Pore Coordination Number Research Articles

Microstructural characterization of a wheat-based food material using image analysis and pore network modeling during baking.

Microstructural properties of wheat-based food materials change during baking. These alterations affect the final product's mechanical properties, physical attributes, and consumer satisfaction. Image processing and pore network modeling were used to analyze the variations in a cookie's microstructural properties during baking. Cookies were baked in an oven set at 184±2°C for 10-60min and then freeze-dried. Over 1500 two-dimensional images were collected for each sample using X-ray micro-computed tomography. Image processing and pore network modeling were utilized to obtain porosity, pore size distribution, tortuosity, pore coordination number, permeability, and other properties. A gas pycnometer was used to validate the obtained porosity values and calculate the solid density. Three stages of expansion, shrinkage, and subsequent expansion were observed during baking. The total porosity ranged between 0.145 and 0.373. The largest pores were observed in the 20-min baked sample, which had a moisture content of 8.53g/100g solids. Cookies baked longer had more interconnected pores than the 10-min sample, enabling them to conduct fluid at a higher rate. The absolute permeability values were between 1.75 × 10-11 m2 and 4.68 × 10-11 m2. The results suggested that porosity and pore coordination number had a similar trend as cookie permeability. Both heat and mass transfer during baking are expected to influence the development of the porous structure. PRACTICAL APPLICATION: Understanding the microstructural properties of wheat-based food materials is expected to help the baking industry control processing conditions, final product quality, and visual texture by adjusting the baking parameters.

A pore network modeling approach to bridge void ratio‐dependent soil water retention and unsaturated hydraulic conductivity curves

AbstractIn geotechnical engineering, understanding the relationship between soil permeability and deformation is essential, particularly for applications like earth dams, where compaction‐induced permeability reduction is crucial for performance optimization. In unsaturated soils, soil moisture content significantly impacts hydraulic conductivity. Traditionally, changes in unsaturated hydraulic conductivity have been linked to soil void ratios. However, a pore network modeling perspective reveals the significance of structural parameters, such as pore and throat size distribution and pore coordination number. This study introduces a pore network model to estimate unsaturated hydraulic conductivity based on void ratio‐dependent soil‐water retention curves. It examines how soil deformation at varying stress levels affects structural parameters and the water phase continuity. The model shows strong potential in predicting unsaturated hydraulic conductivity across different stress levels, aligning well with experimental data and established equations. Notably, the aspect ratio and coordination number parameters are most affected by stress levels. The study also presents relationships to describe changes in pore network structural parameters with soil void ratio, which can be used to predict soil‐water retention curves and unsaturated hydraulic conductivity at various stress levels.

Characterization of Pore Structure and Fluid Mobility of Shale Reservoirs.

Accompanying the commercial exploitation of shale oil and gas in North America, shale oil has gradually become an important resource, sparking great interest among countries around the world in recent years. In this study, focusing on the Paleogene Shahejie Formation in Bohai Bay (Eastern China), techniques such as CT, nitrogen adsorption, mercury injection capillary pressure (MICP), and nuclear magnetic resonance (NMR) were used to characterize the pore structure and mobility of the shale reservoir. Based on the X-ray CT data, the pore radius of the shale reservoir is in the range 0.5-65 μm, and the pore coordination number is concentrated in the range of 1-4. The shale reservoir is poorly connected. The minimum size of the unit body for establishing the digital core model is 380 μm. Based on the experimental data of nitrogen adsorption and MICP, the pores of shale in the study area are mainly classified as ink-bottle-shaped pores, transition-shaped pores, and flat plate slit-shaped pores. The specific surface area and volume of pores are mainly attributed to meso- and macropores. The movable fluid saturation of shale is distributed from 23.59 to 44.42%, the pore throat radius is distributed from 0.001 to 6 μm, and the lower limit of the movable pore throat radius of shale is distributed between 9.0 and 20.1 nm. The movable fluid porosity is mainly distributed between 0.84 and 4.08%, with an average movable fluid porosity of 2.37%. The findings provide a theoretical basis for the efficient development of shale oil resources.

