Enhancing Slurry Pumping Efficiency, Improving Cement Coverage, and Ensuring Zonal Isolation with Temperature-Triggered Anti-Settling Technology

Abstract

A stable cement slurry is critical to the success of a cementing job, from cement placement to long-term zonal isolation. Conventional anti-settling (AS) additives, such as clays and polysaccharides, are commonly applied to improve cement slurry stability, but they are only effective for low-to-mid temperature applications (up to 260°F) due to high temperature thermal thinning effects or thermal degradation. To compensate for such thermal thinning or thermal degradation effects, higher doses of AS additives are often applied, which inadvertently increase slurry placement difficulty with minimal improvement to slurry stability. This paper presents the performance of a novel, thermally activated, free-flowing, and easy-to-use temperature-triggered anti-settling (TTAS) agent that can help reduce the overall AS additive usage, prevent solids settling, and mitigate the formation of free fluid at 200-350°F or higher while having minimal effect on slurry rheology prior to activation. The performance of this novel TTAS agent was evaluated against conventional AS additives, including bentonite clay, diutan gum, and a commercial AS product in 16-lbm/gal and 18-lbm/gal Class H cement slurries. Static sedimentation (SS) and dynamic sedimentation (DS) tests revealed that the conventional AS agent-containing slurries exhibited mixability concerns, noticeable settling at downhole condition and gelation tendency. By contrast, the TTAS agent-containing slurries exhibited good mixability, no adverse effect on rheology at 80°F, and improved slurry stability, evidenced by less than ½ inch cone height and less than 1-lbm/gal differential density (Δρ) in dynamic sedimentation test using as low as 0.3% bwoc dosage.