Dynamic Changes of Pore Structure During CO2 Mineral Sequestration in Shale

Abstract

Abstract The mineralization that occurs after CO2 injection into shale is one possible long-term solution considered for storage of this greenhouse gas. However, the pore structure and connectivity of rocks will be affected in the process of mineralization. The purpose of this paper is to determine the effect of mineralization on reservoir connectivity during CO2 capture and storage (CCS). This mineralization is investigated here experimentally by injecting radially carbonate water into reactors containing rock samples. The rock samples were taken out at different mineralization times (24h, 72h, 120h, 168h), and permeability and scanning electron microscopy (SEM) tests were performed on the rock samples. According to the images of the overall characteristics and intergranular distribution characteristics under scanning electron microscopy, Avizo and Matlab software were used to divide the threshold value of gray value and statistics of gray value distribution, respectively. By defining the pore proportion degree, gray value frequency distribution and dissolution intensity, the dynamic change of pore connectivity in the process of mineralization was quantitatively analyzed. According to the threshold segmentation calculation of gray value, different dissolution modes in different stages of carbonization process were observed, including surface dissolution and particle denudation. The gray values in different ranges are quantized to analyze the influence of different dissolution types on pore connectivity. The synergistic effect of surface dissolution and particle denudation has a positive effect on the mineralization. We demonstrate the existence of a critical reaction time for mineralization, above which reservoir pore connectivity gradually decreases. At the same time, we found that the changes of reservoir connectivity and surface corrosion strength have roughly the same trend. Finally, the decrease of permeability caused by the accumulation of dissolved particles will contribute to the formation of self-sealing phenomenon during CCS. In this paper, the dynamic change of pore connectivity caused by mineralization during CCS is defined for the first time by statistical analysis of gray value, and the synergistic effect between surface dissolution and particle denudation is quantified, and the existence of self-sealing effect is verified. The results are of great significance for CCS.