Effect of Hemihydrate gypsum on the basic properties of oil-well cement

The purpose of the study was to determine the influence of gypsum in different phase states (dihydrate or hemihydrate), an active additive of granulated blast furnace slag, and the total SO3 content on free water separation, the spread of well cement slurry, and the flexural and compressive strength of cement mortar. Laboratory and production cement mills were used to compare the results. The conducted research cycle enabled the quantitative determination of these parameters. Gypsum was preheated in a furnace at 200 °C for 60 minutes. It was found that the presence of hemihydrate gypsum in the cement does not significantly affect free water separation but has some impact on the spread of the well cement slurry. Additionally, the study revealed the influence of hemihydrate gypsum on compressive strength at 28 days and flexural strength at 1 day. The research also discovered that the presence of hemihydrate gypsum in the cement reduces the thickening time by 60 minutes. The presence of granulated blast furnace slag in the cement reduced free water separation in the well cement slurry. The research conducted at the production cement mill confirmed that the presence of hemihydrate gypsum in the cement reduced the spread by 25 mm and free water separation by 1 ml. The results from the production cement mill and laboratory mill are comparable and representative.