LAUSR

Abstract The study of coal adsorption-induced strain is of great significance to the development of coalbed methane (CBM). In this text, the relationship between adsorption-induced strain and injection time, injection pressure, flux and permeability were studied by He and N2 injection respectively. The variation of adsorption strain with time at different stages was mainly studied. It was found that the strain increases linearly with increasing injection pressure within the experimental range. The relationship between strain and time is according to Langmuir's law under the same injection pressure. Meanwhile, there is a free adsorption boundary in the initial linear stage of adsorption. Within the free adsorption boundary, the adsorption-induced strain rate is independent of pore pressure; afterwards the adsorption-induced strain rate begins to be dominated by pore pressure. Moreover, the permeability increases with the increase of pore pressure. Because of the negative effect of adsorption expansion, the variation of N2 permeability with injection pressure is slower than that of He. The lower the initial permeability is, the more serious the permeability damage caused by adsorption expansion will be. The final research results show that pore pressure has a dual effect of “one positive and one negative”. The positive effect is the promotion of gas migration, and the negative effect is the inhibition of adsorption expansion on gas migration.