Oil well cement is a type of Portland cement; designed mainly for cementing (plugging) oil and gas wells. It is produced by joint fine grinding of clinker and gypsum (sometimes with special additives).
The following types of cement cement are produced: weighted, sandy, salt-resistant and low-hygroscopic, designed depending on the operating conditions for cold and hot wells. Mineral additives are introduced into the grouting cement in the following quantities: domain granulated or electrothermophosphoric slag – not more than 20%, active mineral additives – not more than 12%, or silica sand, or limestone – not more than 10%. In ultra-deep oil wells, where the temperature exceeds 100 ° C, the strength of the cement stone decreases. To eliminate this phenomenon, apply sandy backfill cement with a low content of C3S and C3A in the clinker and the content of quartz sand, introduced during grinding in the amount of 20-50%. Cement grouting, shuttered with 50% of water, is capable of giving a moving mass (pulp) that can be pumped into the wells. It is necessary that the hardened cement stone from such a pulp has a high initial strength. The setting time of the dough from cement oil, shuttered 50% of water, is: for cold wells – the beginning of setting no earlier than 2 hours, the end – for oilwell cement no later than 10 hours, for weighted, sandy and low-hygroscopic – no later than 12 hours, salt-resistant – not later than 20 hours after mixing; for hot wells – the beginning of setting no earlier than 1 hour and 45 minutes, the end – no later than 5 hours for all cements, except salt-resistant. For salt-resistant cement, the end of setting should be no later than 10 hours after the moment of mixing. The flexural strength of samples made from cement cement for cold wells at the age of 2 days should be at a hardening temperature of (22 + -2) С not less than 2.7 MPa, for hot wells at the age of one day at hardening temperature (75 + – 3) C – not less than 3.5 MPa.