Search Results (24)

Concrete quality is essential for highway guardrails in mountainous terrain to overcome freeze–thaw cycles, and manufactured sand (MS) concrete is potentially a more sustainable construction material. This paper aims to optimize the mechanical strength and freeze-thaw resistance of MS concrete for highway guardrails. The effects of water-to-binder (W/B) ratio (0.38–0.42), air-entraining agent (AEA) (0–0.5‱), fly ash (FA) (10–30%) and binder contents (360–380 kg/m³) on the properties of MS concrete were investigated. The mechanism behind the factors was further studied with scanning electron microscopy (SEM) and mercury injection porosimetry (MIP). Results showed that increasing W/B ratio, AEA and FA contents led to the reduction of compressive strength, but improved freeze–thaw resistance by reducing the mass loss during the cyclic freeze–thaw. SEM and MIP illustrated that the increase in W/B ratio and AEA addition increased the pore volume and caused a more porous structure, but increasing FA and binder contents densified the structure of MS concrete. This is consistent with the evolution of compressive strength and freeze–thaw resistance. This study offers an optimization method to obtain MS concrete with good compressive strength and freeze–thaw resistance for highway construction. Full article

Reservoir evaluation in multi-source systems is challenging because studies generally follow single-source principles. This limitation has substantially hindered the understanding of reservoir and hydrocarbon accumulation processes in source–reservoir systems. This study examines the Dingbian area of the Ordos Basin, China, and investigates the key factors controlling hydrocarbon accumulation in the Chang 9 reservoir of the Triassic Yanchang Formation within a multi-source system. The study area spans approximately 0.9 × 10⁴ km². First, by comparing the biological markers in Chang 9 crude oil with those of potential source rocks, the oil source of the Chang 9 reservoir was identified. The study area was subsequently divided into three provenance zones—northeast, northwest, and central mixed source areas—based on heavy mineral content and the orientation of sedimentary sand bodies. Additionally, well logging data, oil production data, petrographic thin sections, scanning electron microscopy (SEM), and mercury injection porosimetry were used to investigate the reservoir characteristics, oil reservoir features, and crude oil properties across different source areas. The results indicate that the oil source of the Chang 9 reservoir in the Dingbian area is the Upper Chang 7 source rock. The northwest source area exhibits superior reservoir properties compared to the other two zones. In the northwest source area, lithology-structure oil reservoirs are predominant, whereas the central mixed source area is characterized by structural-lithology oil reservoirs, and the northeast source area predominantly features lithology-controlled reservoirs. From the northwest to the central mixed source areas, and finally to the northeast source area, crude oil density and viscosity increase gradually, while the degree of oil–water separation decreases correspondingly. Based on these findings, the study concludes that the distribution of structures, lithology, and source rocks significantly influences the Chang 9 reservoirs in the Dingbian area. The controlling factors of oil reservoirs differ across the various source zones. In multi-source systems, evaluating oil reservoirs based on source zones provides more precise insights into the characteristics of reservoirs in each area. This approach provides more accurate guidance for exploration and development in multi-source regions, as well as for subsequent “reserve enhancement and production increase” strategies. Full article

To address the issue of uneven shear strength distribution in dredged sediment during electroosmosis treatment, a grouting system was employed to inject CaCl₂ into the anode region and Na₂SiO₃ solution into the central region. An experimental study was conducted to examine the effect of injection timing on the electrochemical treatment of dredged sediment. Five experimental groups, each with different Na₂SiO₃ injection timings, were established. The impact of injection timing on the macroscopic electrochemical reinforcement was assessed based on current, drainage volume, settlement, moisture content, and shear strength. Additionally, the ion concentration of effluent from the cathode was measured, and scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were employed to analyze ion migration and pore characteristics. The results indicated that when CaCl₂ was injected into the anode at the start of the experiment and Na₂SiO₃ was injected into the central region after the current had decayed by 70% from its peak, the drainage volume reached its maximum. Under these conditions, the average shear strength increased from nearly 0 kPa to 48.2 kPa, yielding the optimal reinforcement effect. The strength in both the central and cathode regions also improved, and the strength distribution between the anode and cathode became more uniform, with the strength ratio decreasing from 1.91 to 1.65, thereby enhancing the overall soil strength distribution. The Na⁺ concentration in the cathode effluent was highest, suggesting that Na⁺ migration played a predominant role in electroosmotic drainage. Furthermore, the electrochemical reactions generated cementitious materials that effectively filled the soil pores. SEM imaging and MIP pore size analysis revealed a reduction in porosity and an increase in soil compaction. Full article

