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Pore pressure is disregarded in traditional laboratory rock hydraulic fracturing experiments, and the effect of pore pressure is not clear. An integrated experiment for seepage and hydrofracturing was established and used to perform sandstone hydraulic fracturing experiments under an initial evenly distributed pore pressure. The experimental results show that there is a positive correlation between the breakdown pressure and the pore pressure at the initiation stage. The data fitting results show that the breakdown pressure and pore pressure follow a linear growth trend. As the pore pressure increases, the acoustic emission energy at the moment of borehole wall fracturing correspondingly increases. After borehole wall fracturing, the reduced magnitude of the pumping pressure also increases, indicating that the initial rupture range is positively correlated with pore pressure. During fracturing propagation, the propagation range and opening of the fracture increase as the initial pore pressure increases within the same pumping time. During hydraulic fracturing, a pore pressure gradient is generated on both sides of the mineral particles. When the tensile stress or shear stress induced by the pore pressure gradient reaches the ultimate strength of the mineral particle bonding surface, the particle bonding surface breaks and opens. This experimental process is more similar to the actual hydraulic fracturing process of oil and gas reservoirs. These results provide a more comprehensive theoretical basis for resolving technical problems of unconventional oil and gas resource exploitation.

When hydraulic fracturing is utilized to eliminate coal and gas outbursts and rockburst in dynamic disaster coal-rock formations, the stress disturbance of hydraulic fracturing may have negative effects such as causing local stress concentration. The method of combining physical model experiments and numerical simulations is adopted to study the distribution relationship of pore pressure and matrix stress during hydraulic fracturing. The research results show that the pore pressure and matrix stress gradually attenuate farther away from the hydraulic fracture in the process of hydraulic fracturing. The attenuation rate of matrix stress is less than that of pore pressure. The range of the matrix stress disturbance zone is larger than the range of the pore pressure disturbance zone. With the increase of pumping time, the increasing speed of the matrix stress disturbance zone is greater than that of the pore pressure disturbance zone. This indicates that the squeezing force on both sides of the hydraulic fracture increases correspondingly with the increase in crack opening, which causes the range and magnitude of the matrix stress disturbance zone to increase gradually. The stress disturbance zone around the hydraulic fracture includes the pore pressure disturbance zone and the matrix stress disturbance zone. In the pore pressure disturbance zone, the pore pressure and the matrix stress increase and interact at the same time, which together lead to the deformation and failure of coal and rock mass. The relationship between the pore pressure and the matrix stress in this region conforms to the natural logarithmic attenuation relationship. Outside the pore pressure disturbance zone, the deformation and failure of coal and rock mass are mainly caused by the matrix stress effect.

Directional rupture is one of the difficult problems in deep rock mechanics and engineering. A directional fracturing method with static expansive agent controlled by dense linear multi boreholes is proposed. A physical experiment is designed and performed to investigate the basic laws of this method. The fracture initiation and propagation process, and the mechanism of directional fracturing are analyzed. The results indicate that a directional fracture is formed along the direction of boreholes layout through directionally fracturing with static expansive agents controlled by the dense linear multi boreholes. According to the variation of strain and the distribution of associated acoustic emission (AE) events and energy, the experiment can be divided into three stages. In the first stage, the static expansive agent expand slowly with no fracturing inside the rock. In the second stage, some initial micro-fracturing occurs inside the rock. In the third stage, a wide range of fracturing occurs inside the sample. The internal micro-fracturing planes are connected to form a macro-fracture. Finally, it propagates to the surface of the sample. The directional fracturing plane presents a relatively smooth plane with little bias but much local fluctuation.

The strength and rigidity of proppant and coal are quite different. Proppant is easily embedded in coal, resulting in the decrease of fracture aperture and conductivity. The mechanism of proppant embedded in the coal fracture surface needs further study. In this paper, through theoretical analysis and experimental research of single proppant embedded, the proppant embedded law is analyzed from macro and micro aspects. The damage factor of coal surface is introduced, the damage model of the whole process of single proppant pressure embedded is established, and the mechanism of coal fracture surface embedded pit and cracks is revealed. The results show that, from the center of the contact surface to the outside, the surface failure forms of coal fracture are pressure failure, tensile-shear failure, and tensile failure. The proppant is embedded in the coal fracture surface to form four areas: central compaction area, layered fracture area, fracture development area, and original state area. During the energy release of proppant embedded in coal, the energy of proppant is released first and the energy of coal is released later. Greater than 3 times the contact radius, the influence of single proppant on the coal fracture surface can be ignored.

The behavior of hydraulic fractures initiated along the radial and axial directions of borehole has been investigated by the author in previous hydraulic fracturing experimental and engineering app...

In the tunneling of frozen soil section of shaft sinking by freezing method, the traditional air pick excavation has large consumption of pick and drill rod, low excavation efficiency, and high lab...

