Oil-well cement slurry with hemihydrate gypsum: impact on mechanical properties

Oil well cement slurry properties are influenced by the cement composition, additives, and fineness of grinding. This study examines the impact of hemihydrate gypsum on the mechanical properties of oil-well cement slurry, a laboratory mill and a production cement mill were used to compare results. The purpose of the research was to determine the influence of the gypsum with different phase states (dihydrate or hemihydrate), The active additive of blast granulated slag and the total SO3 content on free water separation, the spread of well cement slurry and the flexural and compressive strength of the cement mortar. The conducted cycle of research made it possible to obtain quantitative dependencies for these parameters. Gypsum preheated in a furnace at 200°C for 60 minutes was used in this research. It was observed that the presence of hemihydrate gypsum in the cement does not significantly impact free water separation but does affect the spread of well cement slurry. Additionally, this research uncovered the influence of hemihydrate gypsum on compressive strength at 28 days and flexural strength at 1 day. It was also observed that presence of hemihydrate gypsum in the cement reduced the thickening time by 60 minutes. The presence of blast-granulated slag in the cement reduces free water separation in the well cement slurry. Research conducted with the production cement mill confirmed that the presence of hemihydrate gypsum reduces spreading by 25 mm and decreases free water separation by 1 ml. The results from the production cement mill and laboratory mill are comparable and representative. Keywords. oil-well cement slurry, effect of hemihydrate gypsum, cement mortar strength, gypsum phase state