Search Results (32)

The mechanism of low- to middle-rank coal seam gas accumulation in the Baode block on the eastern edge of the Ordos Basin is well understood. However, exploration efforts in the Shizuishan area on the western edge started later, and the current understanding of enrichment and accumulation rules is unclear. It is important to systematically study enrichment and accumulation, which guide the precise exploration and development of coal seam gas resources in the western wing of the basin. The coal seam collected from the Shizuishan area of Ningxia was taken as the target. Based on drilling, logging, seismic, and CBM (coalbed methane) test data, geological conditions were studied, and factors and reservoir formation modes of CBM enrichment were summarized. The results are as follows. The principal coal-bearing seams in the study area are coal seams No. 2 and No. 3 of the Shanxi Formation and No. 5 and No. 6 of the Taiyuan Formation, with thicknesses exceeding 10 m in the southwest and generally stable thickness across the region, providing favorable conditions for CBM enrichment. Spatial variations in burial depth show stability in the east and south, but notable fluctuations are observed near fault F1 in the west and north. These burial depth patterns are closely linked to coal rank, which increases with depth. Although the southeastern region exhibits a lower coal rank than the northwest, its variation is minimal, reflecting a more uniform thermal evolution. Lithologically, the roof of coal seam No. 6 is mainly composed of dense sandstone in the central and southern areas, indicating a strong sealing capacity conducive to gas preservation. This study employs a system that fuses multi-source geological data for analysis, integrating multi-dimensional data such as drilling, logging, seismic, and CBM testing data. It systematically reveals the gas control mechanism of “tectonic–sedimentary–fluid” trinity coupling in low-gentle slope structural belts, providing a new research paradigm for coalbed methane exploration in complex structural areas. It creatively proposes a three-type CBM accumulation model that includes the following: ① a steep flank tectonic fault escape type (tectonics-dominated); ② an axial tectonic hydrodynamic sealing type (water–tectonics composite); and ③ a gentle flank lithology–hydrodynamic sealing type (lithology–water synergy). This classification system breaks through the traditional binary framework, systematically explaining the spatiotemporal matching relationships of the accumulated elements in different structural positions and establishing quantitative criteria for target area selection. It systematically reveals the key controlling roles of low-gentle slope structural belts and slope belts in coalbed methane enrichment, innovatively proposing a new gentle slope accumulation model defined as “slope control storage, low-structure gas reservoir”. These integrated results highlight the mutual control of structural, thermal, and lithological factors on CBM enrichment and provide critical guidance for future exploration in the Ningxia Autonomous Region. Full article

A technology that directly injects CO₂-rich industrial waste gas (CO₂-rich IWG) into underground spaces for unconventional natural gas extraction and waste gas storage has received increasing attention. The pore characteristics of coal and shale in a coal-bearing rock series before and after CO₂-rich IWG treatment are closely related to gas recovery and storage. In this study, three coals ranging from low to high rank and one shale sample were collected. The samples were treated with CO₂-rich IWG using a high-precision geochemical reactor. The changes in the pore volume (PV), specific surface area (SSA), and pore size distribution of micropores, mesopores, and macropores were analyzed. The correlations between the Langmuir volume and the PV and SSA of the micropores and mesopores were analyzed. It was confirmed that for micropores, SSA was the dominant factor influencing adsorption capacity. The effectively interconnected pore volume was calculated using macropores to characterize changes in the sample’s connectivity. It was found that the PV and SSA of the micropores in the coal samples increased with increasing coal rank. The CO₂-rich IWG treatment increased the PV and SSA of the micropores in all of the samples. In addition, for mesopores and macropores, the treatment reduced the SSA in the coal samples but enhanced it in the shale. The results of this study improve the understanding of the mechanisms of the CO₂-rich IWG treatment method and emphasize its potential in waste gas storage and natural gas extraction. Full article

