Mercury Intrusion Porosimetry Method Research Articles

Gas permeability characteristics of granite-manufactured sand concrete and its numerical simulation using NMR-MIP modified method

Natural sand resources are becoming increasingly scarce with the rapid development of infrastructure. Therefore, manufactured sand usage is inevitable. However, the significant differences in granite powder content between manufactured- and natural sand have a remarkable impact on the pore structure and permeability of cement-based materials, which are crucial for material durability. In this work, several granite powder dosages (0–32 %) of granite-manufactured sand were considered for preparing manufactured sand concrete, and a suitable physical filling model was chosen to quantify the material particle filling for characterizing the overall pore-filling effect. Mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) were used to examine the pore structure of the specimens. The quasi-stationary flow method was used to test the gas permeability of concrete. Finally, a random hierarchical bundle model using the NMR-MIP method is proposed to predict the gas permeability of cementitious materials based on their pore size distribution. The results show that granite-manufactured sand and an appropriate amount (i.e., 8 %) of granite powder can improve the filling effect and anti-permeability performance of concrete. There is a good correlation between the pore structure parameters and gas permeability, where the physico-mathematical relationships can be modeled. The maximum relative difference between the predicted and experimental values of the random tube bundle model was reduced to 30.93 % using the NMR-MIP method compared to 70.87 % with the traditional MIP method.

Estimation of unfrozen water content of saturated sandstones using nuclear magnetic resonance, mercury intrusion porosimetry, and ultrasonic tests

The unfrozen water content (UWC) is a crucial parameter that affects the strength and thermal properties of rocks in relation to engineering construction and geological disasters in cold regions. In this study, three different methods were employed to test and estimate the UWC of saturated sandstones, including nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and ultrasonic methods. The NMR method enabled the direct measurement of the UWC of sandstones using the free induction decay (FID). The MIP method was used to analyze the pore structures of sandstones, with the UWC subsequently calculated based on pore ice crystallization. Therefore, the MIP test constituted an indirect measurement method. Furthermore, a correlation was established between the P-wave velocity and the UWC of these sandstones based on the mixture theory, which could be employed to estimate the UWC as an empirical method. All methods demonstrated that the UWC initially exhibited a rapid decrease from 0 °C to –5 °C and then generally became constant beyond –20 °C. However, these test methods had different characteristics. The NMR method was used to directly and accurately calculate the UWC in the laboratory. However, the cost and complexity of NMR equipment have precluded its use in the field. The UWC can be effectively estimated by the MIP test, but the estimation accuracy is influenced by the ice crystallization process and the pore size distribution. The P-wave velocity has been demonstrated to be a straightforward and practical empirical parameter and was utilized to estimate the UWC based on the mixture theory. This method may be more suitable in the field. All methods confirmed the existence of a hysteresis phenomenon in the freezing-thawing process. The average hysteresis coefficient was approximately 0.538, thus validating the Gibbs–Thomson equation. This study not only presents alternative methodologies for estimating the UWC of saturated sandstones but also contribute to our understanding of the freezing-thawing process of pore water.

Acidification-Induced Micronano Mechanical Properties and Microscopic Permeability Enhancement Mechanism of Coal.

An acid solution improves the pore-plugging problem in hydraulic fracturing, which in turn improves the permeability of the coal seam. The study aimed to investigate the effect of mixed acid on the micronano mechanical properties and permeability of the coal seam. The surface morphology of acidified coal was analyzed from the micronano scale using atomic force microscopy (AFM) and scanning electron microscopy. Additionally, the micronano scale mechanical characteristics of acidified coal were examined using the mechanical mode in an atomic force microscope. Furthermore, the complexity and connectivity of the micronano pores of samples were investigated using the low-temperature nitrogen adsorption and mercury intrusion porosimetry methods and the fractal theory. The results indicated that the surface minerals of acidified coal were dissolved, loosening the coal and increasing the complexity of the pore structure. Mineral deformation and pore deformation weakened the mechanical properties of coal at the micronano scale, and the mean elastic modulus of acidified coal (B# and E#) decreased by 28.78 and 25.66% compared to that of raw coal. The acid solution effectively enlarged the pore diameter, transitioning from micropores to mesopores and macropores, and the total pore volume of acidified coal increased by 1.88 times and 1.25 times, Kn increased from 0.064 to 0.581 and 0.37, respectively. The type of methane diffusion in the diffusion pores changed from Knudsen diffusion to transition-type diffusion. The tortuosity of the pore structure of acidified coal decreased, the fractal dimension of the tortuosity of the pore structure decreased, and the permeability increased by nearly three times. The research results indicate that the mechanical properties of coal decrease after acidification and that the microstructural changes can promote methane migration (diffusion-seepage), which can provide theoretical guidance for coalbed methane extraction in low-permeability coal reservoirs.

