Macropore Volume Research Articles

Evaluation of Seasonal Effects of Tillage and Drainage Management Practices on Soil Physical Properties and Infiltration Characteristics in a Silt-Loam Soil

The impacts of tillage and drainage managements on soil infiltration characteristics need to be scrutinized for a better understanding and prediction of soil hydrological processes, such as runoff, evapotranspration and soil water storage. The objectives of this study were i) to evaluate the effects of tillage and drainage practices on soil physical properties and water infiltration, and ii) to compare prediction accuracy of estimated and optimized infiltration model characteristics for the observed and predicted quantities of infiltration process in the soil. The research site contains the Crosby-Kokomo soil series (fine, mixed, mesic, Aeric Ochraqualf and fine, mixed, mesic Typic Argiaquoll, respectively). The experiment was a two factorial completely randomized block design with two levels of tillage (chisel plow (CH) and no-till (NT)) and two levels of drainage (drained (D) and undrained (UD)) with three replicates. Soil bulk density (ρb), saturated hydraulic conductivity (Ksat), soil moisture retention curves (SMRC), soil infiltration capacity and piezometric water head in each treatment were also measured. Soil drainage flows at each drain lateral and outlet discharges were measured. The results showed that The UD treatments were always higher for Ksat values than the D treatments regardless of the tillage practices for both depths and the CH treatments always had greater Ksat values than those in the NT at both the depths regardless of drainage practices. The D treatments reduced the soil bulk density by 4.2 and 0.8 % in the surface soil and 4.61 and 6.7% for the subsurface soil in respect to no-till-UD and chisel-UD treatments. The UD treatments had higher bulk density at both of the depths than those of the D treatments regardless of tillage practices except the CH-UD treatments. The NT had higher bulk density at both depths of the soil than those of the CH treatments regardless of drainage practices. Drainage increased pore size distribution significantly higher than the UD treatments (p<0.05). The D treatments had significantly higher storage pores and effective pores (9.37%) (pores retaining water at -10kPa pressure head) than the ones in the UD treatments (8.96%) (p<0.05). The NT treatments yielded higher infiltration rates than the CH and the D treatments produced higher apparent infiltration rates and cumulative infiltration values than the UDs. The changes in soil physical properties were found to be strongly and significantly dependent on season, soil depth, and rainfall (p<0.05). The optimized infiltration models predicted larger range of infiltration rate values for each treatment than the estimated infiltration models, indicating that the optimization produced higher accuracy and validity of the predicted models in the field. To conclude, soil dry bulk density, soil saturated hydraulic conductivity, and increased macropore volumes can significantly impact soil hydrological responses to soil water infiltration, soil water storage and drainage flow under conservation tillage and drainage management practices on a seasonal basis. This impact enhances greater potential to capture water in soil for future crop use in the study site.

Крупногранулированный макропористый адсорбент для адсорбционной очистки тяжелого нефтяного сырья

Upgrading of oil residues by adsorption techniques without hydrogen using macroporous large-granular adsorbents with high mechanical strength, a small surface area and a large volume of macropores, modified with various additives,has been studied. To obtain a macroporous structure, templates were tested - guar gum and wax emulsion. Both templates showed high efficiency; however, the use of wax makes it possible to obtain adsorbents with a larger pore volume. The processof adsorptive purification of feed based on the cracked residue of visbreaking provided a reduction of heavy metals content by 98%, while conversion of the residue boiling above 540°C was 75%. Adsorption treatment on a grained adsorbent can be used to obtain feedstock for a hydrotreating process aimed at obtaining both low-sulphur marine fuel and catalytic cracking feedstock.

