Pore Volume Change Research Articles

Evaluation of Different Fly Ash-Blast Furnace Slag Formulations for Design of Geopolymers in Radioactivity Disposal Applications

Geopolymers in radioactive waste management have in recent times gained dominance in disposal module acceptance. Here is a comparative study on formulations prepared from industrial wastes to be utilized as radionuclide disposal barriers in near surface disposal facilities (NSDFs). Different tools such as isocalorimetry, compressive strength, chemical durability were utilized for screening the formulations. Water leaching of the samples shows that the release of the ions to the leachant is minimal. Durability studies in acids (H2SO4, HCl and HNO3) show that the samples are mostly acid resistant. X-ray tomography suggests low pore volume change over a period of 2 years. The study concludes that the NSDF requirement of low permeability of water and better chemical durability criterion is met by the optimized geopolymerization formulation.

The Early Determination Method of Reservoir Drive of Oil Deposits Based on Jamalbayli Indexes

Summary Historically, the concept of “reservoir drive” aimed to simplify the mathematical modeling in reservoir engineering. Within this framework, the energy of the reservoir, particularly its aquifer, was idealized, leading to classifications such as “partial waterdrive,” “full waterdrive,” “gas cap drive,” and so forth. However, in reality, all existing energy sources interact simultaneously within reservoirs. Accordingly, this study aims to develop a new concept for a more realistic description of reservoir drive mechanisms and evaluation of reservoir energy performance. Numerous computer simulations have revealed a strong correlation between the ratio of relative changes in pore volume to relative changes in reservoir pressure and the reservoir’s energy nature and activity level. Moreover, the noted ratio did not depend on production technology, pressure/volume/temperature properties of hydrocarbon systems, rheological properties of reservoir rocks, or other factors. Based on this correlation, specific parameters termed as Jamalbayli Indexes (JI) have been identified to quantitatively describe reservoir energetic performance. JI consist of two parameters. One of them describes the relative change in pore volume per unit of relative change in reservoir pressure, and the second is the relative change in pore volume per unit of relative change in formation porosity. Here, “relative change” means a change in a parameter relative to its original value. These parameters are dimensionless and can have values around or equal to unity. A new conceptual framework for describing reservoir drive mechanisms based on JI has been formulated. According to this framework, reservoir drive mechanism is determined by comparing the computed JI values with unity rather than relying on subjective assessments of the trend of some functional dependencies. For the first time, it has become possible to express the reservoir drive performance quantitatively and determine the level of energy activity of the reservoirs with the help of JI. Additionally, a technique has been developed to evaluate the numerical values of JI for specific oil (including volatile oil) deposits based on the production data at any stage of production. The proposed methodology was tested using data from the eighth horizon of the Russkiy Khutor field in Russia. The test results not only confirmed the reliability of the obtained model but also demonstrated the adequacy of the proposed concept as a whole. Summarizing the results of other works by the authors, the adequacy of the proposed concept for both oil, gas, and gas condensate deposits has been confirmed. The research findings are expected to contribute to updating the traditional principles used for the mathematical problem statements in fluid flow in porous formations. Additional Key Terms and Phrases Reservoir Drive Mechanism; Early Determination Methods; Reservoir Performance Analysis; Production Data Interpretation; Enhanced Oil Recovery; Reservoir Management; Drive Mechanism Identification; Reservoir Fluid Dynamics; Production Rate Analysis; Reservoir Engineering Techniques; Field Development Planning; Reservoir Simulation; Pressure/Volume/Temperature (PVT) Analysis; Production Monitoring and Evaluation drive mechanisms; production data analysis; volatile oil; Jamalbayli indexes; drive performance indexes

Effect of supercritical carbon dioxide on pore structure and methane adsorption of shale with different particle sizes

Supercritical carbon dioxide (SCCO2) fracturing significantly enhances shale gas recovery, which is influenced by particle size. We soaked shale in SCCO2 and investigated the impact of SCCO2 on different particle sizes. Large-particle shales showed the largest percentage changes in specific surface area and total pore volume (54.11 %, 87.87 %; 58.59 %, 76.32 %) followed by small-particle size shales. This trend was also observed in other pore structure parameters. The particle-size effect is: Large-particle shale, with abundant microfractures, enhances SCCO2 flow and pore alteration. Small-particle shale's high specific surface area facilitates SCCO2 penetration. Medium-particle shale is less affected due to balanced interactions of these factors. Methane is primarily found in large and medium pores and microfractures. Methane adsorption in shale mainly involves multi-layer adsorption. Following SCCO2 treatment, pore fractures narrowed, increasing the proportion of methane molecules adsorbed as a single-layer. This study is crucial for evaluating the fracturing effects on shale gas wells.

