Interparticle Pores Research Articles

Laboratory investigation on effects of solid waste filler on mechanical properties of porous asphalt mixture

The utilization of solid waste materials in pavement construction has become a trend with the increasing awareness of sustainable infrastructure construction. Among them, the use of some powder solid waste as the alternative filler in asphalt mixture has attracted the attention of many researchers. As is known to all, filler plays an important role in the performance of asphalt mixture, and the great difference between solid waste filler and mineral powder will lead to unpredictable performance changes of asphalt mixture. However, the current research on the changes in mechanical properties of asphalt mixture after the use of solid waste filler is very limited, especially for Porous Asphalt (PA) mixture, which undoubtedly hinders the application of solid waste materials in pavement engineering. Therefore, limestone powder and three types of solid waste fillers (fly ash, diatomite, and red mud) were selected to prepare four types of PA mixtures in this paper. Then, Cantabro test, Hamburg Wheel Tracking (HWT) test, Indirect Tensile Strength (ITS) test, Semi-circular Bending (SCB) test, and Fourier Transform Infrared Spectroscopy (FTIR) test were carried out to comprehensively evaluate the raveling resistance, rutting resistance, moisture susceptibility, crack resistance and anti-aging ability of PA mixtures with different fillers. The results showed that fly ash had a positive but not significant effect on the performance of asphalt mixture. Porous fillers like diatomite and red mud significantly enhanced the bonding performance, strength, stiffness, and aging resistance of asphalt mixture due to the super adsorption and hardening effect on asphalt binder. Meanwhile, it was found that red mud had the anchoring and toughening effect with the SBS modifier due to its interparticle pore structure, which was different from the simple hardening and embrittlement effect of diatomite. Also, the selected red mud contained a certain amount of active Na2O, which was unfavorable to the moisture resistance, but still met the specification requirement. This study is of great significance for understanding the influence mechanism of filler on asphalt mixture and the utilization of red mud waste in asphalt pavement engineering.

Pore structure characteristics and their influencing factors: A case study from the middle jurassic mixed siliciclastic carbonate rocks, Turpan-Hami basin, Northwest China

The mixed siliciclastic-carbonate rocks of the second member of the Qiketai Formation (J2q2) in the Turpan-Hami Basin are lacustrine tight oil reservoir with vitrinite reflectance values (%, Ro) ranging from 0.64% to 0.81%. X-ray diffraction (XRD), thin sections, field emission scanning electron microscopy (FE-SEM) of argon-milled thin sections, low-temperature N2 adsorption (LNTA), and nuclear magnetic resonance (NMR) analyses were performed to investigate the pore structure characteristics and their influencing factors of the mixed siliciclastic-carbonate reservoirs. The results show that the tight reservoir has a medium-high total organic carbon (TOC) content, and the sedimentary textures include laminated, massive, and intraclasts-rich types. Nanometer scale interparticle pores and microfractures are dominant in the tight reservoirs. The small pores (2–100 nm) make a dominant contribution to the nanoscale storage space according to the comprehensive analysis of the T2 spectra of NMR. Reversed S-shaped isotherms obtained from N2 adsorption are type IV, and hysteresis loops indicate that the shape of pores include slit-or plate-like, ink-bottle-shaped and mixtures of the two. BET surface areas and BJH total pore volume vary from 1.707 m2/g to 8.556 m2/g and 1.13 cm3/100 g to 3.0 cm3/100 g, with an average of 4.31 m2/g and 1.848 cm3/100 g, respectively. The massive and intraclasts-rich rocks have higher NMR porosities, pore sizes and pore volumes than the laminated rocks. Based on the Frenkel-Halsey-Hill model of low-temperature N2 adsorption, the fractal dimensions D1 and D2 are 2.4305–2.7081 and 2.2667–2.6070, respectively. The correlations between the pore structure parameters and the mineralogical composition, TOC content, and fractal dimension reveal that dolomite makes greater contribution to the pore volume and movable fluid saturation than the siliciclastic gains and organic matter, resulting in higher fractal dimensions and more complicated pore structure. In addition, the clay minerals increase pore specific surface area and its complexity in the tight reservoirs. The samples with high silicate mineral and TOC contents tend to contain lower specific surface areas and pore volumes, resulting in lower fractal dimensions and more simplistic pore structure than clay rich samples. Therefore, the complex mineralogical composition, various sedimentary textures and organic matter content all play important roles in the development of pore network.

