Fremgangsmåter og blandinger for sementering i kalde omgivelser (kaldt miljö)

摘要

A cement slurry composition for cementing a wellbore comprises hydraulic cement, aluminium silicate and metal sulfate. The cement preferably comprises Portland cement and 50% by dry weight of the slurry. The aluminium silicate maybe kaolin, halloysite, dickite or nacrite but is preferably high reactivity metakaolin and may comprise 1-75% by weight. The sulphate is preferably iron or aluminium sulphate and 1-10% by weight. The cement composition may also contain accelerators preferably 1-20% sodium chloride and 1-5% calcium bichloride. It may also comprise silica flour, ceramic spheres, low density additives, weighting agents, thinners, foamers, defoamers, lost circulation material, energising gases such as nitrogen or air, set retarders, stabilizers and substantially no gypsum. The water for the slurry may be fresh, sea, drill or brine water or drill mud. The slurry can preferably cure if used underwater or in conditions below freezing e.g. in permafrost.