Bentonite Prehydration and its Impact on Cementing Job Execution
Authors: Rahmatullah Idham Kholid , Mahmoud Ahmed Abdulhamid , Elkatatny Salaheldin 
Published: August 2024

ABSTRACT:
This paper investigates the significance of bentonite prehydration in oil well cement formulations and its impact on cementing operations. Through laboratory experiments and field case studies, the study aims to enhance cement properties, improve slurry stability, and optimize wellbore integrity. Laboratory experiments analyzed various prehydration methods' effects on cement slurry properties like fluid loss, rheology, and compressive strength. Field case studies assessed real-world applications and practical benefits. Comparative analysis of prehydration techniques such as batch and continuous mixing was conducted, providing comprehensive insights into bentonite prehydration's necessity and efficacy in cementing job success. Findings revealed that bentonite prehydration significantly improved cement slurries' rheological properties, enhancing fluidity and pumpability while reducing fluid loss, thereby stabilizing wellbores. Prehydrated bentonite slurries exhibited higher compressive strength, indicating improved cement quality and bonding. Field case studies reinforced prehydration's importance by reducing gas migration and lost circulation issues during cementing operations, enhancing zonal isolation and cementing job success. The study underscores the critical role of bentonite prehydration in oil and gas cementing operations, offering practical solutions to address various challenges encountered in cementing jobs.

1. INTRODUCTION
Lightweight cement serves as an effective solution for shallow formations with low fracture pressures. By reducing slurry density, it mitigates circulation losses and alters hydrostatic pressure (Alexandre, 2016; Anya, 2018). Various methods are employed to achieve lower density in lightweight cement. The common method applied in cementing operation is the utilization of water extenders, such as bentonite, which absorb excess water without altering cement slurry properties. Alternatively, lower-specific-gravity materials like fly ash can be incorporated to decrease density, while foamed cement, achieved through the addition of air or nitrogen, offers another alternative to produce lightweight cement (Adjei & Elkatatny, 2021; Nelson & Guillot, 2006).
In wellbore cementing operations, bentonite has been widely used due to its accessibility, affordability, and ease of transport compared to other methods. Bentonite is a clay assemblage derived from volcanic ash, rich in montmorillonite minerals. Its exceptional water-absorption capacity allows it to swell up to 18 times its dry volume (Dehn & McNutt, 2015; Lamrani et al., 2021). This ability stems from its unique composition, featuring two silicon tetrahedral sheets sharing an octahedral aluminium sheet, providing water adsorption and swelling. In addition, this unique swelling mechanism can occur due to its negative charge. The critical phenomenon of isomorphic substitution occurs when negatively charged surfaces are balanced by exchangeable cations, with bentonite typically classified as either sodium or calcium bentonite depending on the dominant exchangeable cation, Na+ for sodium bentonite and Ca+ for calcium bentonite. (Adjei et al., 2021; Gleason et al., 1997; Luckham & Rossi, 1999).