Fracture is the flow channel of gas (fluid) body in the exploitation of coalbed methane and other energy sources. It has a great influence on gas (fluid) production and work efficiency. Creep results in the proppant embedded in the coal seam leading to fracture damage, reducing fracture permeability. However, there are few studies on a creep model considering proppant embedding in fractures. In this paper, a creep test of proppant embedment in a fracture of a coal seam is carried out, and a creep model considering the damage to proppant embedment is established. The results show that with an increase of closure stress, the range of strain rate first increases and then decreases, and the mean value of strain rate increases slowly and then increases rapidly when the closure stress levels increases in the stable creep stage. During the creep of coal with a fracture proppant, there is not only the hardening and damage of coal, but there is also the damage to proppant embedding. A creep hardening damage model considering the viscosity damage factor of coal, the stress hardening model, the elastic-plastic damage factor, proppant compaction and the embedded viscosity loss factor is established. The creep hardening damage model can better describe the whole process of decelerating creep, stable creep and accelerating creep of coal with proppant fracture.

During hydraulic fracturing in a high-methane coal seam, there is a water-displacing-methane effect. A pseudo triaxle experimental system, which is opposite to the name of true triaxial system, for the water-displacing-methane effect was created. First, cylindrical coal samples in a methane adsorption equilibrium state, spontaneously desorbed. And then water was injected into the coal samples. The following was shown: (1) The displacement methane volume gradually rises with an increase of injected water, while the displacement methane rate tends to rise at first before declining later. Simultaneously, the water-displacing-methane process is characterised by a time effect. The methane displacement lags behind water injection. (2) Competitive adsorption and displacement desorption between the water and methane will promote adsorption methane into free methane, while the pore pressure increase caused by water injection will turn free methane into adsorption methane. The net free methane of the combination action provides a methane source for the water-displacing-methane effect. (3) A pore pressure gradient, which provides a power source for the water-displacing-methane effect, is formed and reduces gradually at the front of the water seepage along the seepage direction. The increase in water pressure can rapidly improve the pore pressure gradient and boost the displacement methane volume as well as improve displacement methane efficiency. (4) A starting porosity pressure gradient and limit pore pressure exist in the process of water-displacing-methane. When the pore pressure gradient is less than the starting pore pressure gradient, there is free methane in the coal rock, but it cannot be displaced. When the pore pressure is between the starting pore pressure and the limit pore pressure, the free methane can be displaced. When the pore pressure is greater than the limit pore pressure, the methane is almost completely adsorption methane, and water cannot be used to displace the free methane.

Proppant placement concentration, particle size and creep time are important factors that affect the embedment of proppant into coal. Based on multistage creep, an orthogonal test is conducted, and an optimal proppant scheme for different closure stresses obtained. The results show that with increased proppant placement concentration, the number of coal fractures increases and the elastic modulus of the fracture area decreases. As the proppant particle size decreases, the plasticity of fracture-proppant assemblies increases gradually. The yield limit is highest when the particle size is 20/40 mesh. During the proppant embedding process, localization or uneven distribution of proppant results in tensile stress parallel to the fracture surface, which induces tensile fracture in the coal. In the fracture-proppant assembly areas, proppant fractures are severe and yield lines appear. As proppant concentration increases, more energy is accumulated during the proppant compaction stage, resulting in energy release producing craters and crevasses. The energy released also causes increased stress in the proppant-coal contact area and fracturing to the coal mass. The longer the creep time, the weaker the impact and the smaller is fluctuation. Moreover, we find that the orthogonal test can effectively analyze the importance of each parameter. Proppant placement concentration was found to have the highest influence on the process of proppant embedding into coal, followed by particle size and then time. Under experimental conditions, the lowest proppant-embedded value in coal samples was observed with proppant placement concentration of 2 kg m−2 and particle size of 20/40 mesh.

A complex fracture network is composed of many similar structures. The migration law of proppant at each structure is the core and basic content of the migration law of proppant in complex fracture network, and there is little research. In this study, the EulerianEulerian method (TEM) is used to analyze the migration and distribution characteristics of solid–liquid two phases at the fracture corner according to different corner types of the fracture network. The results show that the migration characteristics of proppant in the corner area can be divided into the corner anomaly area, buffer area, and stability area; the influence of the turning angle on proppant migration is mainly concentrated at the corner and in the range of 4 times the fracture width after turning. The probability of sand plugging at the corner of the “Y → T” fracture is lower than that of “L → l”, higher than that of the “X → +” wing branch fracture, and lower than that of the main fracture. At the corner of the fracture network, after the solid flow turns, the proppant will form a high sand area on the side of the impact fracture surface, then rebound back to the fracture, form a sand-free area on the other side, and form a high-velocity core in the refraction interval. At the corner of the “L → l” fracture, there are one high sand area, one non-sand area, two low-velocity areas, and one high-velocity area; there are three low-velocity areas, two sand-free areas, and one high sand area at the corner of the “Y → T” fracture; at the corner of the “X → +” fracture, there is a high sand area and no sand-free area, and the flow velocity of the main fracture is much greater than that of the wing branch fracture.

