Mechanism and experimental study of temperature-coal rock electrical coupling

Aiming at the problem of abnormal response of electrical parameters of rocks overlying coal beds under variable temperature conditions, this paper systematically reveals the thermotropic evolution law of resistivity and dielectric properties of rocks by constructing a multi-physical field coupling model and combining with the in-situ experimental test method. Based on the integration of Archies' pore conductivity modeling framework and Arrhenius' activation energy theory, a resistivity temperature response model is developed to quantitatively describe the synergistic law of carrier activation energy and mobility on the conductive channel. A dielectric constant temperature model is derived in conjunction with the polarization relaxation theory, showing the role of thermal activation in controlling the polarization rate. The electrical parameters of 10 rock samples from Shanxi region were dynamically tested using a high-temperature insulation resistance test system (30–700°C, vacuum − 0.1 MPa) and a precision impedance analyzer (50 kHz-1 MHz). The experiments show that: the rock resistivity exhibits a three-stage characteristic, with the resistivity peaking at T _sρ2 (72.8-303.7°C) due to fissure budding and water evaporation (on the order of 10^8 Ω·m), and then plummeting by 2–5 orders of magnitude in the high-temperature section (after Tsρ3) due to the activation of the carriers at high temperatures; and the dielectric parameter is significantly enhanced after Trε2 (220-483.6°C), with an increase of 40% in dielectric constant. The dielectric constant increases by 40–80% and the dielectric loss tangent increases to 0.1–0.3 at 500°C with a relaxation peak (Trε3), which confirms the dominant role of interfacial and ionic polarization at high temperatures. The frequency characteristics show that the dielectric constant decreases by 15–30% at 1 MHz compared to 50 kHz, revealing that the high-frequency electric field suppresses the polarization response law. The experiments validate the scientific assumption in the theoretical model that temperature modulates carrier mobility and polarizability by regulating activation, and establish a quantitative correlation between temperature and electrical parameters. These results provide theoretical basis and data support for temperature compensation in electrical exploration of deep resources, thermal damage monitoring in mines and thermal damage assessment in rocks.