Abstract: Novel wet-phase modified expandable graphite (WMEG) particles were developed for in-depth profile control in carbonate reservoirs. The harsh environment of carbonate reservoirs (≥ 130 °C, ≥ 22 × 104 mg/L) brings significant challenges for existing profile control agents. WMEG particles were developed to address this problem. WMEG particles were synthesized via intercalation with ultrasound irradiation and chemical oxidation. The critical expansion temperature of WMEG particles is 130 °C, and these particles can effectively expand 3–8 times under high temperature and high salinity water. The core flow experiments show that WMEG particles exhibit a good plugging capacity, profile control capacity, and a better-enhanced oil recovery (EOR) capacity in deep carbonate reservoirs. WMEG particles can be expanded in the formation and form larger particles that bridge the upper and lower end faces of the fracture. Then the high-permeability zones are effectively plugged, and the heterogeneity is improved, resulting in an obvious increase in oil recovery. This research provides a novel insight into future applications of profile control agents for in-depth profile control treatment in carbonate reservoirs.