In order to reveal the change law of apparent resistivity in the process of CH

4

-coal adsorption/desorption of different macroscopic coal petrology compositions

the No.4 coal seam of the Jurassic Yan'an Formation in Dafosi coal mine is taken as the experimental object. By the proximate analysis and apparent resistivity measurement experiments of differe

nt coal samples （the durain

vitrain and mixed samples） with different water content （air dry basis sample

natural water absorption sample and samples dried at 378.15 K） of coal

the relationship between the apparent resistivity

methane adsorption and pressures is studied. The experimental results found that when compared to the vitrain

the durain has higher fixed carbon content

but lower ash content and moisture. The initial resistivity of the samples dried at 378.15 K of the durain is the largest. The influence of the adsorption of methane on the resistivity of the coal body is manifested in that with the adsorption of methane

the apparent resistivity of coal is significantly reduced. During the pressure increasing process that is the process of adsorption

the coal resistivity has a quadratic function relationship with the pressure and the amount of adsorption. The reason is that methane adsorption heat release

coal body expansion

and the spread of water on the inner wall of the pore throat causes the apparent resistivity to decrease. Due to methane adsorption

gas-water replacement occurs on the surface of the coal matrix

free water dissolves soluble minerals

and the ion concentration increases. In the process of adsorption

the apparent resistivity of coal decreases

but due to the limited soluble minerals and the hydrophobicity of coal

the resistivity of coal tends to be stable in the later stage of adsorption. During the depressurization process

that is the process of desorption

since the shrinkage of the coal matrix after expansion is irreversible （deformation）

the apparent resistivity of the coal body cannot be restored to its initial value. Compared to the durain

the pore connectivity of vitrain is poor

but the pore throat curvature is larger

when the number of charged particles in the double electric layer is high and aggregated in piles. This eventually leads to better electrical conductivity of vitrain than durain under the same conditions

i.e.

the apparent resistivity of vitrain is

smaller than that of durain.