低渗透性煤体电脉冲水压致裂效果及规律研究

Study on effect and law of electric pulse hydraulic fracturing of low permeability coal

为了揭示电脉冲水压致裂技术对低渗透性煤体裂纹的作用效果和规律,基于液电效应原理,进行了高压电脉冲水压压裂理论分析和室内实验。共制作了3个试件,在3 MPa静水压力不变的情况下,分别施加不同的电压(9 kV、11 kV、13kV),利用超声波无损检测技术分别对实验前后的煤样进行扫描,分析煤样内部裂纹的分布和扩展情况,建立数值模型分析实验条件下裂纹的扩展规律和周边应力。结果表明:超声波首波声时的变化能够很好的反映出实验前后煤体试件裂纹的变化情况;单纯的3 MPa静水压力产生裂纹效果甚微;随着水中放电电压的增加,试件内部新生裂纹逐渐增多,裂纹密度增大,裂隙区域逐渐从中央钻孔向试件边缘扩展,煤体产生裂纹效果明显;在加载过程中,应力最大值逐渐增大,并随着裂纹的扩展而发生转移。

In order to reveal the effect and rule of hydraulic fracturing by high voltage electric pulse on coal crack,the analysis and the experiment about high voltage electrical hydraulic fracturing was carried out based on the principle of electrohydraulic effect.Then three specimens were made.In the case of constant hydrostatic pressure at 3 MPa,different voltages(9 kV,11 kV and 13 kV)were applied.The coal samples before and after the experiment were respectively scanned by ultrasonic nondestructive testing techniques to analyze the distribution and expansion of the coal internal cracks,and establish the numerical model to analyze the crack propagation rule and the surrounding stress distribution under experimental conditions.The results showed that the changes of the head ultrasonic wave's time could reflect the change of the crack in the coal sample before and after the experiment.The effect of the pure hydrostatic pressure at 3 MPa on the crack was very slight.While with the increase of the discharge voltage in the water,the new cracks inside the specimen and the density of cracks increased,and the fissure area extended from the central drilling to the edge of the test piece,coal crack effect was obvious.During the loading process,the maximum stress increased gradually and changed with the crack propagation.