Optimizing Cement properties in High-temperature Oil Wells with Hybrid Additives: CNT-infused Mineral Wool and Nanoclay

The significant decrease in the structural integrity of Portland cement at temperatures above 110°C made it necessary to conduct an analysis and to investigate the enhancement of mechanical properties and durability of Saudi cement class G for high-temperature oil wells by incorporating mineral wool-impregnated with carbon nanotubes (CNTs) and nanoclay particles. The study aimed to improve the structural integrity of cement mixtures under temperatures up to 300°C. Six cement paste specimens with varying mineral wool contents (0-0.25%) impregnated with 25% CNTs and six cement mortar samples with different nanoclay concentrations (0-3%) were prepared and tested according to ISO 10426-2:2003 standards. It was established that addition of 0.1-0.15% mineral wool containing 25% CNTs significantly enhanced compressive and tensile strengths while reducing permeability. The optimal CNT concentration yielded compressive strength values exceeding 50 MPa, 5-23% higher than additive-free cement at 25°C, and 5.7-6.2 times higher at 300°C. Tensile strength values improved by 1.4 times at 25°C and 3.7-3.9 times at 300°C. Permeability decreased by 2-2.5 times. Additionally, incorporating up to 3% nanoclay improved the rheological characteristics and compressive strength of the cement slurry at high temperatures, with optimal performance at 3% nanoclay content. Beyond this concentration, nanoparticle aggregation adversely affected the microstructure and mechanical properties. A pattern has been revealed that the combined use of mineral wool saturated with CNTs and nanoclay particles effectively improved the thermal stability and mechanical performance of oil well cement at high-temperature environments.