Freeze-Thaw Performance of Silt Sand Treated with Lignin

In cold regions, freeze-thaw action poses a significant hazard to road engineering. In order to avoid the adverse effects of inorganic materials on soil modification, we applied lignin, which is an environmentally friendly and organic polymer, to improve the silt sand from cold regions. The significance of this study is to facilitate the better application of lignin. The macroscopic engineering properties of the soil showed that, before freeze-thaw, as the lignin content increased, thermal conductivity and permeability decreased, pH first increased rapidly and then stabilized between 10 and 11, and dynamic resilient modulus first increased then decreased; after freeze-thaw, as lignin content increased, thermal conductivity and permeability decreased, and dynamic resilient modulus first increased then decreased. The freeze-thaw action reduced the thermal conductivity and dynamic resilient modulus of silt sand treated with lignin and increased its permeability. The test results of soil microstructure indicated that, before freeze-thaw, the silt sand and silt sand treated with lignin were structurally compact; after freeze-thaw, the silt sand showed numerous cracks and pores and had a loose soil structure, whereas the silt sand treated with lignin showed fewer cracks and pores, and its soil structure was more compact under the encapsulation and filling action of cementitious materials. No new chemical elements, mineral components, or functional groups were produced when lignin was mixed with silt sand. The mechanism by which lignin improved the macroengineering properties of silt sand involved the cementitious material produced by the interaction between lignin and soil minerals, which encapsulated the soil particles and filled the interparticle pores. Research results can provide a theoretical reference for engineering application of lignin in cold regions.

Shale lithofacies controls on porosity and pore structure: An example from Ordovician Goldwyer Formation, Canning Basin, Western Australia

The hydrocarbon storage and transport capacity of shale reservoirs are dependent on its complex pore systems. This study focuses on Ordovician Goldwyer Formation (Goldwyer shale) from Canning Basin, Western Australia. Multi-scale qualitative (X-ray diffraction, field emission scanning electron microscope, TESCAN integrated mineral analyser (TIMA) and thin-section analysis) and quantitative (Rock-Eval® pyrolysis, helium porosity on crushed samples, low-pressure gas adsorptions (N2 and CO2) and mercury injection capillary pressure (MICP)) approaches were applied on shale samples. The results indicate that the Goldwyer shale comprises five main lithofacies (namely organic-rich shale, argillaceous shale, siliceous shale, calcareous shale, and mixed shale) based on mineral composition and total organic carbon (TOC) content. The organic-rich and siliceous shales have highest porosity (>10%) followed by mixed shale and other lithofacies. Three types of pores, namely organic pores, interparticle, and intraparticle pores, are identified in Goldwyer shale. Most of the pores are narrow slit-like or bottle-necked shaped pores. The micropore and mesopore volumes and specific surface area (SSA) of all lithofacies are positively related to TOC except for the argillaceous shale. Conversely, the micro and mesopore parameters (SSA and pore volumes) exhibited inverse relations with total clay content for all lithofacies except argillaceous shale. This indicates that the total clay and TOC content is the main controlling factors for pore structure of Goldwyer shale. The whole pore aperture exposed that mesopores are more abundant in Goldwyer shale; however, few micro and macropores are also found in different lithofacies. The organic-rich, siliceous and mixed shales could be deemed as the most essential lithofacies types for fluid flow via pore systems due to high porosity and feasible pore structures.

Pore characteristics and pore structure deformation evolution of ductile deformed shales in the Wufeng-Longmaxi Formation, southern China

Marine shales in southern China experiences multiple complex tectonic movements, which highly affects shale pore characteristics and pore evolution. The effects of tectonic deformation on nanopore structure and petrophysical properties of organic shales remain unclear. Three ductile deformed shale samples were collected and analyzed through an integrated experiment procedure for a comparative research against undeformed shale samples. Field emission-Scanning electron microscopy (FE-SEM), low pressure N2 and CO2 adsorption and mercury injection porosimetry (MIP) analyses were performed to characterize pore structure of the shales. The results reveal that the mineral compositions of these shale samples are controlled by sedimentary environment and source and exhibits no obvious relationship with tectonic deformation. With increasing deformation degree, the micropore proportion gradually decreases (from 17% to 6%), and the macropore proportion increases from 16% to more than 20%. Micropore volumes and proportion in the fold core samples are the smallest (4.2 × 10−3 cm3/g and 6.3%) and account for only one-third of the undeformed shale values, while the meso- and macropore values are larger-1.2 times those of the undeformed shale values. The evolution characteristics and deformation modes of organic matter (OM), interparticle (interP) and intraparticle (intraP) pores and microfractures under ductile deformation were examined. All pore types become interconnected during deformation and form microfractures ranging from a few nanometers to tens of microns, which is the main reason for the enhanced shale connectivity caused by deformation. Under the same porosity conditions, the deformed shale permeability is much higher than the undeformed shale permeability, and stronger deformation corresponds to higher permeability. The fold core permeability is generally higher than the limb permeability and exceeds 30 times. The different ductile deformation positions were divided into five levels, and the corresponding reservoir quality was evaluated. This study is of great significance to better understand the pore structure evolution process for shale exploration and development under tectonic deformation.