Permeability improvement of coal seams by hydraulic fracturing can promote desorption of coalbed methane. However, the water-block effect will restrain desorption of coalbed methane. Based on the essence of the physical adsorption of methane, competitive adsorption, substitution desorption, the capillary effect, and the Jamin effect are analyzed to study the effect of the critical moisture content and liquid water on methane adsorption and desorption. Simultaneously, the effects of the fluid pressure, fracturing fluid, fracturing time, pore pressure, and other variables on methane adsorption and desorption characteristics are analyzed. Then, problems that require further study are described.

This study explored the influence of social position and competition on tree transpiration using spatial structure parameters and competition indices. Transpiration of trees is an important component of water budget of forest ecosystems and it can be greatly influenced by social position and competition pressures of trees. In this study, the response of tree transpiration to social position and competition pressures of trees is investigated for a natural mixed forest consisting of Pinus massoniana, Cunninghamia lanceolata, and Symplocas setchuensis in Jinyun Mountain National Nature Reserve located at Chongqing, China. The tree-level transpiration (T) is estimated using sap flow technique by considering the radial variations of sap flux density. Three spatial structure parameters [i.e., dominance (U), uniform angle index (W), and mingling (M)] were calculated to express the social position of trees and two competition indices [i.e., Hui’s competition index (UACI) and Hegyi’s competition index (HCI)] were calculated to quantify the competition intensity among trees. W showed significantly positive correlation (partial correlation coefficients R ≥ 0.753; p

The Tianping-1B is a 20-kg low earth orbit nanosatellite with a commercial multi-GNSS receiver based on a microelectromechanical system. This receiver collects concurrent code and phase dual-frequency measurements from the global positioning system (GPS) and the second and third generations of the BeiDou Global Navigation Satellite System (i.e., BDS-2 and BDS-3). However, BDS-3 signals with pseudorandom noise code numbers greater than 32 cannot be received. In this study, onboard GPS and BDS measurements from Tianping-1B are collected for days 133–147 of 2019. The performance of the onboard BDS-3 measurements is analyzed, and the potential of the BDS-3-based precise orbit determination (POD) for Tianping-1B is assessed. The carrier-to-noise-density ratio of the BDS-3 is higher than that of the BDS-2 and approaches that of the GPS. The BDS-3 has a smaller code multipath error than the BDS-2 and the GPS and therefore a higher quality of code measurements. The results of the overlap comparison show a GPS-based orbit consistency below 3.5 cm in three dimensions (3D) and below 1.2 cm in the radial direction. The mean of satellite laser ranging validation residual RMS is 1.7 cm. The orbit obtained using onboard BDS measurements is assessed using the GPS-based orbit as a reference: The mean 3D root mean square (RMS) difference between the BDS-3-only-based POD and the reference orbit is 4.57 cm. Thus, a sub-dm-level orbit can be achieved using only onboard BDS-3 measurements. A POD with slightly higher precision than the BDS-3-only-based POD is obtained using both BDS-3 and BDS-2 measurements, using higher weights for the BDS-3 data than the BDS-2 data. Then, the combined BDS-3/GPS POD is performed: The RMS difference between this joint orbit and the GPS-based orbit is 1 cm in 3D. This study can be used as a reference for the development of BDS-3 based POD, which will approve in accuracy and precision upon completion of BDS-3.

Aiming at the problem that a certain type of wireless communication equipment is difficult to achieve online detection and a single maintenance and training means, a method of adapting computer control to the whole machine and circuit board is proposed and implemented. Online detection of various states and main performance indicators of the whole type of communication equipment and circuit board, and provides a teaching mode for maintenance training. It is convenient for maintenance personnel to quickly and effectively detect this type of communication equipment, and to form its maintenance support capability.

Directional rupture is a significant and routine problem for ground control in mines. Directional hydraulic fracturing controlled by dense linear multi-hole drilling was proposed. The physical model experiment, performed by the large-scale true triaxial hydraulic fracturing experimental system, aims to investigate the basic law of directional hydraulic fracturing controlled by dense linear multi-hole drilling, the impact of three different pumping modes on the initiation and propagation of hydraulic fractures among boreholes are particular investigated. The experimental results indicated that there are mutual impacts among different boreholes during crack propagation, which leads to a trend of fracture connection. Furthermore, during propagation, the fractures not only exhibit an overall bias toward the direction in which the boreholes are scattered but also partially offset against the borehole axes and intersect. The directional fracturing effect of equivalent pumping rate in each borehole is better than the other two pumping modes. In practical applications, because of rock mass heterogeneity, there may be differences in terms of filtration rate and effective input volume in different boreholes; thus, water pressure increase and rupture are not simultaneous in different boreholes. Additionally, if the crack initiation directions of different boreholes at different times are not consistent with each other, more lamellar failure planes will occur, and the mutual influences of these lamellar failure planes cause fractures to extend and intersect.