One-time omission of puddling improves soil structure and post-rice soybean yield in clay-rich fields within paddy–soybean rotation systems in central Hokkaido, Japan

A one-time omission of puddling was noted to increase post-rice soybean yields within the paddy–soybean rotation systems in central Hokkaido, Japan. We analyzed the physical, chemical, and biological properties of soil via an onsite survey in 47 farmers’ soybean fields where either puddled transplanted rice (PT), nonpuddled transplanted rice (NT), or dry direct-seeded rice (DS) was cultivated in the previous year (referred to as one-time PT, NT, and DS treatments, respectively). The objective of the study was to determine the key soil parameters that could explain the higher post-rice soybean yield following the one-time omission of puddling (NT and DS treatments). In addition, soybean yield and soil properties were surveyed in an experimental field experiment where PT and NT treatments were applied for 3 consecutive years with the expectation that the increases in post-rice soybean yield caused by the omission of puddling (NT treatment) would be more pronounced. In the survey of farmers’ field, soybean yields were comparable among the one-time PT, NT, and DS treatments when the clay content was < 40%. However, soybean yield decreased as the clay content increased only under the one-time PT treatment. The adverse effects of puddling (PT treatment) on clay-rich soil appeared in a few soil physical parameters but not on any soil chemical and biological parameters. In the 34 selected clay-rich farmers’ fields (clay content >40%), narrow macropore and mesopore volumes, which indicate total available water capacity, were significantly (P < 0.05) lower under the one-time PT treatment than under the other two treatments. At the same time, the narrow macropore volume was significantly (P < 0.05) correlated with soybean yield. The one-time omission of puddling (NT and DS treatments) adopted in the surveyed farmers’ fields did not affect the wide macropore volume. Three consecutive years of NT treatment improved several soil physical properties as well as soybean root development in the experimental field. However, these improvements did not significantly increase soybean yield in the experimental field where the clay content was < 40%. These findings suggest that the one-time omission of puddling (NT and DS treatments) prevents the decreasing in the yields of post-rice soybean in clay-rich soils in central Hokkaido. The stable soybean yield, irrespective of the clay content, after the one-time omission of puddling (NT and DS treatments) in fields was attributed to the increased plant-available water capacity owing to the increased narrow macropore and mesopore volumes without clear changes in the wide macropore volume. By contrast, the effects of the one-time and three-time omission of puddling (NT and DS treatments) were not obvious in non–clay-rich field conditions in central Hokkaido.

Pore evolution model and diagenetic evolution sequence of the Mesoproterozoic Xiamaling shale in Zhangjiakou, Hebei

Current research on diagenesis and its evolution focuses mainly on sandstone reservoirs. Conventional oil and gas reservoir observation techniques for characterizing shale reservoirs are limited, and comprehensive research on nanoscale pore variations, diagenesis and evolution of shale reservoirs, especially immature and low-maturity marine shale reservoirs, is relatively scarce. To reveal the diagenesis and evolution of low-maturity marine shale, geochemical and mineral analyses, quantitative characterization of the pore structure and qualitative characterization of the pore morphology were performed on the Xiamaling shale. With the burial and geothermal history, the Xiamaling diagenetic evolution sequence and the nanoscale pore system evolution were studied. The results show that smectite continually transforms to an illite-smectite (I/S) mixed layer and then quickly transforms to illite and chlorite; the kaolinite content gradually decreases as maturity increases. The hydrocarbon expulsion threshold of the Xiamaling shale is EqRo = 1.0%, and the porosity decreases to a minimum value of EqRo = 1.0% and then increases. The pore structure evolution model shows that the pore volumes (PVs) of micropores and macropores decrease to minima at approximately EqRo = 0.92% and 0.85%, respectively, and then increase; the mesopore PVs continuously decrease. Micropore and mesopore surface areas (SAs) decrease to their minima at approximately EqRo = 0.85% and 1.0%, respectively, and then increase; simultaneously, the macropore SAs continuously decrease. The main diagenetic types of the Xiamaling shale are compaction, dissolution, cementation, thermal maturation of organic matter (OM), and clay mineral transformation; it reaches period B of the middle diagenetic stage, and the diagenetic evolution sequence is determined. The pore system composition and variation characteristics of the Xiamaling shale are analysed, and a corresponding evolution model is established.