Insights into the Pore Structure of Strong Heterogeneous Carbonates in the Mesopotamian Basin

The Cretaceous Late Cenomanian-Early Turonian Mishrif Formation carbonates in the Mesopotamian Basin are characterized by complex pore systems, resulting in strong reservoir quality heterogeneity. Major factors that constitute the complexity of pore structure are types, geometries, and topologies of pores and pore-throats. These factors and the effect of pore structure on reservoir quality were investigated by integration of thin sections, petrographic image analyses, porosity, permeability, and mercury injection capillary pressure measurements. Eight matrix-related and three matrix-unrelated pore types, which are dominated by secondary pores, are identified in the Mishrif carbonates. Pore sizes range from a few microns to more than 1 cm and vary greatly both in the same and in different pore types. Pore shapes range from better circularity and simple boundaries to irregular complex boundaries and similar for the same pore type. Pore-throat radii (PTR) range from 3 nm to 124 μm, and micro pore-throats occur in all carbonates in different proportions. Pore-throat systems show strong heterogeneity and are classified into six classes based on their size distribution characteristics. Carbonate porosity is not solely correlated with pore sizes because pore abundance is another independent factor to determine porosity. Permeability is controlled by PTR rather than pore sizes, and R40 (PTR corresponding to the 40th percentile of mercury saturation) is the most correlated PTR to permeability. There is no apparent correlation between pore size and PTR except for the interparticle pores. Both pore sizes and PTR distributions can reflect reservoir microscopic heterogeneity due to their positive correlations for all pore types other than micropores (pore diameter less than 30 μm).

Evaluation of the fluids saturation in a multi-layered heterogeneous carbonate reservoir using the non-archie water saturation model

The evaluation of fluids saturation represents a continuous challenge in all reservoirs specially the carbonate ones. The variation of the pore structure in the carbonate reservoirs is one of most important factors affecting the determination of the fluids’ saturation. Focke (Focke and Munn, 1987) et al. showed that the variations of the pore structure result in variations of the cementation exponent (m) in the Archie and the modified-Archie water saturation models. They showed that the difference between inter-particle and vuggy pore system results in a variation in (m) of 2 versus (m) of 4. They also found that the fractures porosity has an effect opposite to the vuggy porosity resulting in (m) to be lower than 2.A complex carbonate reservoir in the Middle East composed of twenty-nine layers and sub-layers has complex pore structure, varying laterally and vertically, across the reservoir. To capture this variability based on Focke's findings, the cementation exponent (m) is measured in the laboratory using multiple core plugs representing all layers and the sub-layers. The values of (m) in this reservoir varied between 1.8 and 2.2 confirming combination of fractures, inter-particle, and small vuggy porosity.To calculate the water saturation in this reservoir, the Archie-based Simandoux water saturation model is used where the cementation exponent (m) values are changed on layer-by-layer basis to reduce the uncertainties in the water saturation. This approach represents an economical burden and a technical challenge due to the need to have measured values of the exponent (m) for every drilled well to capture the complexity and the heterogeneity of the reservoir.Recently, Oraby, 2020) developed a non-Archie water saturation model to determine the formation water saturation in conventional reservoirs based on a modification and a generalization of the (Passey et al. 1990, 2010, 2012). Total Organic Carbon, TOC, model that is used in determining the organic richness of the unconventional reservoirs. This model has the advantages of not requiring any of the Archie electrical parameters (a, m, n) or the formation water resistivity Rw.The Oraby non-Archie water saturation model is applied and tested in this complex reservoir. To examine the validity of the Oraby model, the Oraby water saturation model is equated with the Simandoux Archie-based model to back calculate the cementation exponent (m). The calculated values of the exponent (m) are compared to the core measured. The model also pointed out to other variations in (m) that were not captured during the sampling of the core plugs.In this paper, the applications of the Oraby non-Archie model are discussed and comparisons between the calculated cementation exponent (m) with the core measured values are shown and proved the validity of the model.

