水力压裂煤体相位频谱曲线试验研究

Experimental study on phase frequency spectrum curve of hydraulic fracturing coal

为探明水力压裂前后煤体内部结构改变引起的复电阻率变化规律,在实验室开展加载围压下煤体水力压裂试验,测量压裂前后煤体相位和振幅频谱曲线。结果表明:(1)压裂前后干燥煤体相位频谱曲线均为“U”型,压裂后相位频谱曲线移动明显;(2)含蒸馏水的压裂煤体相位频谱曲线呈“W”型;(3)压裂煤体中,“W”型曲线是由于未充分填充的含水次生裂隙和原有裂隙的不充分界面极化共同所致,这与水力压裂对煤体破坏的不均匀性有关;(4)采用等效电路的方法,用不同电容器代替煤体不同频率界面极化,模拟相位频谱曲线从“W”型变为“U”型的过程发现,未充分填充的含水次生裂隙和原生裂隙在不同频率下的不充分界面极化是产生“W”型曲线的原因。

In order to study the change law of complex resistivity of the internal structure of coal before and after hydraulic fracturing,hydraulic fracturing experiments of coal under the condition of loading confining pressure were carried out in the laboratory,and the phase and amplitude spectrum curves of coal before and after fracturing were measured.The results showed that:(1)The phase spectrum curve of dry coal before and after fracturing was“U”-shaped,and the phase spectrum curve moved obviously after fracturing;(2)The phase spectrum curve of fracturing coal containing distilled water was“W”-shaped;(3)In fracturing coal,the“W”curve was caused by the inadequate interfacial polarization of the inadequately filled water bearing sec-ondary fractures and the original fractures,which was related to the unevenness of hydraulic fracturing dam-age to the coal;(4)The equivalent circuit method was used to simulate the process of changing the phase spectrum curve from“W”type to“U”type by using different capacitors instead of coal interface polarization at different frequencies.The results showed that the insufficient interface polarization of inadequately filled water bearing secondary fractures and primary fractures at different frequencies was the reason for the“W”type curve.