LEI D J, LIU L Y, JIA Z Q,et al.Experimental study on the characteristics of complex electrical dispersion response of hydraulic fracturing process in coal body[J].Journal of Henan Polytechnic University(Natural Science) ,2024,43(4):48-55.

doi:10.16186/j.cnki.1673-9787.2023050057

Received:2023/05/30

Revised:2023/08/30

Published:2024/07/05

Experimental study on the characteristics of complex electrical dispersion response of hydraulic fracturing process in coal body

LEI Dongji1,2, LIU Liying1, JIA Ziqiang1, LIU Ning1

1.State Key Laboratory Cultivation Base for Gas Geology and Gas Control，Jiaozuo  454000，Henan，China;2.Collaborative Innovation Center of Central Plains Economic Region for Coalbed /Shale Gas，Henan Province，Jiaozuo  454000，Henan，China

Abstract: Objectives In order to study the dispersion response characteristics of the complex electrical properties of the coal body during hydraulic fracturing，  Methods we measured the real part R and the imaginary part X of the complex electrical resistance of the hydraulically fractured coal body，analyzed their changes to determine the fracture development process inside the coal body，and analyzed their dispersion characteristics by excitation polarization theory.  Results The study shows that：（1）during the hydraulic fracturing process，the dispersion curves of the real part of the coal body at each pressure point are of “hree-stage” type with the change of frequency，and the imaginary part is of"U"type； the dispersion curves of the real part show an "upward shift first and then downward shift with the change of water pressure.The real part of the dispersion curve shows a trend of “first shifting upward，then shifting downward，and then shifting down significantly when fracturing”.（2）The extreme value of the imaginary part can be sensitive to the change of resistance value caused by small-scale elastic deformation and shear damage，and the frequency of the extreme value can identify the larger-scale shear damage，which can be used as an effective indicator to predict the coal body rupture.（3）In the process of hydraulic fracturing，due to the excitation polarization at the solid-gas-solid interface of the coal body，the solid and imaginary parts of the coal body show "three-stage" and "U" type changes with frequency.（4）As the coal body fracture first appears elastic deformation，then shear damage，and finally the water-containing conductive channel of the coal body is completely penetrated，the dispersion curve of the real part shows a trend of "first increasing，then decreasing，and rapidly decreasing when fracturing" with the change of water pressure.  Conclusions In this study，the complex resistivity method is used to monitor the change of complex electric parameters with water pressure during the hydraulic fracturing process of coal body and judge the fracture development process of coal body，and the excitation polarization theory is applied to analyze the response characteristics of complex electric parameters with water pressure and AC frequency in the hydraulic fracturing of coal body，so as to lay the experimental foundation for the evaluation of fracture and fracturing effect of coal seam by the spectral excitation method.

Key words:complex resistivity method;hydraulic fracturing;response characteristics;frequency dispersion mechanism;induced polarization