Evaluation of pore properties in coal through compressibility correction based on mercury intrusion porosimetry: A practical approach

As a commonly used method to evaluate the pore structures of coal, uncorrected MIP data may cause the results to be highly overestimated. In this study, a series of experiments were carried out to characterize the accurate pore structure of coal including MIP, low pressure N2/CO2 adsorption, scanning electron microscopy (SEM) and X-ray computed microtomography (μCT). Base on the process of mercury penetrate the pore by driven-pressure, it is clear that the mercury intrusion under high pressure can induce the coal matrix compression. Meanwhile, the MIP error (from 36.1% to 130.9% of the pore volume) was derived from coal matrix compression at the high pressure, and the interparticle pore and pockmark effects under low pressure. Here, a new and more practical pore volume correction method was proposed by simplifying the coal matrix compressibility calculation. The new method was tested to be valid for the tested coals with comparison of reported corrected data. The relationship model between intrusion pressure of mercury and pore diameter was revised by the pore morphology. The interparticle pores and pockmark effects mainly occur in the pressure range less than 0.01 MPa. In order to minimize the interparticle pores effect and pockmark effect, a new sample preparation method is recommended for MIP test. This study provides a practical approach to characterize the coal pore structure accurately using the MIP technique and the findings are impactful for the future gas transport modeling in various coals.

The characteristics and origins of thief zones in the Cretaceous limestone reservoirs of Central and southern Mesopotamian Basin

Thief zone is a common reservoir unit with super permeability developed in giant carbonate reservoirs and readily leads to the breakthrough of fluids bring the challenge to water flooding development or tertiary oil recovery. To provide insight into the characteristics and origins of thief zones in Cretaceous carbonate reservoirs in Central and Southern Mesopotamian Basin, core analyses, well log, and production performance data analyses were performed in three formations from two giant oilfields. Thief zones are indicated and located by higher water injection and liquid production rates and classified based on their sedimentary environment, that is, rudist shoal thief zone (RS-TZ), tidal channel thief zone (TC-TZ), and bioturbated-associated thief zone (BS-TZ). Both RS-TZ and TC-TZ are characterized by similar or higher porosity, much higher permeability, and much larger pore-throat radii than overlying and underlying adjacent non-thief zones. The RS-TZ comprises microfacies of rudist rudstone and rudist grainstone with interparticle pores, interparticle dissolved pores and vugs. It occurs in the upper-middle section of the uppermost rudist shoal in the shoal complex, shows the sheet-shaped horizontal distribution in the late highstand system tract of the field. The TC-TZ comprises microfacies of bioclastic grainstone with interparticle pores and few interparticle dissolved pores, and presents banded horizontal distribution. The BS-TZ went through strong bioturbation within hardground substrate leading to the great difference of microfacies, pore types and pore structures in burrows and matrix, and this type has lower porosity but much higher permeability than adjacent reservoirs. The key to developing the thief zones is to form the great permeability difference between the thief zone and its adjacent reservoirs. The origins of the three types of thief zones can not only be attributed to the primary porosity having well-connected pore structures resulted from high-energy sedimentary facies or high-energy sediments filling bioturbation-associated burrows, and freshwater dissolution in the eogenesis stage also enlarged the pores and pore-throat sizes and further improved pore connectivity, which enhanced the porosity and significantly improved permeability. Due to the difference in rock textures, pore structures and sedimentary successions, the three types of thief zones have different well log response characteristics which could be used for thief zone identification in non-coring wells and other oilfields that occurred the similar thief zones.

Controls of Distinct Mineral Compositions on Pore Structure in Over-Mature Shales: A Case Study of Lower Cambrian Niutitang Shales in South China