Microstructure and damage characteristics of cement mortar with different aggregate sizes after cooling based on nuclear magnetic resonance technology

This article studies the effects of cooling methods and aggregate sizes (particle size: 0.63–1.25 mm, 1.25–2.5 mm, 2.5–5.0 mm, 5.0–10.0 mm) on the microscopic properties and damage characteristics of cement mortar specimens. After heating the specimens to 400 °C, air cooling (cooling in air as a whole, A), water cooling (cooling in water as a whole, W), and semi-water cooling (half in air and the other half in water, AW) cooling methods are applied. The T2 spectrum, magnetic resonance imaging (MRI), permeability and P-wave velocity of the specimens were tested by low-field nuclear magnetic resonance (NMR), pulse pore permeability tester and digital acoustic wave instrument, respectively. The effect of cooling method and aggregate size on pore size distribution and fractal characteristics, permeability and tortuosity, P wave and damage degree of cement mortar specimens were studied. The relationship between MRI pixel value and damage degree was deeply explored. The results show that the average permeability and MRI pixel value increase after high temperature, and the pore tortuosity decreases. The mass loss rate, the increase of the most probable pore size and the increase of the pore volume are negatively correlated with the aggregate size, and the permeability ratio, the decrease of the tortuosity and the damage degree are positively correlated with the aggregate size. At the same time, the influence of cooling method on mass loss rate, porosity and permeability from large to small is: A, AW, W, while the decrease rate of pore tortuosity from large to small is: AW, W, A. The most probable pore size and pore volume change most obviously after high temperature treatment of W and AW. In addition, with the increase of aggregate size, the fractal dimension increases under air cooling, and the U-shaped change with W2.5 particle size as the threshold decreases first and then increases under semi-water cooling. Finally, there is a good exponential relationship between the average ratio of MRI pixel values and the damage degree, and the damage degree of the sample can be obtained by the average ratio of MRI pixel values.

The Response Characteristics of Pore Volume and Specific Surface Area of Different Phases of Carbon Dioxide Injection into Anthracite Coal Pores

After the coal sample reacts with CO2, the porosity and pore volume change. Compared with dry raw coal sample, the porosity of coal after CO2 adsorption is increased. With the increase of CO2 injection pressure, the porosity of coal will gradually increase, especially when CO2 enters the supercritical phase. In terms of pore capacity of coal samples, CO2 adsorption time, CO2 adsorption pressure and CO2-H2O treatment do not show obvious regularity in the changes of pore capacity of coal samples, but in general, the increase of CO2 adsorption pressure and CO2-H2O treatment have a positive effect on the increase of pore capacity of coal samples, especially ScCO2-H2O. The mesoporous pore capacity increased by 137.1%. In terms of macro pore volume of coal sample, the change of macro pore volume after CO2 adsorption is more regular. Extending CO2 adsorption time, increasing CO2 adsorption pressure and CO2-H2O treatment all have positive effects on the increase of macro pore volume of coal sample. Under 8MPaScCO2-H2O, macro pore volume reaches a maximum of 0.016462ml/g. The increase also reached 130.4 percent. On the mesoporous specific surface area of coal sample, increasing CO2 adsorption pressure, prolongating CO2 adsorption time and CO2-H2O treatment can increase the mesoporous specific surface area of the sample. The mesoporous specific surface area of the sample at 8 MPa ScCO2-H2O is 0.631 m2/g, which reaches the maximum in this experiment, with an increase of 334.27%.

