Microscopic Pore Characteristics Research Articles

Microscopic Mechanism and Reagent Activation of Waste Glass Powder for Solidifying Soil

Glass waste products represent a significant environmental concern, with an estimated 1.4 billion tons being landfilled globally and 200 million tons annually. This results in a significant use of land resources. Therefore, it would be highly advantageous to develop a new method for disposing of waste glass. Waste glass can be recycled and ground into waste glass powder (WGP) for use in solidified soil applications as a sustainable resource. This study is based on solidified soil research, wherein NaOH, Ca(OH)2, and Na2SO4 were incorporated as activators to enhance the reactivity of WGP. The optimal solidified soil group was determined based on unconfined compressive strength tests, which involved varying the activator concentrations and WGP content in combination with cement. X-ray diffraction (XRD) was used to study the composition of solidified soil samples. Microscopic pore characteristics were investigated using scanning electron microscopy (SEM), and the Image J software was employed to quantify the number and size of pores. Fourier-transform infrared spectroscopy (FTIR) was employed to examine the activation effect of waste glass powder. This study investigated the solidification mechanism and porosity changes. The results demonstrate that the addition of activated WGP to solidified soil enhances its strength, with a notable 12% increase in strength achieved using a 6% Ca(OH)2 solution. The use of 2% concentration of Na2SO4 and NaOH also shows an increase in strength of 7.6% and 8.6%, respectively, compared to the sample without WGP. The XRD and SEM analyses indicate that activated WGP enhances the content of hydrates, reduces porosity, and fosters the formation of a more densely packed solidified soil structure.

Experimental Study on Strength and Microstructure of Loess Improved by CG-2 Curing Agent and Cement

In order to study the improvement effect of the CG-2 curing agent and cement on loess, a series of physical and mechanical property tests and microstructure tests were carried out on loess improved with different dosages of curing agent and cement to study the physical and mechanical properties, durability and microscopic pore characteristics of the CG-2 curing agent and cement-improved loess. The results show that the unconfined compressive strength of improved loess increases gradually with the increase in curing agent and cement dosage, and the higher the compaction degree and the longer the curing age, the higher the unconfined compressive strength. In the case of the same cement content, the higher the dosage of curing agent, the more the unconfined compressive strength of improved loess increases. Under the condition of reaching the same unconfined compressive strength, the addition of curing agent can significantly reduce the amount of cement. The more the content of cement and curing agent, the less the unconfined compressive strength decreases after a certain number of freeze–thaw cycles, and the higher the dry-wet cycles index after a certain number of dry-wet cycles, indicating that the addition of curing agent can significantly improve the ability of the sample to resist freeze–thaw cycles and dry–wet cycles. According to the microscopic test results, it is found that the addition of curing agent can reduce the porosity of soil particles, change the contact and arrangement mode between soil particles, and enhance the agglomeration and cementation characteristics between soil particles, and obviously improve the physical and mechanical properties of soil. The research results can provide new ideas and methods for the improvement technology of loess.

Strength and microscopic pore structure characterization of cement-fly ash stabilized organic soil under freeze-thaw cycles

