Patent ID: 8636068

Claim:
A method of reducing corrosion of a hardened cement in a well comprising: (i) hardening in a well a cement composition comprising Portland cement and an additive selected from the group consisting of NaF, KF, [NH 4 ][HF 2 ], NH 4 F, LiF, Na 2 B 4 O 7 , Na 2 B 4 O 7 .10H 2 O, B 2 O 3 , B 8 Na 2 O 13 , BBr 3 , BF 3 , B 10 H 14 , B 2 H 6 , BH 3 , K 2 B 4 O 7 .4H 2 O, B(OH) 3 , Na 4 B 4 O 7 and its hydrate forms, Na 2 B 8 O 13 and its hydrate forms, or combinations thereof; (ii) exposing the well to wet carbon dioxide after the cement composition has hardened in the well; (iii) forming an insoluble calcium salt of calcium fluoride, calcium borate, or combinations thereof from the additive and calcium cations, the calcium cations having been formed from carbonic acid in wet carbon dioxide; and (iv) preventing carbon dioxide from penetrating into the set cement by forming a protective barrier from the insoluble calcium salt, wherein the protective barrier protects the cement from corrosion and further prevents loss of integrity to the hardened cement.