This study aims to effectively control the effects of blast vibrations and improve the safety factor for personnel and facilities in blasting engineering. Using high-precision digital electronic detonators according to the propagation and superposition principle of blasting vibration signals, a superposition prediction method based on single-hole blasting vibration waveform is proposed to determine the group-hole blasting vibration waveform. Experimental results show that the variation law of the predicted blasting vibration wave is consistent with that of the measured blasting vibration wave, and the error rate is less than 16%. Based on the proposed superposition prediction method, the variation law of particle vibration velocity peak with micro-differences in time is studied. Consequently, an optimal differential time interval (delay time) is obtained with regard to the blasting vibration reduction. The results are applied in a site leveling project, and the results show that the slight time difference between zones has an evident effect on vibration reduction. The maximum reduction achieved with the proposed method is superior (69.7%) to that obtained via other controlled blasting delay methods. This result has been successfully applied in a flat project in China.
The stability of the wellbore in multibranch horizontal wells is a critical issue that significantly impacts gas production and service life. To gain a more comprehensive understanding of the effects of stress state on wellbore stability in multibranch horizontal wells in coal seams, a series of biaxial compression tests were conducted on coal specimens with wellholes under varying lateral stress states. Digital image correlation technology was utilized to monitor the deformation and crack propagation throughout the testing process. Furthermore, theoretical analysis was employed to investigate the influence of lateral stress states on the coal wellbore instability. The findings revealed that initial failure of the coal specimens predominantly occurred near the wellbore and primary fractures at different σh values. As Δσ decreased, the self-stabilization time for the wellbore integrity increased. When σh is greater than σv, the upper and lower parts of the wellbore are more susceptible to deformation and collapse. Conversely, when σv is greater than σh, the left and right parts of the wellbore were more prone to collapse. Both the biaxial stress difference and the coefficient biaxial stress difference (Cov) have significant impacts on the wellbore stability in coal seams. Therefore, selecting wells with lower values for Δσ and Cov can effectively enhance the stability of multibranch wells in coal seams, improve the lifespan of coalbed methane wells, and increase coalbed methane production. The research results are of great significance in guiding the design improvements and increasing gas production for the multibranch horizontal wells in Zhi'na and similar coalfields.
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