Top seals and overburden above reservoirs at geological carbon capture and storage (CCS) sites can be major concerns when they are at risk of being mineralogically and texturally unstable in the presence of high-pressure CO₂. Here we report on the pore systems, mineralogy, and surface area attributes of the Palaeocene Lista Shale, the caprock to the Mey Sandstone at the UK’s planned East Mey CCS site. The core was logged, and then mineral quantification was undertaken with X-ray powder diffraction mineralogy, light optics and electron microscopy analyses. Laser particle size analysis was used for grain size determination. Porosity, pore throat diameter, surface area and pore body size were measured via mercury intrusion porosimetry and nitrogen adsorption analyses. The mudstone facies from the Lista Shale are dominated by smectite-rich matrix and silt-grade quartz, with small quantities of chlorite and sodic-plagioclase. Chlorite, sodic-plagioclase, and even smectite are known to be capable of reacting with, and potentially leading to mineral sequestration of CO₂. The mean pore throat and pore body diameters are 17 and nearly 18 nm, respectively, showing that the Lista is mesoporous; the similarity of pore body and pore throat dimensions reveals a predominance of plate and slit pores. Gas adsorption analyses revealed that the overall pore structure is complex, with a high tortuosity of fluid movement through a complex clay-rich matrix (this equates to a mean fractal dimension D2 value of 2.67). Gas adsorption analyses have also shown that grain surfaces are moderately complex (rough) due to the dominance of clay aggregates (this equates to a mean fractal dimension D1 value of 2.56). D2 being higher than D1 suggests that there is a relatively low potential to physically store CO₂ gas on grain surfaces. Conversely, the ability of the CO₂ to react with minor quantities of chlorite and sodic plagioclase, or even with smectite, could lead to increasing surface area of the remaining shale minerals with newly exposed reactive silicates leading to further enhanced mineral trapping of the injected CO₂. The restricted pore throat size linked to small grain size and poor sorting, and reflected by the high fractal D2 value, plus limited grain surface complexity, reflected by the low fractal D1 value, collectively suggest that mineral trapping of the injected CO₂ would be relatively slow (on the order of 1000s of years) if CO₂ penetrated the top seal. Full article

Five different lignocellulosic raw materials (coconut shells, Moso bamboo, sawtooth oak, Chinese fir, and Masson pine) were used to prepare activated carbons by steam activation at 850 °C to evaluate the effects of their structures on physical activation. The chemical compositions, botanic forms, and pore structures of the lignocellulose-based charcoal samples were systematically characterized by proximate and ultimate analyses, scanning electron microscopy, and mercury injection porosimetry. It was found that the rate of the activation reaction between charcoal and steam is determined by the porosity of the precursor. Pore structure results show that the steam activation of coconut shell and bamboo charcoals primarily produced micropores, thus yielding microporous activated carbon materials with just a few mesopores, even following a high burn-off of >66%. The steam activation of sawtooth oak charcoals produced mainly micropores at a low burn-off of <50% and both micropores and mesopores at a high burn-off of >50%. The steam activation of Chinese fir and Masson pine charcoals produced mainly mesopores at a burn-off of 0–80%. These mesopores were remarkably broadened to >20 nm on extending the activation time, resulting in a high vitamin B12 (VB12) adsorption capacity of ~530 mg/g. In conclusion, the raw lignocellulosic materials used as precursors have a decisive effect on the development of pore structures in activated carbon materials obtained through physical activation. Full article

To study the influence of gas pressure on coal permeability evolution, we conducted experiments on coal samples from the No. 9 coal seam in Tangshan Coal Mine, Hebei Province, China. Different gas pressures (helium and nitrogen) were applied, and nitrogen-induced deformations were measured. We also analyzed the coal samples’ pore structure using mercury injection porosimetry, obtaining pore surface fractal dimensions. The increase in nitrogen pressure from 0.3 MPa to 3 MPa resulted in an elevation of adsorption strain from 0.168 × 10⁻³ to 1.076 × 10⁻³, with a gradual decrease observed in the extent of this increase. However, the permeability of coal samples initially decreased from 16.05 × 10⁻¹⁸ m² to 4.91 × 10⁻¹⁸ m² and subsequently rose to 5.69 × 10⁻¹⁸ m². Helium showed similar trends to nitrogen, with average permeability 1.42–1.88 times higher under the same pressure. The lowest permeability occurred at 1.5 MPa for helium and 2.5 MPa for nitrogen. Gas absorptivity plays a crucial role in coal permeability evolution. Additionally, we observed coal’s compressibility to be 7.2 × 10⁻¹¹ m²/N and corrected porosity to be 53.8%, considering matrix compression. Seepage pores larger than 100 nm accounted for 80.4% of the total pore volume, facilitating gas seepage. Surface fractal dimension D_s1 correlated positively with micropore volume, while D_s2 and D_s3 correlated negatively with pore volume and gas permeability. Full article

