Low-temperature Nitrogen Adsorption Research Articles

Study on the mechanism of methane “solid–liquid–gas” conversion controlled by the evolution of coal micro- and nanopore structure

Currently, the utilization of coalbed methane resources in the Guizhou region faces challenges such as complex reservoir structure, high gas content, and microporous development. Based on these, the pore structure and adsorption capacity of Guizhou tectonic deformed coals (TDCs) were evaluated using a suite of integrated diagnostic techniques including low-temperature nitrogen adsorption (LT-N2A), mercury intrusion porosimetry (MIP), methane isothermal adsorption. Through the above methods, the pore structure and adsorption characteristics of the samples were characterized; The samples were divided into the range of joint pores by combining the results of MIP and LT-N2A; Using the molecular simulation software, the 2 nm, 4 nm, 10 nm pores affecting the methane endowment state were investigated respectively, and from the perspective of the heat of adsorption and energy, the concept of the three-phase transition of methane was proposed, and explore the change of the pore spacing affecting the endowment state of methane from the solid state pore to the gas state pore. The results provide new ideas for the in-depth study of gas storage in tectonic coal reservoirs in Guizhou Province.

Application of functionalized carbon nanofibers as a modifying additive to motor oil

Due to the widespread of lubricants, improving their tribological characteristics remains an important practical task. Among the promising modifying additives, carbon nanomaterials attract special attention. Such materials are found to improve the antifriction characteristics of lubricants and oils. In the present research, carbon nanofibers were synthesized via catalytic pyrolysis of a mixture of light hydrocarbons (C2-C4) over the NiCu catalyst. In order to form functional groups on the surface of carbon nanofibers, they were treated with diluted acids HCl, HNO3, and H2SO4 as well as with concentrated HNO3. The functionalized samples were comprehensively characterized by a set of physicochemical methods including atomic absorption spectroscopy, scanning and transmission electron microscopies, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, temperature-programmed desorption/oxidation, and Raman spectroscopy. As defined, the surface oxygen concentration in the samples varies from 3.5 to 16.3 at.%. It was shown that the addition of modified carbon nanofibers to a motor oil leads to an improvement in its tribological characteristics. In particular, the most effective additive was the sample treated with diluted HNO3. The motor oil with this modifying additive exhibited the heating temperature decreased by 10 °C and the contact spot area on the stationary body decreased by 20 %.

Influence of IDS and SDS compound ratio on pore structure and wettability of bituminous coal and anthracite: Experimental and simulation discussion

The pore and wetting characteristics of bituminous coal and anthracite treated with different proportions of tetrasodium iminodisuccinate (IDS) and sodium dodecyl sulfate (SDS) were measured. The pore structure characteristics of the coal were studied via low-temperature nitrogen adsorption analysis and the Frenkel-Halsey-Hill fractal theory. Zeta potential measurements were conducted to quantitatively analyze the degree of aggregation or dispersion of coal particles dissolved in solution. Changes in the coal surface morphology were observed and analyzed by scanning electron microscopy (SEM). The results show that when the ratio of IDS:SDS is 1:3, the specific surface area (SSA) values of bituminous coal and anthracite are the lowest. The composite reagent has a greater effect on improving the pore structure of anthracite than bituminous coal. Compared with bituminous coal, anthracite has better pore connectivity and a wider pore network. The absolute zeta potentials of bituminous coal and anthracite reach the maximum at an IDS:SDS ratio of 1:3, with values of 91.08 mV and 91.35 mV, respectively. The electrostatic potential distributions of the molecules show that the advantages of the electrostatic potential difference with water molecules enable IDS and SDS molecules to effectively attract water molecules and form hydrogen bonds, thus revealing the optimization mechanism of coal wettability.