Effect of corrosion pit distribution of rebar on pore, and crack characteristics in concrete

This research paper delves into the impact of corrosion-induced changes, particularly pit distribution, on pore structures and crack propagation in concrete subjected to galvanostatic accelerated corrosion. Two samples with different pit configurations were investigated—one with larger and spread pits, the other with smaller and localized ones. Various characterizations methods were applied including X-ray Computed Tomography (CT), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), and Raman spectroscopy. The 3D CT images reveals dynamic changes in pore volumes, pit expansion, emergence of new pores at cement-aggregate interfaces, and distinctive crack formation patterns. Image analysis accurately quantifies corrosion products, highlighting their dependence on pit presence and characteristic. The sample with larger pit volume experiences exclusive initial formation of iron hydroxides, while small pit volume contains both iron oxides and hydroxides simultaneously. Raman spectroscopy shows the dynamic interplay of iron oxides and hydroxides, marking an evolution from oxides to hydroxides within the cement paste. Crack formation analysis reveals distinct patterns in samples with high pit dispersion, including cracks originating from pores near reinforcing bar pits, larger cracks diffusing corrosion products outward, and zipper cracks emerging from distant interconnected pores. Conversely, low pit content sample exhibits a different crack pattern with varying origins and narrower apertures. The temporal evolution of cracks in this sample appears simultaneous, possibly linked to ongoing corrosion processes. Elemental mapping indicates elevated corrosion product volumes within and around cracks, possibly due to water migration into the concrete matrix. These insights deepen our understanding of concrete deterioration mechanisms, guiding strategies to enhance structural integrity and durability in critical infrastructure.

On the effect of thermal activation on the surface chemistry of natural mineral sorbents

The article discusses adsorbents, their characteristic features, structural sizes, geometric forms, porosity, the concept of porosity and the influence of their thermal activation on the structure and sorption parameters of natural mineral sorbents - Angren kaolin and Azkamar bentonite. Here is given the chemical composition of kaolin and bentonite clay samples before and after thermal activation. Thermal activation of kaolin clay at 1023K is shown, which has almost no effect on the content of basic oxides in the clay mineral. It leads to the removal of adsorbed moisture and partially constitutional water, as a result of which the mass loss on ignition (WLP) of a thermally activated kaolin clay sample is reduced. The adsorption isotherms of water vapor on thermally activated samples of kaolin and bentonite have an S-shape according to the BET classification, which is due to capillary condensation in the P/P-1.0 region. All isotherms are characterized by the presence of a hysteresis loop over the entire range of relative pressures. The reason for the appearance of a hysteresis loop in the case of sorption of water vapor is associated with the swelling of clays in the vapor phase. The change in the chemical composition of the initial and clays activated at 1023K is shown in the form of a table. Based on the research, it was concluded that during thermal activation of PMS, processes associated with dehydration and dehydroxylation occur, which leads to changes in porosity, specific gravity, and total pore volume.

Sol-gel synthesis of zirconia-based nanoparticles from the side product of tin mining

Indonesia has been one of the world’s primary source of tin since the early of 19th century. Bangka island has the largest tin abundant with a side product is zircon sand (ZrSiO4). The existence of zircon (ZrSiO4) is mostly associated with some of the valuable oxide compounds (VOC) and rare earth oxides (REO). The zirconia powders were synthesized from the zircon sand of PT. Timah Tbk by caustic fusion method followed by sol-gel method. The raw material zircon sand and as-synthesized zirconia were characterized through x-ray fluorescence (XRF), x-ray diffraction (XRD), surface area analysis and porositymeter, thermogravimetric and differential scanning calorimetry analysis (TG-DSC), fourier transform infra-red (FTIR) and scanning electron microscopy (SEM) techniques. The results show that zircon sand from PT Timah Tbk contains some of VOCs, such as ZrSiO4, ZrO2, HfO2, SiO2, Al2O3, TiO2, Fe2O3 and some REOs, such as La2O3, Y2O3, Nb2O5. The fusion temperatures varied from 600 to 800 °C which resulted in an increase of the purity of ZrO2 to 76% based on the XRF analysis. The surface area analysis and porositymeter results showed the significant change in specific surface area, pore size and pore volume of as-synthesized zirconia. The specific surface area increased dramatically from 0.28 m2/g to 173.97, 125.18, and 102.14 m2/g, at fusion temperatures of 600, 700, and 800 °C, respectively. The average particle size of as-synthesized zirconia showed the significant change from 21.31μm to 34.48 nm. The results of this work open new opportunities for the development of zirconia-based nanoparticles from the side product of tin mining.