The Characteristics and Main Controlling Factors for the Formation of Micropores in Shale from the Niutitang Formation, Wenshuicun Section, Southwest China

The characteristics of shale micro-pore development and its main influencing factors have important theoretical guiding significance for shale gas exploration and resource evaluation. In order to clarify the micro-pore development characteristics of lower Cambrian shale and the main controlling factors of micro-pore development, we used the lower Cambrian Niutitang formation shale, in the Wenshuicun section of the Guizhou Province in southwest China. The micro-pore development characteristics of the shale in the region were studied by argon ion profile field emission scanning electron microscopy and a low-temperature liquid nitrogen adsorption and desorption experimental system. The relationship between micro-pore and kerogen maceral composition, total organic carbon (TOC) content and different mineral content was analyzed in combination with mineral and geochemical characteristics. Inorganic pores (clay mineral pores, dissolution pores and pyrite intergranular pores) and micro-fractures (clay mineral shrinkage crack, tectonic fractures and overpressure fractures) were the main type of pore developed in the shale of the Niutitang formation in the Wenshuicun section, and no organic pores had developed. The pore size of shale is usually 2–50 nm, accounting for 58.33% of shale pores, e.g. mesopores. Clay mineral content has an obvious positive correlation with macropore volume and average pore diameter, and an obvious negative correlation with micropore volume. In addition, the content of feldspar in brittle minerals has a strong negative correlation with macropore volume and average pore diameter, and a strong positive correlation with micropore volume and BET-specific surface area. TOC content and the content of different kerogen macerals have no obvious correlation with the development of shale micropores in this region. It is concluded that inorganic mineral composition is the main controlling factor of micro-pore development within lower Cambrian shale, and organic matter abundance and maceral content have little influence on the micro-pore development. This study provides a case study for the characteristics of micropores in lower Cambrian shale in China.

Mechanical and microstructural properties of 3D printable concrete in the context of the twin-pipe pumping strategy

To tackle the conflicts between the pumping and deposition process in 3D concrete printing, a twin-pipe pumping (TPP) system with a helical static mixer can be used. In this way, a cement-based mixture (without accelerator) and a limestone powder-based mixture (with a high dosage of accelerator) are transported separately and mixed within the helical static mixer just before extrusion. However, the helical static mixer will introduce striation patterns in the 3D printed concrete due to flow division and the effect of such a heterogeneous phenomenon on the mechanical behavior has not been studied yet. In this paper, the mechanical (compressive, flexural, and tensile bond strength) and the microstructural behavior of 3D printed specimens made using the TPP system was explored. During the mechanical tests, the cracks initiated within the limestone powder striation. In addition, the difference in the mechanical strength for the specimens under difference loading directions was observed. Microstructural investigations based on mercury intrusion porosimetry revealed that the pore size distribution of 3D printed specimens (critical pore size of 210.0 nm and 197.5 nm for the bulk and interface region, respectively) was distinct from that of the mould cast specimens (critical pore size of 62.7 nm). Although the mould cast specimens had higher porosity (19.75%), the volume of macropores was found to be higher in the 3D printed specimens, which was more detrimental to the compressive strength. Further, porosity analysis of micrographs showed that the macropores in the 3D printed specimens were primarily presented in the limestone powder-based striations. In addition, a small quantity of ettringite was also observed in the bulk of the limestone powder-based striation, which may be caused by ion migration between the two regions after the inline mixing process by the static mixer.

Influence on compressive strength and CO2 capture after accelerated carbonation of combination β-C2S with γ-C2S