In seasonal frost areas, an organic soil stratum is often encountered during engineering construction due to the widespread existence of organic soils. The soil stratum will experience frost heave in winter and thaw settlement in summer, resulting in a significant variation in its engineering behaviour, especially for organic soil stratum. In this study, with the help of cement, fly ash, and fulvic acid, cement-fly ash stabilized organic soil (CFOS) specimens were prepared and the unconfined compressive (UC) and mercury intrusion porosimetry (MIP) tests were carried out on CFOS specimens. The effects of fly ash content, number of freeze-thaw cycles (FT-N), and curing period on the strength, resilient modulus, and porosity were investigated. Test results revealed that the fly ash content increased from 0% to the optimum content of 5%, the unconfined compressive strength (UCS) and resilient modulus of CFOS with FT-12 increased by 50.30% and 118.92%, respectively. The pore size distribution (PSD) curve and fractal dimension (Dn) of specimens were obtained from the MIP test. The proportion of macropores was the main factor affecting the UCS of CFOS. With the increasing FT-N, the macropore proportion of CFOS with 5% fly ash content increased by 333.33%, and the UCS decreased by 28.25%. Based on a freeze-thaw damage model, the damage parameters of the CFOS specimens were extracted with the Dn as an independent variable. The microscopic pore characteristics and the relationship between the strength, Dn and damage parameter were analyzed. The microscopic pore structure of specimens with different fly ash contents experienced a change subjected to freeze-thaw cycles. The lower the strength, the lower the Dn of CFOS. The damage parameters quantitatively reflected the damage degree of specimens after freeze-thaw cycles on the micro scale. The damage parameter of CFOS with 5% fly ash content increased by 341.57% with the increase of FT-N. The introduction of fly ash was able to reduce freeze-thaw damage to the specimens. The damage parameter and CFOS strength exhibited a significant correlation. The relationships of the strength and microscopic pore structure of CFOS subjected to freeze-thaw cycles were conducive to a better understanding of the freeze-thaw damage mechanism of CFOS on the micro scale. These findings are beneficial for engineering construction design in seasonal frost areas.

Micro-dissolution mechanism and macro-mechanical behavior of red-bed soft rock under dry-wet cycle

The microscopic pore characteristics of rocks have an important influence on their macroscopic mechanical behavior. The micro-pore dissolution mechanism of red-bed soft rock was revealed by the dry-wet cycle method, and its macroscopic mechanical behavior was studied by a series of uniaxial compression tests. The results show that with an increase in the number of dry-wet cycles, the micro-pore dissolution and micro-grain spalling of red-bed soft rock result in its porosity increasing nonlinearly. Under the action of the axial load, the number of micro-fractures increases and evolves from tensile fracture to shear fracture, and the macroscopic failure mode changes from brittle splitting failure to ductile conical failure.

Investigation of diffusion behavior, stability of testing ions, interconversion feasibility and microstructures of iodide and chloride in concrete

In coastal areas, the interiors of reinforced concrete (RC) structures are often contaminated or eroded by chloride intrusion. The natural chloride diffusion test method does not accurately assess the service performance status of these structures in terms of their resistance to chloride penetration during maintenance or repair of RC structures. By conducting natural chloride diffusion test and natural iodide diffusion test, the stability of iodide in different environments was analyzed, and the diffusing depth, ion content and diffusing coefficient of chloride and iodide (D(chloride) and D(iodide)) in concrete at different water-cement ratios (w/c) (0.38, 0.47 and 0.53) were determined. The ion-binding capacity of the two ions at different w/c was also analyzed, and the relationship between w/c and D(chloride) and D(iodide) was analyzed by data regression method (DRA), and the accuracy and applicability of the natural iodide diffusion test method were discussed. The microscopic morphology, pore characteristics and chemical phase of matrix were also studied using SEM-EDS, MIP and XRD techniques. The findings show that natural iodide diffusion testing should be performed in dark and airtight conditions to ensure a minimum decrease in iodide concentration. The diffusion behavior of both chloride and iodide in concrete is in accordance with Fick Ⅱ pattern, and both bonding and free ions show an obvious linear relationship. Besides, with the increase of w/c, the content of free chloride and iodide in concrete gradually decreased, while the content of bonding ions gradually increased. However, at the same w/c, the concentration of iodide was relatively higher than that of chloride at the same concrete depth due to the higher molar mass of iodide. As both ions diffuse and migrate in the concrete, this also leads to the generation of two complex salts inside the concrete, 3CaO·Al2O3·CaCl2·10H2O and 3CaO•Al2O3•CaI2•8H2O, and with the w/c decreasing, there is a smaller porosity in matrix and the proportion of macropores gradually increases. Besides, the concept of D(chloride) and D(iodide) conversion coefficient was introduced, and a linear relationship between D(chloride) and D(iodide) was obtained using DRA, and the conversion coefficient also was obtained, and a better quadratic parabolic function relationship was found between the w/c adjustment coefficients. Overall, this study proposes a new natural iodide diffusion test method for the performance assessment of RC structures in some remote islands or marine areas to minimize the test error of ion penetration, and provides a new reference index for the structural design and reinforcement or repair of coastal RC structures.

