•The preferential adsorption of CO2 over CH4 improves with coal rank.•Pore structure of coal affects the thermodynamics of adsorption of CO2 and CH4.•Adsorbed CO2 has a more ordered configuration ...than CH4 on different rank coals.
In this paper, the pore structures of three different rank coals sampled from China (anthracite, bituminous coal and lignite) were characterized by CO2 and N2 adsorption. The isothermal adsorption curves of CO2 and CH4 on three samples were measured by gravimetric method and fitted by Langmuir model. The preferential selectivity (αCO2/CH4) was calculated using the Langmuir parameters of CO2 and CH4, and the Henry’s coefficient (KH) was obtained with the help of virial equation. More importantly, a comparative analysis of adsorption thermodynamics of CO2 and CH4 on three different rank coals, including surface potential (Ω), Gibbs free energy change (ΔG) and entropy loss (ΔS), was presented according to the adsorption data. It is found that the uptakes of CO2 and CH4 on anthracite are the largest, followed by lignite and bituminous coal in sequence. αCO2/CH4 increases with the increase of coal rank. Low temperature helps injected CO2 to displace pre-adsorbed CH4. The KH values on anthracite are the biggest, while KH values on bituminous coal are the smallest. Ω, ΔG and ΔS of CO2 and CH4 all exhibit a U-shaped function with maturity. Anthracite has the highest Ω, ΔG and ΔS, while bituminous coal has the lowest Ω, ΔG and ΔS. The thermodynamics parameters of Ω, ΔG and ΔS are affected by pore size distributions of three coals. Ω, ΔG and ΔS of CH4 are smaller than those of CO2. CO2 adsorption on coal is more favorable and spontaneous, and adsorbed CO2 molecules form a more efficient packing on coal.
•Actual DHF experiments with sandstone were conducted for the first time.•The crack propagation law of DHF was compared by CT scans.•Sample failure characteristic was described and explained.•The ...crack control mechanism of DHF was analyzed in detail.
Hydraulic fracturing is mainly used for increasing large-scale coal seam permeability in coal mines to exploit coalbed methane and prevent coal and gas outbursts. However, conventional hydraulic fracturing cracks tend to propagate along the direction of maximum principal stress, which is inconsistent with reinforcement direction engineering and/or project area needs and makes identification of the orientation or specified location of increased coal seam permeability difficult. To address these problems, we have conducted physical similarity simulation experiments and numerical analysis of directional hydraulic fracturing (DHF) and obtained the crack propagation law of DHF technology. By analyzing the variation law of the maximum principal stress inside the rock mass, the crack propagation control mechanism of DHF technique is revealed. The influence of horizontal stress difference coefficients and angles between the hydraulic slotting direction and maximum principal stress direction (i.e., the hydraulic slotting deviation angle) on the crack propagation deflection is investigated. The results show that the DHF technique can achieve crack-oriented propagation along the desired direction. The maximum principal stress range in the rock mass is redistributed after slotting. A directional fracturing induction region is formed between the slots. In addition, DHF hydraulic pressure curves show a secondary fracturing stage when cracks connect the hydraulic fracturing and hydraulic slotting boreholes. Initiation pressures and values of maximum principle stress in the directional fracturing zone increase with increasing horizontal stress difference coefficients and slotting deviation angles. However, increasing the horizontal stress difference coefficient does not significantly influence the directional fracturing zone range. The results provide a reliable basis for subsequent theoretical research and engineering applications.
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The combined effects of surface chemistry and pore structure on water vapor adsorption characteristics of coal were studied by evaluating the equilibrium, thermodynamic and kinetic ...properties. Four coal samples of different rank were fully characterized with gas (N2 and CO2) sorption and Fourier Transform infrared spectroscopy (FTIR) methods. Then measurements of water vapor adsorption equilibrium and kinetics were undertaken at elevated temperatures. Equilibrium and kinetic data were fitted by the modified BET model and the unipore model, respectively. The thermodynamic parameters, as well as diffusion activation energy were estimated based on the adsorption data. The results demonstrate that water vapor adsorption depends on the surface chemistry but unrelated to the pore structure, because the pore space is not completely filled by water molecules even at the saturation pressure. The monolayer adsorption capacity decreases with increasing coal rank. Moreover, water vapor needs lower work to attain equilibrium on high-ranked coal. Also, the binding affinity of water molecule with primary sites is stronger than secondary sites. Furthermore, the diffusion coefficient decreases with coal rank, and the diffusion activation energy for high-volatile bituminous is higher than the other coals, as a result of the complexity and poor connectivity of its pore network.