Investigating the impacts of rock composition on pore structure is of great significance to understand shale gas occurrence and gas accumulation mechanism. Shale samples from over-mature Niutitang formation of Lower Cambrian in south China were measured by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), low pressure N2 and CO2 adsorption to elucidate the controls of distinct mineral composition on pore development. Two distinct lithofacies, namely siliceous shale and argillaceous shale, were ascertained based on their mineral composition. Due to the variability of mineral composition in different lithofacies, pore structure characteristics are not uniform. Pores in siliceous shales are dominated by interparticle pores and organic matter (OM) pores, among which the interparticle pores are mainly developed between authigenic quartz. Furthermore, most of these interparticle pores and cleavage-sheet intraparticle pores within clay minerals are usually filled by amorphous organic matter that is host to OM pores. Due to the lack of rigid minerals, argillaceous shale was cemented densely, resulting in few interparticle pores, while cleavage-sheet intraparticle pores within clay minerals are common. Comparing siliceous shales with argillaceous shales, specific surface areas and pore volumes are higher on the former than on the latter. The content of total organic carbon (TOC) and authigenic quartz have a great influence on micropore structures, but less on mesopore structure for siliceous shales. The rigid framework structure formed by authigenic quartz is believed to be able to prevent primary interparticle pores from mechanical compaction and facilitate the formation of organic matter-associated pores. In terms of argillaceous shales, due to the lack of authigenic quartz, interparticle pores were rarely developed and its pore structure is mainly controlled by illite content.

X-ray Computed Microtomography Characterization of Ti6Al4V/CoCrMo Biomedical Composite Fabricated by Semi-solid Sintering

The semi-solid sintering of a novel Ti6Al4V/CoCrMo biomedical composite was investigated for the first time by semi-in situ X-ray computed microtomography. Composite was fabricated by dry mixing 15 vol% CoCrMo reinforcing particles with Ti6Al4V particles as matrix. The mixture was poured into a 1 mm diameter quartz capillary. 3D images of the same sample were acquired before and after sintering at different temperatures between 1050 and 1130 °C. Qualitative and quantitative analysis of the 3D images was carried out to observe the evolution of the microstructure. Formation and evolution with temperature of eutectic phase were monitored. It was found that the eutectic reaction started between Ti6Al4V and CoCrMo particles at 1050 °C, first in the contact area and then the liquid of eutectic phase was distributed over the surface of Ti6Al4V particles and filled the interparticle pores. Size and sphericity of Ti6Al4V and CoCrMo particles diminished as the volume fraction of eutectic phase increased. After sintering at 1130 °C most of CoCrMo particles disappeared because they react with Ti6Al4V to form the Ti2Co phase. Porosity is reduced 15% mainly by reducing the smaller pores that can be filled by the eutectic phase. Thus, it was concluded that semi-in situ X-ray computed microtomography is an effective tool to investigate the semi-solid state sintering and to analyze the microstructure evolution and densification mechanisms.

Micron-Nano Pore Structures and Microscopic Pore Distribution of Oil Shale in the Shahejie Formation of the Dongying Depression, Bohai Bay Basin, Using the Argon-Scanning Electron Microscope Method

To investigate the pore structure of shale oil reservoirs, seven organic-rich shales from the Shahejie Formation in the Dongying Depression were studied by rock pyrolysis analysis, X-ray diffraction analysis and scanning electron microscopy with argon ion beam polishing. The proportions of the different types of pores at different scales, the statistical relationships between the mineral contents and pore development, and the development of pores in the mineral laminae combination were discussed. The results demonstrated that the nanometer to micron pore structures were divided into intraparticle pores, interparticle pores, intercrystalline pores, organic pores, microfissures and diagenetic contraction fractures. Interparticle pores and intraparticle pores are both essential components of the sample pores. The original residual pores are mainly small pores and mesopores, while the secondary dissolution pores are primarily mesopores and macropores. For different pore sizes, there are small surface pore contributions of diagenetic contraction fractures, microfissures, intercrystalline pores, and organic pores. The carbonate minerals content controls the oil storage capacity of shale by dominating the development of the various pore types, while the clay mineral bands content can affect the permeability of shale by influencing the development of large-scale microfissures. In the laminae development sample, surface pore development is closely related to the sedimentary mineral microcircle, which consists of a falling semicycle and a rising semicircle. The total surface porosity, including microfissures, diagenetic contraction fractures, interparticle pores and intraparticle pores, mainly developed at the intersection of the rising semicircle and the falling semicircle, and this development corresponds to the highest level of a cycle. In summary, interparticle pores and intraparticle pores are the main components of pores developed in low thermal maturity shale and shale laminae where their heterogeneity is influenced by mineral composition and laminae microcircles.

