Study on hydraulic fractured gas drainage effect based on Hoek－Brown Criterion

In order to accurately analyze the surrounding stress distribution and pressure released scope of the gas drainage borehole，with the water bole was a case，a softening and volume expansion mechanics model of the gas drainage borehole was established based on the Hoek－Brown Criterion and the stress theoretical calculation process of the borehole surrounding elastic zone，plastic softening zone and broken zone was inferred． A COMSOL software was applied to analyze the stress distribution surrounded along the borehole without a con- sideration of the coal plastic softening and volume expansion features． The pressure released and plastic zone scope surrounded along the borehole increased was considered when the coal was softened and expanded． In Huoerxinhe Mine，the hydraulic fracturing technology was tested and the mechanics model of the gas drainage borehole was applied to analyze the pressure released and plastic zone scope surroun- ded along the borehole after the test． The results showed that the pressure released and plastic zone scope was increased over 2 times． The gas drainage influence scope was increased and reached at the pressure released and permeability improved effect． In comparison with the conventional gas drainage parameters of the borehole，the gas drainage concentration from the hydraulic fractured borehole and the daily drainage pure volume would be slow with the time decayed and the gas drainage effect was improved．