复合加砂抗高温防衰退水泥浆体系路

普通加砂G级水泥无法满足异常高温固井，水泥石高温强度衰退严重。针对高温深井固井问题，开展了在145~180℃下35%硅粉加量水泥石强度衰退机理研究，探索了170~200℃高温下硅粉粒度、加量及硅粉复配对水泥石强度发展的影响规律，优化出抗高温防衰退水泥浆体系。研究结果表明:①在温度大于160℃下，加量为35%硅粉的水泥石养护30 h时开始强度衰退，温度越高，衰退越早；②根据粗、细硅粉对水泥石强度发展的影响，得出0.18、0.09 mm硅粉及液硅比例为30:60:10，复合加量70%时，可以抑制200℃水泥石强度衰退；③优化出抗温为170~200℃、密度为2.08~2.41 g/cm3的复合加砂抗高温防衰退高密度防气窜水泥浆体系。通过以上研究，不但抑制了水泥石强度持续衰退，也改善了水泥石长期力学性能，对高温高压气井的良好封固提供技术支撑。 

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.