Coal and gas outbursts are increasingly frequent occurrences in coal mining production. Furthermore, geological anomaly areas are the primary sites of outburst incidents. This research proposed a coal seam model containing gas in geological anomaly area to better understand the impact of regional geological anomaly variables on the outburst. It was discovered that the excavation length had a larger effect on the plastic zone and energy instability than gas pressure and dip angle. Coal’s elastic energy was mostly impacted by excavation length, which subsequently had an impact on the chance of an outburst. Adsorbed gas’s expansion energy was mostly influenced by the original gas pressure, while both energies were impacted by the inclination angle. The outburst energy increased more under the influence of excavation spacing or gas pressure. When combined with the outburst case, it was discovered that the geological anomaly area raised the composite coal seam’s outburst probability. Additionally, when a geological anomaly area was present, the increase in gas pressure has a considerably larger effect on the energy than the excavation length. This paper’s research is of great significance for preventing mechanical failure of soft and hard composite coal seam (SHCC) in geological anomaly areas.

The flow channel plays a pivotal role in the heat and mass transfer of proton exchange membrane fuel cell (PEMFC). To optimize channel geometry, this study introduces a novel nozzle-like flow (NLF) channel and investigates the effects of transition segment (TS) width, jet segment (JS) number, and position through a PEMFC model. The results indicate that the NLF improves reactant transport rates by nearly 40%. The mass transfer rate at the interface of the porous layer in the shrinking cross section is mapped for the first time. Oxygen concentration and temperature increase with the expansion of the TS width but decrease with an increase in the JS number, whereas pressure drop and water content show the opposite trend. Additionally, optimal performance occurs at a TS width of 0.7 mm, with JS near the inlet, occupying 70% of channel length. This configuration yields net power density enhancements of 1.72% over the straight channel (SF) and 2.56% over the 0.3 mm NLF.

A hydrokinetic turbine produces power using the kinetic energy of water flowing through a river or canal. The current study was carried out on a modified Savonius hydrokinetic turbine to study the effect of Reynolds number and differential head–based Froude number on the performance of the turbine. The experiments were carried out for seven different flow velocities in a laboratory canal. Different Reynolds numbers and differential head–based Froude numbers were achieved by altering the flow velocity using a variable frequency drive (VFD) pump. ANOVA analysis was carried out to evaluate the effect of Reynolds number and differential head–based Froude number on the performance parameters of the turbine such as coefficient of torque, coefficient of power, torque, and power. From the ANOVA analysis, it is observed that Reynolds number has a significant influence on the torque and power output of the turbine; however, its effect on coefficient of torque and coefficient of power is not significant, while the effect of differential head–based Froude number is significant for all four performance parameters like torque, power, coefficient of torque, and coefficient of power. Also, the results indicate that the trend of the variation of the coefficient of power almost matches that of the differential head–based Froude number. This indicates that small variation in the coefficient of power with flow velocity occurs due to variation in water level across the rotor, which is presented in the current work as differential head–based Froude number.

Efficient heat exchange in fractured geothermal reservoirs is crucial for improving geothermal energy extraction and optimizing operational costs. However, the impact of shear-induced permeability changes on heat transfer remains poorly understood. This study aims to systematically investigate the effect of shear displacement (us) on nonlinear flow properties and convective heat transfer characteristics in three-dimensional (3D) rough-walled fractures. Four fracture models were constructed based on Brazilian splitting test data, with shear displacements of 4.44, 8.88, 13.32, and 17.76 mm applied under constant normal stiffness boundary conditions. Four assumptions are made. First, the rock matrix is impermeable and homogeneous. Second, the solids and fluids are undeformable. Third, no-slip and no-flow conditions are assigned at the fracture walls. Fourth, the constant-temperature boundaries are maintained at 300 °C. Numerical simulations were performed using COMSOL Multiphysics, coupling “Heat Transfer in Solids and Fluids” and “Turbulent Flow (SST)” physics to solve Navier–Stokes and energy equations. Fluid flow velocities ranging from 0.001 to 1 m/s were applied at the inlet. The results show that as us increases from 4.44 to 17.76 mm, the nonlinear coefficient (β) in Forchheimer’s law decreases from 2.29×1012 to 3.5×10 Pa·s2·m−6. The β characterizes the degree of deviations from linear (Darcy) flow, and its increase indicates earlier onset of nonlinear fluid flow induced by inertial and turbulent effects. The increase in us from 4.44 to 17.76 mm reduces the maximum convective heat transfer coefficient (hmax) from 3795.4 W·m−2·K−1 (Re=1423.5) to 1243.5 W·m−2·K−1 (Re=342.33) due to reduced turbulence and insufficient fluid–solid contact time. An optimal flow rate (Qbest) that balances heat extraction efficiency and outlet temperature was proposed. These findings can provide critical insights for optimizing thermo–hydro–mechanical processes in enhanced geothermal systems.

