Experimental study on flow rate sensitivity of coal in typical coal mining area of Qinshui Basin and its control mechanism

By using medium and high rank coal samples from three typical coal mines in Qinshui Basin,an experimen-tal study on flow rate sensitivity has been carried out. The permeability variation under different flow conditions is ana-lyzed and the relationship models between coal reservoir permeability and flow rate are established. Furthermore,the control mechanisms of flow rate sensitivity about medium and high-rank coals are revealed. It is shown that the coal sample permeability varies with the flow rate,and there is a critical flow velocity. Before the critical flow rate,with the increase of injection flow rate (or velocity),the permeability of coal sample increases. When the velocity exceeds the critical value,coal permeability will decrease with the rise of injection flow rate. The flow rate sensitivity is mainly con-trolled by coal physical properties and flow rate sensitive minerals. With the increase of porosity,permeability and fluid flow rate of coal reservoir,the flow sensitive damage rate of coal reservoir increases as logarithmic function. The clay minerals in the experimental coal samples accounts for 66. 63% -99. 89% ,and are mainly kaolinite and illite. So it in-dicates these coals exist potential flow rate sensitive damage. The results of flow rate sensitive experiment show that the coal samples in this area have different degrees of flow rate sensitive damage,and the flow rate sensitive damage degree of coal sample is from weak to moderate strong,the critical velocity is lower. With the increase of clay mineral content in coal,the flow sensitive damage rate of coal reservoir is also increased. In the process of CBM well drainage,pressure drop rate of Sihe and Xishan Coal Mine should be about six times of that of Zhaozhuang Coal Mine.