Xiaodong GUO, Shicheng ZHANG, Jingchen ZHANG
et al.
Objectives and MethodsDeep coalbed methane (CBM) reservoirs commonly exhibit well-developed beddings, strong mechanical heterogeneity, and high in-situ stress gradients. These characteristics result in pronounced nonlinear fracture propagation and strong multi-field coupling effects during hydraulic fracturing. Consequently, it is challenging to accurately describe the mechanisms governing fracture complexity in deep coal reservoirs using conventional mechanical models for fractures. Using a super-large true triaxial system with dimensions of 2.0 m × 2.0 m × 1.0 m, this study conducted physical simulation experiments on hydraulic fracturing under varying injection rates and viscosities of fracturing fluids. In combination with fracture mechanics and energy conservation theory, this study established an energy balance equation for fracture propagation, a convection-diffusion equation for proppant transport and settling, and a model for the coupling relationships among fracture complexity and the injection rate and viscosity of fracturing fluids. Accordingly, both the dynamic mechanisms behind fracture evolution and the pattern governing the fracture network complexity were systematically elucidated.Results The results indicate that fracture propagation is jointly controlled by the in-situ stress field, fluid pressure field, and bedding structures, representing a unsteady energy conversion process. The fracture propagation rate exhibits a power-law relationship with the energy release rate. The injection rate of fracturing fluids primarily determines the energy input rate and fracture propagation velocity. A high injection rate results in energy concentration in the front of the primary fracture, promoting fracture interconnectivity while suppressing branch development. Accordingly, fracture complexity is reduced. In contrast, a low injection rate corresponds to a more uniform energy distribution, enhancing the accumulation and lateral diffusion of energy. This facilitates multi-point initial cracking and fracture branching, increasing fracture complexity by approximately 25%–35%. Fracturing fluid viscosity significantly influences the energy transfer between fluids and solids, as well as proppant settling behavior. A high viscosity (45 mPa·s) is associated with a significant decrease in the proppant settling velocity. Compared to a low viscosity of 15 mPa·s, the high viscosity increases the proppant transport capacity by approximately 40%, promoting more uniform proppant placement in far-wellbore zones and creating favorable conditions for the formation of continuous hydraulically conductive pathways.ConclusionsEmpirical relationships derived from experiments and fitting indicate that the fracture complexity exhibits power-law coupling relationships with the injection rate and viscosity of fracturing fluids. Notably, the low-injection-rate and high-viscosity combination is more favorable for the development of 3D fracture networks, with a fractal dimension reaching up to 1.46. The proposed theoretical-experimental coupling framework reveals the energy transfer mechanisms governing fracture propagation and proppant transport in deep coal reservoirs, providing a quantitative theoretical basis for optimizing hydraulic fracturing parameters and predicting fracture complexity in deep unconventional reservoirs.
In order to study the micro-fracture mechanisms of metal cylinders and the methods for predicting fragment scale relations, the correlation between the formation of circumferential and axial cracks in explosively driven metal cylinders and the fragment scale parameter (characteristic mass) μ was analyzed. Previous classical theories and studies only focused on the circumferential scale relations of fragments, but there is no reliable theoretical model for the formation and distribution of axial cracks. Three new types of high-strength, high-fracture steel were prepared by varying the B content and made into metal cylinders for underwater explosion fragmentation tests, obtaining the mass distribution and scale parameters of the fragments. Numerical simulations were used to study the fracture process of explosively driven cylinders, establishing the relationship between strain rates and fracture modes. Based on the statistical characteristics of grain size obtained by electron backscatter diffraction (EBSD) tests, the reasons for the different size characteristics of fragment groups in axial and circumferential directions were revealed. The combined effect of the two fracture modes on fragment size characteristics, along with the differences in circumferential and axial distributions, led to the scale parameter differences of fragments in these two directions. In this study, the fragmentation scale relations based on the microstructure were explained through fracture mechanics, and the results provide support for the establishment of a more accurate fragment scale calculation model.