The Use of Thermoporometry in the Study of Frost Resistance of Rocks.

From an engineering point of view, it is important to know the factors influencing the frost resistance of rocks with porosity above 2% due to their different frost resistance. The article focused on frost durability research using the thermoporometry method (TMP) and the assessment of water phase transition in the pore spaces of selected rocks. For this purpose, the differential scanning calorimetry method (DSC) was used with the adoption of an original algorithm for eliminating the thermal inertia of the measurement system. The results of the DSC method were supplemented with the results of pore size distribution using the mercury intrusion porosimetry method (MIP) and standard rock frost resistance tests. Based on the research carried out using the thermoporometry method, it was confirmed that the ability of water to freeze in the temperature range from -5 °C to -20 °C was important, as well as the ability of rocks to increase the degree of water saturation during freeze-thaw cycles. Based on calorimetric tests combined with thermoporometry, in the case of non-frost-resistant rocks, a significant (dominant) share of pores with a radius of under 10 nm (amounting to over 0.008 cm3/cm3) was found. Pore connections in the water freezing process do not influence the investigated rocks' frost resistance.

The anti SARS-CoV-2 activity of nanofibrous filter materials activated with metal clusters.

Nanofibrous filter materials were prepared by electrospinning a solution of 28wt% poly(vinylidene fluoride) in N,N-dimethylacetamide with and without the addition of 2wt% AgNO3, Cu(NO3)2·2.5H2O or ZnCl2. X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectroscopy, thermogravimetric analysis, contact angle measurement, nitrogen sorption, and mercury intrusion porosimetry methods were used for the characterization of physical structure as well as the chemical composition of the electrospun materials. Particle filtration efficiency and antiviral activity against the SARS-CoV-2 alpha variant were tested in order to estimate the suitability of the prepared electrospun filter materials for application as indoor air filtration systems with virucidal properties. All filter materials prepared with salts demonstrated very high particle filtration efficiency (≥98.0%). The best antiviral activity was demonstrated by a material containing Cu(NO3)2·2.5H2O in the spinning solution, which displayed the decrease in the number of infectious virions by three orders of magnitude after a contact time of 12h. Materials with the addition of AgNO3 and ZnCl2 decreased the number of infectious virions after the same contact time by only ∼8 and ∼11 times, respectively.

A comparative study of micro-CT and mercury intrusion techniques for predicting permeability and surface area evolution during chemical dissolution

In this paper, we report on experimental and computational studies investigating the evolution of pore structure and permeability of a microporous carbonate rock during chemical dissolution using information provided from X-ray micro-computed tomography (µ-CT) and mercury intrusion porosimetry (MIP) techniques. We consider a chemical dissolution in a core sample by a nonacidic solution wherein a quasi-uniform modification of pore structure occurred. First, we conduct a comparative analysis on the capabilities and limitations of the µ-CT and MIP methods to quantify the evolution of pore size and pore surface area. In particular, we incorporate micropores into the calculations of the pore size-related parameters to highlight the uncertainties that ignoring microporosity causes. In the second part of the paper, we present predictive results on the fractional changes in the permeability of the rock using the Katz-Thompson (KT) and Kozeny-Carman (KC) models. The predictions are based on two characteristic parameters of the pore phase, i.e., the critical pore diameter and the specific pore surface area, and two characteristic macro-scale properties, i.e., porosity and formation factor, all calculated from both the MIP and µ-CT methods. The predicted changes in permeability are compared with those calculated directly on the images using the lattice-Boltzmann (LB) flow simulation on segmented images. The effect of changes in microporosity is also assessed to investigate its role in permeability evolution. The results showed that the KT model could reasonably predict the fractional changes in permeability in terms of the pore structure and macroscale parameters calculated from the MIP and µ-CT methods.

