Potential impact of CO2 injection into coal matrix in molecular terms

Abstract

Coal seams are one of the targeted geological bodies for CO2 sequestration. Coal structure deformation is a significant feature of the interaction between CO2 and coal seams. The rearrangement of macromolecular structure is a recognized deformation mechanism whose process has not been quantified. We used a high-order coal macromolecular model to reveal specific processes of coal macromolecular rearrangement caused by CO2 injection through molecular dynamics. In addition, the potential impact of this injection on the sequestration and mechanical properties of CO2 in the coal matrix was investigated. The rearrangement of the coal macromolecular structure is accomplished through the mutual coupling of the pore structure and macromolecular ordering. The compression of closed pores and the expansion of open pores together cause the swelling of macromolecular volumes. The concentration of closed pores was an important indicator for the quantification of the rearrangement of macromolecular structure. The greater the content of closed pores in the coal, the higher the potential for macromolecular structure transformation after CO2 injection. Furthermore, the more disordered the direction of the coal macromolecular layer, the lower the peak strength of the coal matrix. The amount of CO2 sequestration in the coal matrix is gradually saturated near the critical pressure point. Our findings contribute to the study of CO2 sequestration in coal seams and CO2 leakage risk prediction.