Experimental Study On Response Characteristics Of Complex Resistivity In Hydraulically Fractured Coal Seams

In order to evaluate the hydraulic fracturing effect of the coal seam,a comprehensive analysis of the damage and failure process of the coal seam during the hydraulic fracturing process was established.The hydraulic fracturing process,the complex resistivity and strain measurement system of the coal seam samples before and after hydraulic fracturing were established;a single frequency of 100 Hz And constant alternating current to measure the complex resistivity modulus and strain response data of coal seam samples during hydraulic fracturing;using 0 Hz to 200 kHz frequency conversion and constant alternating current to measure complex resistivity of coal seam samples before and after hydraulic fracturing(Complex resistivity modulus,phase)and dispersion data of capacitance;analyze the response characteristics of the complex resistivity of the coal seam sample during the hydraulic fracturing process and before and after hydraulic fracturing through the dispersion mechanism of the coal resistivity;Changes in complex resistivity parameters of coal seam samples before and after fracturing;Cole-Cole model was used to fit the dispersion data of complex resistivity modulus values of coal samples before and after fracturing,and the pore fissures of coal samples before and after fracturing were calculated.Variation of resistance capacity;qualitative and quantitative methods to comprehensively characterize the hydraulic fracturing effect of coal seam samples.The results show:(1)The current resistivity is within the frequency range of 0 Hz to 200 kHz.The measured complex resistivity of the Jiaozuo Zhaogu mine and Jiulishan mine coal seam samples has a dispersion characteristic and is similar to rock.And the regular decrease,the absolute value of complex resistivity phase increases first and then decreases with increasing frequency.The main reason for the complex resistivity dispersion of coal seam samples is induced polarization,and the influence of electromagnetic induction is small.(2)The complex resistivity modulus values of the coal seam samples before and after hydraulic fracturing all decrease with increasing frequency,and the curve after fracturing is shifted downward as a whole compared to the curve before fracturing.In the frequency range of 0 Hz to 100 Hz,the excitation polarization of coal seam samples is less affected by frequency,and the amount of current at any frequency in the interval can be used to monitor the hydraulic fracturing process.The greater the difference between the complex resistivity modulus values before and after fracturing,the better the fracturing effect.(3)Before and after hydraulic fracturing,the phase of coal seam samples changed significantly.In the low frequency band,the absolute value of the phase after fracturing is greater than that before fracturing;in the high frequency band,the absolute value of the phase before fracturing is greater than that after fracturing.The peak point of the phase is affected by the current frequency and the capacitance of the coal seam sample.After hydraulic fracturing,the internal cracks in the coal seam sample are increased.The capacitance of the coal seam sample changes,which causes the phase peak point to shift downward,and the larger the offset,The better the fracturing effect.(4)The response curve of the complex resistivity modulus of the coal seam sample over time during hydraulic fracturing can comprehensively evaluate the hydraulic fracturing effect.From this curve,the time of fracturing hole initiation and fracture propagation can be known,and fracture initiation can be seen.Stage characteristics.In addition,the difference between the complex resistivity modulus values of coal seam samples at the beginning and end of hydraulic fracturing can comprehensively reflect the overall effect of fracturing.(5)Fit the complex resistivity modulus values of the coal seam samples before and after hydraulic fracturing to the Cole-cole model.The calculated changes of the fitting parameters R3 and X are in line with reality and satisfy the induced polarization phenomenon.The changes of R3 and C before-after can comprehensively characterize the hydraulic fracturing effect of coal seam samples.