Experimental study on dispersion characteristics of complex resistivity of hydraulic fracturing coal

In order to evaluate the hydraulic fracturing effect with complex resistivity,the principle of hydraulic fracturing complex resistivity response is introduced,and a hydraulic fracturing complex resistivity measurement system is established.The capacitance,complex resistivity modulus and phase of the coal before and after hydraulic fracturing were measured in a frequency range from 0 to 200 kHz using a constant alternating current.By comparing the pre-fracturing and post-fracturing resistivity modulus and phase dispersion characteristics,the dispersion mechanism is analyzed. The results show that in the frequency range from 0 to 100 Hz,the induced polarization of coal sample is little affected by frequency,and the current with arbitrary frequency can be used to monitor hydraulic fracturing. Because of the water filling to the new fracture,the modulus value decreases after fracturing,and the modulus value curve shifts downward as a whole compared with the curve before fracturing. The larger the difference is,the better the fracturing effect is.The peak point of the phase is affected by the current frequency and the capacitance of the coal sample. The hydraulic fracturing increases the crack inside the coal sample,and the capacitance of the coal sample changes,causing the phase peak point to shift. The larger the offset is,the better fracturing effect is.