Reusing waste red brick powder as partial mineral precursor in eco-friendly binders: Reaction kinetics, microstructure and life-cycle assessment

A large number of solid wastes are produced in the process of demolishing old buildings, and waste red brick is one of such wastes. To discuss the reutilization of waste red brick powder (WRBP) in alkali-activated material, a novel ternary eco-friendly binder was prepared by using slag, fly ash and WRBP as precursor. The impact of WRBP on the reaction kinetics, microstructure and life-cycle assessment of alkali-activated cement paste were evaluated. The Johnson-Mehl-Avrami-Kolmogrov model was established based on the heat release results. With the incorporation of WRBP, the degree of reaction was deepened, supporting the enhancement of matrix strength. X-ray diffraction and thermogravimetric analysis results show the consistent mineralogical composition of reaction products and increase of gel quantity. Pore characteristics determined by mercury intrusion porosimetry method exhibit that large capillary pores were refined by enrichment of gels and filling effect of WRBP. From the economic and environmental aspects, the reuse of WRBP significantly saved the energy consumption and reduced the carbon dioxide (CO2) emission. On the basis of the optimal compressive strength, the energy consumption efficiency index and CO2 intensity index were 27.3 MJ/MPa and 1.7 kg/MPa, which can provide 38.55% energy consumption and 44.90% carbon footprint savings. Such work may shed valuable insights to the recycling of various types of solid waste and low-carbonation of building field.

Evaluations of frost and scaling resistance of fly ash concrete in terms of changes in water absorption and pore structure under the accelerated carbonation conditions

In this study, the frost and scaling resistance of concrete with various fly ash (FA) replacement ratios exposure to air and accelerated carbonation conditions were investigated. The changes in water absorption were measured by RILEM / CIF test and in pore structure were measured by the Archimedes method and the mercury intrusion porosimetry method due to carbonation. Results show that the influence of FA and carbonation on the frost and scaling resistance of concrete can be ignored due to air bubbles by air entraining (AE) admixture in case of AE FA concrete. For Non-AE FA concrete, carbonation of FA concrete does not change the gel porosity/capillary porosity ratio, which is the reason for the frost resistance is not influenced by carbonation of FA concrete. Additionally, it is noteworthy to note that the scaling resistance is strongly connected to the pore volume above 75 nm, and that when exposed to carbonation, the scaling resistance tends to rise as a result of the increase in pore volume above 75 nm that occurs as a result of carbonation. Because of the addition of FA and carbonation, the frost and scaling resistance are far more reliant on the changes in pore structure than they are on the water absorption.

Role of pore structure on resistance to physical crystallization damage of calcium sulfoaluminate belite (CSAB) cement blends

The resistance to physical sulfate damage was tested for a variety of cementitious mixtures including ordinary portland cement, calcium sulfoaluminate belite (CSAB) cement, a CSAB-fly ash blend and an air-entrained CSAB. Mortar bars were exposed to DI water or 5 % sodium sulfate solutions under cyclical wet-dry conditions. The expansions of the specimens were measured after each wetting cycle. A water sorptivity test, thermogravimetric analysis, x-ray diffraction analysis, mercury intrusion porosimetry method, and micro-computed tomography were applied to study differences in expansion and cracking in the mixtures. The results showed that the incorporation of fly ash into the CSAB matrix reduced cumulative pore volumes and slightly increased micropore sizes – both of which contributed to failure of the CSAB-fly ash systems. Use of the air-entraining agent in CSAB produced more, smaller, and more uniform pores, but did not influence the performance of CSAB. Both the CSAB and air entrained CSAB mixtures showed good resistance to physical sulfate damage. Samples with average pore diameters <15 nm prevented infiltration of sulfate ions and slowed the onset of salt crystalization damage.