Research on types of gas reservoirs divided by seepage capacity and their seepage mechanism, law and productivity

In view of the diversity of gas reservoir classification and the differences of characteristics of geology and development in different gas reservoirs, it is necessary to study the adaptability of gas reservoir classification. This paper analyzes and summarizes the current classification methods of gas reservoirs, studies the microscopic pore characteristics and seepage mechanism of different gas reservoirs. The commonalities and individualities of seepage laws in different gas reservoirs are determined, the key factors that determine the development dynamics and effects of gas reservoirs are proposed, and the gas reservoirs types are divided from the perspective of development. The results show that the development characteristics of gas reservoirs are determined by the seepage law, and the seepage law is determined by the microscopic pore characteristics. Therefore, from the perspective of development, the microscopic pore characteristics are the fundamental of gas reservoir classification. Gas reservoirs can be divided into four types: tight, low permeability, medium and high permeability, and fractured. This classification method can unify the types of gas reservoirs according to the seepage laws of different gas reservoirs, establish corresponding seepage models, evaluate productivity, and predict performance. It is of great significance for rational, efficient and scientific development of gas fields.

The durability of basalt-fiber-reinforced cement mortar under exposure to unilateral salt freezing cycles

Basalt fiber and cement-based materials have been widely applied in engineering structures. In this context, the durability of basalt-fiber-reinforced ordinary silicate mortar was systematically studied under exposure to unilateral salt freezing. The mechanical durability, chloride ion diffusion characteristics, and microscopic pore characteristics of cement mortar with basalt fiber content levels in the range of 0 kg/m3–1.5 kg/m3 were tested under exposure to 0–40 freeze–thaw cycles. The relationships of changes in the internal pore structure with mass loss, mechanical damage, and the physical properties of the material were also analyzed under exposure to salt freezing cycles. The results demonstrated that even a small amount of basalt fiber could significantly improve the mechanical properties of cement mortar under unilateral salt freezing and its resistance to salt freezing erosion. In particular, cement mortar with 1.2 kg/m3 basalt fiber content exhibited good durability of compressive and flexural strength, while the specimens with no basalt fibers exhibited a relatively large degree of internal porosity under exposure to unilateral salt freezing. Our work provides concrete evidence for changes in the porosity of mortar under exposure to unilateral salt freezing, with these changes showing an exponential relationship with mortar mass loss and a strong linear correlation with changes in the compressive strength, flexural strength, and chloride ion diffusion coefficient of the material.

Pore Structure and Fractal Characteristics of Marine–Continental Transitional Black Shales: A Case Study of the Permian Shanxi Formation in the Eastern Margin of the Ordos Basin

To study the microscopic pore characteristics of marine–continental transitional shale, we studied the Daning–Jixian block of the Shanxi Formation using low-pressure CO2 adsorption (LP-CO2A) and low-temperature N2 adsorption (LT-N2A) methods in conjunction with field emission scanning electron microscopy (FE-SEM), geochemistry, and mineral composition analysis in order to obtain pore structure characteristic parameters. The fractal dimension of the pores was calculated using the Frankel–Halsey–Hill (FHH) model, and the study also discusses the factors that influence the pore structure. The study found that the marine–continental transitional phase shale of the Shanxi Formation has clay mineral contents ranging from 36.24% to 65.21%. The total organic carbon (TOC) contents range from 0.64% to 9.70%. Additionally, the organic matter maturity is high. The FE-SEM and gas adsorption experiments revealed that the transitional shale of the Shanxi Formation possesses a diverse range of pore types with relatively large pore sizes. The dominant pore types are organic and intragranular pores, with pore morphologies predominantly appearing as slit and parallel plate structures. According to the experimental data on gas adsorption, the total SSA values range from 11.126 to 47.220 m2/g. The total PV values range from 0.014 to 0.056 cm3/g. Micropores make up a greater proportion of the total SSA, whereas mesoporous pores make up a greater proportion of the total PV. The distribution of shale pore fractal dimensions D1 and D2 (D1 is 2.470 to 2.557; D2 is 2.531 to 2.755), obtained through LT-N2A data, is relatively concentrated. D1 and D2 have a positive correlation with the TOC content, clay mineral content, and BET-SSA, and D1 and D2 have a negative correlation with the quartz content. D2 is positively correlated with the Langmuir volume, showing that D2 can be used to evaluate the methane adsorption capacity.

