A High Temperature CO₂ Resistant Hydroxyapatite Cement Slurry

Cement slurries used in high temperature gas wells must have corrosion resistance. Reports on corrosion resistance of set cement in high temperature wells are rarely seen because of the corrosion of the cement slurries to the testing equipment and the lack of high temperature polymer corrosion inhibitors. A high temperature CO₂ resistant hydroxyapatite cement slurry was formulated with the hydroxyapatite as inorganic corrosion inhibitor and a self-made polymer emulsion as the polymer corrosion inhibitor. Laboratory evaluation results have sown that the cement slurry has good rheology and anti-channeling performance. Depth of corrosion on the set cement in 90 d is less than 0.5 mm. XRD and SEM analyses of the set cement have demonstrated that the gelatinous substance and calcium hydroxide almost disappeared in the high temperature area. The only corrosion reaction was the reaction between the xonotlite and CO₂. LKseal polymer corrosion inhibitor minimizes the corrosion of the set cement by CO₂ through filming action. The hydroxyapatite repairs the vugs and pores formed by corrosion on the set cement through adsorption of CO₂ which then produces laminated carbonate hydroxyapatite, thereby enhancing the corrosion resistance of the hydroxyapatite cement.