Study on microscopic pores and permeability changes of coal frozen by liquid nitrogen based on CT scanning

ABSTRACT Liquid nitrogen freezing has a certain promoting effect on improving the permeability of coal samples. In order to study the quantitative changes in the pore structure and permeability of coal samples after liquid nitrogen freezing, this paper carried out a three-dimensional reconstruction of the pore space structure of coal samples based on CT scanning experiments, and based on this, the porosity, connected pore volume, the equivalent pore radius, pore coordination number and permeability were studied based on the reconstruction model. The results show that the porosity of the coal samples in group B is 42.02% higher than that in group A after freezing with liquid nitrogen, the average value of the total connected pore volume, pore equivalent radius and coordination number of coal samples in group B are greater than those in group A, and they have increased by 16.5%, 2.95% and 14.8% respectively; the permeability in group B is 26.86% higher than that of group A, indicating that the pore connectivity and permeability of the coal samples in the liquid nitrogen freezing group have been significantly improved.

Study on the pore structure characteristics of maize grain piles and their effects on air flow distribution

The airflow in grain piles is affected by the content of broken grains, which causes changes in the pore structure within the grain pile. To investigate the changes in structural parameters at different broken grain contents, CT scanning and image processing were used to study the pore structure characteristics of broken maize grain contents of 0 %, 4 %, 8 % and 15 % respectively. The airflow distribution in the grain pile under different broken grain contents was studied by numerical simulation. The results showed that as the broken kernel content increased from 0 to 15 %, grain pile porosity gradually decreased, with a change rate of 6.97 %. An increase in the content of broken grains causes a decrease in the diameter and volume of the pores in the grain piles. The average value of the pore coordination number in the grain pile decreased as the broken grain content increased. When the content of broken grains is 0–15 %, the rates of change of pore diameter and tortuosity in the grain piles are 14.94 % and 24.94 %, respectively. As the broken grain content increased, the length and diameter of the pore throat in the grain pile decreased, while the fractal dimension and tortuosity increased. The increased broken grain content in the grain piles impedes the flow of air through the pores, thus affecting ventilation efficiency.

Product characterization and pore structure evolution of a tar-rich coal following pyrolysis under nitrogen, steam/nitrogen, and oxygen/nitrogen atmospheres

Steam and an oxidative medium could be the most promising atmosphere for the in-situ pyrolysis of tar-rich coal. This study investigated the influence of these two atmospheres by comparing product yields, tar properties, and pore evolution characteristics of a tar-rich coal following pyrolysis under nitrogen (N2), steam/nitrogen (steam/N2), and oxygen/nitrogen (O2/N2). Compared with N2 pyrolysis, steam/N2 pyrolysis increased the tar yield by 0.54–1.33 wt% at 350–600 °C; further, O2/N2 pyrolysis increased the tar yield from 0.57 wt% to 3.53 wt% at 350 °C while decreasing this value by 0.31–1.83 wt% at 400–600 °C. At 450 °C and 500 °C, steam addition suppressed the formation of oxygenated compounds, thereby decreasing the O/C ratio of tar from 0.099 and 0.088 to 0.073 and 0.074, respectively. Conversely, O2 introduction presented the oxygen addition of tar by oxidation reactions. Meanwhile, steam inhibited the aromatization of alkanes and the condensation of monocyclic aromatic hydrocarbons (MAHs). By contrast, O2 was able to promote the condensation of phenols and MAHs. At 450 °C, steam/N2 was thought to assist in the cracking of the plastic mass by providing a H2-rich atmosphere, which decreased the pitch content of tar and increased the contents of light fractions. O2/N2 was also beneficial for the formation of light fractions by intensifying the thermal cracking effect. Micro-CT and SEM analysis showed that H2O could promote the formation of micro-sized pores within the coal matrix, decreasing the average pore diameter (APD) from 150.95 μm to 102.67 μm and increasing the average coordination number (ACN) of pores from 6.27 to 8.59. O2 was inclined to enlarge the pyrolysis-induced pore network, which imposed a contrasting effect on APD and ACN parameters. Steam is recommended as the preferred atmosphere for the in-situ pyrolysis of tar-rich coal.