Main controlling factors and oil-bearing potential characteristics of a tight sandstone reservoir: A case study of southwest Ordos Basin

Clarifying the main controlling factors of reservoirs and their oil-bearing potential is vital for predicting tight sandstone reservoirs. The Chang 8 reservoir in the southwest of Ordos Basin is a typical tight sandstone reservoir and is widely distributed. Observation description and sampling analysis of cores, the grain size analysis, casting thin section, scanning electron microscope, mercury pressure, nuclear magnetic resonance, and conventional physical analysis are used to clarify the main controlling factors and oil-bearing potential characteristics of the Chang 8 reservoir in southwest Ordos Basin. The results show that delta front subfacies are mainly developed in Chang 8 member, including distributary channel, natural dike, estuary bar and distributary bay. The main rock type of reservoir is lithic feldspathic sandstone, followed by feldspathic lithic sandstone. The types of reservoir space are mainly intergranular pores and intragranular dissolved pores, with a small amount of clay-related pores and micro-fractures. The average porosity and permeability of the reservoir are 11.67% and 0.52 × 10−3μm2, respectively. The reservoirs with high oil saturation are mainly distributary channels and thicker mouth bar sand bodies. Compaction is the main factor of reservoir compaction (porosity loss rate is 55.73%), followed by cementation (porosity loss rate is 29.23%). The favorable diagenesis is the dissolution of feldspar grains and some cement. The Chang 8 tight reservoir contains various nano-scale pore-throat. For tight reservoirs with similar physical properties, the pore-throat structure controls the oil saturation of the tight reservoir. Favorable conditions for tight sandstone reservoirs oil saturation include favorable sedimentary environment (distributary channel or thick mouth bar) and suitable microscopic pore characteristics.

Mechanism Study of Differential Permeability Evolution and Microscopic Pore Characteristics of Soft Clay under Saturated Seepage: A Case Study in Chongming East Shoal

Artificial reclamation is one of the main means of land expansion in coastal cities. However, the permeability of underlying soft clay (USC), derived from the dredged load, has not been paid enough attention, although it is closely related to the long-term deformation and stability of foundation soil. Hence, this paper analyzes the relationship between permeability characteristics and microscopic pore characteristics of USC in Chongming East Shoal (CES), a typical multi-phase reclamation area, through a variable head permeability test, mercury intrusion porosimetry (MIP) test, and scanning electron microscope (SEM) test. Furthermore, grey relation entropy and Pearson correlation analysis are implemented to analyze the influence of micropore parameters on permeability. The results revealed that the seepage process of clay showed a transition from unstable seepage to relatively stable seepage. Meanwhile, the permeability coefficient (PC) attenuated with time cyclically, indicating the alternating effect of the closed and opened unstable seepage channels. During seepage, clay particles could be entrained by pore water and intercepted by pores, thus clogging seepage channels. Then, the increased pore water pressure could break through new seepage channels. The degree of pore clogging was positively correlated with the average cycle period of PCs, and this was also present in the relatively stable stage of PCs. A lower mesopores content, higher fractal dimension, and aggregated flocculate microstructure could promote the clogging effect and result in lower permeability efficiency. Affected by unstable seepage channels, soft clay may face long-term potential deformation in the future, which needs further investigation.