Geological storage of CO₂ in coal seam is an effective way for carbon emission reduction. Evaluating the adsorption-induced swelling behavior of confined coal is essential for this carbon emission reduction strategy. Based on the thermodynamic theory and the Gibbs adsorption model, a thermodynamic method for evaluating the gas adsorption-induced swelling behavior of confined coal was established. The influences of factors such as stress, gas pressure, and the state of gas on the adsorption-induced swelling behavior of confined coal were discussed. The predicted swelling deformation from the thermodynamic method based on the ideal gas hypothesis was consistent with the experimental result only under the condition of low-pressure CO₂ (<2 MPa). The predicted swelling deformation from that method was larger than the experimental result under the condition of high-pressure CO₂ (>2 MPa). However, the method based on the real gas hypothesis always had better prediction results under both the low- and high-pressure CO₂ conditions. From the perspective of phase equilibrium and transfer, in the process of CO₂ adsorption by the confined coal, gas molecules transfer from the adsorption site of high chemical potential to the low chemical potential. Taking the real gas as ideal gas will result in the surface energy increase in the established model. Consequently, the prediction result will be larger. Therefore, for geological storage of CO₂ in coal seam, it is necessary to take the real gas state to predict the adsorption-induced swelling behavior of the coal. In the process of CO₂ adsorption by the confined coal, when its pressure is being closed to the critical pressure, capillary condensation phenomenon will occur on the pore surface of the confined coal. This can make an excessive adsorption of CO₂ by the coal. With the increase in the applied stress, the adsorption capacity and adsorption-induced swelling deformation of the confined coal decrease. Compared to N₂ with CO₂, the coal by CO₂ adsorption always shows swelling deformation under the simulated condition of ultra-high-pressure injection. However, the coal by N₂ adsorption will shows shrinking deformation due to the pore pressure effect after the equilibrium pressure. Taking the difference in the adsorption-induced swelling behavior and pore compression effect, N₂ can be mixed to improve the injectivity of CO₂. This suggests that CO₂ storage in the deep burial coal seam can be carried out by its intermittent injection under high-pressure condition along with mixed N₂. Full article

Carbon dioxide (CO₂) storage in sandstones is vital for enhancing oil/gas recovery and reducing CO₂ emissions. The introduction of CO₂ into sandstone reservoirs leads to chemical reactions between CO₂ and minerals present in sandstone, which changes the pore structure of the sandstone reservoir. Herein, tight sandstone samples from the Coal-Measure Strata of the Shanxi Formation in the Huxiang area, Henan Province, were selected for simulation in this experimental study under supercritical CO₂ (ScCO₂)–H₂O treatment in reservoir conditions. Further, mercury intrusion porosimetry and low-pressure nitrogen adsorption/desorption methods were used to analyze the evolution of the pore structures of tight sandstones, and the mechanism of pore structure evolution was discussed. The results show that pore volumes and specific surface areas in the micropores and transitional pores decreased after the ScCO₂–H₂O treatment, while those in the mesopores and macropores increased. In the micropores and transitional pores, some of the pores changed from open pores and ink-bottle-shaped pores to semi-closed pores after the ScCO₂–H₂O treatment, and the pore morphology became narrower, which might have deteriorated the pore connectivity. A pore structure evolution model of ScCO₂–H₂O-treated tight sandstones was proposed. The evolution of pore structure is a result of the synergistic effect of pore enlargement caused by mineral dissolution and secondary mineral precipitation, which together play a controlling role in pore structure evolution. This study is conducive to understanding the pore structure evolution under ScCO₂–H₂O treatment and implementing CO₂ storage and enhancing oil/gas recovery in sandstone reservoirs. Full article

Coal gangue is a solid waste produced in the coal mining process. During the mining process, mining-induced overburden fractures are a favorable place for the storage of coal gangue; therefore, coal gangue can be incorporated into filling materials for harmless disposal. Overburden isolated grout filling is a better technology for solid waste reduction, which is currently in development. This paper delves into the methodology of large-scale coal gangue disposal, utilizing this specific technology. With reference to fly ash granules and their slurry characteristics that have been previously applied successfully, raw gangue was pulverized and transformed into a slurry. This experiment then investigated the fundamental characteristics of the gangue powder solids and slurry. This study’s findings reveal that the composition types of granule oxides following gangue pulverization closely resemble those of fly ash, with minimal content differences observed between identical oxides. Regarding slurry characteristics, the plastic viscosity of fly ash slurry ranged from 0.45 to 145.2 mPa·s, whereas the plastic viscosity of gangue slurry varied between 2.1 and 56.4 mPa·s. Notably, the stability and fluidity of the gangue slurry surpassed those of the fly ash slurry. Furthermore, regarding the filling efficiency, the compaction coefficient of gangue slurry is less than that of fly ash. Consequently, under identical grouting conditions, a larger mass of solids can be disposed of using gangue slurry compared to fly ash. The research findings facilitate the implementation of a practice involving the overburden isolated grout filling of over million tons of coal gangue in the 21404 working face of the Hulusu coal mine, located in Inner Mongolia, China. This practice has demonstrated a daily filling capacity of up to 4000 t, accumulating to a total gangue filling mass of 1,068,000 t. This study’s findings present a viable and efficient approach to the large-scale, environmentally friendly disposal of coal gangue. Full article