Damage characteristics of pore and fracture structures of coal with liquid nitrogen freeze thaw

Liquid nitrogen (LN2) fracturing technology is a novel waterless fracturing technology that has significant potential for application in the development of coalbed methane. However, the changes in the microstructure after coal samples are treated with LN2 freeze thaw are poorly understood. Therefore, a combination of mercury intrusion porosimetry and micro-computed tomography (micro CT) was employed to investigate the evolution of pore and fracture structure of coal samples treated with LN2. The experimental results showed that the pore volume and average pore size of coal samples increase after LN2 freeze thaw. After 12 freeze thaw cycles, the change in pore volume of micropores and minipores of coal samples was not significant, while the pore volume of mesopores and macropores increased significantly before LN2 freeze thaw. The specific surface area of the pores in different size ranges of coal samples increases with the increase in the number of LN2 freeze thaw cycles; the structure of micropores and miniopores were damaged by thermal stress and frost heave force during LN2 freeze thaw; and the pore size gradually increases to form mesopores and macropores. Micro-CT images of coal samples after LN2 freeze thaw indicated the primary fractures of coal sample expanded and generated a large number of secondary fractures. The primary and secondary fractures are interconnected and ultimately form penetrated fracture enhancing the connectivity of fractures, enhancing the connectivity of the fracture structure. The key finding study is expected to provide a theoretical basis for LN2 fracturing.

The chemical damage of sandstone after sulfuric acid-rock reactions with different duration times and its influence on the impact mechanical behaviour

The low-permeability characteristic of sandstone-type uranium deposits has become the key geological bottleneck during the in-situ leaching mining, seriously restricting the development and utilization of uranium resources in China. At present, the blasting-enhanced permeability (BEP) and acidizing-enhanced permeability (AEP) are confirmed to be mainstream approaches to enhance the reservoir permeability of low-permeability sandstone-type uranium deposit (LPSUD). To clarify the synergistic effect of BEP and AEP, the acid-rock reaction and dynamic impact experiments were conducted, aiming to study the effect of chemical reactions on pore structure, dynamic mechanical properties and failure pattern of sandstone. Results show that with the increasing acid-rock reaction time, the total pore volume of samples is promoted largely and exhibits obvious chemical damage. The change of pore volume depends on the pore size, the 100–1000 nm and 1000–10000 nm pores are more susceptible to acid-rock reactions. The dynamic peak strength and the dynamic elastic modulus are decreased and the dynamic peak strain and strain rate are increased when lengthening the acid-rock reaction time, whose evolution laws can be fitted by the logistic expression, the linear expression and the exponential expression, respectively. The acid-rock reactions also have an influence on the fracture development of samples after the dynamic impact. The damaged fractures on the end faces of samples grow from the isolated short fracture, the isolated long fracture to the fracture network, and the damaged fractures on the sides of samples develop from the non-penetration fractures, penetration fractures to the multi-branch fractures. This study clarifies the physical and chemical combined damage mechanism, demonstrates the potential of reservoir stimulation by uniting the BEP and the AEP, and provides a theoretical reference for the reservoir stimulation of LPSUD.

Simulating the structural phase transitions of metal-organic frameworks with control over the volume of nanocrystallites

Flexible metal-organic frameworks (MOFs) can undergo structural transitions with significant pore volume changes upon guest adsorption or other external triggers while maintaining their porosity. In computational studies of this breathing behavior, molecular dynamics (MD) simulations within periodic boundary conditions (PBCs) are commonly performed. However, to account for the finite size and surface effects affecting the phase transition mechanism, the simulation of non-periodic nanocrystallite (NC) models without the constraint of PBCs is an important alternative. In this study, we present an approach allowing the analysis and control of the volume of finite-size structures during MD simulations by a tetrahedral tessellation of the (deformed) NC’s volume. The method allows for defining the current NC’s volume during the simulation and manipulating it regarding a particular reference volume to compute free energies for the phase transformation via umbrella sampling. The application on differently sized DMOF-1 and DUT-128 NCs reveals flexible pore closing mechanisms without significant biasing of the transition pathway. The concept provides the theoretical foundation for further research on flexible materials regarding targeted initialization of the structural phase behavior to elucidate the underlying mechanism, which can be used to improve the applications of flexible materials by targeted controlling of the phase transition.