Pore structure analysis of glacial till under freeze-thaw cycles based on calibration CT data

ABSTRACT Acquiring the interior pore characteristics is essential to the utilisation of glacial till which is the material of permeability barrier to many engineering projects in cold regions. In this work, the pore space of glacial till samples with different cementation degrees and freeze-thaw cycles was investigated by CT technique. Representative elementary volume method (REV) was utilised to ensure a suitable scale of CT volume data, and a novel calibration method was proposed to detect the accuracy of CT segmentation. Subsequently, the effect of cyclic freeze-thaw action on the pore structure of glacial till samples was investigated. Quantitative pore structure analysis shows that cyclic freeze-thaw action resulted in a decrease in porosity of both well cemented and poorly cemented glacial till. The accessible porosity, fractal dimension, and coordination number of glacial till pores also decrease with the increment of freeze-thaw cycles. It can be observed that blocking of the channels of macropores is the main morphological evolution characteristic of glacial till with cyclic freezing and thawing, which can provide reference in designing permeability barrier in glacial till layers.

Pore structure characterization of sandstone under different water invasion cycles using micro-CT

The meso-structural changes of rocks during repeated cycles of water invasion are the fundamental cause of macroscopic physical property damage. In this paper, based on the computed tomography scan images of rock samples under different numbers of water invasion cycles, a three-dimensional pore network model was constructed to analyze the changes in pore structure under the action of water invasion. The damage variable was introduced to quantitatively characterize the parameter damage of each pore and reveal the evolution of rock meso-damage. The results show that 81% of the pore radius is less than 10 μm under 0 water invasion cycles and that 76% of the pore radiuses are less than 10 μm after 10 water invasion cycles. After 10 water invasion cycles, the peak range of the pore radius distribution enlarged from the initial range of 2–4 μm to that of 4–6 μm and the proportion of pore throats with a radius less than 10 μm decreased from an initial 82–72%. With an increase of water invasion cycles, the proportion of large pores increased and the connectivity among pores enhances gradually. The damage variable of each pore parameter changed the most during 2–5 water invasion cycles. After 10 water invasion cycles, the maximum degree of damage that the pore volume reached was up to 41.44% and the minimum degree of damage of the pore coordination number was 5.80%. The test results helped to reveal the pore structure changes and the damage of rock samples during water invasion cycles.

Analysis of the microstructure of microbial solidified sand and engineering residue based on CT scanning

A close relationship exists between the pore network structure of microbial solidified soil and its macroscopic mechanical properties. The microbial solidified engineering residue and sand were scanned by computed tomography (CT), and a three-dimensional model of the sample was established by digital image processing. A spatial pore network ball-stick model of the representative elementary volume (REV) was established, and the REV parameters of the sample were calculated. The pore radius, throat radius, pore coordination number, and throat length were normally distributed. The soil particle size was larger after solidification. The calcium carbonate content of the microbial solidified engineering residue’s consolidated layer decreased with the soil depth, the porosity increased, the pore and throat network developed, and the ultimate structure was relatively stable. The calcium carbonate content of the microbial solidified sand’s consolidated layer decreased and increased with the soil depth. The content reached the maximum, the hardness of the consolidated layer was the highest, and the development of the pore and throat network was optimum at a depth of 10–15 mm.

