125. Cementing deep wells

In principle, all portland cement the well borehole. They differ from conventional standard cements requirement that they should be produced without the addition of recycled fuel and distillate. They can not even be used intensify the additive. Cements are usually manufactured in a batch mode with fineness of 3000 cm2 / g Blaine, i.e. they are relatively coarse. Today Base uses two class G cement and Class H. Tampon Their technical properties controlled can be adjusted with suitable retardants for use in almost any desired downhole temperature to 250 ° C and thus, they are universal cements. According to API standard mortar class G is tested with W / C ratio is 0.44, Class H cement tested at the W / C ratio is 0.38. These indicators are only slightly deflected by praktike.Skvazhinnoe pressure increases the temperature and results in faster hardening of Portland cement and, therefore, accelerates well cementing accelerates hydration product formation. As a result, at a temperature of about 110 ° C C-S-H gel forms a highly-S2SH crystallinity and, thus, most of the hydration products becomes denser. This conversion process requires a strong shrinkage and partial loss of strength of the hardened cement paste, with devastating consequences for the well density. In a class of standardized G- slurries reduction in compressive strength may be 80%, and 100-fold increase in permeability (typically 0.1 mDarsy) is observed at 230 ° C. This is "the power of regression." The marked technical problem is solved by reducing the ratio CaO: SiO2 - solution ratio is about 1. For this purpose, for oil wells, operating at temperatures above 110 ° C, prepared slurries containing 30-40% quartz flour. Under these conditions, it is obtained as the preferred phase C-S-H - tobermoritopodobny (C5S6H5) mineral which is not formed at normal temperature and elevated temperature.Pri calcium aluminates and others in hydrated form products. It turns C3A at a temperature of about 80 ° C instead of hexagonal C2AH8 cubic C3AH6 (Kato). Ettringite at about 110 ° C becomes unstable and decomposes with the formation of C-A-N phase CaSO4.Burovoy hemihydrate and cement, in particular, two basic Class G Cement and Class H iz-za fit their well-defined composition and preparation method as for manufacturing of complex building structures is responsible oil and gas wells. Their purity and quality make them particularly interesting for research.

101