A rock’s brittleness index (BI) aids in pinpointing the optimal formation for hydraulic fracturing in shale reservoirs. The two main methods for estimating BI in the petroleum industry are mineral composition and elastic parameters. Nevertheless, not all wells can use these methods to determine BI because of the lack of mineralogical composition and shear wave slowness data. This paper introduces a machine learning (ML) method for forecasting BI utilizing easily accessible Marcellus shale drilling cuttings. This study attempted to develop an approach that uses the bulk elemental composition of crushed samples measured by X-ray fluorescence (XRF) to predict the BI. The study first used the elemental composition of XRF data to infer mineralogy, and then mineral composition to predict the BI of the target formation along the wellbore. In comparing the neural network algorithm model, random forest algorithm model, and ensemble model, the prediction effect of the ensemble model is more accurate than the single model, and the BI depth curve obtained conforms to the previous understanding of mineralogy and mechanics. The study revealed that the difference between ML prediction results and the effectiveness of standardized calculations is relatively small. However, ML demonstrated acceptable prediction performance with higher efficiency, and the prediction accuracy can reach 83.3%. The method proposed can be widely used to establish the BI of unconventional formations by utilizing XRF tests on drill cutting samples, which is a low-cost, reliable, and fast method. Also, drilling cuttings are often widely available through the whole lateral interval.

우리나라의 2050년 탄소중립 및 2030년 감축목표 이행 가능성을 분석하기 위하여 국가, 17개 시⋅도, 226개 시⋅군⋅구의 제1차 탄소중립 녹색성장 기본계획을 대상으로 탄소중립 목표연도와 2030년 감축목표의 부합성을 분석하였다. 17개 시⋅도는 늦어도 국가 탄소중립 목표연도인 2050년까지 탄소중립을 목표로 하고 있다. 시⋅도는 관리권한 부문 배출량을 대상으로 감축률목표를 수립하고 있으며, 시⋅도 계획의 목표배출량을 합산하여 산정한 2030년 감축률목표는 2018년 총배출량 대비 43%이며, 2033년 감축률목표는 51%이다. 이는 국가 2030년 온실가스 감축목표(2018년 총배출량 대비 40% 감축)을 상회하는 수준이다. 탄소중립 목표연도를 시⋅도 계획에 부합하는 수준으로 설정한 시⋅군⋅구는 226개 중에서 206개(91%)이다. 17개 시⋅도 계획의 2030년 감축률목표와 비교하여 하위 시⋅군⋅구 계획의 2030년 목표 배출량을 합하여 산정한 2030년 감축률이 미흡한 지역은 7개이었다. 시⋅도의 2033년 감축률목표와 비교하여 하위 시⋅군⋅구의 목표배출량을 합산하여 산정한 2034년 감축률목표가 미흡한 곳은 8개이었다. 국가, 시⋅도, 시⋅군 ⋅구 계획 간 탄소중립 목표연도 및 2030년 감축목표 등이 부합성을 갖도록 탄소중립 녹색성장 관련 지방조례를 개정하고, 2050 지방 탄소중립녹색성장위원회에서 계획간 부합성을 심의하고, 상위 정부의 모니터링 및 지원 등이 필요하다.