The tectonically deformed coal (TDC) reservoirs with abundant gas resources and low permeability are expected to become one of the target coal seams for carbon dioxide geological storage-enhanced coalbed methane recovery (CO₂-ECBM). The pore–fracture structure plays a crucial role in determining the effectiveness of CO₂ storage. Fractal analysis provides a valuable approach to quantitatively describe the complex and heterogeneous pore–fracture structures across various scales in coal matrixes. Accordingly, the TDC samples in the Huainan–Huaibei coalfield and primary-undeformed coal (PUC) samples in the Qinshui Basin were selected for pore–fracture structure parameter tests using the mercury intrusion porosimetry (MIP) and low–temperature nitrogen adsorption (LNA) methods. Their multiscale pore–fracture parameters were analyzed using different fractal methods based on pore diameter. According to the fractal results, a multiscale classification standard for pore–fracture structures was devised in this study that is suitable for the controlling gas migration process. A parameter of 8 nm is set as the separating pore diameter for gas migration and storage. It was observed that the connectivity of migration pores (>8 nm) in TDC samples was stronger compared to PUC samples, reflected in larger pore volumes and smaller fractal dimensions. However, its complex development of seepage pores (150–300 nm) may hinder the flow of CO₂ injection. As for the storage pores (<8 nm), the fractal dimension of the 2–8 nm pores in TDC was found to be similar to that of PUC but with larger pore volumes. The fractal dimension of the filling pores (<2 nm) in TDC samples was relatively lower, which facilitates efficient gas volume filling. Therefore, the pore–fracture structure of the TDC samples is found to be more advantages for CO₂ injection and storage compared to the PUC. This suggests that TDC reservoirs holds promising geological potential for CO₂-ECBM implementation. Full article

Exploring the compressibility of the deeply buried marine shale matrix and its controlling factors can help achieve efficient petroleum production. Taking ten sets of deeply buried marine shale core samples from Ning228 wells in the Yanjin area as an example, the matrix compressibility and pore characteristics of deeply buried marine shale reservoirs were investigated by applying mercury intrusion porosimetry (MIP) and nitrogen adsorption/desorption isotherms at a low temperature of 77 K. Mathematical models (based on MIP and nitrogen adsorption/desorption isotherms) were established to analyze the effects of TOC, mineral components, and pore structure on matrix compressibility. The relationship between the compressibility coefficient and the brittleness index was also established. The results show that the compressibility of the shale matrix is significant when the mercury injection pressure ranges from 8.66 to 37 MPa. For deeply buried marine shale, the matrix compressibility is in the range of 0.23 × 10⁻⁴–22.03 × 10⁻⁴ MPa⁻¹. The influence of TOC and minerals on matrix compressibility is mainly reflected in the control effect of pore structure. High TOC content decreases the overall shale elastic modulus, and high clay mineral content enhances shale stress sensitivity, resulting in a significant matrix compressibility effect. For the effect of pore structure on compressibility, the pore content in shale has a positive effect on matrix compressibility. In addition, the pore-specific surface area is critical to the effective variation of shale matrix compressibility, indicating that the complexity of the shale pore structure is a key factor affecting matrix compressibility. Full article

Transitional upper carboniferous Shanxi Formation coal-bearing strata in Qinshui Basin have been proven to be a set of mixed unconventional gas-bearing reservoirs forming a multi-superimposed gas system that consists of multiple independent fluid pressure systems vertically through the strata. An experimental protocol was designed to compare the pore networks in high-rank coal, shale, and tight sandstone reservoirs from Shanxi Formation using quantitative and qualitative experimental methods, including high-pressure mercury injection porosimetry (MIP), low-pressure nitrogen gas adsorption (LN₂GA), and argon ion polishing–field emission scanning electron microscope (AIP-FESEM). The results show that genetic and structural differences in pore types, morphology, abundance, and proportion in coal, shale, and tight sandstone reservoirs are significant, reflecting strong heterogeneity characteristics. Pore networks determine the roles of different types of reservoirs in gas-bearing systems through differentiated pore structure, development degree, and spatial distribution. Due to the differences in nanopore development and connectivity, coal and tight sandstone reservoirs provide important reservoir spaces for adsorbed and free gas in the system. Thus, they become influential factors controlling the relationship between the gas-bearing subsystems with different fluid pressures. The lack of mesopores in shale and relatively weaker heterogeneity between layers lead to the phenomenon that continuously developed shales of a specific thickness are more likely to be the interlayers that divide the superimposed gas-bearing system. Systematic comparison of pore development characteristics will provide scientific support to further explain the formation mechanism of multi-superimposed gas systems in coal-bearing strata from the perspective of pore networks and provide guidance for the development of unconventional natural gas in coal-bearing strata. Full article

