Typical additives used to help suspend cement slurries at high temperatures include either biopolymers, such as polysaccharides, or synthetic polymers. The biopolymers typically degrade at elevated temperatures while the synthetic polymers tend to severely thermal thin leading to inadequate performance from either. This work describes an additive to improve cement slurry stability at higher temperature ranges in horizontal well. A modified thickening time test, commonly referred to as a dynamic settling test, was used to demonstrate the stability of cement slurries at high temperatures. Free fluid tests were also performed where the cement slurries were exposed to downhole conditions prior to evaluating their stability. Ambient rheology profiles were examined to assure that the slurries can be mixed, pumped, and placed without excessive pressures. The effectiveness of this novel additive on fluid loss control is also exhibited by performing stirred fluid loss tests at elevated temperatures. Cement slurry stability is especially difficult to achieve in long, horizontal well cementing, where the slurry is exposed to high temperatures over long periods. The novel cementing additive presented here can help simplify otherwise complex cement slurry designs, which are needed to help meet all operational requirements. In particular, the material helps eliminate the need for excessive viscosifying agents in combination with large quantities of dispersant in order to maintain slurry stability at higher temperatures. The paper compares the effectiveness on cement slurry properties such as stability, free fluid, rheology, and fluid loss control. The tests were conducted from 200 °F to 400 °F in the laboratory at varying concentrations and cement densities. The problems, current solutions, newly developed solution and case history will be discussed in the paper. The work detailed shows that the new additive improves high-temperature cement slurry stability without high surface rheology and the associated mixing/pumping challenges. By providing this stability for horizontal wells, the cement slurry will prevent undesirable consequences which could result in remedial work, poor fracture treatment, communication between zones, and millions of dollars spent in additional completion costs and lost production.
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