In recent years, the international community has reached a consensus on carbon dioxide emission reduction. Carbon capture and storage technology is an important means of carbon dioxide emission reduction, and marine storage is one of the most promising methods to achieve carbon dioxide emission reduction. At present, the developed gas fields in X Sag of a certain sea area are mainly condensate gas reservoirs. Some gas fields have entered the late stage of development and are facing exhaustion. The exhausted gas reservoirs are good carbon dioxide storage boxes. In order to further clarify the sequestration potential of exhausted gas reservoirs in X Sag, this study selected the buried storage estimation based on structural, bound and dissolution storage mechanisms to estimate the theoretical storage. It is estimated that the theoretical carbon dioxide storage capacity of exhausted gas reservoirs in X Sag is 732 million tons, and the effective storage capacity is 239～463 million tons, indicating that the carbon dioxide storage potential of X Sag in this sea area is relatively large. It provides a basis for the demonstration of subsequent carbon dioxide storage projects.