During diagenesis, the transformation of unconsolidated sediments into a sandstone is usually accompanied by compaction, water expulsion, cementation and dissolution, which fundamentally control the extent, connectivity and complexity of the pore structure in sandstone. As the pore structure is intimately related to fluid flow in porous media, it is of great importance to characterize the pore structure of a hydrocarbon-bearing sandstone in a comprehensive way. Although conventional petrophysical methods such as mercury injection porosimetry, low-pressure nitrogen or carbon dioxide adsorption are widely used to characterize the pore structure of rocks, these evaluations are based on idealized pore geometry assumptions, and the results lack direct information on the pore geometry, connectivity and tortuosity of pore channels. In view of the problems, X-ray micro-CT was combined with ImageJ software (version 1.8.0) to quantitatively characterize the pore structure of Berea Sandstone. Based on its powerful image processing function, a series of treatments such as contrast enhancement, noise reduction and threshold segmentation, were first carried out on the micro-CT images of the sandstone via ImageJ. Pores with sizes down to 2.25 μm were accurately identified. Geometric parameters such as pore area, perimeter and circularity could thus be extracted from the segmented pores. According to our evaluations, pores identified in this study are mostly in the range of 30–180 μm and can be classified into irregular, high-circularity and slit-shaped pores. An irregular pore is the most abundant type, with an area fraction of 72.74%. The average porosity obtained in the image analysis was 19.10%, which is fairly close to the experimental result determined by a helium pycnometer on the same sample. According to the functional relationship between tortuosity and permeability, the tortuosity values of the pore network were estimated to be in the range of 4–6 to match the laboratory permeability data. Full article

Investigation on the pore-fracture features and crack propagation behavior of coal is necessary to prevent coal mine disasters. The pore structure features of coal samples taken from high gas seam were obtained by mercury injection porosimetry (MIP) and gas adsorption methods. The process of deformation and failure for coal samples under three-point bending conditions were obtained. The results demonstrate that the adsorption pores with diameter less than 100 nm are the most developed and their surfaces are the roughest (the average surface fractal dimension D_s is 2.933). The surface of micro-cracks is smoother (D_s is 2.481), which is conducive to gas seepage. It may be the explanation for that 14-3# coal seam is a high gas seam, while there was almost no gas outburst accident so far. At the initial stage of crack propagation, the main crack on the coal sample expanded along the direction of the natural cracks. In the process of crack propagation, the surface fractal dimension of the main crack increased, suggesting that the bending degree of the main crack enhanced. The brittle characteristics of coal samples can be reflected by the ratio of the dissipated energy to the accumulated energy. Full article

It is well known that underground in situ pyrolysis technology for oil shale production is a promising field. In the in situ modification mining process, the permeability property of a shale matrix has a great effect on the transport capacity of pyrolytic products. For oil shale undergoing pyrolysis, the changes of internal structure (fracture and pore space) have a considerable influence on the permeability network which further affects the migration of hydrocarbon products. In this study, based on an oil shale retorting experiment performed under different temperatures (20 °C, 100 °C, 200 °C, 300 °C, 325 °C, 350 °C, 375 °C, 400 °C, 425 °C, 450 °C, 475 °C, 500 °C, 525 °C, 550 °C, 575 °C, 600 °C), an investigation on the distribution characteristics of the fractures was conducted using micro-CT technology. Meanwhile, mercury injection porosimetry was used to characterize the pore structure of the oil shale samples under different temperatures. Finally, a fracture-pore dual medium model was constructed to calculate the percolation probability to quantitatively describe the permeability variation of oil shale with temperature. The test results indicated that the higher the temperature, the larger were the pore spaces. The increase in pore volume due to pyrolysis temperatures mainly affected the pores ranging from 10 nm to 100 nm and occurred in the specific temperature range (400 °C to 425 °C). Additionally, CT images show that the fracture morphology varied with increasing temperature and the number and length of fractures at different temperatures were in great accordance with the fractal law statistically. On the other hand, simulation of the percolation probabilities discovered that in a single pore media model over the whole range of tested temperatures they were too low to exceed the threshold. In contrast, in the dual medium model, the theoretical threshold of 31.16% was exceeded when the temperature reached 350 °C. Moreover, the results demonstrated that fractures dominated the seepage channel and had more significant effects on the permeability of oil shale. What has been done in this study will provide some guidance for the in situ fluidization mining of oil shale. Full article