Frictional and poromechanical properties of the Delaware Mountain Group: Insights into induced seismicity in the Delaware Basin

The Delaware Basin in West Texas and Southeast New Mexico has experienced a proliferation in seismic activity since 2016. The seismic activity is primarily due to subsurface injection of wastewater into shallow and deep reservoirs. However, the precise mechanisms connecting fluid injection to seismic activity are not well understood. To shed light on these processes, we measured rate-state friction and poromechanical properties of rocks sampled from the Delaware Mountain Group (DMG) at pressures and stresses representative of in-situ conditions. Experiments were conducted inside a pressure vessel and loaded at a true-triaxial stress state. The samples exhibit velocity-strengthening behavior and transition to velocity-neutral behavior with increasing slip. We also measure frictional healing and demonstrate that the healing rates are consistent with those measured from quartz-feldspathic-rich rocks. Experiments were conducted under a constant pore-pressure boundary condition where transient changes in pore-volume were compensated by modulating the fluid volume within the fault. Our data show that a step increase in sliding velocity leads to dilatancy and causes an influx of fluid into the fault. In contrast, a step decrease in sliding velocity causes the fault zone to compact and reduces fluid flow into the fault. Data show that changes in flow rate scale systematically with fault slip velocity. Broadly speaking, the frictional and poromechanical data indicate that shallow faults within the DMG should favor aseismic creep as opposed to unstable slip. Our data are consistent with elastic dislocation models of fault slip and InSAR data, indicating that faulting in the DMG is predominantly aseismic. The lack of velocity weakening behavior observed in our samples indicates that heterogenous frictional properties are needed to explain the co-existence of both aseismic and seismic slip in the DMG.

Pengaruh Kadar Air Terhadap Pengembangan Tanah Ekspansif

Expansive soil is one type of problematic soil, very sensitive to changes in moisture content. This soil has the characteristics of large shrinkage expansion due to changes in pore volume which can cause lifting forces on existing construction can cause damage to the construction. This research aims to determine the effect of water content on expansive soil in increasing the percentage of swelling soil. The research was conducted experimentally with materials used in this test is expansive soil taken from Sambungmacan, Sragen, Central Java. The main test equipment used in this test is a steel cylindrical mould. Cylindrical mould is filled with expansive soil then compacted a depth of 12 cm. Then the expansive soil is gradually moistened with water until it reaches maximum moisture content to determine its effect on the swelling value. The results of this study show that the increasing water content, then swellin percentage increases in expansive soils until the soil no longer expands at a certain water content.

Analysis of the bond behavior of a GFRP rebar in concrete by in-situ 3D imaging test

Computed tomography combined with mechanical tests offers completely new insight into the behavior of concrete samples under stress. Particularly the development of new fiber reinforcement materials for concrete elements requires appropriate material models and thus for investigating the interior of the concrete structure. In 3D image data obtained by computed tomography, local structural changes within the sample due to mechanical loading can be observed without further altering the sample. We applied this state-of-the-art approach to a concrete core with an embedded glass fiber reinforced polymer rebar under increasing forces applied to pull out the rebar. In this paper, authors describe a novel in-situ setup for non-destructively 3D imaging during the pull-out test. Conducting the pull-out test leads to the formation of local pore volume changes along the rebar. These pore volume changes are not only visualized but quantified analytically based on the images. Interpreting these volume changes, we derive a novel method for calculating strain and normal stresses in the rebar. Our new method captures the detailed distribution of the bond stresses between rebar and concrete and consequently describes the bond behavior more accurate. It turns out that the observed bond behavior cannot be explained completely by commonly assumed material laws. This emphasizes the need for further, more extensive research combining 3D imaging, mechanical testing, and quantitative image analysis.