Structure – Catalytic Behavior Relationships in TiO2-Carbon Composite Supported Pt Electrocatalysts: A Case Study

Composite types of supports made of TiO2 and carbonaceous materials provide higher stability for the Pt electrocatalysts under the working conditions of polymer electrolyte membrane fuel cells than the traditional carbon supports. We have demonstrated in our previous work that composites with general formula of 75 wt.% Ti(1-x)MoxO2-25 wt.% C (x = 0–0.2; C = traditional Black Pearls (BP) carbon) were promising supports which provided increased stability for the Pt electrocatalysts. In this study, the effect of nitrogen doping of the carbonaceous component of the composite was explored. 75 wt.% TiO2-25 wt.% carbon composite supports were prepared using graphite oxide (GO), N-doped GO and N-doped multilayer graphene. Electrocatalysts were made by loading the supports with 20 wt.% Pt. The systems were compared based on their physicochemical properties determined by low-temperature nitrogen adsorption, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and conductivity measurements. The activity of the catalysts was investigated by conventional methods in a 3-electrode electrochemical cell. The results of various characterization methods contributed to the understanding of the difference in the electrochemical properties of N-free and N-containing catalyst samples. While GO was favorable for this composite supported catalyst, its N-doping strongly influenced the growth of TiO2, forming an almost continuous coating of small TiO2 crystals. This quasi-insulating TiO2 layer between the Pt catalytic sites and the conductive part of the composite resulted in poor electrochemical activity. Mixing the sample with carbon improved its conductivity, which resulted in a significant increase in the oxygen reduction activity.

Exploring in-situ combustion effects on reservoir properties of heavy oil carbonate reservoir

Laboratory modeling of in-situ combustion is crucial for understanding the potential success of field trials in thermal enhanced oil recovery and is a vital precursor to scaling the technology for field applications. The high combustion temperatures, reaching up to 480°C, induce significant petrophysical alterations of the rock, an often overlooked aspect in thermal EOR projects. Quantifying these changes is essential for potentially repurposing thermally treated, depleted reservoirs for CO2 storage.In this study, we depart from conventional combustion experiments that use crushed core, opting instead to analyze the thermal effects on reservoir properties of carbonate rocks using consolidated samples. This technique maintains the intrinsic porosity and permeability, revealing combustion's impact on porosity and mineralogical alterations, with a comparative analysis of these properties pre- and post-combustion. We characterize porosity and pore geometry evolution using low-field nuclear magnetic resonance, X-ray micro-computed tomography, and low-temperature nitrogen adsorption. Mineral composition of the rock and grain-pore scale alterations are analyzed by scanning electron microscopy and X-ray diffraction.The analysis shows a significant increase in carbonate rocks’ porosity, pore size and mineral alterations, and a transition from mixed-wet to a strongly water-wet state. Total porosity of rock samples increased in average for 15%–20%, and formation of new pores is registered at the scale of 1–30 μm size. High-temperature exposure results in the calcite and dolomite decomposition, calcite dissolution and formation of new minerals – anhydrite and fluorite. Increased microporosity and the shift to strongly water-wet rock state improve the prospects for capillary and residual CO2 trapping with greater capacity. Consequently, these findings highlight the importance of laboratory in-situ combustion modeling on consolidated rock over tests that use crushed core, and indicate that depleted combustion stimulated reservoirs may prove to be viable candidates for CO2 storage.

Influence of shale reservoir properties on shale oil mobility and its mechanism

Given the tremendous potential for continental shale oil in China, many oilfields in the central and eastern parts of the country are involved in the exploration and development of shale oil resources. Besides engineering factors, shale oil mobility is the key to determining its commercial viability. This study explores the Hetaoyuan Formation in the Biyang Depression as an example to determine the influence of reservoir properties on the movable oil volume and its mechanisms. Multiple techniques were used, including displacement nuclear magnetic resonance (NMR), low-temperature nitrogen adsorption (LTNA), X-ray diffraction (XRD) bulk mineral analysis, and scanning electron microscopy (SEM), and the results suggest that large average pore diameter, high throat to pore ratio, single pore morphology, and small specific surface area can weaken the boundary layer effect and reduce the amount of adsorbed oil. Our observations reveal that compared to the dissolution pores and intergranular pores in brittle minerals, the intercrystalline pores in terrigenous clastic clay minerals are more affected by compaction. Furthermore, authigenic clay minerals notably block the intergranular pores in the interbedded sandstones. Clay minerals are identified as the main contributor to the specific surface area, with high clay mineral content enhancing the pore heterogeneity of the reservoir. Thus, positive shale oil mobility occurs in shale with a weak boundary layer effect, which is attributed to the high brittle mineral content, large average pore diameter, small specific surface area, single pore morphology, and reservoir homogeneity.