Experimental research on different metamorphic grades of coal bodies with macro–mesoscopic structure fractal characteristics

This paper studies the Daliuta mine, Xinglongzhuang mine, Qingdong mine and Qincheng mine. Here, nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were performed on different metamorphic grades of coal samples from 4 main mining areas in China. The coal body fissure–pore structure parameters were measured in the range of 100 nm∼5000 nm, and the fractal characteristics were obtained for the different metamorphic grades of coal bodies at macro–meso-structure scales, revealing the influence of reservoir formation on the complexity of the coal body structure. The results show that with the increase in metamorphic degree, the ratio of total pore volume occupied by pores and macropores in coal samples gradually decreases, while the volume ratio of transition pores and micropores increases; in addition, the influence of coal reservoir formation processes on fissure–pore structure parameters of coal is obtained. Based on computer graphics theory and fractal geometry theory, the relationship between the 3D volume fractal dimension of the coal bodies, as measured by NMR, MIP and other fluid intrusion methods, and the box-dimension statistical method of SEM to measure the surface fractal dimension is analyzed. The 3D volume fractal dimension calculated by NMR and MIP is consistent with the change in metamorphism degree; that is, with the increase in metamorphism degree of the coal sample, the 3D volume fractal dimension increases. In addition, the 3D volume fractal dimension measured by NMR is larger than that measured by the MIP; the difference between the 3D volume fractal dimension measured by NMR and 2D surface fractal dimension measured by SEM is approximately 1. Here, the influence of reservoir formation on the characteristics of coal structure fractal is obtained. The research results provide important scientific guidance for enhancing coalbed methane recovery and mine disaster prevention.

Mercury intrusion porosimetry and centrifuge methods for extended‐range retention curves of soil and porous rock samples

AbstractThe water retention function is essential for modeling flow and transport in porous media. Its experimental determination is still challenging because each of the standard methods is limited to partial moisture ranges. The pore‐size distribution (PSD) obtained by the mercury intrusion porosimetry (MIP) may be used as a unifying property that spans across the individual ranges of retention properties obtained with standard methods. This study compares the MIP and quasi‐steady centrifuge (QSC) methods with standard ones (suction table, evaporation, and dewpoint potentiameter) to determine the retention curves of subsoil clods and calcareous rocks over most of the moisture range. The selected soils, having a relatively rigid structure compared with other soils, are more similar to the rocks even if there is a non‐negligible difference in terms of mechanical strength. The QSC, developed for rock samples, was tested for soil to see if the method is also applicable for mechanically less stable media. The porosity characteristics of soil and rock samples showed bi‐ and trimodal PSDs. The single MIP test allowed describing the mercury retention curve (MRC) for most of the volumetric mercury content range. The MRCs could be used to fill the gaps in the retention curves that occur with the standard retention procedure when switching from one measurement range to the other. The MIP and QSC methods proved to be relatively fast and reliable for measuring a wider range of the retention curve. However, the application of QSC method to soil samples is limited by effects of compaction due to centrifugal force.

Estimating soil porosity and pore size distribution changes due to wetting-drying cycles by morphometric image analysis

Porous systems such as soils tend to present great complexity when analyzed at the micrometer-scale. Processes such as tillage and repeated wetting and drying (W-D) cycles tend to continuously alter the structure of the soil. X-ray computed microtomography (μCT) is one of the techniques that can be utilized for quantifying changes in the soil micrometer-scale structure. The objective of this study was to analyze the effect of W-D cycles in the soil porous system of core samples submitted to contrasting management practices (conventional tillage – CT, minimum tillage – MT, no-tillage – NT). An algorithm based on the Mercury intrusion porosimetry method (MIP) was utilized for this purpose. An area of secondary forest (F) was used as a reference. The results of the porosity and functionality of the pores showed that the W-D cycles altered the pore distribution in all management systems. MT was the management that showed the most significant changes in the soil physical properties, where the application of W-D cycles caused fractions of transmission pores to become fissures. In CT, a significant reduction of transmission pores was observed, which indicates the effect of harrowing and plowing operations. Our results show that, depending on the management system adopted, the soil will respond differently to the action of W-D cycles with a direct influence on water retention and movement due to the induced changes in the soil porous system.

