Performance Evaluation and Mechanism Study of a Fluid Loss Additive in a Cement Slurry

For cementing operations in oil and gas wells to maintain the cement sheath integrity, effective fluid loss management is essential. In order to improve fluid loss management in cement slurries, this study examines the mechanism of action of a new copolymer fluid loss additive (FLA) made of sodium styrenesulfonate (SSS), N-methacrylamide (HAM), and itaconic acid (IA). The performance evaluation results indicate that under conditions of 180 °C and saturated brine, the water loss can still be controlled within 70 mL, and the cement exhibits excellent settling stability. After additives were added, the compressive strength of the cement samples in freshwater, semi-saturated brine, and saturated brine systems decreased by 15.9%, 25.3%, and 20.6%, respectively, compared to the control samples. Although there is a certain degree of reduction, these values still meet industry standards and do not affect on-site construction. The mechanism of action of the SSS/HAM/IA copolymer is elucidated through comprehensive testing, including total organic carbon test, zeta potential, environmental scanning electron microscopy test, mercury intrusion porosimetry, and X-ray diffraction analysis. The copolymer's adsorption onto cement particles dynamically alters the zeta potential of the cement slurry system, with the extent of adsorption directly correlating with fluid loss reduction. As the hydration reaction progresses, the copolymer's adsorption on cement particles increases, enhancing the system's stability without altering the composition of the cement hydration products. This study contributes to the development of an advanced FLA, paving the way for more efficient and reliable cementing operations in the oil and gas industry.