Lin Baiquan

Crack propagation patterns and energy evolution rules of coal within slotting disturbed zone under various lateral pressure coefficients

Lateral pressure coefficient is an important parameter in geological engineering, and it influences significantly the damage zone around boreholes. In accordance with the fundamental principles of the Particle Flow Code (PFC), various models were established to investigate the crack propagation patterns and energy evolution rules of coal in disturbed zones of hydraulic slotting for various lateral pressure coefficients. Cracks around a slotted borehole propagate in the horizontal direction when the lateral pressure coefficient λ is less than 1, distribute uniformly when λ is equal to 1, and extend mostly in the vertical direction when λ is greater than 1. The total number of cracks increases linearly with λ. The variation in kinetic energy for coal failure was recorded; kinetic energy evolution observes a similar rule and its process can be divided into four stages, namely, the quick-release, rapid dissipation, drastic fluctuation, and stabilized stages. The peak value of the kinetic energy increases linearly with λ. The acoustic emission events distribute discretely when λ is small and uniformly when λ is equal to 1. The variation in acoustic emission events tends to increase sharply before decreasing when λ is greater than 1. The research findings are significant to the exploration of pressure relief mechanisms for hydraulic slotting from a microcosmic perspective.

Impact of the geological structure on pulsating hydraulic fracturing

In order to study the impact of the geological structure on pulsating hydraulic fracturing (PHF), the industrial experiments of PHF were carried out in the tectonic zone and the non-tectonic zone, and then, the differences of PHF process and effect were analyzed. The results show that the fault structure brings out a weak surface in the area of PHF, easily inducing the seam crack extension to the fault, and pulsating water constantly moves to the direction of fault. Pulsating injection time and injection quantity of PHF in the tectonic zone are significantly larger than that in the non-tectonic zone, producing large water blocking effect to gas drainage and hindering gas migration dynamics. There is a natural relief area existing in the fault so that the pulsating pressure of PHF cannot be increased, reducing the effect of PHF. Geological structure reduces the increment of the stable gas concentration and improves the initial gas concentration before and after PHF.

Numerical analysis on influence of initial pressure on attenuation characteristics of gas explosion

Through a roadway model whose cross-section area is 80×80 mm2 and length is 100m, the attenuation characteristics of explosive shock wave of methane-air mixtures with concentration of 9.5% and filling ratio of 10% were simulated by using AutoReaGas software at the initial pressure of 20 KPa, 60 KPa, 101.3 KPa, 150 KPa and 200 KPa. The results show that when shock wave propagates in roadway, the distances where peak overpressure and maximum gas velocity attenuate to zero are the same as those of maximum temperature and maximum density reduce nearly to their corresponding initial values. With the increase of initial pressure, the safety distance presents the change law of decrease, increase and decrease, the peak overpressure, the maximum density, the maximum combustion rate gradually increase, and their laws can be approximated by means of some linear functions, however, the changes of maximum temperature and maximum gas velocity are not obvious.