PoreSkel: Skeletonization of grayscale micro-CT images of porous media using deep learning techniques

Skeletonization, a crucial step in pore network modeling, traditionally involves the extraction of skeleton pixels from binarized, segmented X-ray images of porous materials. However, this conventional approach often suffers from user bias during segmentation, potentially leading to the loss of essential image details. This study addresses this limitation by developing deep learning model, called PoreSkel, designed to directly perform skeletonization and distance map extraction from unprocessed grayscale images, thus eliminating the need for additional image processing steps. The model was trained, validated, and tested using an expansive databank of micro-CT images from 20 distinct sandstones, carbonates, and sand pack samples, a total of 10,240 images, with each sample represented by a cube of size 5123. A fifth of these images, specifically 15.6 % from sixteen sandstone and sand pack samples, were used for training, while the remainder served for model validation (4.4 %) and extensive testing (80 %). PoreSkel showed an excellent performance, achieving a mean f1-score of 0.964 for skeletonization and an RMSE of 0.057 for distance map extraction during the testing phase. Our assessments revealed that the model is robust to bias toward the majority class, namely the background pixels. Furthermore, the model showed high generality, maintaining its performance when tested using unseen images from three carbonates and an additional sandstone. Notably, PoreSkel effectively handles disruptions caused often by the presence of minerals in pore spaces and perturbations on pore boundaries - a common challenge for the medial axis technique - resulting in fewer nodes (i.e., pore junctions) and pore coordination numbers, but a higher number of connected skeletons. Therefore, PoreSkel provided a more precise and representative pore structures of porous material that is needed for accurate pore network generation and modeling.

Research and application of construction technology of digital mud cake formed by drilling fluid filtration

In drilling engineering, mud cake is formed when drilling fluid invades the near-wellbore zone, which can reduce drilling fluid leakage and reservoir pollution and maintain wellbore stability. To study the three-dimensional spatial characteristics of mud cakes, such as heterogeneity, particle accumulation, and porous media, CT scan images of cores and mud cakes before and after drilling fluid intrusion are used as the research object. The composite filtering and segmentation method for typical regions of images based on grayscale values and the batch segmentation method for large regions of images based on deep learning are investigated. On this basis, a visualized digital mud cake is constructed, and microscopic evaluation indexes such as the percentage, equivalent radius, throat length, sphericity, and coordination number of pores and particles in the mud cake are established. The application results show that the number of isolated pores in the outer mud cake formed by static filtration of drilling fluid is more than that of dynamic ones, the connectivity of pores is poor, and the particles have a better sealing effect on pores. The combined effect of the outer and inner mud cake results in different effects on core intrusion. The construction technique of digital mud cake can study the structure at a micron scale. This technique can provide more detailed guidance for engineering situations, such as optimization of drilling fluid systems in fractured formations, damage evaluation of reservoirs by drilling fluid, and influence of mud cake on cementing quality.

Impacts of mineralogy and pore structure on spontaneous imbibition in tight glutenite reservoirs

Spontaneous imbibition plays a critical role in the two-phase flow in hydraulic fractures of tight reservoirs. Although massive contributions have been devoted to addressing this issue, very few studies focus on tight glutenite reservoirs, which is an important member of tight reservoirs. As a result, the imbibition mechanism and its influencing factors are still unclear, several key factors fail to be captured, and in-depth analyses are lacking in spontaneous imbibition for tight glutenite reservoirs. In light of the current knowledge gaps, this study conducted a series of water imbibition experiments, combined with X-ray diffraction tests, thin section and scanning electron microscopy observations, high-pressure mercury intrusion experiments, and corrected contact angle experiments to reveal the impacts of rock mineralogy and pore structure on spontaneous imbibition, and significance levels of main influential factors were determined by grey relation analysis. Results show that: 1) the hydrophilic mineral that exceeds 94% provides a strong driving force for water imbibition. Intergranular pore and gravel boost imbibition recovery through enhancing imbibition and drainage ability, respectively. However, intergranular dissolved pore is unfavorable for water imbibition due to extremely rough surface and small radius. Medium-size sand also has a negative impact because of incremental flow tortuosity and pore coordination number reduction; 2) A large percentage of micropore and macropore can significantly enhance imbibition rate and recovery. Three fractal characteristics in micropore, identified for the first time, complicates water imbibition process in tight glutenites. A critical total fractal dimension of micropore is observed, above which the negative influence magnitude of complex pore structure on spontaneous imbibition gradually decreases; 3) Water imbibition sequence and diversities of imbibition phenomena are significantly affected by the combination of multi-fractal dimensions and heterogeneous distributions of pore volume in different fractal regions. The superposition of smallest fractal dimension and the largest pore volume leads to the best imbibition recovery in the transition stage of imbibition, which is an extremely time-consuming process; 4) Upon grey relation analysis, oil drainage ability is the most critical factor for water imbibition in tight glutenites. These observations deepen our understanding of the distinctive imbibition mechanisms in tight glutenite reservoirs.

