High Temperature Anti Strength Retrogression Cement Slurry with Compounded Silica Powder

Conventional Class G cement with silica powder is not able to satisfy the need of extra high temperature well cementing because of serious retrogression of the high temperature strength of the set cement. The mechanisms of set cement (with 35% silica powder) strength retrogression at 145-180℃, and the effect of particle sizes, concentrations and compounding of silica powder on the development of the strength of set cement at 170-200℃ have been studied to resolve strength retrogression of set cement at elevated temperatures. A high temperature anti strength retrogression cement slurry has been developed. These studies showed that (1) at temperatures above 160℃, the strength of a set cement with 30% silica powder begins to decline after curing for 30 h, and the higher the temperature, the earlier the process of strength retrogression. (2) The ratio of 0.18 mm silica powder, 0.09 mm silica powder and liquid silica is determined to be 30:60:10 based on the effect of coarse and fine particle silica powders on the development of the strength of set cement. When the compounded silica is added at a concentration of 70%, strength retrogression of set cement at 200℃ can be inhibited. (3) a high temperature high density anti strength retrogression anti-channeling cement slurry with compounded silica powder has been developed with density between 2.08 g/cm³ and 2.41 g/cm³, and it can be used at high temperatures such as 170-200℃. Through these studies, the continual strength retrogression of set cement is inhibited, the long-term mechanical performance is improved, and the technology developed can be used in perfectly cementing HTHP gas wells.