The Polish economy, and especially the energy sector, is facing an energy transformation. For decades, most electricity in Poland has been generated from hard coal, but in recent years, renewable energy sources have been gaining an increasing share of the market. The aim of the energy transformation is to reduce the carbon footprint in electricity production, which translates into the decarbonization of the economy, including manufactured products. Currently (2024), increasing the share of renewable energy sources raises major challenges in terms of energy storage or other activities and forces cooperation with flexible sources of electricity generation. One of the challenges is to determine what a decarbonized energy mix in Poland could look like in 2050, in which there would be sources (with a smaller share of coal sources in the mix than currently) of electricity generation based on hard coal with CCS technology. In order to do this in an economically efficient manner, there are aspects related to the location of power plants that would remain in operation or repower current generating units. The added value of the study is the simulation approach to the analysis of the problem of assessing the effectiveness of CCS technology implementation together with the transport and storage infrastructure, as well as the multi-aspect scenario analysis, which can determine the limits of CCS technology effectiveness for a given power unit. Positive simulation results (NPV amounted to 147 million Euro) and the knowledge obtained in the scope of the correlated and simultaneous impact of many important cost factors and prices of CO₂ emission allowances make this analysis and its results close to reality. Examples of analyses of the effectiveness of CCS system implementations known from the literature are most often limited to determining linear relationships of single explanatory variables with a specific forecasted variable, even if these are multifactor mathematical models. Full article

The steep decline in the price of wind turbines and solar photovoltaics provides a possibility to decarbonize electricity deeply and affordably. This study uses the HOMER Pro energy modeling tool to model an optimized grid-connected renewable energy system for a community in southern Alberta, Canada. The study’s goal is to identify the best renewable energy technology combinations that can provide electricity at the lowest levelized cost of energy (LCOE) and has lower greenhouse gas emissions as compared to the electricity produced by traditional fossil fuel. Gleichen is a small town in southern Alberta that is close to numerous commercial wind and solar projects given the region’s high quality renewable resources. “Tri-brid” systems consisting of wind turbines, solar photovoltaics, and battery energy storage systems (BESS) are considered and compared based on electricity prices, net present cost, and greenhouse gas emissions savings. This tri-brid system is connected to the grid to sell excess generated electricity or buy electricity when there is less or no availability of solar and wind energy. The tri-brid energy system has an estimated LCOE of 0.0705 CAD/kWh, which is competitive with the price of electricity generated by natural gas and coal, which is 0.127 CAD/kWh. Full article

Water inrush from separation layers is a special type of water inrush disaster that occurs during coal mining. It is characterized by the absence of precursors before the inrush, a sudden and massive influx of water, strong destructive power, and significant difficulty in prevention and control. This disaster causes substantial economic losses and casualties in mines. To study the dynamic evolution characteristics of the overlying rock strata in Guojiahe coal mine, field investigations, theoretical analysis, physical simulations, and numerical simulations were conducted. The development state of the overlying rock strata and the height of the water-conducting fractures in the 1304 working face during continuous mining were analyzed, and the spatial position of the strata where water hazards could form was determined. Through theoretical calculations, the height of the water-conducting fracture zone was found to be approximately 205 m, forming a water-storable separation space about 248 m above the coal seam roof. A physical similarity model was constructed to study the development state of overlying rock strata separation in the 1304 working face. Experimental results indicate that, as the working face advances, the rock strata gradually develop lateral separation spaces from bottom to top, and vertical fractures increase progressively in a similar manner. The spaces and fractures formed in the early stages of the working face advance gradually close and form a compaction zone. However, new fractures develop near the working face side. As mining continues, the asynchronous movement of the overlying rock promotes the development of vertical fractures, providing water-conducting channels for water inrush from the separation. Based on numerical simulation analysis of the development state of overlying rock strata separation and the height of the water-conducting fracture zone, it can be concluded that the water-storable separation space develops between the 8th layer of the formation of sandy mudstone and the 9th layer of the Yijun Formation conglomerate, which is 248 m from the coal seam roof. When excavated to 280 m, the separation space reaches its maximum, with a width of about 19 m and a height of about 1.2 m, and the water storage capacity increases to its maximum. The height of the water-conducting fracture zone eventually increases to 202 m. Full article

