Armouring of well cement in H2S-CO2 saturated brine by calcite coating -- experiments and numerical modelling
Résumé
The active acid gas (H2S-CO2 mixture) injection operations in Nortn America provide practical experience for the operators in charge of industrial scale CO2 geological storage sites. Potential leakage via wells and their environmenal impacts make well construction durability an issue for efficiency/safety of gas geological storage. In such operations, the well cement is in contact with reservoir brines and the injected gas, meaning that gas-water-solid chemical reactions may change the physical properties of the cement ans its ability to confine the gas downhole. The cement-forming Calicum silicate hydrates carbonation (by CO2) and feriite sulfidation (by H2S) reactions are expected. The main objective of this study is to determine their consequences on cement mineralogy and trasfert ability. 15 and 60 days duration batch experiments were performed, as welle as numerical simulation of the experiments. The work suggest that in both acid gas and CO2 geological storage, clogging of cement or at least mineral assemblage conservation and slowing of carbonation progress could occur in near-well zones where slight water flow occurs e.g. in the vicinity of caprock shales.