Due to complex geological structures and a narrow safe mud density window, offshore fractured formations frequently encounter severe lost circulation (LC) during drilling, significantly hindering oil and gas exploration and development. Predicting LC risks enables the targeted implementation of mitigation strategies, thereby reducing the frequency of such incidents. To address the limitations of existing 3D geomechanical modeling in predicting LC, such as arbitrary factor selection, subjective weight assignment, and the inability to achieve pre-drilling prediction along the entire well section, an improved prediction method is proposed. This method integrates multi-source data and incorporates three LC-related sensitivity factors: fracture characteristics, rock brittleness, and in-situ stress conditions. A quantitative risk assessment model for LC is developed by combining the subjective analytic hierarchy process with the objective entropy weight method (EWM) to assign weights. Subsequently, 3D geomechanical modeling is applied to identify regional risk zones, enabling digital visualization for pre-drilling risk prediction. The developed 3D LC risk prediction model was validated using actual LC incidents from drilled wells. Results were generally consistent with field-identified LC zones, with an average relative error of 19.08%, confirming its reliability. This method provides practical guidance for mitigating potential LC risks and optimizing drilling program designs in fractured formations.
The Gomułka period of fourteen years includes one of the investment cycles characteristic of the centrally managed economy in Poland. After an initial, short period of stabilization of outlays, in the years 1959–1969 they were significantly increased and clearly focused on the fuel, raw materials and chemical industry. The aim was to reduce the disproportions that had become apparent in the economy in the first half of the fifties, when heavy industry was particularly favored. Additional investments were focused on obtaining new production capacities in the scope of lignite and hard coal mining and the production of copper and sulfur, heat energy, liquid fuels and petrochemical products, non-ferrous metals and inorganic chemical products. As a result of the intensification of outlays, refinery and petrochemical plants in Płock, copper mines and metallurgy in Lower Silesia, chemical plants in Police and Puławy and coking coal mines in the Jastrzębie-Zdrój region gained a permanent position in the Polish economy. In the 1990s, the process of liquidation of the sulfur basin in the Tarnobrzeg region began, mainly under the influence of technological
changes in the industry. At the beginning of the 21st century, the role of brown coal basins and the related energy industry in Lower Silesia and Wielkopolska decreased due to the gradual depletion of deposits.
Summarizing the current development status of intelligent and digital technologies in the coal industry, analyzing the new situations and requirements for research and application of intelligent technologies and complete sets of equipment for efficient coal mining. Addressing challenges such as comprehensive perception of the state of high-strength mining surrounding rock and equipment under different coal seam conditions and integrated coordinated advancement and linked control of equipment groups, the paper explores the deep integration of advanced information technologies such as the Internet of Things, cloud computing, big data analytics, and high-precision inertial navigation with coal mining technologies. This integration has enabled condition monitoring and data integrated management of coal mining equipment, improving monitoring, management, and decision-making efficiency in the coal mining process through precise perception, real-time data analysis, and intelligent control. It has also enhanced the adaptability of complete mining equipment sets to different coal seam conditions. To address the challenges of integrated advancement and coordinated control of equipment groups in ultra-long workfaces for medium-thick coal seams, the paper introduces synchronous mapping of geological information ahead of the mining face through dynamic perception of geographical information and real-time model updating technology. High-power rapid advancement equipment suitable for ultra-long workfaces has been developed, and a multi-area synchronous advancement process system covering all aspects of support, mining, and transportation has been established. This forms a linked mechanism for support equipment groups in ultra-long workfaces and achieves coordinated control among equipment groups, significantly improving mining efficiency and resource recovery rates for medium-thick coal seams. For complex geological conditions in deep thick coal seams, refined control of supports and intelligent coordinated control technologies for equipment groups have been developed, enabling perceptual coordination and adaptive precise control between equipment, thus improving system reliability and efficiency. Addressing challenges such as coal wall protection in ultra-large mining spaces, intense dynamic loads on surrounding rock in the workface, and significant variations in coal flow loads in 8−10 m ultra-high mining height workfaces, the paper proposes adaptive control technology for coupling hydraulic supports with surrounding rock, enhancing the adaptability of equipment to ultra-high mining height workface environments. Key technologies such as a guard plate monitoring system, adaptive cutting technology for shearer stability, coal flow load balancing, and dynamic chain tensioning control have been developed, enabling efficient mining under conditions of significant coal seam thickness variations and strong mining pressure. In the overseas promotion of intelligent and digital complete sets of equipment for efficient coal mining, the paper addresses challenges such as differences in coal mine conditions, safety requirements, and technical standards through customized adjustments to technical equipment. An integrated monitoring and big data analytics system has been developed, improving the response to abnormal situations and enabling autonomous perception, high-reliability data transmission, intelligent analysis and decision-making, precise control and execution among equipment groups within the workface. A technical system for intelligent and digital complete sets of equipment for efficient coal mining adaptable to different working conditions has been established and has achieved good results in engineering practice. This provides support for the high-quality development of coal mine intelligence and solutions to key technical challenges in coal mine intelligent construction.
