This article presents an experimental study of the effect of chromium (III) oxide, recovered from chromium-containing catalyst sludge, on the properties of grouting mortars used for well cementing in permafrost zones. The necessity of modifying grouting mortars to increase the strength of the cement stone for intervals in permafrost formations is justified. A method for reducing Cr(VI) to the stable form Cr(III) has been developed, and Cr₂O₃ has been obtained for use as an active mineral additive. Four grouting mixture compositions are considered: a base mixture, commonly used at sites, based on Portland cement with a setting accelerator; a mixture based on Portland cement; a mixture based on Portland cement with the addition of chromium (III) oxide; and a mixture based on Portland cement with calcium chloride and the addition of chromium (III) oxide. The experiments include testing of the four compositions at two water-to-solid ratios (W/S = 0.4 and 0.5) with an assessment of flowability, compressive and flexural strength, microstructure (microtomography, SEM) and phase composition (XRD) at normal and sub-zero temperatures, including cyclic temperature changes. The data obtained show that at W/S = 0.5, the addition of Cr₂O₃ increases the compressive and flexural strength of the cement stone; a reduction in the content of free Ca(OH)₂ is observed, the proportion of calcium silicate hydrates (CSH) increases, and a more homogeneous and dense microstructure is evident. This modification increases the flowability of the grout, which facilitates better replacement of the drilling fluid. The use of Cr₂O₃ to improve the durability and watertightness of support structures in cryolithozone conditions is clearly advisable.

Article provides a brief overview of the complications arising during the construction of oil and gas wells in conditions of abnormally high and abnormally low formation pressures. Technological properties of the solutions used to eliminate emergency situations when drilling wells in the intervals of catastrophic absorption and influx of formation fluid have been investigated. A technology for isolating water influx in intervals of excess formation pressure has been developed. The technology is based on the use of a special device that provides control of the hydrodynamic pressure in the annular space of the well. An experiment was carried out to determine the injection time of a viscoelastic system depending on its rheology, rock properties and technological parameters of the isolation process. A mathematical model based on the use of a special device is presented. The model allows determining the penetration depth of a viscoelastic system to block water-bearing horizons to prevent interformation crossflows and water breakthrough into production wells.