CEMENTS CONTAINING HIGH-SILICA MINERALS FOR WELL CEMENTING

摘要

A method of cementing high-temperature wells (e.g. above 110°C [230°F]) by pumping into the well a cement blend comprising Portland cement and a silica-rich mineral, the blend having a C/S molar ratio of less than about 2.0, preferably less than 1.6. This avoids the use of finely divided silica while preventing strength regression. The slurry can comprise a blend of Portland cement and pozzolanic materials (blast furnace slags, fly ash, etc.) such that the chemical composition (expressed in oxides) has a Ca0/Si02 molar ratio below 1.7. A preferred composition is a mixture Portland cement and blast furnace slags with more than 60% of slags. The Blaine fineness of this material can be between 2,500 and 12,000 cm<2>/g and preferentially between 3,000 and 5,000 cm<2>/g.