Coalbed methane (gas) is a high quality and clean resource, but it also causes disasters in coal mines in China. The low permeability of coal seams is the main reason that developing coalbed methane ...(CBM) as an energy resource is difficult, so increasing coal seam permeability is the key to CBM development in China. In this paper, the principal techniques for seam permeability enhancement are presented. The paper focuses on hydraulic technology for seam permeability enhancement (HTSPE), which is considered an economic and highly efficient technology for seam permeability enhancement. The process of HTSPE development is reviewed and the current status of the theories behind HTSPE and the technology and equipment for its use are summarized. The goal is to identify the gaps in HTSPE research and the problems in its implementation. In the future, integration and diversification of the technologies along with on-board intelligence and miniaturization may be the trends for the equipment. Finally, it is shown that tree-shaped borehole fracturing can be used to develop CBM in underground coal mines. This study could be used as a valuable example for other coal deposits being mined under similar geological conditions.
The isothermal sorption experiments of CH4, CO2 and CH4/CO2 mixture gases on shale were performed. The sorption affinities of CH4, CO2 and CH4/CO2 mixture gases were compared using Henry’s ...coefficient (KH). The thermodynamics of sorption of CH4, CO2 and their mixture were discussed based on surface potential (Ω), entropy loss (ΔS) and change of Gibbs free energy (ΔG). It is shown that the uptakes of CO2 is largest, followed by CH4/CO2 mixture gases and CH4 in sequence. The introduction of a small amount of CO2 into mixture gases can significantly enhance the adsorption quantity of mixture gases and suppress the adsorption of CH4. The lower pressure and the smaller CO2 mole fraction in bulk phase (yCO2) improve separation factor and boost the displacement of adsorbed CH4 by CO2. KH, Ω and ΔS for CO2 are higher than those for CH4, and KH, Ω and ΔS for CH4/CO2 mixture gases are between those for CH4 and CO2. Increasing yCO2 increases KH, Ω and ΔS. ΔG of CO2 and CH4/CO2 mixture gases are bigger than that of CH4. CO2 adsorption is more spontaneous and the introduction of CO2 enlarges the spontaneity degree of adsorption of mixture gases.
Investigating the adsorption characteristics of CO2, N2 and CH4 on kaolinite clay is beneficial for enhanced shale gas recovery by gas injection. In this paper, the experiments of CO2, N2 and CH4 ...adsorption at 288 K, 308 K and 328 K on kaolinite clay were conducted, and the thermodynamics analysis of adsorption of three gases was performed. The findings reveal that the order of the uptakes of three gases on kaolinite clay is as follows: N2 < CH4 < CO2. Reducing temperature enlarges the separation coefficients of CO2 over CH4 (αCO2/CH4), CO2 over N2 (αCO2/N2), and CH4 over N2 (αCH4/N2). The value of αCO2/CH4 greater than one validates that CO2 is capable to directly replace the pre-adsorbed CH4. The spontaneity of CO2 adsorption is the highest, while N2 has the lowest adsorption spontaneity. Injecting N2 into gas-bearing reservoir can cause CH4 desorption by lowering the spontaneity of CH4 adsorption. Adsorbed CO2 molecules form a most ordered rearrangement on kaolinite surface. The decrease rate of entropy loss for N2 adsorption is higher than those for CO2 and CH4 adsorption.