Investigation on parameters optimization for gas permeability testing of concrete: Inlet-gas pressure and confining pressure

Permeability is an important characteristic associated with the durability of cementitious materials. Gas permeability testing could overcome some shortcomings of traditional methods but its key parameters have so far not been identified for long periods, reducing comparability of test results. In this study, coarse-aggregate settlement in concrete was taken into consideration by dividing concrete cores into smaller segments and the gas-permeability of concrete specimens was measured by the modified CemBureau method. Apparent gas-permeability (Ka) values of the segments were determined under multiple inlet-gas pressures (1.0 bar–40.0 bar) and various confining-pressures (30 bar–90 bar), which then were applied to calculate the intrinsic permeability (Kint) values and Klinkenberg coefficient (βk) to obtain optimal parameters of inlet-gas pressure and confining-pressure. Meanwhile, X-ray computed tomography (X-ray CT), mercury intrusion porosimetry method (MIP) and specific gravity method (SG) were used for auxiliary calibration of test parameters. The results showed that four zones with different inlet-gas pressures were observed for apparent gas-permeability: unstable zone, metastable zone, stable zone, and anamorphic zone. Combined with gas-permeability, pore characteristics were employed for auxiliary calibration of parameter optimization. In sum, 15.0 bar–30.0 bar inlet-gas pressure and 50 bar confining-pressure were determined as the best parameters for concrete gas-permeability testing.

Elaboration of geopolymers based on clays by-products from phosphate mines for construction applications

Yellow clays from Moroccan phosphate mines are extracted with other waste rocks lithologies and stored in large dumps within the mine site. The present paper investigates the use of this by-product as a new aluminosilicate source for geopolymers elaboration at the laboratory scale. Yellow clays studied are mainly composed of montmorillonite, dolomite and quartz as major phases. The Toxicity Characteristic Leaching Procedure (TCLP) showed no existence of contaminant. In order to reach thermal activation, the raw clays were first calcined at different temperatures between 500 and 900 °C. Raw and calcined clays were characterized using thermogravimetric analysis (TGA), X-Ray Diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy. For the synthesis of geopolymers, calcined powder was mixed with an alkaline solution presenting different NaOH/Na2SiO3 ratios. The compressive strength was measured at 7, 14 and 28 days and material porosity was determined using Mercury Intrusion Porosimetry method in order to explain the mechanical behavior. XRD, 27Al and 29Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy, Fourier transformed infrared and TGA have been used to investigate the gel structure.The thermal treatment at 900 °C allowed the destruction of crystalline structure of montmorillonite clays, as well as the formation of new phases such as periclase (MgO) and gehlenite (Ca2Al2SiO7). Furthermore, the 27Al - 29Si MAS-NMR and the XRD analysis of the elaborated materials confirmed the formation of two cementitious gels C-A-S-H (Calcium aluminum silicate hydrate) and N-A-S-H (Sodium aluminum silicate hydrate). The compressive strength was around 25 MPa at 28 days. The obtained results are promising; they have shown that elaborated materials can be adapted for construction applications. In this case, it is recommended that economic and commercial study be developed.