Pore-scale morphology effects on colloid deposition by trajectory tracking simulations

The migration and deposition of colloids in natural porous media is a phenomenon of high importance in hydrocarbon recovery, wastewater treatment and contaminant hydrogeology. Commonly described by colloid filtration theory (CFT), and using a single representative collector element, the theoretical framework is not accounting for morphological effects and heterogeneity of realistic porous media, including the local variations of balance of forces or presence of hydraulically stagnant regions in the vicinity of grain-to-grain contacts. So far developed numerical models of colloidal transport in porous media accounting for all major interactions and pore structure were applied to 2D systems. Known 3D simulations are limited to particulate flow with a reduced set of interactions.We propose a coupled colloid transport model combining computational fluid dynamics (CFD) and discrete element model (DEM) approaches, where the former provides the velocity field at a given time step, while the second calculates the updated colloid positions accounting for a set of forces acting on each colloid. Relationships between colloid retention and morphological characteristics, such as the pore coordination number and surface to volume ratio of a random sphere pack are investigated by pore partitioning of a digitized representation. The role of stagnation zones is quantified by expressing the capture probability of colloids as a function of distance to the nearest grain-to-grain contact measured along the curved surface.The analysis of pore space morphology of the collector and the simulated filtration process reveals a strong relation between colloid retention and pore connectivity. The simulations successfully mimic the expected effects of ionic strength of the carrier fluid, such as the increasing role of grain-to-grain contacts in colloid retention at low ionic strength.

Quantitative Characterization of Pore Structure Parameters in Coal Based on Image Processing and SEM Technology

The pore structure parameters of coal have an important influence on the exploration and development of coalbed methane. In this study, a series of pore structure parameters, including porosity, pore radius, pore throat radius, pore coordination number, pore throat ratio, and specific surface area, are identified, extracted, and calculated in the scanning electron microscopy (SEM) images of coal reservoir samples using algorithms and application programs in MATLAB. Constant rate-controlled mercury injection and low-temperature N2 adsorption experiments were carried out to determine the accuracy of the SEM image-based processing analysis results. Characterization results show that the distribution of pore radius in the target coal samples of different organic matters range from 15 nm to 500 μm with porosity of 1.87–8.31% and radius distribution of 12.7 nm to ~100 μm. A noise-reduction system was constructed to eliminate the optical noise of non-porous features and repair the space affected by binarization noise. It is suggested that the characterization processing in this study is suitable for coal or other organic-rich porous materials with porosity > 2% and pore radius > 15 nm.

Transport Behavior of Methane Confined in Nanoscale Porous Media: Impact of Pore Evolution Characteristics

