From Hematite to Magnetite: A Comparative Study on Weighting Materials in Well Cementing

Maintaining wellbore integrity in deep oil wells requires high-density cement slurries to counteract high formation pressures. While various heavy materials can increase slurry density, they can also impact the properties of both the slurry and the resulting cement sheath. In this study, we suggest the use of magnetite as a weighting material for preparing well cementing slurry of 18-ppg density and investigate its effect on different cement properties; then, we compare the change in properties with that caused by using hematite weighting materials. The properties investigated include rheological behavior, density variation, and compressive and tensile strength. The results indicate that both hematite-weighted and magnetite-weighted slurries have the same rheological characteristics; however, the 10-minute gel strength (10-m GS) increased significantly for the magnetite-weighted slurry. The hematite-weighted samples exhibited a density variation of 8.7% over a 4-in. sample, which was decreased to 7.3% for the magnetite-weighted samples; this decrease in the density variation was also confirmed by the computed tomography (CT) scan images and CT number change along the samples. The magnetite-weighted samples experienced higher compressive and tensile strength; they also showed more elastic behavior as indicated by the increase in the Poisson’s ratio (PR) and the decrease in the Young’s modulus (YM) for these samples compared with the hematite-weighted samples.