In accordance with the programme of closure works and the implementation of ecological spatial rehabilitation in the area of the Slovenian coal mine Trbovlje–Hrastnik (RTH), there is a great opportunity to exploit shallow geothermal energy from water and ground sources. In the RTH area, there is great energy potential in the utilisation of underground water and heat from the earth. In our research, we have focussed on the use of geothermal energy with heat pumps from groundwater (water/water system) and from ground collectors and wells up to a depth of 150 m (rock/water system). With the water/water system, we have an average of 2.7 MW of thermal energy available, with the rock/water system having 7.5 kW of thermal energy from a 150 m deep well. With the rock/water system in particular, the development of an industrial zone in the RTH area can also provide for a greater demand for thermal energy. The thermal energy obtained in this way is utilised via heat pumps to heat and cool commercial, residential and industrial buildings. The utilisation of shallow geothermal energy can make a major contribution to carbon neutrality, as the use of geothermal energy has no negative impact on the environment and causes no greenhouse gas emissions. The aim of the paper is to provide an overview of the methods used to analyse heat storage in aquifers of abandoned coal mines, to represent these storages in RTH with a basic mathematical–statistical inventory of what is happening in the aquifer, and to investigate the possibility of using shallow geothermal energy with the help of modelling the use of shallow geothermal energy. The results and analyses obtained can make an important scientific contribution to the use of geothermal energy from abandoned and closed mines. Full article

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. Full article

Capturing and storing CO₂ (CCS) was once regarded as a significant, urgent, and necessary option for reducing the emissions of CO₂ from coal and oil and gas industries and mitigating the serious impacts of CO₂ on the atmosphere and the environment. This recognition came about as a result of extensive research conducted in the past. The CCS cycle comes to a close with the last phase of CO₂ storage, which is accomplished primarily by the adsorption of CO₂ in the ocean and injection of CO₂ subsurface reservoir formation, in addition to the formation of limestone via the process of CO₂ reactivity with reservoir formation minerals through injectivities. CCS is the last stage in the carbon capture and storage (CCS) cycle and is accomplished chiefly via oceanic and subterranean geological sequestration, as well as mineral carbonation. The injection of supercritical CO₂ into geological formations disrupts the sub-surface’s existing physical and chemical conditions; changes can occur in the pore fluid pressure, temperature state, chemical reactivity, and stress distribution of the reservoir rock. This paper aims at advancing our current knowledge in CO₂ injection and storage systems, particularly CO₂ storage methods and the challenges encountered during the implementation of each method and analyses on how key uncertainties in CCS can be reduced. CCS sites are essentially unified systems; yet, given the scientific context, these storage systems are typically split during scientific investigations based on the physics and spatial scales involved. Separating the physics by using the chosen system as a boundary condition is a strategy that works effectively for a wide variety of physical applications. Unfortunately, the separation technique does not accurately capture the behaviour of the larger important system in the case of water and gas flow in porous media. This is due to the complexity of geological subsurface systems, which prevents the approach from being able to effectively capture the behaviour of the larger relevant system. This consequently gives rise to different CCS technology with different applications, costs and social and environmental impacts. The findings of this study can help improve the ability to select a suitable CCS application method and can further improve the efficiency of greenhouse gas emissions and their environmental impact, promoting the process sustainability and helping to tackle some of the most important issues that human being is currently accounting global climate change. Though this technology has already had large-scale development for the last decade, some issues and uncertainties are identified. Special attention was focused on the basic findings achieved in CO₂ storage operational projects to date. The study has demonstrated that though a number of CCS technologies have been researched and implemented to date, choosing a suitable and acceptable CCS technology is still daunting in terms of its technological application, cost effectiveness and socio-environmental acceptance. Full article