In order to deal with the current global climate crisis, it is urgent to reduce greenhouse gas emissions and store CO2 in the atmosphere through Carbon Capture and Storage (CCS) technology. Both C3S and C2S are the main mineral components of Ordinary Portland Cement; through accelerated carbonation reaction, C2S could sequestrate more CO2 and gain a rapid development of early strength. β-C2S and γ-C2S, as two stable crystallines of C2S, can both capture CO2. Compared to β-C2S, the γ-C2S essentially shows no hydration activity, but γ-C2S shows higher reactivity to CO2 during the carbonation process. The conversion of β-C2S to γ-C2S would cause volume expansion, saving electricity during the grinding process and reducing CO2 emissions. To synthetic different proportions of β and γ polymorphic of C2 S, the different weight content of B2O3 (B2O3 wt%) was mixed with the analytical pure chemical reagent of CaCO3 and SiO2, and different cooling rates were used. The synthetic C2S (F1, S1, F2, S2) were exposed to pure CO2 gas with 2 bar pressure for 2 h. After carbonation, compressive strength was tested, carbonation degree was calculated. The synthetic C2S (S2) containing 57.8 wt% β-C2S and 42.2 wt% γ-C2S showed the highest compressive strength and the higher CO2 sequestration capacity, with the compressive strength of 46.3 MPa and the 14.14% CO2 uptake. The XRD results and TG-DTG analysis have proved that different calcium carbonates, including calcite, aragonite, vaterite, and ACC (amorphous calcium carbonate), were formed after carbonation. FT-IR observed the characteristic vibration of calcium carbonate, the microstructure of different calcium carbonate crystals was observed by FE-SEM. The calcite in the S2-C group showed more thermodynamic stability, confirmed by TG analysis at the temperature stage of 680℃～820℃. The mechanical bond force of rhombic calcite contributed to the high compressive strength. And S2-C group had the lowest porosity, which contained the highest volume of capillary pores and the lowest volume of macropores among the 4 groups. The combination of β-C2S with γ-C2S exhibited rapid strength development and high sequestration of CO2 after carbonation. The carbonation of combination of β-C2S and γ-C2S was able to devote to the rapid development of compressive strength and rather a high capacity of capturing CO2, and the proper proportions of β-C2S and γ-C2S were beneficial to develop belite-rich cement, as well as speed up the absorption and storage of CO2 in the atmosphere.

Pore structure evolution characteristics of continental shale in China as indicated from thermal simulation experiments

Organic matter (OM) pores in shale can provide abundant storage space for gas. However, there are different types of OM with different compositions and structures in continental shale, and their pore structure evolution lacks direct observations. In this study, anhydrous thermal simulation experiments in an open system were conducted on a continental Jurassic Ziliujing Formation shale sample with a low initial thermal maturity, taken from an outcrop in the northeastern Sichuan Basin. Changes in the pore structure of a specific OM at different thermal maturities were captured by field emission–scanning electron microscopy (FE-SEM). These FE-SEM images processed by image processing software were combined with N2 adsorption and high-pressure mercury intrusion porosimetry data to help clarify the pore structure evolution characteristics. Our results show that OM developed in Ziliujing Formation shale can be divided into four types based on their morphological characteristics. The pore structure evolution process is closely related to the processes of petroleum generation, migration, and thermal cracking. More specifically, the filling of pores by generated oil at lower temperature caused a decrease of the macropore volume in the shale sample and these filled macropores were released at higher temperature by thermal cracking of oil. In addition, there were no OM pores larger than 10 nm created during thermal simulation experiments, which indicates that the development of such sized OM pores is largely dependent on the original composition and structure of the parent OM.

Pore Fractal Characteristics of Suancigou Long-Flame Coal after Electrochemical Treatment: An Experimental Study through the Implementation of N2 Adsorption and Mercury Intrusion Prosimetry Techniques.

The application of electrochemical treatment in coal seams for enhancing coalbed methane (CBM) recovery can also decrease the risks of outburst disasters. The long-flame coal samples were electrochemically modified with 0, 1, 2, and 4 V/cm electric potential gradients, and the pore structures were measured and analyzed by combined low-temperature nitrogen gas adsorption, mercury intrusion prosimetry, and fractal theory. The experimental test results indicated that the pore volumes of macropores (>50 nm) and mesopores (2–50 nm) increased after electrochemical modification and further increased with the increase in electric potential gradient. The fractal dimensions of pores showed a decreasing trend except for the slight fluctuation of the mesopores with a size of 2–4.5 nm after modification, which indicated that the overall roughness and irregularity index of pores decreased. The evolution mechanisms of pore size distributions and their fractal dimensions were explained by the dissolution of minerals and the falling off of alkane side chains in the coal surface, which would expand and connect the pores during the electrochemical modification process. The results obtained from this work were crucial for CBM exploration via an electrochemical method.

