Study on the Complex Electrical Response Characteristics of Loaded Coal and the Control Mechanism of the Main Fracture System Structure

Jian Li; Xiaokai Xu; Jie Wu; Yugui Zhang; Zhiqi Guo; Zehua Zhang; Zhengzheng Xue

doi:10.1021/acsomega.3c09733

Study on the Complex Electrical Response Characteristics of Loaded Coal and the Control Mechanism of the Main Fracture System Structure

ACS Omega. 2024 Feb 15;9(8):9686-9701. doi: 10.1021/acsomega.3c09733. eCollection 2024 Feb 27.

Authors

Jian Li¹, Xiaokai Xu², Jie Wu³, Yugui Zhang¹, Zhiqi Guo⁴, Zehua Zhang², Zhengzheng Xue²

Affiliations

¹ School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan 454003, China.
² School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan 454003, China.
³ State Key Laboratory of Coal and Coalbed Methane Co-Mining, Jincheng, Shanxi 048012, China.
⁴ Henan Energy Group Research Institute, Zhengzhou, Henan 450000, China.

Abstract

The structure of coal seam fractures is the main physical property of coalbed methane reservoir evaluation, and the complex resistivity method is a potential geophysical evaluation method for coal seam fractures. In this study, cylindrical coal samples with axial directions perpendicular to the bedding, face cleat, and butt cleat were prepared. The complex electrical parameters of the loaded specimens were tested with test frequencies ranging from 1 Hz to 10 kHz. The complex electrical response characteristics of the loaded coal are summarized, and the control mechanism of the main fracture system structure is analyzed. The results indicated that (1) as the loading pressure increased, the resistance R and the absolute values of reactance X(|X|) gradually decreased, especially in the frequency band where R slowly decreased and the characteristic frequency of X, the decreased amplitude was more significant, and the cutoff frequency of R and the characteristic frequency of X all gradually increased. (2) The complex electrical properties of coal show obvious anisotropic characteristics. Both R and |X| decreased sequentially according to the direction perpendicular to the bedding, face cleat, and butt cleat; the cutoff frequency of R and the characteristic frequency of X all increased sequentially. (3) The dispersion phenomenon of the complex electrical properties of coal is attributed to the induced polarization; the elevated loading stress enhances the polarization effects of the molecular-induced moments of the coal skeleton, and the anisotropic difference of the complex electrical properties is due to the difficulty in the degree of transport of charged particles induced by structural differences of the main fracture system. (4) The resistance R₃ and capacitance X_c were selected as the complex electrically sensitive parameters of the loaded coal orthogonal fracture structures. A logarithmic inversion model reflecting the main fracture system structure of coal was constructed. This provides a certain theoretical basis for efficient electrical exploration of coal reservoir fracture structures.