Abstract: To revitalize the abandoned oil and gas reservoir resources in continental shelf basins along the eastern coast of China, this study takes M Oil & Gas Field in East China Sea as the research object to demonstrate the feasibility of a carbon capture and storage (CCS) pilot test, focusing on selecting the optimal storage formation and quantitatively assessing its storage potential. Based on the geological conditions and current production infrastructure of the field, a comprehensive geological and geophysical analysis was conducted, identifying the M11 formation in the X4 well block of the MW structure as the target formation for the CCS pilot test. A theoretical model incorporating structural, solubility, and mineral trapping mechanisms was established, and the theoretical and effective storage potentials were calculated using the effective storage coefficient method. The results indicate that the M11 formation features medium porosity and permeability (average porosity 12.9%) and a stable mudstone caprock, and is currently underpressured, exhibiting favorable geological conditions for CO₂ storage. The theoretical CO₂ storage capacity of this formation is estimated at (4.87~8.56)×10⁴ t, with structural trapping playing the dominant role. The P50 effective storage capacity ranges from 2.12×10⁴ t to 2.22×10⁴ t, which fully meets the injection requirements of the pilot test. The M11 formation in the X4 well block of the MW structure is an ideal candidate for implementing the CCS pilot test, offering high storage security and resource utilization potential. This study confirms the feasibility of utilizing depleted offshore gas reservoirs for large-scale carbon storage, providing a crucial reference for carbon emission reduction in similar basins along the eastern coast of China.