Infiltration tests to assess the permeability and hydraulic conductivity of 3D printed plaster parts under different conditions

In the postprocess of infiltration in the Binder Jetting technology, the permeability (k) and hydraulic conductivity (K) are essential factors in the penetration of the infiltrant within the three-dimensional printing (3DP) model and thus get to improve its mechanical strength. This study experimentally evaluated the influence of 3DP sample thickness, infiltrant type, build orientation, binder saturation and colour of model 3DP on its permeability and hydraulic conductivity. Permeability and hydraulic conductivity were determined based on Darcy’s law in a custom-made falling-head permeameter with low- and high-viscosity mineral oils that simulated the infiltrants. In addition, porosity and the pore-size distribution were estimated using the liquid saturation and mercury intrusion porosimetry methods. In decreasing order, the build orientation and binder saturation of the sample showed a statistical significance for k, whereas for K the infiltrant type and build orientation were significant. The cumulative volume curves of intruded/extruded mercury to the 3DP model showed liquid entrapment, and this seems to be related to kinetic effects over mercury extrusion, together with the tortuosity and surface chemistry of the pores in the porous system. More than 90% of the pores detected are macropores (> 0.05 µm); however, the predominance in the absorption of the intruded mercury occurred in pores between 10 and 30 µm.

Pore Distribution Characteristics of Thawed Residual Soils in Artificial Frozen-Wall Using NMRI and MIP Measurements

Artificial ground freezing method is widely applied in the construction of metro tunnel and significantly impact the microstructure of soils in artificial frozen-walls. To delve into the pore distribution characteristics of thawed residual soils, Nuclear Magnetic Resonance Imaging (NMRI) measurements were performed to investigate the relaxation time (T2) spectrums and T2-weighted images of saturated samples after freezing at different temperatures. The pore volume distributions were determined from T2 spectrums based on the surface relaxation coefficient ( ρ 2 ) and the pore structures were visualized by T2-weighted images. Subsequently, the pore size distribution curves from NMRI were compared and validated by mercury intrusion porosimetry (MIP) tests. According to the results, the peak areas of T2 spectrums were linearly related to freezing temperatures in a positive manner. Pore volume distribution curves of thawed soils have two peaks, which are the major peaks with diameters of 0.5–20 μm and the secondary peaks with diameters of 20–500 μm. As the freezing temperature drops, the volumes of pores with different diameters all increased. The damage degree of microstructure in thawed soils increases as the temperature drops, according to the visualized pore structure. Besides, NMRI measurements of saturated soils are more accurate to reflect the full diameter range of pores, compared to MIP method.

Characterization of pore structure and the gas diffusion properties of tectonic and intact coal: Implications for lost gas calculation

Accurate calculation of the amounts of lost gas from coal are of great importance in underground mining. In this study, the effects of pore structure and the gas diffusion properties on the lost gas from tectonic and intact coals were investigated by the mercury intrusion porosimetry method (MIP), N2 (77K) and CO2 (273K) adsorption methods, and gas adsorption equilibrium/desorption tests. The results indicated that mesopore and macropore volumes increased after tectonic damage, as did the specific surface areas (SSA) and porosities. However, there was little change for the micropore volumes. Additionally, the desorption experiments indicated that the initial desorption and gas flow capacities of tectonic coal were greater than those of intact coal. Both laboratory and field results demonstrate that there is more higher lost gas for tectonic coal, which is directly influenced by the developed mesopore and macropore structure and by the initial gas desorption capacity. The logarithmic function method is a relatively better choice. When the gas content is determined in coal mines, the sampling exposure times should be kept as short as possible. From the perspective of engineering, this study provides a reference for the calculation of lost gas in tectonic coals.

Change in pore-size distribution of collapsible loess due to loading and inundating

It is well known that the hydromechanical behavior of both saturated and unsaturated loess soils is significantly influenced by the soil fabric. However, there is limited understanding of how the soil fabric or structure evolves due to mechanical, hydraulic and chemical changes on loess soils. Information of the microstructural evolution or change in pore-size distribution (i.e., PSD) of loess soils along different stress paths is valuable for proposing an advanced constitutive model that considers the microstructure and can better model the hydromechanical behavior of loess soils. For this reason, in the present study, the microstructure is characterized on intact and saturated loess specimens before and after oedometer consolidation tests, using scanning electron microscopy and mercury intrusion porosimetry methods. The results suggest that the loading-induced change in PSD varies with stress level and saturation state of the loess soil. A reduction arises in the cumulative intrusion void ratio due to an increase in vertical stress, which accounts for compression of inter-aggregate pores greater than 6 μm. However, loading saturated loess leads to transformation from a bimodal PSD into a trimodal one that defines three major pore series, namely large-pore series (i.e., more than 6 μm), medium-pore series (i.e., between 0.1 and 6 μm) and small-pore series (i.e., less than 0.1 μm). The trimodal nature of PSD is, however, destructed under higher vertical stresses. Both large pores and medium pores are compressed under higher vertical stresses (i.e., > 600 kPa). The inundating-induced change in PSD is dependent on loading condition and can be discerned to take place in the same three pore series. Not only large pores but also medium pores collapse upon inundating under higher vertical stresses (i.e., > 600 kPa). The microstructural evolution is consistent with the mechanical responses of both intact and saturated loess.