In recent years supercritical CO₂ power plants have seen a growing interest in a wide range of applications (e.g., nuclear, waste heat recovery, solar concentrating plants). The Allam Cycle, also known as the Allam-Fetvedt or NET Power cycle, seems to be one of the most interesting direct-fired sCO₂ cycles. It is a semi-closed loop, high-pressure, low-pressure ratio, recuperated, direct-fired with oxy-combustion, trans-critical Brayton cycle. Numerical simulations play a key role in the study of this novel cycle. For this reason, the aim of this review is to offer the reader a wide array of modeling solutions, emphasizing the ones most frequently employed and endeavoring to provide guidance on which choices seem to be deemed most appropriate. Furthermore, the review also focuses on the system’s performance and on the opportunities related to the integration of the Allam cycle with a series of processes, e.g., cold energy storage, LNG regasification, biomass or coal gasification, and ammonia production. Full article

The underground coal mining process is closely associated with frequent energy storage and consumption of coal mass with natural and induced fractures. Exploring the energy evolution characteristics of intact and fractured coal samples could be helpful for dynamic disaster control. In this study, laboratory true triaxial tests on the energy evolution characteristics of intact and fractured coal samples have been carried out and systematically discussed. The results show that the brittleness and peak strength are weakened due to the presence of macro-fractures in coal. The mean peak strength and brittleness for fractured coal are 29.00% and 74.59% lower than the intact coal samples. For both intact and fractured coal, the energy evolution curves are closely related to the deformation stages under true triaxial stresses. When subjected to the same intermediate stress, intact coal stores more elastic strain energy compared to fractured coal. Additionally, the rate of dissipative energy variation is two–three times lower in fractured coal samples compared to intact coal samples. Full article

In this work, MgAl-layered double hydroxides (LDH) were synthesized by co-precipitation method using a colloid mill and characterized by XRD and SEM. It was found that the environmentally friendly LDHs had greater performance than the traditional antioxidant. By adding LDHs into large electric shovel grease (GRK-A) in open-pit coal mine, the service lifetime of grease was extended by 20%. With the increase in LDH addition, the grease sample attains greater activation energy, and the thermal oxidation and decomposition resistance become stronger. Comparing the energy storage modulus and flow transition index at different temperatures, adding the right amount of LDHs needs close attention for the system oxidation resistance and viscoelasticity. For the electric shovel grease, the best oxidation resistance and rheological properties can be achieved by adding 2% of LDHs. The rheological viscosity–temperature curves show that the grease samples with different ratios of solid LDHs have better low-temperature properties than the mine grease. This work outlines a simple method for creating an environmentally sustainable lubricant additive with the use of LDH. LDH serves as a novel inorganic antioxidant additive that is optimal for open gear lubrication and sliding friction. Full article

The damage and fracture of coal is accompanied by a complex energy conversion process, and these different stages of energy evolution are closely related to coal failure. In this paper, an evolution model describing the behavior of coal failure was proposed using the energy dissipation under cyclic loading/unloading. The energy growth pattern and energy consumption characteristics of the coal fracture were analyzed under cyclic loading/unloading. An evolution model of the energy behavior of coal fracture was established. The damage variables of energy dissipation were defined, and a theoretical model was established. The parameters included the relationship between the energy state, damage state, and strength state according to the uniaxial cyclic loading/unloading test. The results show that there are energy excitation and inhibition effects in the process of coal fracture; that is, the accumulation rate and level of energy are affected by the energy storage state, and the energy storage rate changes in the mode of “low promotion and high inhibition”. The abrupt increase in dissipated energy can be regarded as the precursor of coal fracture. Based on the analysis of the characteristics of the damage and failure state and dissipated energy, the discriminant equation for the stability of the coal energy state was constructed; it is a meaningful discovery for predicting and evaluating coal failure. Full article