Durability of cement stones in injection wells

Abstract

Cement stone is the weakest component of the wells, it is easily destroyed when working inside the casing and is vulnerable to the action of most formation fluids. In injection wells, under the action of water injected into the reservoir, intensive leaching of the cement stone occurs, which leads to its complete degradation after several years of well operation. The consequence of this is the injection of fluid into other formations and increased corrosion of the casings. Analysis of the field experience of injection wells showed that inter-reservoir crossflows result in cement stone complete collapse in 4-6 years, while in production wells it retained its properties after 20 years. Theoretical consideration of the leaching corrosion process made it possible to determine the main directions of reducing the corrosion rate, aimed at improving the structural characteristics of cement stone. Among these, a decrease in the initial water-content and optimization of the porous structure should be optimized. Analysis of the loads acting on the cement sheath in wells showed that during perforation, hydraulic fracturing and well drilling for deepening, the stresses arising in the cement stone exceed its strength characteristics. Therefore, it is advisable to use reinforced and self-healing cements to minimize these negative effects.