An efficient coal and gas outburst hazard prediction method using an improved limit equilibrium model and stress field detection

Abstract

Abstract Accurate prediction of coal and gas outburst (CGO) hazards is paramount in gas disaster prevention and control. This paper endeavors to overcome the constraints posed by traditional prediction indexes when dealing with CGO incidents under low gas pressure conditions. In pursuit of this objective, we have studied and established a mechanical model of the working face under abnormal stress and the excitation energy conditions of CGO, and proposed a method for predicting the risk of CGO under abnormal stress. On site application verification shows that when a strong outburst hazard level prediction is issued, there is a high possibility of outburst disasters occurring. In one of the three locations where we predicted strong outburst hazards, a small outburst occurred, and the accuracy of the prediction was higher than the traditional drilling cuttings index S and drilling cuttings gas desorption index q. Finally, we discuss the mechanism of CGO under the action of stress anomalies. Based on the analysis of stress distribution changes and energy accumulation characteristics of coal under abnormal stress, this article believes that the increase in outburst risk caused by high stress abnormal gradient is mainly due to two reasons: (1) The high stress abnormal gradient leads to an increase in the plastic zone of the coal seam. After the working face advances, it indirectly leads to an increase in the gas expansion energy that can be released from the coal seam before reaching a new stress equilibrium. (2) Abnormal stress leads to increased peak stress of coal body in front of working face. When coal body in elastic area transforms to plastic area, its failure speed is accelerated, which induces accelerated gas desorption and aggravates the risk of outburst.

Keywords

• Coal and gas outburst
• Mechanical model
• Instability
• Seismic wave tomography
• Prediction method