A Temperature-Controlled Apparatus for Gas Permeability under Low Gas Pressure

The measurement of soil gas permeability is influenced by the temperature and pressure fluctuation in the low gas pressure region. In order to investigate these influences, a soil temperature-controlled apparatus connected to a low-gas-pressure supply equipment is proposed in this study. The low constant gas pressure is supplied by two Mariotte bottles, by which the airflow rate is measured. Meanwhile, the soil specimen is controlled by a temperature-controlled apparatus. During the test, the negative pore water pressure and volume change of the soil specimen are measured. Through the temperature-controlled apparatus, it is observed that as the temperature increases from 25 °C to 60 °C, there is a corresponding increase in soil sample porosity by 5.4%, while the negative pressure of pore water decreases by 11.1%. This can be attributed to the reduction in the surface tension of contractile skin caused by elevated temperatures. Furthermore, due to variations in gas viscosity with temperature, there was a significant decrease in the gas flow rate by 50.5%. And, the relationship between permeability and volumetric gas content at different temperatures in low-pressure regions well confirms the existing power-law model. In addition, the existence of a temperature-independent critical negative pore water pressure is observed, beyond which the intrinsic permeability remains constant. At 36 kPa of negative pore water pressure, the intrinsic permeability at 60 °C exhibits an 81.8% reduction compared to that at 25 °C. This decline in intrinsic permeability can be attributed to a diminished pore connectivity, resulting from elevated temperatures.

The relative dominance of surface oxygen content over pore properties in controlling adsorption and retrograde behavior of gaseous toluene over microporous carbon

The adsorption potential of activated carbon (AC) derived from macadamia nut shells (product code of Procarb-900: namely, AC-P) has been investigated using gaseous toluene as the target pollutant. The powder AC-P with high-microporosity (96%) and oxygen content (5.62%) exhibited very high adsorption capacity (214 mg·g−1) and partition coefficient (PC: 25 mol·kg−1·Pa−1) against 100 ppm (10 Pa) toluene at 99% breakthrough levels (1 atm dry N2). The factors governing toluene adsorption were explored with respect to the key variables such as surface functional groups, pore size distribution, sorbent bed mass (50, 100, and 150 mg), and particle size (i.e., 0.212–0.6 mm (powder AC: PAC)) vs. 0.6–2.36 mm (granular AC: GAC)). Accordingly, the adsorption process was physical, mainly due to the non-polar interactions (i.e., π-π interactions) between the adsorbent and adsorbate molecules. The high affinity of AC-P at low breakthrough levels was obtained through a combination of smaller particle size (PAC) and larger adsorbent mass (i.e., 150 mg) with the appearance of a very pronounced retrograde phenomenon (e.g., at < 1% breakthrough level). As such, toluene adsorption appeared to be affected more sensitively by particle size and adsorbent mass (especially at low breakthrough levels) than by high microporosity. Most importantly, the oxygen content of AC emerges as one of the key factors governing the maximum capacity, as the changes in pore volume are not crucial to explain the observed adsorption patterns of toluene.

CHANGES OF SURFACE CHARACTERISTICS&#x0D; AND PORE SIZE DISTRIBUTION OF PETROLEUM COKE&#x0D; DURING ITS CALCINATION IN THE PRESENCE OF POTASSIUM HYDROXIDE

Change of surface properties and pore distribution in petroleum coke at carbonization stage at 900 °C in presence&#x0D; of potassium hydroxide has been studied. CO2 adsorption and desorption isotherms at 298 K have been obtained&#x0D; for samples of raw and carbonized petroleum coke without and with potassium hydroxide addition. For pore shape and&#x0D; size distribution analysis GCMC (Grand Canonical Monte Carlo) computer simulation method has been used. Regularity&#x0D; of changes in volume, specific surface area and distribution of cylindrical and slit-shaped pores depending on the&#x0D; amount of potassium hydroxide added prior to carbonization stage in petroleum coke has been revealed. Extreme dependence&#x0D; of change in specific surface area and pore volume on potassium hydroxide content in carbonized coke has&#x0D; been identified. It has been found that addition of potassium hydroxide of less than 50% wt. reduces pore quantity and&#x0D; specific surface area of carbonized coke. The main contribution to the coke specific surface area is made by slit-shaped&#x0D; and cylindrical mesopores, as well as cylindrical macropores. It has been shown that by varying the amount of potassium&#x0D; hydroxide added to petroleum coke prior to its carbonization it is possible to regulate the formed pores distribution&#x0D; in terms of shape and size.

