Chemical interaction of well composite samples with supercritical CO2 along the cement - sandstone interface

Chemical interaction of Portland cement with supercritical CO2 along the cement - sandstone interface was investigated. To model a well in a CO2 geological storage site, we prepared the well composite sample consisting of casing, Portland cement and sandstone. Using this sample, we conducted batch experiments in a laboratory scale to estimate the chemical interactions of CO2 under a reservoir condition (10MPa, 50 degrees C, 0.5M NaCl). The elemental and crystal phase analysis of CO2 exposed samples were carried out by SEM-EDS and mu-XRD. In the cement region, a carbonation zone of the cement occurred adjacent to the sandstone with both samples exposed to CO2. From the results of SEM-EDS analysis, it was found that Ca concentration in the carbonation zone increased about 20% in comparison to that in the unaltered cement zone while concentration of Mg, Si, S at the carbonation zone decreased. Crystal phase at the carbonation zone were predominantly CaCO3 (calcite, aragonite and vaterite) and trace Friedel's salt. In addition, CaCO3 were sparsely precipitated in the pore spaces of sandstone along the sandstone-cement interface. These results indicate that the formation of carbonation layer provides as an effective barrier to further CO2 attack. (C) 2014 The Authors. Published by Elsevier Ltd.