Assessment of Silt as a Sustainable Raw Material in High Sulfate Resistant Oil-Well Cement

Abstract

This study investigates the feasibility of using natural silt as a partial substitute for clay in the production of high sulfate-resistant (HSR) oil-well cement. The research involved the chemical characterization of locally sourced raw materials — including silt, limestone, iron ore, and gypsum — followed by the design and preparation of raw mixes tailored to meet the requirements of API Specification 10A and the Iraqi Standard Specification No. 5 (2019).

Clinker was synthesized under controlled laboratory conditions, and comprehensive chemical and physical tests were carried out on the produced cement. Chemical evaluations included oxide composition and phase estimation (C₃S, C₃A, etc.), calculated via Bogue’s equations, while physical testing covered slurry density, thickening time, free fluid content, compressive strength (at 8 and 24 hours), and detailed rheological behavior.

The results demonstrated that the incorporation of silt improved the silica-to-alumina ratio, minimized the reliance on expensive iron ore by reducing its content from 6% to 3%, and maintained C₃A and C₃S levels within standard limits. Cement samples incorporating silt exhibited excellent slurry properties, with density ranging from 1.87 to 1.89 g/cm³, thickening times within the API recommended window (90–120 min), and negligible free fluid. Compressive strength values exceeded 800 psi after 8 hours and reached over 1600 psi after 24 hours, confirming full compliance with API criteria.

Additionally, rheological testing revealed stable flow behavior and suitable yield points, confirming good pumpability and workability of the cement slurry. When compared to the control cement (produced without silt), the silt-modified samples showed comparable or slightly improved performance across most parameters, with only minor reductions in early compressive strength due to slightly lower C₃S content.

Overall, this research highlights the technical viability and economic benefits of partially replacing clay with locally available silt in HSR oil-well cement. The findings confirm that silt can serve as a sustainable raw material, reducing production costs and raw material consumption, while ensuring compliance with international cementing standards. These outcomes have strong implications for future large-scale applications in Iraqi cement plants and oilfield operations