This study explores an electrochemical approach for the synthesis of electrolytic manganese dioxide (MnO 2 ) with improved efficiency and environmental sustainability through the integration of ferrous iron (Fe 2+ ) regeneration. A divided electrolytic cell was employed to facilitate the deposition of high-purity MnO 2 from Mn 2+ solutions, concurrently enabling Fe 2+ regeneration at the cathode. X-ray diffraction analysis identified the deposited MnO 2 as predominantly pure pyrolusite. Experimental results demonstrated that increasing the current density led to a reduction in cell voltage, attributed to enhanced Fe 2+ regeneration, thereby decreasing overall energy consumption. Polarization curve analysis revealed distinct electrochemical behaviors between Fe 3+ reduction and hydrogen evolution, suggesting avenues for further process optimization. This method offers reduced operational costs and energy requirements, positioning it as a more environmentally sustainable alternative to conventional MnO 2 production techniques. The findings contribute to the advancement of MnO 2 electrodeposition and support the development of sustainable electrochemical technologies for applications in battery materials.
A comprehensive and comparative study of the thermal-oxygen aging and tribological properties of antioxidant 6PPD synergized with carbon nanotubes (CNTs) and graphene (GE)-reinforced hydrogenated nitrile rubber (HNBR) composites was performed using molecular simulations and experiments. The results indicated that GE exhibits superior capabilities in inhibiting the volatilization and migration of the antioxidant 6PPD compared to CNTs and enhancing the thermal and oxygen aging resistance of HNBR. The surface morphology of the HNBR composites was characterized using scanning electron microscopy (SEM) and X-ray spectroscopy (XPS), which revealed the different enhancement mechanisms of CNTs and GE. The mechanical and tribological properties of the HNBR composites were experimentally investigated before and after the thermal-oxygen aging. The results revealed that the tensile and tear strengths of the 6PPD/HNBR composites with added GE increased by approximately 4% compared to those of the 6PPD/HNBR composites with added CNTs. The coefficient of friction decreased by approximately 7%. Finally, the wear surface morphologies of the HNBR composites were characterized using SEM and energy dispersive spectrometer (EDS). These results further indicate that the larger specific surface area of GE can be better combined with HNBR, improving its overall thermal-oxygen aging and tribological properties.
Superhydrophobic coatings for umbrella canopies have the potential to solve the issue of rain residue. However, achieving both impalement resistance and mechanical robustness in these coatings poses a significant challenge and limits their practical applications. In this study, we propose a similar “pole erecting” method utilizing perfluorodecyl polysiloxane modified SiO2 nanoparticles (F-silica) as the pole and poly(dimethylsiloxane) (PDMS) as the screw to enhance impalement resistance and mechanical robustness, which is attributed to the three-tier hierarchical micro-/micro-/nanostructure bonded by PDMS, along with a reduction in aspect ratio. The obtained PDMS0.5-F-silica could withstand 150 min of water drop impacting (equivalent to approximately 19,000 water drops) and 60 s of 50 kPa water jetting, also showed exceptional endurance against various mechanical tests, including 200 cycles of reciprocating abrasion, 1000 cycles of Martindale abrasion and 200 cycles of tape peeling. Moreover, when applying the PDMS0.5-F-silica coating to umbrella canopies, we observed an absence of rain residue after subjecting the umbrella to 20 h rain. These findings are promising for the development and practical implementation of superhydrophobic coatings.