Evolution of shale wetting properties under long-term CO2/brine/shale interaction: Implications for CO2 storage in shale reservoirs

In the case of Carbon Geological Storage (CGS), the wettability is one of the main parameters controlling the CO2 injection capacity and CO2 plume movement, which affects the safety of long-term CO2 storage. A full evaluation of this parameter is essential for risk evaluation and storage capacity estimation. The objective of this study was to investigate the wettability changes of shales from the Chang 7 Formation in the Ordos Basin by exposing the samples to ScCO2/brine for 10/20/30/and 60 days. The mineral composition, pore structure, chemical functional groups, and surface morphology changes of the shale were analyzed using x-ray diffractometer (XRD), low-temperature nitrogen adsorption (LN-N2), infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). In addition, the solid-drop method was used to measure the contact angle of shale samples at different times of ScCO2 soaking. The results show that after 60 days of continuous ScCO2 soaking, the shale water contact angle and chemical group peak spectrum generally show an increasing trend, which is caused by the reduction of carbonate and clay mineral content. The prolonged time of ScCO2 soaking weakens the shale's water wettability and reduces the water-locking effect (water has a sealing effect in the pore channel of the reservoir), capillary force, and the height of CO2 sequestration columns, which is favorable for shale gas extraction (a method of extracting natural gas from shale rock by CO2 fracturing), but it may increase the CO2 geological leakage risk. The results have important implications for regulating the change of shale water wettability, and this study can also better provide theoretical references for Carbon Geological Storage programs.

CoM-ZSM5 (M = Zn and Ni) Zeolites for an Oxygen Evolution Reaction in Alkaline Media

An ion-exchange procedure of synthetic zeolite ZSM-5 (Si/Al = 15) was used to prepare three cobalt ZSM-5 zeolites (CoM-ZSM5 (M = Zn and Ni)) that were examined for OERs in alkaline media. The structural, morphological, and surface properties of the prepared materials were studied by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, and low-temperature nitrogen adsorption. All three electrocatalysts showed OER activity where CoNi-ZSM5 presented the highest current density (9.5 mA cm−2 at 2 V), the lowest Tafel slope (134 mV dec−1), and the lowest resistances of the charge transfer reaction (31.5 Ω). Overpotential (ηonset) at an onset potential of 410 mV for both CoNi-ZSM5 and Co-ZSM5 and 440 mV for CoZn-ZSM5 electrodes was observed. Co-ZSM5 showed somewhat lower OER catalytic activity than CoNi-ZSM5, while CoZn-ZSM5 demonstrated the lowest OER catalytic activity. The Rct of CoZn-ZSM5 is significantly higher than the Rct of CoNi-ZSM5, which could lead to their different OER activities. Good OER stability and low price are the main advantages of the synthesized CoM-ZSM5 samples in this study.

Synthesis, properties and applications of new hybrid material based on native/magnetically modified sepiolite and chitosans

The study introduces novel hybrid materials containing native and magnetite-containing sepiolite (Sep, SepM respectively) and chitosans (Ch) of different molecular weights. The main objective of this work was to determine the properties of these materials, including the different types of stability (colloidal, gravitational and thermal) in systems containing sepiolite, in order to obtain effective, stable and easily producible hybrid materials with great potential for water and wastewater treatment. The following measurements and methods were performed to characterize the investigated system: low-temperature nitrogen adsorption–desorption, zeta potential analysis, UV–Vis, FT-IR, XRD, XRF, SEM-EDS, TGA, DSC and DTG. It was found that the complexes with high molecular weight chitosan exhibited the best stability of the systems. The same tendency was observed for the concentration dependence: the higher the chitosan concentration, the better the stabilization of the composites. Overall, this study shows that chitosan effectively improves the colloidal and gravitational stability of the composites. Due to its unique structure, the synthesized magnetic hybrid material has shown great advantages in the adsorptive removal of textile dyes such as anionic acid red 88 (AR88) and cationic methylene blue (MB) which can be easily removed from the dye solutions after its use using an external magnetic field.

Experimental research on the influence of acid on the chemical and pore structure evolution characteristics of Wenjiaba tectonic coal.