As a key technical aspect contributing to shale gas development, nanoconfined methane flow behavior has received tremendous research interest, which remains challenging to understand clearly. The majority of previous contributions put emphasis on the mechanism model for methane confined in a single nanopore; at the same time, the other part focusing on an upscaling approach fails to capture the spatial pore-network characteristics as well as the way to assign pressure conditions to methane flow behavior. In light of the current knowledge gap, pore-network modeling is performed, in which a pore coordination number, indicating the maximum pores a specified pore can connect, gas flow regimes classified by Knudsen numbers, as well as different assigned pressure conditions, are incorporated. Notably, the pore-network modeling is completely self-coded, which is more flexible in adjusting the spatial features of a constructed pore network than a traditional one. In this paper, the nanoconfined methane flow behavior is elaborated first, then the pore network modeling method based on the mass conservation principle is introduced for upscaling, and in-depth analysis is implemented after that. Results show that (a) as for porous media with pore sizes ranging from 5~80 nm, dramatic advancement on apparent gas permeability takes place while pressure is less than 1 MPa; (b) apparent gas permeability evaluated at a specified pressure shall be underestimated by as much as 31.1% on average compared with that under the pressure-difference condition; (c) both a large pore size and a high coordination number are beneficial for strong gas flow capacity through nanoscale porous media, and the rising ratio can reach about 6 times by altering the coordination number from 3 to 7, which is quantified and presented for the first time.

Fine characterization of pore structure of acidified anthracite based on liquid intrusion method and Micro-CT

Acidification erosion can seriously affect the pore structure characteristics of anthracite. In this paper, the low-temperature nitrogen adsorption method, mercury intrusion method, and Micro-CT scanning are used to analyze the pore structure of coal samples. The microscopic morphology and spatial distribution of coal pores are characterized by fractal dimension calculation and three-dimensional reconstruction. The results show that HCl has the highest removal efficiency of minerals in the Yuwu coal sample, which reduces the mass of coal samples by about 4%. HNO3 increases the proportion of micropore volume by 4.93%. HCl increases the proportion of mesoporous pore volume by 11.4%. Through the 3D reconstruction of coal, it is found that the mineral content in coal decreased by 48.14% after HCl dissolution, and the maximum diameter of mineral particles decreased from 173.588 μm to 57.449 μm. The spatial distribution of minerals is uneven, and the mineral content of coal samples decreases significantly along the direction of strong fluidity. At the same time, HCl increases the pore connectivity of coal samples, the pore roar increases by 56.72%, the isolated pores decrease, and the peak frequency of pore coordination number increases by 4 units, which greatly improves the transport capacity of fluid in coal matrix.

Study on Failure Mechanism of Mudstone Based on Digital Core and Digital Volume Correlation Method

In order to study the damage evolution law and failure mechanism of mudstone under different stress states, with the help of high-resolution CT scanning equipment, in situ CT scanning experiments of mudstone under uniaxial compression were carried out. Combined with digital core technology and the digital volume image correlation method, the 3D characterization of meso-structure and the evolution process of localized damage in mudstone were analyzed. The research shows that brittle minerals such as quartz in mudstone often exist in the form of agglomerated strips, resulting in the formation of weak structural planes at the contact surfaces of different minerals. There are a large number of primary intergranular pores near the mineral accumulation zone. With the increase in axial load, the connectivity of pores will gradually increase, cracks will gradually emerge, internal pores will develop abnormally, and rocks will reach the critical state of failure; at this time, the throat number and coordination number of pores increase obviously. There was no obvious difference found in the distribution of mineral particles of different sizes, and the slip between mineral zones was mainly dominated by small particles. The accumulated mineral zone was able to easily form a weak surface, and the aggregated mineral zone under loading was easily able to produce local deformation, which is related to the mechanical properties of the mineral zone and its surrounding rock matrix, with the rock failure easily occurring along the junction of the two minerals. The displacement in the polymeric mineral zone was small, the deformation displacement of the rock skeleton dominated by clay minerals near the quartz mineral zone was larger, and the stronger quartz minerals restrained the rock skeleton deformation in the region.

