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As a crucial exploration technique for unconventional reservoirs, hydraulic fracturing enables the formation of complex fracture networks, thereby facilitating the flow of oil and gas. The closure of natural fractures decreases stimulation performance. Microparticle proppants are used to fill natural fractures and effectively increase the stimulation area. The 100-mesh proppant conventionally used in field operations may be insufficiently small to effectively access natural fractures. In order to effectively overcome natural fractures closure, microparticle proppants (i.e., proppants with a diameter of 75 ^m (200mesh) or less) are required. The particle size threshold test of microparticle proppants placement is conducted to determine the size threshold of proppants flowing into natural fractures. The microparticle proppants placement experiment in multi-branch fractures is conducted to investigate the volume difference of proppants in different fractures. Numerical simulations are performed to model proppant transport within fractures of actual dimensions to facilitating the optimization of stimulation parameters. The main conclusions are as follows: (1) Effective inflow of microparticle proppants requires a size threshold of proppants. For the 200-mesh proppants, the size should be less than half of natural fractures width when microparticle proppants effectively flow into natural fractures. (2) Sand concentration affects the size threshold of microparticle proppants. The size threshold should appropriately increase to ensure the inflow of proppant. (3) Difference of multi-branch fracture width has a significant effect on volume of microparticle proppants inside fractures. When the width ratio of multi-branch fractures exceeds 2, this effect becomes obvious. (4) Particle size has an effect on proppant placement. 200-mesh proppants can obtain uniform distribution of proppants among natural fractures. 140-mesh proppants can obtain maximum proppant volume among natural fractures. Sand concentration significantly affects proppant placement performance. The optimal sand concentration is 60kg/m3. The pumping rate for a single cluster fracture should not be excessively low. The pumping rate should be larger than 0.5m3/min and the optimal pumping rate 2m3/min. In this paper, the particle size and concentration of particulate proppant are optimized and the geometric characteristics of fractures are considered. These conclusions provide important practical guidance and scientific basis for the optimization and application of hydraulic fracturing technology. [ABSTRACT FROM AUTHOR]

Normally, most researches on phase calibration of shipborne USB system focus on the means of phase calibration. This article starts with the research on the channel of the system. The composition of the channel is introduced, and the characteristics of the channel is analyzed. Taking the channel of the field effect amplifier front-end as the research object, a mathematical fitting algorithm is used to derive the functional relationship between the phase of the field effect amplifier front-end and the working frequency. The actual calibration data is used for simulation analysis to obtain the fitting order of the function. Combining the phase-frequency relationship of the field effect amplifier front-end and the microwave self-checking phase correction of the field effect amplifier back-end, a new phase calibration method is proposed.

Hydrologists pursue the long-term goals of studying the relationship between hydrological processes and geomorphological processes, establishing quantitative relationships between these processes and finding ways to directly derive hydrological processes from topographic parameters to reduce the dependence on hydrological data. In this study, the river network of the Haihe River Basin was extracted based on DEM, and 18 representative small basins were selected as samples. Four river network parameters (the river network density, average branch ratio, average length ratio and fractal dimension) and four topographic parameters (the slope, topographic relief, surface roughness and roundness rate) were calculated for 18 small basins. The river network features and topographic features of the basin were analysed. Correlation analysis, one-dimensional linear regression, partial correlation analysis and multiple linear regression (stepwise regression) methods were used to analyse the quantitative relationship between topographic parameters and river network parameters. The analysis results were tested by a significance test, the final goodness of fit of the regression model was good, and the results were reliable. The correlations are spatially heterogeneous and may show variable results in different regions. This study guides river network planning and management, and managers should pay attention to the correlation between river networks and topography in the long term. [ABSTRACT FROM AUTHOR]

Intra-fracture temporary plugging and diverting fracturing are important technical means of improving the complexity of fractures in unconventional oil and gas reservoirs. The key to this technology is whether diverted fractures can be formed; therefore, a prediction model of the fracture initiation pressure needs to be established. Owing to the plugging effect of the temporary plugging agent, net pressure in the fractures before and after the temporary plugging section is discontinuous, which affects the induced stress field distribution around the fractures. However, it is difficult for the conventional induced stress calculation model to solve the induced stress field quickly when the pressure in the fracture is discontinuous. In this study, based on the superposition principle, an analytical model for the prediction of the initiation pressure considering discontinuous pressure is established and the initiation law of diverted fractures is analyzed. The simulation results show that the initiation position of the new fracture is at the temporary plugging position. The closer the temporary plugging position is to the fracture tip, the more difficult it is for new fractures to initiate. [ABSTRACT FROM AUTHOR]