The chemical and pore structures of coal play a crucial role in determining the content of free gas in coal reservoirs. This study focuses on investigating the impact of acidification transformation on the micro-physical and chemical structure characteristics of coal samples collected from Wenjiaba No. 1 Mine in Guizhou. The research involves a semi-quantitative analysis of the chemical structure parameters and crystal structure of coal samples before and after acidification using Fourier Transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) experiments. Additionally, the evolution characteristics of the pore structure are characterized through high-pressure mercury injection (HP-MIP), low-temperature nitrogen adsorption (LT-N2A), and scanning electron microscopy (SEM). The experimental findings reveal that the acid solution modifies the structural features of coal samples, weakening certain vibrational structures and altering the chemical composition. Specifically, the asymmetric vibration structure of aliphatic CH2, the asymmetric vibration of aliphatic CH3, and the symmetric vibration of CH2 are affected. This leads to a decrease in the contents of -OH and -NH functional groups while increasing aromatic structures. The crystal structure of coal samples primarily dissolves transversely after acidification, affecting intergranular spacing and average height. Acid treatment corrodes mineral particles within coal sample cracks, augmenting porosity, average pore diameter, and the ratio of macro-pores to transitional pores. Moreover, acidification increases fracture width and texture, enhancing the connectivity of the fracture structure in coal samples. These findings provide theoretical insights for optimizing coalbed methane (CBM) extraction and gas control strategies.

Pore heterogeneity analysis and control mechanisms in Cambrian shale of the Shuijingtuo Formation, Yichang area, China

This study focuses on understanding the fractal characteristics and controlling factors of micropore structures within organic-rich shale of the Cambrian Shuijingtuo Formation in the Yichang area of Hubei Province. Mineralogy, petrology, and organogeochemical characteristics were confirmed through comprehensive testing methods, including whole-rock X-ray diffraction and organic geochemical analyses. Additional experiments included low-temperature carbon dioxide adsorption, low-temperature nitrogen adsorption, and high-pressure mercury injection. Fractal dimensions of micropores, mesopores, and macropores were calculated using the V-S, FHH, and MENGER sponge models, respectively. Results indicate that the Cambrian Shuijingtuo Formation represents a typical deposit from an alkaline water body, resulting in high-calcareous shale. Fractal dimensions were as follows: micropores (D1) ranged from 2.1138 to 2.3475 (average 2.2342), mesopores (D2) ranged from 2.5327 to 2.7162 (average 2.6171), and macropores (D3) ranged from 2.7361 to 2.9316 (average 2.82905). Correlations were observed between total organic carbon (TOC) content and Ro with D1 and D2 (positive) and D3 (negative). Shale pore volume and specific surface area exhibited positive correlations with D1 and D2 but negative correlations with D3. High bio-deposited silica positively influenced micropore and mesopore development, while clay mineral compaction and dehydration transformations favored macropore development. Carbonate minerals primarily contributed to regular macropores, with complex correlations involving fractal dimensions D1, D2, and D3. The research results provide theoretical support for analyzing pore fractal characteristics of shallow old Marine shale reservoirs and the prediction and development plan of high-quality reservoirs of the Shuijingtuo Formation in the Yichang area.

STUDY OF CATALYTIC BEHAVIOURS OF THE SPINEL STRUCTURE NdxMg1- xAl2O4 COMPOSITION WITH ZSM-5 ZEOLITE IN ETHYLBENZENE DISPROPORTIONATION

Nanosized (10–15 nm) powders of spinel structures NdxMg1–xAl2O4 were obtained by low-temperature combustion of aluminium, magnesium, neodymium nitrate solutions, diethylmalonate, and hydrazine monohydrate with further calcination of nanopowders at 1000 °C, which were used in the preparation of catalytic compositions with ZSM-5 zeolite. The obtained catalytic compositions were characterized by X-ray diffraction, pyridine adsorption, and low-temperature nitrogen adsorption. The acidic properties and porosity of the catalysts were altered by controlling the concentration of nanopowder (1.0–7.0 wt.%) in the catalytic composition. The interaction of the modifier with HZSM-5 zeolite leads to a decrease in specific surface area and pore volume, as well as reduse of strong Bronsted acid sites (B) and an increase in the concentration of medium Lewis acid sites (L), resulting in a change in the B/L ratio from 3.61 to 0.23. The ongoing variations contributed mainly to an enhancement of the para-selectivity of the catalytic composition in the ethylbenzene disproportionation reaction. The catalytic composition of 5% Nd0.1Mg0.9Al2O4 with a pore volume of 0.15 cm3/g and an acid site B/L ratio of 0.27 demonstrates a maximum selectivity to p-diethylbenzene of 75.6% with a conversion of ethylbenzene of 23.7%.

