Adsorption and migration behaviors for CO2 within nanopore structure of coal seams: three-dimension rough surface influence
摘要
To study the adsorption and diffusion behaviors of CO2 on the rough coal matrix surface during CO2 geological sequestration in deep coal seams from a microscopic perspective, and to reveal the mechanism of the effect of three-dimensional surface roughness on CO2 storage and transport in coal, this study first obtained roughness data of nanopore surface of coal based on atomic force microscopy (AFM) testing, and proposed a new method for constructing three-dimensional rough surface by combining molecular simulation technology. Then, a more realistic three-dimensional surface rough anthracite model was constructed to explore the differences and underlying mechanisms of adsorption and diffusion behaviors of CO2 on different rough surfaces at temperature of 318 K and pressure of 0−20 MPa. The results show that: ① The surface roughness has a more significant effect on CO2 adsorption in micropores. Compared with the smooth surface, the rough surface can enlarge the CO2 adsorption area (3.08 times for 1 nm slit pore, 1.30 times for 3 nm slit pore, and 0.73 times for 6 nm slit pore), increase the average density of CO2, accelerate the adsorption rate of CO2, and facilitate the adsorption saturation of CO2 at low pressure. Meanwhile, the surface roughness can also promote the transformation of CO2 adsorption configuration from smooth rectangle to concave convex shape, which has a significant impact on the distribution pattern of CO2 occurrence. ② In the rough-surfaced coal matrix slit nanopore system, due to the superposition effect of the adsorption force field, groove space can form lower-energy adsorption sites, thereby enhancing gas-solid and gas-gas interactions and increasing the adsorption capacity in this area. ③ The surface roughness is negatively correlated with the horizontal diffusion coefficient of CO2, while the pore size is positively correlated with the horizontal diffusion coefficient of CO2. ④ The adsorption potential of CO2 in the rough coal matrix shows a