The thick hard rock strata (THRS) are widely distributed among coal-bearing strata. In the process of coal mining, the strong dynamic load will be produced after the THRS are broken, which will lead to dynamic disasters such as mine earthquake, rock burst, and so on. Therefore, revealing the breaking law of THRS is helpful to prevent and control the dynamic disasters. This paper constructed the mechanical model of THRS based on thick plate theory and obtained the breaking distance of THRS, which is applied to Yangliu Coal Mine. And we constructed the numerical stratigraphic model and analyzed the caving characteristics, the changing rules of displacement, and the stress of THRS under different advancing distances. Then the above results are verified by the change of hydraulic support resistance. The research shows that the critical instability distance of THRS overlying Coal Seam #10 in Yangliu Coal Mine was 296.4 m. Based on the numerical simulation, the displacement and stress of the main THRS increased greatly at the position of 250–300 m and a large-scale collapse occurred. The hydraulic support resistance of the working face increased sharply, and microseismic energy was released rapidly when the mining reached about 330 m; the reliability of the theoretical analysis and numerical simulation was verified by the engineering tests.

Horizontal wells combined with effective fracture stimulation enabled economic development of shale gas reservoirs. During fracturing, propping agents are placed in the created hydraulic fractures to maintain a highly conductive flow path for fluid flow. While, post stimulation, proppant flowback and production may occur. To date, mechanisms of proppant production are not well understood, even though past experimental and theoretical studies indicated that fracture width, hydrodynamic forces, and closure stress are primary factors affecting proppant production. This study aims to investigate the mechanism that affects and induces proppant production in shale gas reservoirs during the recovery period. In this paper, we will (1) first understand the physics of proppant production through a critical review and analysis of laboratory studies and published work in the literature; (2) build a reservoir model with an unpropped arch to simulate long-term gas recovery and proppant production; (3) develop a script to compute the percentage of the arch capable of producing proppant based on gas flow velocity, Reynolds number, and Shields number with various arch conductivity, pore pressure, fracture spacing, landing point, and propped height; (4) conduct a comprehensive and systematic analysis to investigate how proppant production occurs; and (5) provide guidelines to mitigate and prevent proppant production. On the basis of our results and analyses, proppant production mainly occurs due to creeping. Higher arch conductivity and higher pore pressure lead to more severe proppant production. In the field, gas production management and changing the landing point from top to bottom of the formation are ways to prevent and minimize proppant production. When landing at the bottom of a formation, proppant production could be avoided, while landing at the upper of the formation could result in 11% to 29% of proppant production. The guidelines developed in this study can help mitigate proppant production in field applications, maintain fracture conductivity, and increase long-term gas recovery.

Pulse hydraulic fracturing can enhance the productivity of oil and gas wells in low permeability formations. During pulse hydraulic fracturing, natural fractures significantly influence the propagation path of hydraulic fractures and the fracturing effects. The impact mechanism of natural fractures on the propagation of hydraulic fractures under different pulse pressures remains unclear. A combination of experimental, theoretical, and numerical approaches is employed to examine the propagation characteristics and stress distributions of hydraulic fractures under different pulse pressures and natural fractures. Stress fields around the tips of hydraulic fractures, considering the influence of natural fractures, are established. Natural fractures exert a significant influence on the stress field at the tips of hydraulic fractures, either promoting or hindering their propagation and altering the propagation path of the hydraulic fractures in rocks. Under low pulse loading stress ratios (0.6, 0.75), natural fractures have a considerable effect on the stress distribution and the propagation path of hydraulic fractures. As pulse pressures rise to 0.9, the influence of natural fractures on the propagation of hydraulic fractures diminishes, resulting in hydraulic fractures extending along the direction of the stress difference. Pulse pressures and natural fractures influence fracturing effects on rocks. Under low pulse loading stress ratios (0.6, 0.75), a greater number of hydraulic fractures are generated in rocks and propagate along the natural fractures, enhancing the fracturing effects. When the pulse pressure increases to 0.9, high pulse pressures cause stress concentration in the direction of stress difference, which leads to less damage and a decrease in the number of hydraulic fractures, and hydraulic fractures are prone to penetrating natural fractures at larger azimuth angles (90°). The research results can reveal the influence mechanism of natural fractures on the propagation paths of hydraulic fractures under different pulse pressures and guide the design of pulse hydraulic fracturing.