Experimental investigation of the pore fractal characteristics and damage degradation mechanism of sandstone after cyclic Freeze‒thaw treatments

To reveal the microscopic pore characteristics and strength weakening mechanism of rock under the influence of cyclic freeze-thaw treatment, uniaxial compression tests and MIP (mercury intrusion porosimetry) were conducted on red sandstone specimens with different numbers of freeze-thaw cycles (0, 20, 40, 60, and 80). The experimental results showed that cyclic F-T (freeze-thaw) treatment can lead to an increase in porosity and the expansion of the pore structure. Specifically, the porosity increased by nearly 30.22% from 8.467% without freeze-thaw to 11.026% after 80 freeze-thaw cycles. The distribution ratios of mesopores (2–10 μm) and micropores (less than 0.1 μm) changed from 0.7% to 19.9% without freeze‒thaw to 12.6% and 11.6% after 80 freeze‒thaw cycles, which showed an expansion trend from small to large pores. For the PFD (pore fractal dimension) of sandstone, three fractal models (capillary pressure model, Menger sponge model and thermodynamic model) were used to calculate the pore fractal dimension of different freeze-thaw cycles, which gradually increased with the increase in freeze‒thaw cycles. Specifically, the PFD increased by 3.02, 3.01 and 2.65% after 20, 40, 60, and 80 freeze-thaw cycles, respectively. Additionally, the PFD calculated by the capillary pressure model and Menger sponge model had piecewise characteristics, which can better characterize pore fractal characteristics with pore diameters less than 2 μm. In summary, based on thermodynamic theory and pore water frost heaving deformation theory, a freeze-thaw damage degradation model based on the porosity of a fractured rock mass was established, and the theoretical value obtained was in good agreement with the experimental results.

Analysis of Microscopic Pore Characteristics and Macroscopic Energy Evolution of Rock Materials under Freeze-Thaw Cycle Conditions

The repeated cyclic freeze-thaw effect in low-temperature environments causes irreversible damage and deterioration to the microscopic pore structure and macroscopic mechanical properties of a rock. To study the effects of the freeze-thaw cycle on the porosity and mechanical properties, the indoor freeze-thaw cycle test and mechanical tests of sandstone-like materials were conducted. Based on nuclear magnetic resonance, the influence of the freeze-thaw cycle on microscopic pores was analyzed, and the intrinsic relationship between porosity and mechanical strength was discussed. Meanwhile, the energy change in the uniaxial compression test was recorded using the discrete element software (PFC2D). The influence of freeze-thaw cycles on different types of energy was analyzed, and the internal relationship between different energies and freeze-thaw cycles was discussed. The results showed that the microscopic pore structure is dominated by micropores, followed by mesopores and the smallest macropores. With an increase in the freeze-thaw cycle, both micropores and mesopores showed an increasing trend. The porosity showed an exponentially increasing trend with the increase in freeze-thaw cycles. The peak strength and elastic modulus decreased exponentially with the increase in freeze-thaw times, while the peak strain showed an exponentially increasing trend. The strain energy and bond strain energy showed a trend of increasing and decreasing in the front and back stages of the peak strength, respectively. However, the frictional energy always showed an increasing trend. The total energy, strain energy, bond strain energy, and friction energy all showed exponential increases with the increase in the number of freeze-thaw cycles.