Hydraulic fracturing techniques for developing deeply buried coal reservoirs face routine problems related to high initial pressures and limited control over the fracture propagation direction. A ...novel method of directional hydraulic fracturing (DHF) based on hydraulic slotting in a nonuniform pore pressure field is proposed. A mechanical model is used to address crack initiation and propagation in a nonuniform pore pressure field, where cracks tend to rupture and propagate towards zones of high pore pressure for reducing the effective rock stress more. The crack initiation pressure and propagation morphology are analyzed by rock failure process analysis software. The numerical results show that the directional propagation of hydraulic fracturing cracks is possible when the horizontal stress difference coefficient is less than or equal to 0.5 or the slotting deviation angle is less than or equal to 30°. These findings are in good agreement with experimental results, which support the accuracy and reliability of the proposed method and theory.
This paper adopted theoretical derivation and experiments to investigate the stress wave propagation characteristics in rock under water jet impact and fracture response of coal. The evolution model ...of stress and displacement was presented to analyze the formation, propagation and attenuation of stress wave during rock fragmentation. The rock failure criterion for shear and tensile failure under dynamic impact loads, and crack propagation criterion under quasi-static pressure of water jet were established. And the broken pit range formed by shear component of stress wave and the damage range caused by tensile stress were obtained. Based on scanning electron microscopy and binarization method, experiments on water jet impinging coal under various velocities were conducted to study the failure patterns and fracture characteristics of coal. It is indicated that during the water-hammer pressure and its unloading stage, the radial stress and tangential stress decrease first and then increase, accompanying the occurrences of the radial and tangential tensile stresses peaks and the maximum compression displacement. In the subsequent stagnation pressure stage, the radial and tangential stresses trend to be the stable compressive stress and tensile stress, respectively. The peak values of radial stress and tangential stress at different stages all decay exponentially with the propagation distance. Moreover, the broken pit surrounded with radial and annular cracks is formed on coal when the jet velocity exceeds the threshold value, while the split fracture of coal will occur for the high impact velocity. The rock-breaking specific energy consumption decreases first and then increases with the increasing jet velocity. Besides, the theoretical damage scope is verified and close to the experimental value before the splitting fracture of coal. Combined with fracture morphology of coal debris with different sizes, two microscopic damage-failure modes of coal impacted by water jets are revealed, namely shear failure and tensile failure.
•Evolution models of stress and displacement in rock impacted by water jets were established.•Formation, propagation and attenuation of stress wave during rock fragmentation were analyzed quantitatively.•Threshold criterions including rock failure and crack propagation, and rock damage scope were obtained and verified.•Failure patterns, fragmentation efficiency and crack distribution of coal subjected to water jets with different velocities were observed.•Failure mechanism of coal impacted by water jets was investigated based on SEM and binarization method.
Diabetic cardiomyopathy (DCM) is characterized by impaired diastolic and systolic myocardial performance and is a major cause of morbidity and mortality in patients with diabetes. Surgical bariatric ...procedures, such as sleeve gastrectomy (SG), result in remission of type 2 diabetes (T2DM) and have benefits with myocardial function. Maintaining cardiac mitochondrial homeostasis is a promising therapeutic strategy for DCM. However, whether SG surgery affects mitochondrial function and its underlying mechanism remains unclear. This study aimed to investigate the effect of SG surgery on mitochondrial homeostasis and intracellular oxidative stress in rats with DCM. We also examined cellular phenotypes and molecular mechanisms in high glucose and high fat-stimulated myocytes. The rat model of DCM was established by high-fat diet feeding and low-dose streptozotocin injection. We observed a remarkably metabolic benefit of SG, including a reduced body weight, food intake, blood glucose levels, and restored glucose tolerance and insulin sensitivity post-operatively. Also, SG ameliorated the pathological cardiac hypertrophy, myocardial fibrosis and the dysfunction of myocardial contraction and diastole, consequently delayed the progression of DCM. Also, SG restored the mitochondrial dysfunction and fragmentation through the AMPK signaling activation mediated nuclear receptor subfamily 4 group A member 1 (NR4A1)/DRP1 suppression
. H9c2 cardiomyocytes showed that activation of AMPK could reverse the mitochondrial dysfunction somehow. Collectively, our study provided evidence that SG surgery could alleviate mitochondrial dysfunction in DCM. Moreover, AMPK-activated NR4A1/DRP1 repression might act as a significant reason for maintaining mitochondrial homeostasis in the myocardium, thus contributing to morphological and functional alleviation of DCM.
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