Abstract: Good performance of low-density ceramic proppant is particularly important during the exploration of unconventional energy. In view of the performance degradation of low-density ceramic proppant upon serving in the formation water, two specifications of proppant were selected to be soaked in the formation water for different time. The proppant before and after soaking was characterized by XRF, XPS, XRD, SEM and TEM, and its aging mechanism was explored. The results show that the content of ClO₂ in the proppant increases, while the content of Al₂O₃ and SiO₂ decreases, and the content of Cl^- and HCO^-₃ in the formation water decreases. The peaks of Cl 2p and Cl 2s appear by XPS, and the new phase SiCl₄ is detected by XRD. These results confirm that Cl^- in the formation water diffuses to the proppant surface and reacts with SiO₂ to form SiCl₄, which further hydrates to generate silicone gel or silicic acid gel and coats the proppant surface. Al₂O₃ in the proppant can react with H⁺ (acidic environment) of the formation water to form Al³⁺, and then Al³⁺ reacts with HCO^-₃ to form Al(OH)₃ precipitating into the formation water. A large amount of Cl^- and H⁺ in the formation water erode the proppant from the surface, reducing the densification within the structure and making the structure loose, which reduces the proppant crushing resistance and degrades its performance.

Key words: low-density ceramic proppant, formation water, silicon gel, aging mechanism, Cl^- erosion, acidic environment