Gas and water geochemistry in the No.2 coal reservoir of the Yanchuannan CBM block in the southeastern Ordos basin reflects a complex interaction of tectonic, hydrodynamic, thermogenic, and biogenic processes. Stable isotope and component analyses of gas and water samples from the No. 2 coal seam of 17 CBM wells were performed to determine the correlations between stable isotopes of gases and co-produced water, and to understand the controls of structure and hydrology on isotope distribution. The results show that the co-produced water continuously ranges from brackish, isotopically lighter Na-HCO3/Na-HCO3-Cl water to hypersaline, isotopically heavier Na-Cl/Na-Ca-Cl brine. Based on the hydrochemical features, fault development, and burial depth of coal seam, four structure-controlled hydrodynamic zones are distinguished, including strong through-flow, medium through-flow, weak through-flow, and stagnant zones. The gas isotope analysis shows that thermogenic methane is the dominant source of CBM, and secondary biogenic gases only exist in the strong through-flow zone. δ2H-CH4 is ultimately inherited from formation water, and more 2H can be transferred during the formation of thermogenic gases. δ13C-CH4 and δ13C-CO2 are mainly controlled by thermal maturity and gas genesis respectively, and there is a negative correlation between them. The stable isotopes of coalbed gases and water show strong spatial heterogeneity with the changing hydrodynamic strength. Owing to the influence of water recharge, gas leakage, and secondary biogas formation, the strong through-flow zone is characterized by the most negative δ13C-CH4, δ2H-CH4, δ18O-H2O, δ2H-H2O and the most positive δ13C-CO2, Δ2H-(H2O-CH4) and Δ13C-(CO2-CH4). However, the stagnant zone has maintained stable in a long geological period, which leads to the high concentration of original connate water and mass preservation of coalbed gases, and hence its isotopic feature is completely opposite to the strong through-flow zone. This study confirms the significant controls of hydrogeological conditions on the migration of water and gas and the application of isotopic indicators in the exploration of deep CBM.

Higher aspect ratio (height/width) AgVO3 nanobelts were fabricated via a hydrothermal route. The reaction system was simple and the length of the nanobelts could be adjusted by modulating reaction parameters. Also, with or without surfactant hexadecyl trimethyl ammonium bromide (CTAB), straight or curled nanobelts were obtained, respectively. With α-Aminopropionic acid as both surface modifying agents and reducing agents, Ag nanoparticles with size of 5–10 nm were produced uniformly on the surface of AgVO3 nanobelts. The formation of Ag nanoparticles created surface-enhanced Raman scattering (SERS) hot spots on the AgVO3 nanobelts. Moreover, the synergistic effect between Ag hotspots and AgVO3 semiconductor made the as-synthesized AgVO3/Ag nanocomposites exhibit higher SERS sensitivity and better signal reproducibility. Using the composite SERS substrate, 4-Mercaptobenzoic acid (4-MBA) with a concentration down to 10−8 M was identified. Moreover, such kind of combination prevented the aggregation of Ag nanoparticles, so the substrate could be stored for a long time, which was another merit of the substrate from the viewpoint of its application.

In order to solve the problems of stress concentration and large deformation of surrounding rock of secondary gob-side entry retaining in thin coal seam caused by hard overhanging roof, the method of cutting off overhanging roof on both sides of roadway by manual pre-cutting seam is adopted. It can transfer high stress to goaf on both sides of roadway and reduce roadway deformation. The mechanism of roadway formation, the conditions of double side overhanging roof subsidence and the stress reduction of roadway side support of secondary gob-side entry retaining after double side roof cutting are given. This paper studies the pressure relief law of secondary gob side entry retaining after double side roof cutting in thin coal seam. After double side roof cutting, the stress of roadway side support is reduced by 76%, the maximum vertical displacement of roof is reduced by 84%, and high stress is transferred to goaf. The influence of different double side roof cutting thickness and angle on the pressure relief effect is analyzed. On the premise that the collapsed gangue can fill the goaf, the smaller the thickness of double side roof cutting is, the better the pressure relief effect is, and the greater the double side roof cutting angle is, the better the pressure relief effect is. It has been successfully applied in the left five roadway of No. 69 coal seam in Xinqiang coal mine, and the deformation of roof and floor is reduced by 47% and the deformation of two sides is reduced by 56% after double side roof cutting. It has important reference value for the future secondary gob-side entry retaining.