Reservoirs characteristics and environments evolution of lower permian transitional shale in the Southern North China Basin: Implications for shale gas exploration

Marine-continental transitional shale gas is an important resourceinaddition to shale gas in marine facies. Transitional facies strata are rich in type III organic matter and shales with obvious lamellation, but there has been no “breakthrough” for shale gas. The main reason for this may be that the sedimentary environment and characteristics of favorable shale reservoirs differ from those of marine shale. It is imperativeto understand the environment and reservoir characteristics to advance the exploration of transitional shale gas.Typical lower Permian transitional shale has been collected continuously in an exploratory well in the Southern North China Basin. A complete set of experimental procedures, including elemental geochemical methods (XRF and ICP-MS) and petrophysical techniques (N2/CO2 adsorption, MIP, NMR and FE-SEM), were used. The results indicate that, in addition to the contribution of mesopores (2–50 nm), transitional shale in the SNCB has a higher macropore (>50 nm) volume (average = 0.00616 cm3/g) and proportion (average45.85%) than in marine shale. The precipitation and dissolution of dispersed pyrite in the Shanxi Formation formed more macropores (average = 0.00649 cm3/g) than pyrite and calcite aggregates (filled with bitumen and clays) in the Taiyuan Formation. Total organic carbon (TOC) has no obvious relationship with micropores and mesopores, but has a weak positive correlation with macropores, unlike marine shale. Sulfur enrichment in the presence of organic matter mixed with terrigenous iron causes dispersed pyrite (FeS) precipitation under anoxic conditions, which improves the reservoir (intergranular and dissolution pores). With decreasing sea levels, the salinity of water decreases gradually, while weathering increases gradually; however, the shale reservoir conditions do not simply improve or deteriorate. Favorable shale reservoirs are mainly lagoonal facies characterized by a low SiO2content (<58 wt%), high TOC (>2.0%), intermediateV/Cr ratios (1.5–2), and a high chemical index of alternation (CIA; >88) and formed in an environment with little clastic input, hypoxia and strong weathering.However, due to the strong connectivity, high proportions of macropores and thin single-layers, it is necessary to study the preservation capacity in future to determine whether the natural gas formed in shale is lost.

Comparative analysis of pore structure parameters of coal by using low pressure argon and nitrogen adsorption

The accurate characterization of coal pore structure is of great significance for in-depth understanding of interior properties and gas adsorption, desorption and diffusion characteristics. In this study, the low pressure argon adsorption (LP-ArGA) and low pressure nitrogen adsorption (LP-N2GA) were all used to analyze the pore parameters of coal with different metamorphism. The results indicated that the adsorption isotherm type and desorption hysteresis type of coal samples obtained by the LP-ArGA and LP-N2GA belong to the same type, but the adsorption capacity of the former is higher than that of the latter. The pore size distribution (PSD) of coal samples shows a significant multi-peak distribution feature. Compared with the LP-N2GA, the LP-ArGA can accurately analyze the pore parameters between 2 and 4 nm or part of 2–7 nm. The mesopore volumes obtained by the LP-ArGA is 1.66–2.84 times that of the LP-N2GA, and there is no obvious law of macropore volume. The macropore volumes of QN and PM samples decreased by 17.2% and 50.9%, respectively, while GHS sample increased by 166.0%. The corresponding specific surface area (SSA) showed the same properties. Fractal curve fitting results obtained by the two methods are highly correlated, but compared with LP-ArGA, D1 and D2 obtained by the LP-N2GA can well reflect pore characteristics. The fractal dimension obtained by the two methods and the variation trend with the metamorphic degree are all different, which is mainly due to the difference of adsorption volume. The purpose of this paper is to introduce a new method for the analysis of coal pore structure in order to better understand the pore characteristics.

