Degradation of oil well cement with sodium chloride content exposed to supercritical carbon dioxide conditions: Temperature and pressure effects

Abstract

Understanding the effects of temperature and pressure on the supercritical CO₂ degradation of wellbore cement with NaCl content is essential for cementing oil wells in Brazil's deepwater pre-salt basin. The behavior of the cement paste used in cementing oil wells in this environment is very complex, with significant amounts of CO₂ and a thick salt layer that requires a high demand on special wellbore cement capable of adequately sealing and assuring stability to the oil wells. For these reasons, the objective of this study was to investigate the effect of NaCl in cement on oil wells exposed to supercritical CO₂ simulating pre-salt reservoir conditions. Cement slurry samples were prepared using Class G Portland cement (API 10 A), NaCl, water-to-cement (w/c) ratio of 0.46, and deionized water with (0 and 10% NaCl content). Supercritical CO₂ experimental runs were carried out under different conditions for 7 h. Before and after exposure to CO₂, the material was characterized by multiple analytical techniques. The results indicate that salt under temperature and pressure and the scCO₂ environment accelerates the carbonation process by decomposing the hydrated product, increasing the CaCO₃ content. In this scenario, investigations of the effect of adding NaCl to cement pastes are limited.