Pore structure and fractal characteristics of Wufeng–Longmaxi formation shale in northern Yunnan–Guizhou, China

In this study, the microscopic pore characteristics of shale in marine strata are evaluated. Based on field emission scanning electron microscopy (FE-SEM), low-temperature N2 adsorption (LT-N2GA), low-pressure CO2 adsorption (LP-CO2GA) and high-pressure methane adsorption (HPMA) experiments, the pore characteristics of 12 shales from the Wufeng–Longmaxi Formations in northern Yunnan and Guizhou are characterized qualitatively and quantitatively. Fractal Frenkel–Halsey–Hill (FHH) theory is used to analyse the fractal characteristics, and the adsorption pore characteristics of shale are discussed. The correlation between the fractal dimension and pore structure and adsorption performance is determined. The results show that the total organic carbon (TOC) contents of the 12 shales are in the middle–low level, ranging from 0.43% to 5.42%, and the shales are generally in the highly mature to overmaturity stage (vitrinite reflectance (Ro) values between 1.80% and 2.51%). The mineral composition is mainly quartz and clay minerals. The average clay mineral content is 40.98% (ranging from 24.7% to 63.3%), and the average quartz content is 29.03% (ranging from 16.8% to 39.6%), which are consistent with those of marine shale in the Sichuan Basin. FE-SEM and LT-N2GA isotherms reveal a complex shale pore structure and open pore style, mainly ink bottle-shaped and parallel plate-like pores. The total pore volumes (PVs) range from 0.012–0.052 cm3/g, and the specific surface area (SSA) values range from 18.112–38.466 m2/g. All shale samples have abundant micropores and mesopores, accounting for >90% of the total SSA. The fractal dimensions, D1 and D2, were obtained from N2 adsorption data, with different adsorption characteristics at 0–0.5 and 0.5–1.0 relative pressures. The fractal dimensions increase with increasing BJH PV and BET SSA and decrease with decreasing average pore diameter (APD). The fractal dimensions are positively correlated with the TOC and clay mineral contents and negatively correlated with the quartz content. The fractal dimension can be used to evaluate the methane adsorption capacity; the larger the fractal dimension is, the larger the methane adsorption capacity is. Fractal analysis is helpful to better understand the pore structure and adsorption capacity of shale gas reservoirs.

Study on the Low Temperature Cracking Mechanism of Steel Slag Asphalt Mixture by Macroscale and Microscale Tests

Steel slag’s physical and mechanical properties are close to natural gravel, which can replace natural aggregate with paving asphalt mixture pavement. Based on macro- and microscales, it is necessary to study the low-temperature cracking characteristics of steel slag asphalt mixture (SAM). This paper aims to study the low-temperature cracking characteristics and influence mechanism of steel slag asphalt mixture by macro- and microscale tests. This article analyzes the strain field distribution and cracks propagation law of SAM at low temperatures by the three-point bending test combined with digital image correlation (DIC). The microscopic pore characteristics of SAM were studied by nuclear magnetic resonance (NMR). Based on fracture mechanics and weight function theory, the variation law of the stress intensity factor at the crack tip of the asphalt mixture with crack propagation is derived. The correlation between microscopic pores and low-temperature cracking characteristics of asphalt mixture was analyzed based on the grey correlation theory. The results show that SAM has more small and less large pores, and its total porosity is lesser than that of the basalt asphalt mixture (BAM). The initial elastic stage of SAM resisting bending deformation is longer than that of BAM, the bending strain energy density (dW/dV) is larger, and the crack penetration is slower. The horizontal strain energy density (DE) of SAM is greater than BAM, and the crack tip stress is greater. The porosity correlates well with the low-temperature crack resistance of the asphalt mixture.

A Novel Carbon Dioxide Phase Transition Rock Breaking Technology: Theory and Application of Non-Explosive Blasting

As a non-explosive low-disturbance rock breaking technology, carbon dioxide phase transition blasting (CDPTB) is widely used in rock breaking projects such as pressure relief and permeability enhancement in coal mines, open-pit mining, road subgrade excavation, foundation pit excavation, etc. In this paper, the principle and equipment of CDPTB are systematically analyzed, and the characteristics of a reusable fracturing tube and disposable fracturing tube are determined. Different energy calculation methods are analyzed to determine the magnitude or equivalent explosive equivalent of CDPTB. According to the characteristics of impact stress wave and high-pressure gas, the cracking mechanism of CDPTB is proposed. Under the action of medium-impact stress, rock mass will produce multi-point cracking, and high-pressure gas will produce a gas wedge effect in the initial fracture, which determines the comprehensive action path of the stress wave and high-pressure gas. In terms of fracture characteristics, the fractal method is used to evaluate the macroscopic crack and fragment, microscopic fracture and pore characteristics. In terms of vibration characteristics, the attenuation law of CDPTB vibration with distance is statistically analyzed, and the Hilbert–Huang transform method is used to analyze the time–frequency characteristics of CDPTB. This rock breaking technology can be widely used in different projects, and the existing problems and future challenges are put forward.