Investigation on petrophysical properties of fractured tight gas sandstones: a case study of Jurassic Xujiahe Formation in Sichuan Basin, Southwest China

Integrated characterization methods from micro-scale to macro-scale were applied to thoroughly study petrophysical properties of the Upper Triassic Xujiahe fractured tight gas reservoirs. The lithology, pore types, pore structure, and porosity-permeability relationship were described based on experimental results of thin section analysis, computer tomography, and porosity and permeability measurements. And special attention was paid to characterize natural fractures and try to reveal the effects of fractures on gas storage and transportation. A dual porosity-dual permeability (DPDP) dynamic model of well L150 was established, and effects of natural fractures on natural gas productivity were studied. The lithology is mainly lithic arkose, feldspathic litharenite, and litharenite. The formation is highly tight due to compaction and cementation during the early and middle burial stages, and only some interparticle pores and grain dissolution pores remained. Fractures are classified into two types, which are structural fractures and interlayer fractures. The first type is caused by tectonic movement and is mainly developed in siltstone and fine sandstone, while the second type is developed between coarse sandstone beddings. Mercury injection capillary pressure experiment reveals that the pore size of the tight sandstone is 2–200 nm. Porosity of the samples is in the range of 2–6%, and permeability is 5 × 10−3–1 × 10−1 mD. Yet permeability of some samples may be as large as 1000 mD because of the micro-fractures. Results of history matching and production predictions of the dynamic model indicate that natural fracture is important to natural gas production.

Nanopore Formation and Structural Changes in Black Shale During the Initial Weathering Stage: A Longmaxi Formation Profile in Northwestern Hunan, China.

Understanding the controls on composition changes and porosity evolution in the critical zone of shale remains a major challenge. The aim of the present study is to develop a model of the changes in mineral compositions, chemical compositions and nanopore formation in shale during the initial weathering stage. To understand these processes, we selected a Silurian shale profile rich in pyrite and organic matter located in South China. Based on X-ray diffraction (XRD) and bulk elemental data, the variations in mineralogical and chemical compositions with depth were studied. To characterize the full pore size spectrum and to gain insight into the nature of secondary pores and their relationship with weathering, nuclear magnetic resonance (NMR) measurements and petrographic observations were combined with scanning electron microscopy (SEM) imaging. The results show that Al and K are enriched slightly, while Ca and Na are depleted in the upper part of the weathering profile. Si, Mn and Ti are relatively stable from the bottom to the top of the profile. Quartz, feldspar, mica, illite and chlorite are the main minerals in the parent rock, and they are relatively stable along the profile. The rock density gradually decreases from 2.6 g/cm³ to 2.1 g/cm³ from the bottom to the top, and the color of the shales changes from black to grayish yellow, but no secondary minerals are detected. The chemical weathering of black shale is dominated by the oxidation of pyrite and organic matter, giving rise to color variation and nanopore formation. The increase in interparticle pores at the nanometer-micron scale is initiated by the dissolution of easily weathered components such as organic matter and pyrite. The removal of clay minerals and tiny particles by groundwater seepage may be the main cause of porosity enhancement during the initial weathering stage. This study suggests that nanoporosity may play an important role in the process of fluid-rock interaction within black shale during the initial weathering stage.

Micro-Pore Reservoir Spaces and Gas-Bearing Characteristics of the Shale Reservoirs of the Coal Measure Strata in the Qinshui Basin.

To study the exploration potential of the Carboniferous-Permian transitional shale reservoirs in the Qinshui Basin, the Y5 well was selected as the research object, and experiments including organic geochemical tests, microscopic observations, scanning electron microscopy, X-ray diffraction analysis, high-pressure mercury intrusion, methane isothermal adsorption, and low-temperature nitrogen adsorption were carried out to analyse the physical properties of the shale reservoirs of interest. The results show that (1) The organic matter type of the samples is type III, the total organic carbon contents range from 0.27% to 20.52% (avg. 3.15%), the RO values are between 2.45% and 3.36% (avg. 2.86%), and the Tmax values range from 311.00 °C to 575.20 °C (avg. 493.31 °C). These results indicate that the organic matter in the study area is abundant and has experienced a high degree of thermal evolution. (2) The brittleness index is low (avg. 43.81%), and the shale pores in the study area are well developed. The pores contain organic matter-hosted pores, intraparticle pores, interparticle pores, and micro-cracks. (3) The methane isotherm adsorption average contents of the two samples are 0.2968 m³/t and 1.0824 m³/t, and the average contents of the on-site desorbed gas content and measured total gas content are 0.55889 m³/t and 0.8624 m³/t, respectively. (4) The kaolinite and illite contents have a significant negative effect on the specific surface area of the macro-pores and the specific pore volume of the meso-pores. The illite content is conducive to the development of the pore diameter and specific surface area of the meso-pores, and the quartz content has a positive correlation with the specific pore volume of the macro-pores. (5) The measured total gas content has a significant positive correlation with the total organic carbon and a weak positive correlation with the contents of quartz and illite, and the desorbed gas content shows the same correlations. This study demonstrates the physical properties, microscopic pore characteristics, and gas-bearing characteristics of shale reservoirs and their influencing factors in detail.