Permeability in porous media has an important role in many engineering applications, which depends mainly on the pore size, distribution, and connectivity of porous media. As the pore structure distribution of coal has a multi-scale fractal dimension characteristic, this study aimed to propose a multi-scale fractal dimension characteristics units model (MFU) to describe the pore structure distribution by analyzing the multi-scale fractal dimension characteristics of coal pore media. Then, a multi-scale fractal permeability model was established based on MFU. The pore structure distribution was obtained by mercury injection porosimetry (MIP) and nuclear magnetic resonance (NMR) experiments. Based on MIP and NMR experimental data, the permeability contribution of different pore diameters were calculated. The results show that the permeability contribution of the micropore was minimal and can be ignored. The permeability contribution of mesopores was about 1–5%, and the permeability contribution of macropores was about 95–99%, which plays a decisive role in the seepage process. The calculated results, based on multi-scale fractal permeability model and the experimental permeability data, are in the same order of magnitude. The permeability prediction based on proposed model is better than classical single fractal permeability model. Full article

This study is predominantly about the differences in shale pore structure and the controlling factors of shale gas content between Lower Silurian and Lower Cambrian from the upper Yangtze plate, which are of great significance to the occurrence mechanism of shale gas. The field emission scanning electron microscopy combined with Particles (Pores) and Cracks Analysis System software, CO₂/N₂ adsorption and the high-pressure mercury injection porosimetry, and methane adsorption were used to investigate characteristics of overall shale pore structure and organic matter pore, heterogeneity and gas content of the Lower Paleozoic in southern Sichuan Basin and northern Guizhou province from the upper Yangtze plate. Results show that porosity and the development of organic matter pores of the Lower Silurian are better than that of the Lower Cambrian, and there are four main types of pore, including interparticle pore, intraparticle pore, organic matter pore and micro-fracture. The micropores of the Lower Cambrian shale provide major pore volume and specific surface areas. In the Lower Silurian shale, there are mesopores besides micropores. Fractal dimensions representing pore structure complexity and heterogeneity gradually increase with the increase in pore volume and specific surface areas. There is a significant positive linear relationship between total organic carbon content and micropores volume and specific surface areas of the Lower Paleozoic shale, and the correlation of the Lower Silurian is more obvious than that of the Lower Cambrian. The plane porosity of organic matter increases with the increase in total organic carbon when it is less than 5%. The plane porosity of organic matter pores is positively correlated with clay minerals content and negatively correlated with brittle minerals content. The adsorption gas content of Lower Silurian and Lower Cambrian shale are 1.51–3.86 m³/t (average, 2.31 m³/t) and 0.35–2.38 m³/t (average, 1.36 m³/t). Total organic carbon, clay minerals and porosity are the main controlling factors for the differences in shale gas content between Lower Cambrian and Lower Silurian from the upper Yangtze plate. Probability entropy and organic matter plane porosity of the Lower Silurian are higher than those of Lower Cambrian shale, but form factor and roundness is smaller. Full article

This article presents a novel methodology for data integration including laboratory data, the results of standard well logging measurements and interpretation and the interpretation of XRMI imager data for determination of the porosity and permeability of the fracture system in carbonate rock. An example of the results of the micro computed tomography applied for carbonate rock is included. Data were obtained on the area of the Polish Lowland Zechstein Main Dolomite formation. The input set of data included the results of mercury injection porosimetry (MICP), thin section and polished section analysis, well logging measurements and comprehensive interpretation and micro computed tomography. The methodology of the macrofractures’ analysis based on borehole wall imagery as well as estimation of their aperture was described in detail. The petrophysical characteristics of the fracture systems were analyzed as an element of standard interpretation of well logging data along a carbonate formation. The results of permeability determination, with micro-, mezzo- and macrofractures’ presence in the rock taken into consideration, were compared with outcomes of the drill stem tests (DSTs). Full article