An in-situ technique for the direct structural characterization of biofouling in membrane filtration

In the present work, a convenient and direct technique which enables to characterize the intrinsic structure and the mechanical properties of the biofilm without altering its chemical and physical properties is proposed. By utilizing the Optical Coherence Tomography (OCT) as a structural imaging tool coupled with an advance mathematical framework, thickness, micro-porosity, normal stress-strain curve, bulk modulus and total permeability of the biofilm structures are determined. The accuracy of this mathematical technique for the in situ characterization is validated by analyzing two different membrane structures for porosity and permeability values against the mercury intrusion porosimetry method. Three-dimensional images of biofouling were obtained with high resolution aided to numerically analyze the intrinsic biofilm structure at microscale. Growth of biofilm in a dead-end filtration experimental setup was investigated by varying the feed flow rate which allowed uniform compression and decompression to compute normal stress-strain relation of the evolving biofilm structure. At early development of biofilm (day 3), the thickness and normal stress/strain curve showed that the biofilm structure behave similar to elastic material. However, hysteresis-like trend starts to appear with the growth of biofilm suggesting the deviation of biofilm properties to viscoelastic nature at day 8. The microstructure porosity increased from 0.214 (day 3) to 0.482 (day 8) at a feed flow rate of 15 mL/min. The total membrane/biofilm permeability decreased with biofilm age to reach 5.19 × 10−15 m2 at day 8 at the same flow rate, leading to a reduction of permeate flux over time. All the structural properties were found to be time dependent as the biofilm continuously evolved.

Pore structure and multi-fractal analysis of tight sandstone using MIP, NMR and NMRC methods: A case study from the Kuqa depression, China

The pore structure and fractal characteristic of tight gas sandstone from Cretaceous Bashijiqike Formation in Kuqa depression were investigated, using thin section, scanning electronic microscope (SEM), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR) and NMR cryoporometry (NMRC) measurements. The pores of tight sandstone samples mainly contain residual primary intergranular pores, intergranular and intragranular dissolved pores, micropores related to clay aggregates and microfractures. The MIP, NMR and NMRC analyses show that the pore structure of tight sandstone is complex and heterogeneous at different pore scales, displaying as a multi-fractal feature. Fractal dimension Dg-s (with respect to small pore throats) from MIP and Dn-l (long T2 relaxation time, representing large pores and fractures or movable-fluid pores) are negatively correlated with porosity, permeability, median pore throat radius and skewness, and have inverse relationships with bound water saturation (Sbnd). Fractal dimension Dg-b (>3.0, with respect to larger pore throats) and Dn-s (<2.0, short T2 relaxation time, representing small pores or bound-water pores) from NMR don't present clear relationships with most of pore structure parameters. Fractal dimension Dc-1 and Dc-2 from NMRC show more complex or inconspicuous relationships with pore structure parameters, in the pore diameter size <500 nm. Hence, Dg-s from MIP and Dn-l from NMR can be considered as effective parameters for pore structure and fluid properties characterization of tight sandstone. Fractal dimension Dg-b (>3.0) and Dn-s (<2.0) have no practical significance to characterize the pore structure of tight sandstone. The formation of residual primary intergranular pores and intergranular dissolution pores can reduce the fractal dimension which could be an important sign of effective reservoirs in the study area.