Effect of different types of fracturing fluid on the microstructure of anthracite: an experimental study

ABSTRACT A systematic understanding of the effects of different fracturing fluids on the chemical and pore structure of coal is of great significance for the exploitation of coalbed methane (CBM). In this study, Fourier-transform infrared spectroscopy and mercury intrusion porosimetry were used to analyze the chemical and pore structure of coal samples treated by different fracturing fluids. The results show that fracturing fluid treatment has little effect on the coal aromatic structure. The oxygen-containing and hydroxyl structures of the coal samples treated by acidic and viscoelastic surfactant (VES) fracturing fluids increased by >17%, which is beneficial for gas desorption and thereby increases CBM yield, whereas those of the coal sample treated with deionized water decreased by 3.8%. The acidic and VES fracturing fluid treatments are also beneficial for coal pore connectivity, which promotes gas migration. The three types of fracturing fluids increased the macropore volume by >350%. The deionized water treatment reduced mesopores and micropores by 20% and 5%, respectively, while the transition pores increased by 2.3%, resulting in a 2.6% increase of the specific surface area, which is not conducive to gas desorption and migration. The acidic fracturing fluid treatment increased the mesopore volume by 53.3%, reduced the transition pore and micropore volumes by 5.3% and 32.5%, respectively, and reduced the surface area by 13.2%, which reduces the amount of adsorption sites and facilitates gas migration. However, the adsorption pores and mesopores after VES fracturing fluid treatment decreased by 17.6% and 26.7%, respectively, which indicates that this treatment does not transform most adsorption pores into migration pores.

Effects of Microwave Heating Paths on Pores and Cracks in Bituminous Coal.

To follow the effect of the microwave heating path on the structure of coal, eight 50 mm diameter, 30 mm long dry coal cores from the same coal seam with similar pore structure characteristics were microwave-treated using 4 pathways. The T2 spectrum, pore-volume, temperature, mass, and visual changes of coal samples were analyzed before and after microwave heating. The microwave heating path affected the macropores and microcracks and the crack development mode. When the same microwave energy was applied, microwave heating on the coal was mainly manifested by the opening of closed pores, before the pyrolysis temperature of the coal was reached. Increasing the energy density caused the water vapor to move from constant pressure expansion to constant volume expansion. This resulted in an exponential growth of the mesopore and macropore volumes. Meanwhile, the micropore volume increased due to the collapse of pore structures. As a result, high-power microwave heating could accelerate the vaporization rate of water. The rapid expansion of water vapor volume brought about a microwave heating effect similar to the “steam explosion”. The resulting local tensile stress enabled the cracks to develop, expand, and connect to others continuously. Thus, it formed a complex crack network leading to the outside of the coal sample.

Effect of particle size on gas energy release for tectonic coal during outburst process

Based on the particle size evolution of tectonic coal in formation process, the differences between tectonic coal and intact coal in pore structure and initial gas desorption characteristics were studied. Then, the influences of particle size reduction on pore structure and initial gas desorption characteristics were investigated; and the initial gas energy release model was derived, which was used to calculate the gas expansion energy of tectonic coals with different particle sizes. This study concludes that the particle size of tectonic coal will be reduced under the pulverization effect during the formation process, and the particle sizes of these types of tectonic coal reach millimeter level or even smaller scale under pulverized state. The pore volume and specific surface area of minipores (pore size: 10–100 nm), mesopores (pore size: 100–1000 nm) and macropores (pore size: 1000–10000 nm) in tectonic coal are larger than those in intact coal by over 10 times. Tectonic coal’s average gas desorption rate in the first 10 s reaches up to 11.47 times of that of intact coal. Within the 5 particle size greater than 0.074 mm, the pulverization obviously transforms the minipores and mesopores in coals, but its effect on micropores (pore size: 0.9–10 nm) is limited. When the particles are pulverized to blow 0.074 mm, the micropores are obviously transformed. The initial gas energy release model for coal samples with different particle sizes is derived and verified through the experimental data. As calculated using the initial gas energy release model, the gas expansion energy will be reduced sharply with the particle size reduction when the particle size is smaller than 1 mm. Therefore, the particle size of tectonic coal decides its initial gas desorption capacity, which is of critical significance to the gas energy release in the outburst process. This study will be of great scientific significance for exploring the outburst mechanism and prevention.

