Wettability modification of a nano-silica/fluoro surfactant composite system for reducing the damage of water blocking in tight sandstone reservoirs

Abstract

In the process of drilling and development of tight sandstone reservoirs, a large number of external fluids can invade the pore structure of the reservoir due to its strong hydrophilicity, resulting in blockage of the pore structure and a decrease in oil and gas production capacity. To reduce the aqueous phase trapping damage of tight sandstone reservoirs, the SiO₂@KH550/FC-A nano-composite system was prepared to construct hydrophobic surfaces in core samples. First, the surface of nano-SiO₂ was modified by KH550 to prepare nanoparticles with good dispersion. FTIR, XRD, SEM, and TG were used to characterize the nanoparticles before and after modification. The fluorosurfactant FC-A was prepared in the laboratory and combined with SiO₂@KH550 to produce the SiO₂@KH550/FC-A composite system. The system increases the contact angle of the hydrophilic surface from approximately 20° to 130°, achieving wetting modification. Excellent stability of hydrophobicity was obtained, and the contact angle did not significantly decrease within 5 minutes. In contrast, using FC-A and SiO₂@KH550 individually, the contact angle of the hydrophilic surface could not be increased to over 90°. The SEM results showed that after treatment with the composite system, a layer of micro–nanoscale particles was attached to the hydrophilic surface. It was proved that SiO₂@KH550 and FC-A were adsorbed on the surface, forming a low surface free energy solid interface at the micro and nano scales, which greatly improved the surface hydrophobicity. Furthermore, after the composite system was used to treat tight sandstone cores aged at 100° for 16 hours, the amount of imbibition of the core samples treated with SiO₂@KH550/FC-A significantly decreased from 2.6 mL of brine to only 0.5 mL after 8 hours. The core spontaneous imbibition rate was also reduced to 0.0004 g min⁻¹ within 5 minutes, while the maximum brine water spontaneous imbibition rate was 0.27 g min⁻¹. The core displacement experiment further showed that the fluid in the core pores can be more easily flowed back under gas displacement after wetting modification. The water saturation of the core samples decreased to 16.3% after displacement, and the core permeability recovered to 88.4%, indicating that the SiO₂@KH550/FC-A composite system can significantly improve the liquid phase flowback ability.