Development and Evaluation of a Nano-SiO2-Enhanced Fluid Loss Additive for High-Temperature, High-Salinity Cementing Applications

Summary Deep well cementing often faces high temperatures and saline environments, which can degrade polymer-based fluid loss additives (FLAs) through hydrolysis, impacting the cement quality. We synthesized a novel polymer-based FLA by copolymerizing 2-acrylamido-2-methylpropanesulfonic acid (AMPS), itaconic acid (IA), and allyl-alcohol polyoxyethylene ether (APEG) with γ-methacryloyloxypropyltrimethoxysilane (KH570)-modified nano-SiO2 (KH570@SiO2) and named it AIAN. Thermal stability tests indicated the decomposition temperature of AIAN was 373°C. Filtration tests demonstrated that AIAN effectively controlled fluid loss. When AIAN was added to the oilwell cement (OWC) slurry at a mass fraction of 3% and a temperature of 180°C, the fluid loss volume measured according to American Petroleum Institute (API) standards reached only 42.4 mL. In 36% saturated brine, fluid loss in the OWC slurry with 3% AIAN was 52.5 mL. This FLA demonstrated outstanding tolerance to high-temperature and high-salinity conditions. Mechanistic studies, including zeta-potential measurement, X-ray diffraction (XRD), and scanning electron microscopy (SEM) examination, demonstrated that the introduction of KH570@SiO2 further enhanced the stability of the polymer FLA through structural pore blocking and denser filter-cake formation. Meanwhile, the strong adsorption and film-forming properties of AIAN still effectively promoted cement hydration, resulting in a denser paste structure. Thus, AIAN has excellent potential for high-temperature deep-well-cementing applications.