Thermal Desorption Temperature Affects Water Retention and Hydraulic Conductivity of Three Contrasting Soils

ABSTRACT Thermal desorption is an effective approach to removing petroleum hydrocarbons from soil. However, the resultant environmental function and revegetation potential of the soil can be reduced by high temperatures. This study evaluated the effect of nine temperatures of heating (60–800°C) on water retention and hydraulic conductivity in three soils of contrasting mineral and physical properties. Fredlund-Xing water release curves were developed using the HYPROP system. Features of the release curves were compared for differences: the water content (%Vol) at which air first enters the macropore volume (AEV), the slope of the rapid desorption portion of the curve, field capacity, and the residual water content. A Hearne sandy loam showed an increase in the %Vol at saturation (0.354 to 0.557 cm3 H2O cm−3 soil), but a decrease in plant available water with increasing temperature. A Rader sand showed a decrease in field capacity and plant available water. A Weswood clay showed no change in field capacity, but an increase in plant available water 10.87 to 18.39 cm3 H2O cm−3 soil through 700°C. Saturated hydraulic conductivity (Ksat) increased for both the Hearne and the Weswood soils with increasing temperature. However, the Rader soil Ksat saw an increase from 0.002 to 0.007 cm s−1 to 450°C but declined to <0.0005 cm s−1 between 500°C and 800°C. This study shows the release curve comparison approach can be effective to quantify changes or differences in soil water relationships by treatment or soil property. Additional insight is provided by electron microscope imaging.

Correlation between adsorbed methane concentration and pore structure of organic-rich black shale from the Liard Basin, Canada

Evaluating the adsorbed gas content in shale gas reservoirs is crucial for calculating total gas production potential of the reservoir. In this study, we analyzed the chemical composition and total organic carbon content of the black shale samples collected from different depths in the Liard Basin, Canada. The samples were identified as siliceous-rich shale samples; specifically, organic-rich black shale with a total organic carbon content of more than approximately 3%. We also analyzed the adsorbed methane gas content and the pore structure of the shale samples. We conducted a mechanistic study to identify the important factors affecting the amount of adsorbed CH4 gas in the shale by evaluating the correlation between the adsorbed CH4 gas content and quantitative pore structure results (i.e., specific surface area and micropore, mesopore, and macropore volume). The results indicate that the micropore volume can be effectively used to predict the content of adsorbed CH4 gas in organic-rich black shale samples from the Liard Basin.

Influence of sequestered supercritical CO2 treatment on the pore size distribution of coal across the rank range

The influence of supercritical CO2 (SC-CO2) fluids on pore structure characteristics of coal plays a vital role in geo-sequestration of CO2 into deep coal seams. Changes in coal pore structure and mineral content after exposed to SC-CO2 fluids are quantitatively evaluated by N2/CO2 adsorption and X-ray diffraction (XRD) for a lignite, bituminous and anthracite coals. The SC-CO2 exposure has a notable effect on coal pore distribution. Affected by SC-CO2, the micropore volume within coal is reduced by 12.6 to 34.8%, while both the average pore diameter and macropore volume are remarkably increased. XRD analysis shows that no newly-formed mineral compositions were detected in treated coals, but the mineral content is altered. As the main carbonate minerals of coal, both calcite and dolomite are consumed during SC-CO2 treatment. Due to the strong extraction capacity for small organic molecules, the influence of SC-CO2 is related to coal rank, and the largest increment in macropore volume is observed in lignite. The greatest reduction of micropore volume is identified in anthracite treated sample, indicating that SC-CO2 has the most impact on micropores in high-rank coal. Mineral dissolution likely accounts for this reduction in micropore contribution by increasing mesopores and macropores.