Fractal Characteristics and Microstructure of Coal with Impact of Starch-Polymerized Aluminum Sulfate Fracturing Fluids

The degree of irregularity and complexity of the pore structure are comprehensively reflected in the fractal dimension. The porosity of coal was determined by its fractal dimension, where a larger dimension indicates a lower porosity. Fractal theory and the Frenkel–Halsey–Hill (FHH) model were applied to explore the variation rules of concentration on functional groups and pore structure in this study. Combined with infrared spectroscopy (FTIR) and low-temperature nitrogen adsorption, a starch-polymerized aluminum sulfate composite fracturing fluid was prepared, which plays an important role in methane adsorption and permeability of coal samples. The test results showed that, compared with the original coal, the pore volume and specific surface area of each group of coal samples were reduced, the average pore diameter was initially enlarged and then declined, and fractal dimension D1 dropped by 5.4% to 15.4%, while fractal dimension D2 gained 1.2% to 7.9%. Moreover, the nitrogen adsorption of each group of coal samples was obviously lower than the original coal, and the concentration of starch-polymerized aluminum sulfate solution existed at a critical optimal concentration for the modification of the coal samples, and the nitrogen adsorption reached a minimum value of 0.6814 cm3/g at a concentration of 10%. The novel composite solution prepared by the combination of starch and flocculant in this paper enhanced the permeability of the coal seam, which is of great significance in improving the efficiency of coalbed methane mining.

Mechanical Properties and Corrosion Resistance of Hot-Pressed Dysprosium Molybdate Samples

The purpose of this work was to study the consolidation features using hot pressing method of dysprosium molybdate billets and to study their mechanical properties and corrosion resistance.Methods. The technological and physical properties of the mechanosynthesised dysprosium molybdate powder were investigated. Properties and structure of the obtained dysprosium molybdate powder were studied by methods of chemical and X-ray phase analyses and scanning electron microscopy. Bulk density of dysprosium molybdate powder was studied according to GOST 19440-94. Flowability of dysprosium molybdate powder was determined according to GOST 20899-75. The specific surface of dysprosium molybdate was determined using a specific surface analyser NOVA 1200e (USA) by the method of low-temperature nitrogen adsorption (BET). X-ray phase analysis of mechanosynthesised dysprosium molybdate powder was carried out on a diffractometerResults. The bending strength of hot-pressed dysprosium molybdate specimens was determined, it was found that the highest value of the bending strength was recorded for these specimens at a pressing pressure of 35 MPa and is 314 MPa. The corrosion resistance of hot-pressed dysprosium molybdate samples in aqueous coolant at a temperature of 100 °C was studied. It was recorded that the mass of the mechanosynthesised dysprosium molybdate specimens remained practically unchanged throughout the corrosion resistance test in aqueous coolant.Conclusion. Tests on corrosion resistance have shown absence of change of mass of samples from dysprosium molybdate during 60 hours. The bending strength of samples from dysprosium molybdate obtained by hot pressing at pressure 35 Pa, temperature 1400 oÑ and time of holding under pressure 5 min is 314 MPa.

Coupling control of organic and inorganic rock components on porosity and pore structure of lacustrine shale with medium maturity: A case study of the Qingshankou Formation in the southern Songliao Basin