Analysis of Developmental Characteristics and Dominant Factors of Pore-Fracture Systems in Lower Cambrian Marine Shale Reservoirs: A Case Study of the Niutitang Formation, Fenggang Block, Southern China.

Due to breakthroughs in the Lower Silurian Longmaxi Formation in the Sichuan Basin and multiple strata around the basin, the northern part of Guizhou adjacent to the Sichuan Basin has become a key area for shale gas exploration. Compared with the Longmaxi Formation, the Niutitang Formation displays greater TOC (total organic carbon) content, depositional thickness and distribution area, but the details remain undetermined. In the study area, the Lower Cambrian Niutitang Formation typically has high TOC content, maturity and brittle mineral content. The study area has experienced multiple periods of tectonic movement, which have great influence on the fracture and pore characteristics. The fractures are mainly structural fractures and have obvious zoning. The primary types of pores are intraparticle pores, organic matter pores, and interparticle pores. Further, macropores and mesopores less than 50 nm contribute most of the pore volume, while pores less than 2 nm contribute most of the specific surface area. Many factors affect the pore-fracture system, such as tectonism, TOC content, mineral composition, and sedimentary environment. Tectonic movements produce fractures based on the changing stress field, but the degree of fracture development does not agree well with the degree of pore development. The TOC content has good positive correlations with the development of fractures and micropores, especially for nanoporosity, while clay minerals show a negative correlation with the development of fractures but a strong positive correlation with the growth of micropores. Quartz displays a positive correlation with the development of fractures but no good correlation with pore development. Finally, the lithofacies, lithologies and mineral compositions under the control of sedimentary environments are internal factors that can impact the development of pore-fracture systems.

Nano/Micro Pore Structure and Fractal Characteristics of Baliancheng Coalfield in Hunchun Basin.

The pore structure characteristic is an important index to measure and evaluate the storage capacity and fracturing coal reservoir. The coal of Baliancheng coalfield in Hunchun Basin was selected for experiments including low temperature nitrogen adsorption method, Argon Ion milling Scanning Electron Microscopy (Ar-SEM), Nuclear Magnetic Resonance (NMR), X-ray diffraction method, quantitative mineral clay analysis method. The pore structure of coal was quantitatively characterized by means of fractal theory. Meanwhile, the influences of pores fractal dimension were discussed with experiment data. The results show that the organic pores in Baliancheng coalfield are mainly plant tissue pores, interparticle pores and gas pores, and the mineral pores are corrosion pores and clay mineral pores. There are mainly slit pore and wedge-shaped pore in curve I of Low temperature nitrogen adsorption. There are ink pores in curve II with characteristics of a large specific surface area and average pore diameter. The two peaks of NMR T₂ spectrum indicate that the adsorption pores are relatively developed and their connectivity is poor. The three peaks show the seepage pores and cracks well developed, which are beneficial to improve the porosity and permeability of coal reservoir. When the pore diameter is 2-100 nm, the fractal dimensions D1 and D₂ obtained by nitrogen adsorption experiment. there are positive correlations between water content and specific surface area and surface fractal dimension D1, The fractal dimension D₂ was positively and negatively correlated with ash content and average pore diameters respectively. The fractal dimensions DN1 and DN2 were obtained by using the NMR in the range of 0.1 μm˜10 μm. DN1 are positively correlated with specific surface area of adsorption pores. DN2 are positively correlated volume of seepage pores. The fractal dimension DM and dissolution hole fractal dimension Dc were calculated by SEM image method, respectively controlled by clay mineral and feldspar content. There is a remarkable positive correlation between D1 and DN1 and Langmuir volume of coal, so fractal dimension can effectively quantify the adsorption capacity of coal.

Multi-Angle Investigation of the Fractal Characteristics of Nanoscale Pores in the Lower Cambrian Niutitang Shale and Their Implications for CH₄ Adsorption.