In order to further clarify the influence of multistage pulse ultrasound on the characteristics of gas desorption in water-bearing coal, the ultrasonic stimulation test system of gas-containing coal is used to analyze the pore structure and gas desorption of coal under the condition of continuous ultrasonic stimulation of coal with different moisture contents and multistage pulse stimulation of water-saturated coal, and the mechanism of multistage pulse stimulation of water-bearing coal is revealed. The results show that the average pore diameter, specific surface area and total pore volume of coal increase with the increase of ultrasonic power and water saturation degree. When ultrasonic power is 1000 W, compared with dry coal, the increase of specific surface area and total pore volume of coal increases from 4.369% and 3.504% of 25% moisture content to 7.699% and 8.992% of 100% moisture content, respectively. There is a Langmuir-type relationship between coal gas desorption and time, and coal gas desorption amount and desorption rate are positively correlated with ultrasonic power and water saturation degree of coal. Compared with dry coal, the gas desorption capacity and desorption rate increase linearly with the increase of water saturation degree of coal, and ultrasonic stimulation has the best effect on the pore reconstruction and gas desorption of water saturated coal. With the increase of ultrasonic multistage pulse times, the specific surface area, total pore volume, gas desorption capacity and desorption rate of water-saturated coal increase. Compared with the 1000 W ultrasonic excitation, the increase of specific surface area and total pore volume of coal is a positive power function of the number of multistage pulses. The increase of gas desorption amount and desorption rate of coal increases from 2.745% and 4.598% of the first multistage pulse to 27.222% and 11.106% of the third multistage pulse, respectively, which is in a positive linear relationship with the number of multistage pulses. The combined effect of vibration and cavitation generated by multi-stage pulse ultrasonic stimulation of water-bearing coal causes fatigue damage to the coal matrix, strengthens the pore transformation of coal, and increases the molecular kinetic energy of gas, thus promoting gas desorption in coal. On site, the gas extraction in coal seam can be enhanced through the development of multi-stage pulse ultrasonic emitter combined with hydraulic technology.
The article analyzes the current situation and upcoming tasks of the Azerbaijan metallurgical industry. The activities of enterprises producing metal products in the country are assessed. It is noted that for the dynamic development of the metallurgical industry, a deep study of the mineral resource base existing in the territory of the Republic of Azerbaijan is required and it should be put into operation. In the near future, for the accelerated development of the metallurgical industry of the country, there is a mineral resource base, energy reserves, material and technical base, engineering and scientific and pedagogical potential. The tasks arising from the orders of the President of the country, stimulating the development of the metallurgical industry are shown and promising directions in this area are presented. The need to use local resources for the accelerated development of the metallurgical industry is noted. The industrial capacities of operating companies and plants are assessed, new goals are presented for them. At the same time, the article notes the acceleration of gold mining in the country and shows the ways of using their locations, liberated from the occupation of the Karabakh region. In recent years, in contact with the development of the non-oil sector, the order of the President of the country on the establishment of a steel production complex in Azerbaijan will determine the concept of sustainable development of the metallurgical industry. The article also provides information showing the dynamics of growth in the production of steel pipes, construction reinforcement and other products of ferrous metallurgy. A diagram is presented in the aspect of the prospective development of the ferrous metallurgy industry in Azerbaijan. The indicators of import and export in the Republic of Azerbaijan for ferrous metallurgy in 2002-2022 are given. It is noted that the metallurgical industry of the country will experience a new stage of development and in order to achieve new successes in this area, the development and implementation of innovative technologies are of great importance.
To explain the effect of joint roughness on joint peak shear strength (JPSS) and investigate the effect of different contact states of joint surface on JPSS, we try to clarify the physical mechanism of the effect of joint cavity percentage (JCP) on JPSS from the perspective of the three-dimensional (3D) distribution characteristics of the actual contact joint surface, and propose a JPSS model considering the JCP. Shear tests for red sandstone joints with three different surface morphologies and three different JCPs were performed under constant normal load condition. Based on test fitting results, the reduction effect of the JCP on JPSS is investigated, and a JPSS model for cavity-containing joints is obtained. However, the above model only considers the influence of JCP by fitting test data, and does not reveal the physical mechanism of JCP affecting the JPSS. Based on the peak dilation angle model for consideration of the actual contact joint morphology, and the influence of JCP on the roughness of the actual contact joint surface, a theoretical model of the JPSS considering the JCP is proposed. The derivation process does not depend on the test fitting, but is entirely based on the joint mechanical law, and its physical significance is clear. It is proposed that the essence of the influence of the JCP on JPSS is that the JCP first affects the normal stress of the actual contact joints, further affects the roughness of actual contact joints, and then affects the shear strength.