Shale components affect organic–inorganic diagenesis, control the formation and evolution of pore structure, and lead to heterogeneity of shale reservoirs. Therefore, revealing the coupling control of shale components on the porosity and pore structure is crucial for selecting the dominant lithofacies. In this study, the lacustrine shale with medium maturity in the first member of the Qingshankou Formation (Qing1 Member) in the Changling Sag, southern Songliao Basin, China, was analyzed. Using pressurized sealed original shale samples and 2-D nuclear magnetic resonance (2D-NMR) analysis, the effective porosity of shale was accurately determined. The pore structure was characterized via experiments such as low-temperature nitrogen adsorption, NMR, and scanning electron microscope (SEM) analyses. In addition, the joint influences of the shale rock components, sedimentary structure, and maturity on the porosity and pore structure were investigated. Finally, the favorable reservoirs in the lacustrine shale with medium maturity and their formation conditions were identified. Studies have shown that for lacustrine shale with medium maturity: (1) a moderate total organic carbon (TOC) content (between 1% and 2.5%) is a key factor for improving the effective porosity and the proportions of mesopores (100–1000 nm) and small-pores (30–100 nm). This is related to the generation of organic acids and the cracking of organic matter into pores. An excessive TOC content can lead to increased plasticity of the rock and filling of the pores by bitumen. (2) The porosity and pore structure are controlled by the organic matter and inorganic minerals as well as sedimentary structure. Organic matter has dual impacts on the porosity improvement related to clay minerals, promotion of clay conversion and filling of clay-related pores, and the ratio of the clay content to the TOC (Vsh/TOC) can reflect the degree of influence of organic matter, the greater the Vsh/TOC ratio is, the greater the effective porosity and proportion of micropores are. (3) Organic matter and felsic minerals jointly effect the improvement of the effective porosity and larger pores (>30 nm), which is related to their good compression resistance, organic pore retention, and dissolution-enhanced porosity effect. The product of the TOC and felsic mineral content (Vsi*TOC) can reflect the degree of their coupled effect. For moderate TOC contents, a higher felsic mineral content, and moderate shell laminae (Vca>10%) are conducive to the development of the effective porosity and larger pores. (4) The organic medium-rich argillaceous laminated felsic shale and organic-medium argillaceous laminated clayey shale have a higher effective porosity and higher proportion of larger pores, making them the dominant lithofacies for shale oil sweet spots.

Thermal diffusity in copper benzene-1,3,5-tricarboxylate–reduced graphite oxide mechanical composites

AbstractMetal organic frameworks (MOFs) and particularly copper benzene-1,3,5-tricarboxylate (HKUST-1) are excellent materials for gas storage (e.g., CH4, N2, H2 adsorption) and gas separation. In this work, reduced graphene oxide (RGO)–HKUST-1 mechanical mixtures were studied in order to reveal the effect of RGO content on the pressure tolerance of the texture and heat conductivity. HKUST-1 was obtained by two different synthesis routes. Air-dried MOF and RGO were thoroughly mixed prior to the compression. Powder XRD and Raman spectroscopy were used to characterize the response of the crystal structure, while low-temperature nitrogen adsorption was used the follow the adsorption properties of the pellets. Finally, the "flash" heat pulse method was used to assess the thermal properties. The gas adsorption isotherms revealed that the adsorption capacity decreases when RGO is added. Based on Raman and XRD results, we found that the synthesis route has an effect on multiple scales. We experimentally confirmed that evaluation of the thermal diffusivity requires a model more complex than the simple Fourier equation, due to the inherent heterogeneous structure of the material. A good approximation of the Fourier coefficient of thermal diffusivity was obtained using the parameters of the Guyer–Krumhansl equation. The heat pulse experiments also revealed possible size-dependent behavior.

Removal of chromium (VI) from aqueous solutions by granular composites based on laponite and alginate ionotropically cross-linked by iron and zirconium ions

The conducted research established the porous structure of the materials through low-temperature nitrogen adsorption. It was demonstrated that the nitrogen sorption isotherms for the investigated samples belong to Type IV with H4 hysteresis associated with bottle-like pores. The specific surface area of the granulated composite samples was determined, ranging from 99 to 111 m2/g. Additionally, it was shown that an increase in iron content in the samples leads to a reduction in micropore content. Active centers on the material's surface, primarily composed of hydroxyl groups, were investigated using infrared spectroscopy. The kinetics of chromium (VI) adsorption were explored, and it was established that the iron-to-zirconium ratio in the reinforcement solutions hardly affects the duration of establishing adsorption equilibrium, which is approximately 60 minutes. Pseudo-first-order and pseudo-second-order models were applied to describe the kinetics of the adsorption process. The dependence of the chromium (VI) removal efficiency on the solution pH was determined. It was demonstrated that the synthesized samples exhibited high adsorption in acidic conditions with a sharp decline when transitioning to neutral and alkaline environments. It was shown that the maximum sorption capacities of the synthesized granulated composite samples significantly depend on the ratio of iron and zirconium ions. One of the most efficient samples is that with 50% Fe and 50% Zr, exhibiting a maximum sorption capacity of 13.29 mol/g at pH 6. The use of Langmuir and Freundlich models allowed establishing the fundamental adsorption properties of the materials.