3D quantitative characterization and flow simulation of granite residual soil based on CT scanning

<p indent="0mm">This paper aims to reveal the water transport mechanism in soils with macropores. Based on the combination of the X-ray CT scanning and image processing technologies, a three-dimensional (3D) equivalent pore network model (PNM) with macropores (&gt;0.15 mm) is constructed, and the size of the optimal representative volume unit (REV) is determined to be 300×300×300. Then, the quantitative characterization of the topological structure of the macropore space is carried out followed by the PNM single-phase flow and the 3D macropore water-gas two-phase flow simulation. The results show that there are more pores with smaller pore diameters, and more than 80% of the pores are concentrated within <sc>0.15–1.00 mm.</sc> The pore topological space structure is quite different, and the coordination number is mainly less than 20, but some can reach more than 60. The average coordination number of pores is between 3–7, and the average connected pore radius is greater than <sc>2.00 mm.</sc> The single-phase flow simulation find that the complexity of the pore structure and the resolution of X-ray CT scanning resulted in a certain difference between the simulated and measured permeability, but the difference of the main seepage direction is only 3.81%. The two-phase flow simulation find that the front edge of flow is almost linear at the beginning of seepage, then it tend to be fingering, and finally, it become irregular. The residual gas in the pores is mainly distributed in blocks at the edges of pores, dead ends, and sudden changes of pore throats. With the increasing seepage time, the saturation of the water phase shows an upward trend, while the saturation of the gas phase shows a downward trend, then gradually tend to be stable, and finally, the saturation of the water phase and the residual gas phase maintain at 94.92% and 5.08%, respectively. This study can better reveal the meso-seepage mechanism of reconstructed soil, and provide a certain reference for further understanding the law of pore flow in soil.

Pore characteristics and permeability simulation of porous asphalt mixture in pouring semi-flexible pavement

Filling grouting material into the voids of porous asphalt mixture (PAM) is one of the important steps in the construction of pouring semi-flexible pavement (SFP), and the pore characteristics play a dominant role in the slurry permeability performance of PAM. Therefore, understanding the influence of pore characteristics on the slurry permeability performance and revealing the penetration mechanism of grouting materials in the void of PAM are essential for guiding the design of PAM used in SFP and improving the quality and efficiency of the grouting construction. Firstly, the effects of porosity and aggregate size on slurry permeability and water permeability of PAM are experimentally studied. Then, the 3D pore structure parameters, such as porosity, equivalent diameter, coordination number, pore throat dimension and tortuosity are quantitatively and statistically analyzed via X-ray CT and 3D reconstructed model. Finally, the slurry permeability simulation of PAM is conducted. The results show that the porosity and aggregate size have a significant influence on the complexity and spatial anisotropy of the pore structure of PAM. Increasing the porosity and aggregate size can effectively increase the connected porosity ratio, 3D pore size and throat size of PAM, while reduce the number of small pores (D3d < 1 mm2) and isolated pores. Besides, the slurry and water permeability coefficients of PAM are also positively correlated with the porosity and aggregate size. Moreover, to be consistent with the real condition, the slurry permeability coefficient is more suggested as the technical index of PAM to ensure the perfusion effect of PAM. In the simulation, the slurry permeability values in the vertical direction are higher than those in the horizontal direction. The pore characteristics are ranked according to their effect on the seepage of grouting material: connected porosity > pore size and throat size ≫ pore coordination number (CN) and tortuosity.

A Pore Network Approach to Study Throat Size Effect on the Permeability of Reconstructed Porous Media

Permeability is usually considered to be related to porosity. However, rocks with the same porosity may have different permeabilities in some cases, because of the variations in pore and throat size and pore space connectivity. It is vitally important to understand the effect of throat size on the transport property. In this work, five sets of regular pore network models and six core-based models are employed to study the effect of throat size on permeability. Four kinds of random distributions, i.e., uniform, normal, Weibull, and log normal, are utilized to generate random pore size. Pore coordination number is set to be two and six for the verification of the effect of connectivity on permeability. Then, single-phase flow simulation is conducted based on the constructed pore network models. The simulation results show that permeability decreases significantly when only one of the nine throats reduces to half size in terms of diameter. The influence of pore coordination number on permeability is not obvious compared to that of small throat size. This study indicates that small throats play an extremely important role in determining permeability.