Raman Evidence of Multiple Adsorption Sites and Structural Transformation in ZIF-4

The zeolitic imidazolate framework, ZIF-4, exhibits soft porosity and is known to show pore volume changes with temperatures, pressures, and guest adsorption. However, the mechanism and adsorption behavior of ZIF-4 are not completely understood. In this work, we report an open to narrow pore transition in ZIF-4 around T ∼ 253 K upon lowering the temperature under vacuum (10-6 Torr) conditions, facilitated by C-H···π interactions. In the gaseous environment of N2 and CO2 around the framework, characteristic Raman peaks of adsorbed gases were observed under ambient conditions of 293 K and 1 atm. A guest-induced transition at ∼153 K resulting in the opening of new adsorption sites was inferred from the Raman spectral changes in the C-H stretching modes and low-frequency modes (<200 cm-1). In contrast to a single vibrational mode generally reported for entrapped N2, we show three Raman modes of adsorbed N2 in ZIF-4. The adsorption is facilitated by dispersive and quadrupolar interactions. From our temperature-dependent Raman results and theoretical analysis based on the density functional tight-binding approach, we conclude that the C-Hs are the preferred adsorption sites on ZIF-4 in the following order: C4-H, C5-H > C2-H > center of the Im ring (interacting with C-H centers) > center of the cavity. We also show that with an increasing concentration of N2 adsorbed at low temperatures, the ZIF-4 structure undergoes shear distortion of the window formed by 4-imidazole rings and consequent volumetric expansion. Our results have immediate implications in the field of porous materials and could be vital in identifying subtle structural transformations that may favor or hinder guest adsorption.

Experimental analysis of the pore structure, relative permeability, and water flooding characteristics of the Yan'an Formation sandstone, southwestern Ordos Basin

The oil and gas potential of the Yan'an Formation in the Ordos Basin has yet to be fully tapped. In this study, the pore structure, mobile fluid saturation, and water flooding micro-mechanism of the Yan'an Formation sandstone are systematically studied through the application of a series of rock physics and fluid experiments. The results show that there is a good positive correlation between porosity and permeability, and the reservoirs are divided into types Ⅰ, Ⅱ, and Ⅲ. Mercury injection tests show that the average pore throat radius of the oil-bearing reservoir ranges from 1 to 7 μm. The displacement pressure of the Yan'an Formation is also relatively low, and it decreases from 0.1 MPa to 0.01 MPa as the rock porosity increases from 11% to 18%. NMR tests show that small (diameter <0.5 μm) and medium pores (diameter ranging from 0.5 to 2.5 μm) are predominant in the reservoir. Different types of reservoirs have different characteristics of relative permeability curve. In addition, when the average oil recovery rate is less than 1 ml/min, the oil displacement efficiency increases faster. However, when the average oil recovery rate is between 1–3.5 ml/min, the oil displacement efficiency is maintained at around 27%–30%. Physical properties of the reservoir, pore-throat structure, experimental pressure difference, and pore volume injected — all have significant effects on oil displacement efficiency. For Type Ⅰ and Type Ⅱ reservoirs, the increase of the pore volume injected has a significant effect on oil displacement efficiency. However, for Type Ⅲ reservoirs, the change of pore volume injected has insignificant effect on oil displacement efficiency. This study provides a reference for the formulation of estimated ultimate recovery (EUR) measures for similar sandstone reservoirs.

The effect of surfactant type and concentration on the pore structure of alumina aerogels

Alumina aerogels are excellent materials for thermal insulators used at high temperatures due to the good thermal stability of aluminum oxide. In this study, alumina aerogels treated with various types of surfactants (non-ionic (Triton X-100), cationic (cetyltrimethylammonium bromide), or anionic (sodium dodecyl sulfate)). The effect of the surfactant depended on the charge-charge interactions between it and the cationic inorganic species in the aluminum precursor. As determined by using small-angle scattering and pore volume change measurements, these interactions induced a change in the pore structure that could be controlled by controlling the concentration of the surfactant. The hindrance effect due to the ionic interference was more pronounced at a higher surfactant concentration than at a lower one. Thus, the concentration of surfactant plays an important role in determining the pore structure of the alumina aerogel.