Shale permeability and microstructural alternation during CO2 pre-fracturing: A mechanistic study

CO2 pre-fracturing technology represents a novel approach to CO2 fracturing, effectively enhancing carbon capture efficiency in shale reservoirs while increasing the recovery of hydrocarbon resources. This study systematically quantifies the impact of water injection on the pore structure and permeability of shale samples saturated with pre-injected CO2. Based on X-ray diffraction (XRD) and low-temperature nitrogen adsorption (LT-NA) results, the dominant mechanism of the swelling-chemical coupling effect in shale property is clarified. Pre-injected CO2 can effectively mitigate the impact of water absorption. After a reaction time of 7 days, the permeability of the CO2-involved hydrated shale samples is four times that of samples without CO2. Nevertheless, the influence of subsequently injected water on shale permeability persists, resulting in an 80% reduction in shale permeability. XRD and LT-NA results indicate that the swelling-chemical coupling effect is the dominant factor in shale property variation during CO2 pre-fracturing. In the initial stage, the decline in calcite and clay mineral content is significant, and chemical dissolution dominates the change in pore structure. As the reaction progresses, the intensity of chemical reactions weakens, and clay mineral swelling becomes the primary factor affecting the shale properties. In this stage, K+ generated from original minerals effectively inhibits clay mineral swelling. Therefore, the swelling-chemical coupling effects should be comprehensively considered during the CO2 pre-fracturing process, and an appropriate soaking time should be selected to maximize CO2 storage efficiency and oil and gas production.

Reservoir Characteristics of the Main Coal Seams in the Longtan Formation, Guxu Coal Mining Area, Sichuan

To facilitate the efficient exploration and development of coalbed methane of the Longtan Formation in the Guxu coal mining area, Sichuan, it is essential to evaluate the reservoir characteristics of the main production layers. In this study, scanning electron microscopy, low-temperature liquid nitrogen adsorption experiments, high-pressure mercury pressure experiments, and isothermal adsorption experiments were conducted to investigate the reservoir characteristics of favorable coalbed methane reservoirs. The results indicate that the main coal seams in the Longtan Formation are medium-to-high ash content anthracite with a well-developed pore–fracture system. The pore size distribution exhibits both unimodal and bimodal types, while the pore morphology includes impermeable pores closed at one end, open permeable pores, and ink bottle-shaped pores. It shows that the middle part of Longtan Formation acts as an enrichment zone for coalbed methane, which is characterized by a stronger adsorption capacity, high Langmuir volume, high gas content, and high gas saturation distribution. The pH value, mineralization degree, and hydrogen–oxygen isotope of the produced water in the main coal seams indicate that the enrichment zone is typically located in a stagnant flow zone with a reducing environment and favorable storage conditions.

Control of complex lithofacies on the shale oil potential in saline lacustrine basins of the Jimsar Sag, NW China: Coupling mechanisms and conceptual models

The heterogeneity of lithofacies is a pivotal factor influencing the shale oil potential. A comprehensive understanding of the intricate influence of rock complexity on hydrocarbon generation properties, microscopic pore-throat structure, and fluid occurrences is crucial for shale oil exploration and development. The Lucaogou Formation in the Jimsar Sag is a type of saline lacustrine shale oil, which was chosen as a research example in this paper. To unravel the causal linkage and confirm the coupling relationship between lithofacies, pores, and fluid mobility in the sedimentary sequence of saline lacustrine basins, a series of experiments were conducted. These included total organic carbon (TOC), X-ray diffraction (XRD), vitrinite reflectance (Ro), Rock-Eval pyrolysis, field emission-scanning electron microscopy (FE-SEM), low-field nuclear magnetic resonance (LF-NMR), mercury intrusion porosimetry (MIP), and low-temperature nitrogen adsorption (LTN2A). The results revealed significant differences in pores, oiliness, and fluid mobility among the four dominant lithofacies. Employing an innovative comprehensive evaluation method, high-carbon silty dolomite manifests significant potential for hydrocarbon generation, substantial storage capacity, effective oiliness and mobility, heightened brittle mineral content, and facile fracture production. Consequently, it was the most favorable lithofacies. Furthermore, TOC, pore size, and pore types emerged as key factors influencing the movable oil content of different lithofacies. More importantly, a detailed multiscale model illustrated potential linkages across the three different scales of lithofacies associations, pores, and fluid mobility. The study’s outcomes can offer enhanced guidance for accurately assessing shale oil resources, particularly in the identification of crucial “sweet spots”.