Carbon Monoliths with Hierarchical Porous Structure for All-Vanadium Redox Flow Batteries

Carbon monoliths were tested as electrodes for vanadium redox batteries. The materials were synthesised by a hard-templating route, employing sucrose as carbon precursor and sodium chloride crystals as the hard template. For the preparation process, both sucrose and sodium chloride were ball-milled together and molten into a paste which was hot-pressed to achieve polycondensation of sucrose into a hard monolith. The resultant material was pyrolysed in nitrogen at 750 °C, and then washed to remove the salt by dissolving it in water. Once the porosity was opened, a second pyrolysis step at 900 °C was performed for the complete conversion of the materials into carbon. The products were next characterised in terms of textural properties and composition. Changes in porosity, obtained by varying the proportions of sucrose to sodium chloride in the initial mixture, were correlated with the electrochemical performances of the samples, and a good agreement between capacitive response and microporosity was indeed observed highlighted by an increase in the cyclic voltammetry curve area when the SBET increased. In contrast, the reversibility of vanadium redox reactions measured as a function of the difference between reduction and oxidation potentials was correlated with the accessibility of the active vanadium species to the carbon surface, i.e., was correlated with the macroporosity. The latter was a critical parameter for understanding the differences of energy and voltage efficiencies among the materials, those with larger macropore volumes having the higher efficiencies.

Experimental study on the effect of high-voltage electrical pulses on the nanoscale pore structure of coal

Research on electric pulse fracturing technology has led to significant advances in the field of coal mine fracturing and permeability enhancement. However, few studies have focused on nanoscale pores. In this study, we investigate the effect of high-voltage electric pulses on the nanoscale pore structure of coal using a custom-built experimental device. The results revealed that the high-voltage electric pulse breakdown process decreased the specific surface area, pore volume, and number of micropores (pore size < 2 nm) and increased the specific surface area, pore volume, and number of macropores (pore size > 50 nm). In particular, the number of pores that were>100 nm increased significantly. Field emission scanning electron microscopy revealed that macropores were widely distributed on the surface of the post-breakdown coal samples and were connected to each other. The number of mesopores (pore size = 2–50 nm) were not significantly altered as they were supplemented by the formation of new pores while simultaneously expanding into larger pores. The electric pulse breakdown process increased the total pore volume, average pore size and pore connectivity, decreased structural complexity, and significantly improved the nanoscale pore structure of the coal samples. Raman spectroscopy further confirmed this observation. From a molecular point of view, post breakdown, the aromatic system in the coal sample dehydrogenated, the directly connected methyl groups broke, the carbon atoms were arranged in a more orderly manner, and the microcrystalline structure gradually improved, thereby providing suitable conditions for convenient gas desorption and diffusion.

Experimental analysis of the effect of temperature on coal pore structure transformation

Coal has a complex pore network, which affects the reserves and production capacity of coalbed methane. To analyze the feasibility of coal seam heat injection mining and improve the theory of the influence of temperature on coal adsorption and desorption characteristics, scanning electron microscopy, mercury intrusion, and low-temperature liquid-nitrogen adsorption were used to evaluate the pore structure of coal at different temperatures. With the increase in temperature, the volume of macropores increased from 0.0249 to 0.0454 mL/g, and the specific surface area of micropores decreased from 2.6836 to 0.7250 m2/g. In addition, the pore fractal dimension of the large pore section, D1, increased gradually, while the pore fractal dimension of small pore section, D3, decreases with the increase in temperature. A higher temperature led to a larger pore fractal dimension of the large pores in coal and more developed pores, which is conducive to the migration of gas in the coal seam. The pore fractal dimension of the small pores decreased with the increase in temperature. The structure of the micropores became increasingly regular. The temperature has an obvious transformation effect on the structure of coal pores, especially on macropores and micropores.