various pore types and evaluate their implications on shale effective porosity and gas storage capacity in potential, we performed fractal analysis based on experimental results of low-field nuclear magnetic resonance (LF-NMR) and low-pressure N2 gas adsorption (LP-N2-GA) in Permian Carynginia shales. By comparing the calculated fractal dimensions based on the two approaches, we analyzed the 'surface fractal dimension' for ineffective pores occupied by clay bound water (CBW) and the 'volume fractal dimension' for effective pores (Deff) holding removable fluids for the first time in shales. The NMR-based CBW pore fractal dimension (Dcbw) is linear positively correlated with the fractal dimension of micropore surface (D1) (R2 = 0.91) and the volume of CBW (R2 = 0.58), while negatively correlated with effective porosity (R2 = 0.58). The NMR-based effective pore fractal dimension (Deff) is linear positively correlated with the fractal dimension of meso/macropore volume (D2) (R2 = 0.82) and presents a good positive correlation with gas storage capacity (R2 = 0.80). The results indicate that CBW largely complicates the fractal geometry of nanoscaled pore network and potentially resist effective fluid flows in shales. The pore surface of higher heterogeneity (higher D1) associates with larger surficial CBW retention and would further block the effective pore space for fluid transport. The meso/macropore volumes of higher complexity (higher D2) is intimate with the larger heterogeneity in effective pores for the higher potential of hydrocarbon storage capacity in gas shales.

New methods of geothermal potential assessment in the Pannonian basin

AbstractThe Pannonian basin in Central Europe is well known for its rich geothermal resources. Although geothermal energy has been utilised, mainly for direct use purposes, for a long time, there are still a lot of untapped resources. This paper presents novel methods for outlining and assessing the theoretical and technical potential of partly still unknown geothermal reservoirs, based on a case study from the Dráva basin, one of the sub-basins of the Pannonian basin along the Hungarian–Croatian border. The presented methods include reservoir delineation based on combining geological bounding surfaces of the Upper Pannonian basin-fill units with a set of isotherms deriving from a conductive geothermal model. The geothermal potential of each identified reservoir was calculated by a Monte Carlo method, which was considered as being represented by the heat content of the fluids stored in the effective pore space (‘moveable fluid’). The results underline the great untapped geothermal potential of the Dráva basin, especially that of the reservoir storing thermal water of 50–75°C, which has the largest volume and the greatest stored heat content.

Quantitative characterization of pore connectivity using NMR and MIP: A case study of the Wangyinpu and Guanyintang shales in the Xiuwu basin, Southern China

Pore connectivity is one of the most important characteristics of shale reservoirs because it significantly impacts the effective pore space, the fluid migration, and the gas production. In this work, pore connectivity and its primary controlling factors were investigated using a combination of field emission-scanning electron microscopy (FE-SEM), focused ion beam-scanning electron microscopy (FIB-SEM), mercury intrusion porosimetry (MIP), and nuclear magnetic resonance (NMR). The results show that using the difference between NMR and MIP is a reliable method to characterize pore connectivity. NMR pore size distribution (PSD) curves converted from T2 spectra, and MIP PSD curves were observed to have consistent shapes. The amplitude of NMR PSD curves is higher than that of MIP PSD curves for S-group pores (<200 nm), while the relationship is opposite for L-group pores (200 nm–10 μm), which may be due to the permeability of shale. A low permeability allows a smaller amount of mercury to intrude into the small pores. Based on experimental results, the pores of 8–20 nm make a contribution of 5%–11% to pore connectivity, whereas the pores of 200–700 nm are mainly interparticle pores and microfissures, contributing from 38% to 72% of pore connectivity. Stratification and pore morphology in the Lower Cambrian Wangyinpu and Guanyintang shales in the Xiuwu Basin are the two critical influencing factors of pore connectivity. The pore connectivity of well-laminated shale is higher than that of less-laminated shale. The laminated structures are usually composed of argillaceous and siliceous lamina, which tend to give rise to fissures during hydrocarbon generation or under confining stress. As a result, the pores around the microfissures are more likely to be communicating. Shales with the structure of uniformly distributed organic and inorganic minerals have the best pore connectivity. Both the interparticle pores and microfissures between organic matter and inorganic minerals or between inorganic minerals can effectively connect organic pore networks and greatly improve the pore connectivity.