Reservoir Physical Properties and Micropore Nanocharacteristics of Cores in the Shihezi Formation, Sudong District, Sulige Gas Field, Ordos Basin.

Sulige gas field is a very complex large-scale gas field with low porosity, low permeability, low abundance, and strong heterogeneity. In this study, the nanopore structure of the reservoir in the study area was analyzed. The analysis of reservoir physical properties and core microscopic pore characteristics of Shihezi formation in Sudong District, Sulige gas field, Ordos Basin, was put forward. According to core observation, thin section identification, and grain size analysis, the lithology of gas reservoirs in Shan-1 member and He-8 member in the study area is mainly lithic sandstone, lithic quartz sandstone, and quartz sandstone. According to the analysis of physical data in the study area, the reservoirs in Shan-1 member and He-8 member have typical characteristics of low porosity and low permeability. According to that microscopic observation of sandstone thin section and cast thin section combined with the analysis of scan electron microscope, the results show that both Shan-1 member and He-8 member of Sudong area 2 in Sulige gas field are dominated by class I reservoirs and class II reservoirs. Especially, class I reservoirs are widely distributed, with the cumulative area of this type of reservoirs accounting for 70.12% of the total area in Shan section and 64.12% in He-8 section. Class I reservoirs are scattered in the study area, accounting for 0.27% of the total area in the mountain section and 0.36% in the He-8 section. Class IV reservoirs are distributed dispersedly and have a small distribution area. The cumulative area of reservoirs in mountain section accounts for 5.38% of the total area and that in He-8 section accounts for 5.46%. Therefore, Sudong area 2 in Sulige gas field is a typical low porosity and low permeability reservoir. On the basis of geological background, sedimentary microfacies, diagenesis, and pore structure characteristics of the study area, it is considered that the pore structure of sandstone in the study area is mainly controlled by sedimentary characteristics and diagenesis of sandstone.

Modifying effect of anionic polyacrylamide dose for cement-based 3DP materials: Printability and mechanical performance tests

Cement-based materials have been broadly applied as constructional materials in 3D printing (3DP) civil engineering due to their high mechanical strength, yet their non-ideal performance in ductile and compaction during the printing process always limits their further application. To improve the buildability and antisettling capability of 3D printing materials, a new cement-based 3DP material is proposed by partly replacing traditional hydroxypropyl methyl cellulose (HPMC) with anionic polyacrylamide (APAM). To compare the modifying effect of APAM to that of the cement-based 3DP (APAM-3DP) material, the printability, physical–mechanical performance of APAM-3DP material are tested, and the corresponding microstructural characteristics of mortars with different replacement ratios are analysed. The experimental results show that under the same dosage, APAM can reduce the fluidity of cement-based materials, shorten the setting time and slow down the hydration process compared with HPMC. Addition of the appropriate amount of APAM can improve the buildability of cement-based materials by 57 % and the compressive strength of the samples is increased by 7.7%, but the deformation rate is also doubled. When the APAM dosage is appropriate the samples were more prone to brittle failure and overall failure, if the APAM dosage is too large, the sample is prone to ductile failure and local failure. The modification mechanism of APAM was also analyzed from the microscopic pore characteristics and the morphology of hydration products of the samples.

