Experimental study on time effect and deformation anisotropy of shale and coal under CO2

To investigate the adsorption and deformation characteristics of shale and coal under CO2 ,two kinds of sam- ples including shale in Longmaxi Formation and coal in Tashan mine were collected to conduct a 2 000 hours isother- mal adsorption test which was operated at 0-16 MPa CO2 pressure by “shale adsorption and expansion instrument un- der high temperature and high pressure”. The results showed that under the combined influence of permeability and CO2 density,the adsorption equilibrium time of shale and coal increased gradually at first,then decreased sharply to the bottom (shale 9. 3 h,coal 4. 8 h) when CO2 pressure reached the critical level,finally raised again. The deforma- tion anisotropy of shale decreases with the increase of pressure which is caused by the different elastic modulus. While the isothermal adsorption curves of shale and coal are similar, and have the maximum adsorption capacity of 0． 082 mmol / g and 1． 421 mmol / g respectively in the vicinity of 10 MPa and 7 MPa. It was found that the deforma- tion characteristics of shale and coal are obviously different:the volumetric strain and the adsorption capacity modelled an appropriate quadratic function on shale,but fitted a good linear relationship on coal.