Experimental Investigation of Residual Acid Effects on Flushing Efficiency, Rheological Compatibility, and Thickening Behavior in a Novel Pre-Cementing Acidification Process
Wei Wang1, Hao Guo1, Cheng Jian1, Yi Yu1, Quanmin Jiang1, Chunyu Wang2,*
1 CNOOC China Limited, Zhanjiang Branch, Zhanjiang, China
2 School of Materials Science and Engineering, Nanjing Tech University, Nanjing, China
* Corresponding Author: Chunyu Wang. Email: 
Fluid Dynamics & Materials Processing https://doi.org/10.32604/fdmp.2026.085147
Received 06 May 2026; Accepted 30 June 2026; Published online 20 July 2026
Abstract
To overcome the inherent limitations of conventional post-cementing acidification, including limited acid penetration into the formation and the potential impairment of zonal isolation, a novel pre-cementing acidification approach is proposed. This method aims to remove near-wellbore formation damage before cementing operations. Its feasibility, however, critically depends on the physicochemical compatibility between residual acid and the subsequent cementing fluids, namely spacer fluids and cement slurries. In this study, a comprehensive series of laboratory experiments was conducted to evaluate the effects of residual acid on flushing efficiency, rheological compatibility, and thickening time. The results show that residual acid significantly enhances the ability of spacer fluids to remove drilling fluid filter cakes, increasing the flushing efficiency from 82.61% to 91.90%. In the presence of 2% corrosion inhibitor, increasing the acid dosage further improves flushing performance. Although mild rheological incompatibility is observed between the spacer fluid and the cement slurry, residual acid effectively reduces the R-value, thereby improving fluid compatibility, with a 50% acid concentration providing greater improvement than a 25% concentration. High-temperature and high-pressure tests conducted at 80°C and 150°C show that the thickening times of mixtures containing different acid concentrations and dosages are comparable to, or longer than, that of the neat cement slurry, indicating no risk of flash setting or excessive retardation. These findings demonstrate that the proposed pre-cementing acidification process is compatible with subsequent cementing fluids under the investigated conditions, providing experimental evidence supporting its technical feasibility.
Keywords
Pre-cementing acidification; flushing efficiency; rheological compatibility; thickening compatibility; high-temperature and high-pressure
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