Semiquantitative microscopic pore characterizations of the metamorphic rock reservoir in the central paleo-uplift belt, Songliao Basin

Currently, metamorphic rock is a common target for natural gas exploration, and reservoirs are the key factors restricting natural gas exploration and development in metamorphic rocks. The deep metamorphic rock gas reservoir in the central paleo-uplift of the northern Songliao Basin has good exploration and development potential. In this study, we use a combination of qualitative descriptions and quantitative analysis to comprehensively analyze the pore characteristics of the reservoir and explore the factors controlling the pore characteristics of the metamorphic rock reservoir in the central paleo-uplift belt of the Songliao Basin. The metamorphic rock reservoir in the central paleo-uplift belt contains three types of lithologies: chlorite schist, mica schist and mylonite, each with different protoliths and metamorphic histories. The results of high-pressure mercury intrusion and nitrogen adsorption indicate that the pore size distributions of the schist and mylonite differ. Compared with the mylonite, the schist has larger reservoir space, more heterogeneity, smaller pore size, larger specific surface area and larger adsorbed gas storage capacity. This paper also studies the formation process of the reservoir and divides it into four stages. Finally, this article discusses in detail the factors controlling the microscopic pore characteristics of metamorphic rock reservoirs in the central paleo-uplift belt; the metamorphic rock protolith is the most important controlling factor.

Research on Strength Prediction Model and Microscopic Analysis of Mechanical Characteristics of Cemented Tailings Backfill under Fractal Theory

In order to further study the internal relationship between the microscopic pore characteristics and macroscopic mechanical properties of cemented tailings backfill (CTB), in this study, mine tailings and ordinary Portland cement (PC32.5) were selected as aggregate and cementing materials, respectively, and different additives (anionic polyacrylamide (APAM), lime and fly ash) were added to backfill samples with mass concentration of 74% and cement–sand ratios of 1:4, 1:6 and 1:8. After 28 days of curing, based on the uniaxial compressive strength test, nuclear magnetic resonance (NMR) porosity test and the fractal characteristics of pore structure, the relationships of the compressive strength with the proportion and fractal dimension of pores with different radii were analyzed. The uniaxial compressive strength prediction model of the CTB with the proportion of harmless pores and the fractal dimension of harmful pores as independent variables was established. The results show that the internal pores of the material are mainly the harmless and less harmful pores, and the sum of the average proportions of the two reaches 73.45%. Some characterization parameters of pore structure have a high correlation with the compressive strength. Among them, the correlation coefficients of compressive strength with the proportion of harmless pores and fractal dimension of harmful pores are 0.9219 and 0.9049, respectively. The regression results of the strength prediction model are significant, and the correlation coefficient is 0.9524. The predicted strength value is close to the actual strength value, and the predicted results are accurate and reliable.

Influence of pore structural properties on gas hydrate saturation and permeability: A coupled pore-scale modelling and X-ray computed tomography method

Gas hydrate, as an alternate hydrocarbon source, has attracted significant attention in past decades. A precise estimation of permeability of the gas hydrate-bearing formation is essential for predicting the flow behaviors and the associated gas production performance. In this research, the influence of gas hydrate saturation on pore structural properties and then affect permeability was investigated using a three-dimensional micro X-ray computed tomography dataset that records an experiment of xenon hydrate formation in a sand pack at selected times during the experiment. Unlike the previous work, the goal of this work is to characterize pore space evolution, during gas hydrate formation, using a set of key microscopic pore characteristics, i.e. pore and throat radii, pore throat ratio, coordination number and tortuosity, by applying pore network analysis, on larger and therefore more representative sub-volumes. The same segmented volume of that dataset was used in this work to estimate gas hydrate saturation and permeability, recalculated by the lattice Boltzmann method, on those larger sub-volumes at selected snapshots. Besides, the analysis provides further insights into the links of gas hydrate localities and local pore characteristics and therefore their controls on the permeability. New evidence of semi-quantitative nature emerges that grain-coating gas hydrate formed at low gas hydrate saturations play a crucial role on reducing permeability, while pore-filling and/or cementing gas hydrate become dominating at high gas hydrate saturations, and these can be explained by gas hydrate formation mechanisms.