Shale gas has received widespread interest due to its successful commercial development in China. Pore structures in shale can directly control its gas storage and migration properties. In this study, field emission scanning electron microscopy (FE-SEM), low-pressure N₂/CO₂ adsorption and highpressure methane adsorption were used to investigate the nanoscale pore structures of the Lower Cambrian Niutitang Formation in the southeastern Upper Yangtze platform. The fractal parameters of the pore structures were also calculated using the Frenkel-Halsey-Hill (FHH) model. The relationships between the fractal dimensions and TOC content, mineral composition and pore structure parameters were also discussed. The results show that organic matter and clay minerals are primary factors affecting the nanoscale pore development. Slit-shaped pores and ink-bottle-shaped pores are the predominant pore types in the Niutitang shale. The Brunauer-Emmett-Teller (BET) surface areas vary from 4.91 m²/g to 34.33 m²/g, and the pore volumes range from 0.689 m³/100 g to 2.964 m³/100 g. Two fractal dimensions (D1 and D₂) of the Niutitang shale were obtained using the FHH model, with D1 ranging from 2.605 to 2.684, and D₂ ranging from 2.681 to 2.865. D1 adequately characterizes the surface roughness of the pore structures, while D₂ represents the complexity of the pore types. Inter-particle (InterP) pores commonly have greater shape complexities than OM pores and intra-particle (IntraP) pores, based on analyses using Image-Pro Plus software. In addition, the TOC content and clay minerals have great effects on the fractal dimension D1. Meanwhile, the fractal dimension D1 increases with increasing BET surface area, but there is no definite relationship between the fractal dimensions and pore volumes. Both the fractal dimensions D1 and D₂ are negatively correlated with pore sizes. Further investigation indicates that the fractal dimension D1 exhibits a strong positive relationship with the methane adsorption capacity indicating that Niutitang shales with greater values of the fractal dimension D1 have higher methane adsorption capacities.

Micro- and Mesopores Occurring in Transitional Shales: An Examination Based on Pore Radius and Origin.

The microscopic pores in shales can be characterized based on different features, including pore morphology, pore size distribution and pore origin. In this work, shale samples from the Lower Permian Shanxi Formation and Upper Carboniferous Taiyuan Formation in the Linxing Block of the Ordos Basin were examined via experiments including X-ray diffraction (XRD), total organic carbon (TOC) analysis, field emission scanning electron microscopy (FE-SEM), automatic acquisition of large-image technology (MAPS), and low-temperature gas (CO₂ and N₂) adsorption/desorption experiments. The results show that clay minerals (average value of 53.9 wt.%) and quartz (average value of 39.0 wt.%) dominate the sample composition, with some K-feldspar, plagioclase, siderite, etc. The TOC values are between 1.15% and 8.46%, and all the shales are of middle-high maturity (the vitrinite reflectance (Ro) ranges from 1.23% to 1.75%). Based on FE-SEM images, the observed pore types include interparticle (interP) pores, intraparticle (intraP) pores, and organicmatter (OM) pores, and the pores and fractures at different scales are examined by MAPS. The distributions of micro- and mesopores and the proportions of the different pore sizes were determined from the N₂ and CO₂ adsorption results. The pore size distribution results suggest that N₂ mainly penetratesmesopores (2-50 nm), while CO₂ mainly penetrates large micropores (0.7-2 nm). Micropores are the largest contributors to the total pores. The mesopores were further classified as small, medium and large mesopores, and the proportion of mesopores decreased with increasing pore size.

Carbon nanocoils decorated with a porous NiCo2O4 nanosheet array as a highly efficient electrode for supercapacitors.

Well-organized substrate materials are of considerable significance in the development of energy-efficient pseudocapacitor electrodes. Herein, functionalized three-dimensional (3D) carbon nanocoils on nickel foam (CNCs/NF) have been used as the substrate to grow faradaic nickel cobaltite (NiCo2O4) via a solvothermal method. The arrays of NiCo2O4 were assembled by interconnected ultrathin nanosheets with random inter-particle pores. The number of electroactive sites increased specifically because of the porous feature of NiCo2O4 nanosheets and the 3D structure of CNCs/NF. Moreover, the CNCs/NF network aided the electrolyte ions in diffusing deeply within the architecture. The NiCo2O4/CNCs/NF composite exhibited an outstanding specific capacitance of 2821 F g-1 at the current density of 1 A g-1, a remarkable rate capability (82.4%) and long cyclic stability (91.7% after 3000 cycles). Such encouraging electrochemical performance was attributed mainly to the synergistic interactions of NiCo2O4 arrays and CNCs/NF substrate that helped achieve efficient redox reactions, enhanced ion diffusivity and excellent electron conductivity. In summary, this binder-free NiCo2O4/CNCs/NF composite electrode paves a way towards the synthesis of highly efficacious electrodes for supercapacitors.