Effects of NaCl on the Rheology, Consistency Development, and Early Strength of API Class G Cement Slurries

<jats:p>Elevated salinity can significantly affect the rheological behavior, thickening time, and early strength development of API Class G cement slurries. This study experimentally investigated the effect of NaCl additions of 0, 4, and 8 wt.% BWOC on cement slurries with densities of 1.5 and 1.9 g/cm³ at temperatures of 25, 50, 75, and 90 °C. Rheological parameters, the time required to reach a consistency of 30 Bc under atmospheric pressure, the times required to attain selected compressive strength thresholds, and the ultrasonic cement analyzer (UCA)-estimated compressive strength after 12 and 24 h were evaluated.The results demonstrated that the effect of NaCl was not pro-portional to its concentration but depended on slurry density, temperature, and the property being evaluated. NaCl generally reduced plastic viscosity and yield stress, whereas gel strength exhibited a non-uniform response with a pronounced dependence on temperature. Its influence on thickening time and early strength development was likewise non-monotonic. Under certain test conditions, higher NaCl concentrations accelerated the attainment of the initial strength thresholds; however, they did not consistently increase the UCA-estimated compressive strength after 24 h or improve all evaluated operational properties. Among the investigated salinity levels, the slurry containing 4 wt.% NaCl exhibited the most balanced overall performance in terms of rheological behavior, thickening time, and early mechanical properties across both slurry densities and the investigated temperature range. Nevertheless, this concentration did not provide the best performance for every individual parameter or under all test conditions. The findings provide a basis for the further op-timization of cement slurry formulations intended for use in high-salinity environments. Since the experimental program did not include independent repetitions, the observed differences should be interpreted as descriptive trends that require statistical validation in future studies.</jats:p>