Coal is porous medium of complexity,composed of a great number of organic matters and a small amount of inorganic minerals.Pore size with various ranges in coal determines the complication of methane diffusible behavior.Therefore,in this paper,based on the complexity of material composition and pore structure in coal,the effect of changes of material composition and pore structure in coal on methane diffusion property was discussed after solvent treatment.Coal samples with different coal body structures,collected from Huoerxinhe coal mine in Qinshui basin,China,were treated with organic solvents such as tetrahydrofuran(THF),carbon disulfide(CS2),and inorganic solvents such as hydrochloric acid(HCl),chlorine dioxide(ClO2).With the removal of part inorganic matters or small molecular phase in coal,pore structure is bound to be modified.Based on the modern testing methods,the change law of pore structure,hy hydrophilicity,and diffusion property of coals with different coal body structures before and after different solvents treatments was analysed relatively,to discover the influencing mechanism of solvent action on methane diffusion.The results show that:(1)Extraction/dissolution yield has a tendency to ascend with increasing damage degree of coal body.(2)Compared to raw coals,specific surface area(SSA)increase after organic solvents extraction.However,SSAs of fragmented and mylonitic coals decrease after inorganic solvents(HCl and ClO2).As to the pores of different sizes,in comparion to raw coal,the SSA of transitional pore has no obvious change,but the one of micropore and mesopore shows various changes.(3)For raw coal,pore volumetric fractal dimension(DA)grows but pore surface fractal dimension(DB)has no clear change with increasing coal damage.As damage degree of coal body increase,after organic solvents extraction,DA tends to ascend but DB has no clear trend;after inorganic solvents treatments,with increasing coal damage,DA tends to descend but DB tends to ascend.With the same damage degree of coal body,DA tends to descend after organic solvents extractions,which is consistent with increasing mesopore volume;for fragmented and mylonitic coals,after inorganic solvents treatments DA obviously decrease;DB has no clear trend after different solvents treatments.(4)As the damage degree of coal body enhances methane diffusion coefficient and amount increase.When coal damage is same,methane diffusion coefficient and amount decrease as follows after different solvents treatments:CS2>untreated coal>THF>ClO2>HCl.(5)The changes of coal methane diffusion after different solvents treatments are assoiciated with pore structure and wettability.Based on the change laws of pore structure,wettability,and diffusion property before and after solvent treatment,the effect of soluble components in coal on pore structure and wettablility was deeply analysed.And the mechanism of soluble components influencing coal methane diffusion was revealed.There is theroretical meaningness for the abundance and perfection of coalbed methane(CBM)reservoir’s stimulation theory,and the formulation of well-directed CBM extraction scenario. |