Abstract: The geological characteristics of gas injection and production performance by water flooding are comprehensively studied and evaluated in Ren-11 reservoir. It is considered that the geological condition in the reservoir is favorable for rebuilding underground gas storages. The capacity evaluation of underground gas storages after being rebuilt in Ren-11 fractured bottom water reservoir is conducted, in particular, the lab experiment and the research on numerical stimulation are conducted. Learning from the experimental experience in the gas displacement field by injecting nitrogen in the Huabei Yanling Oilfield, the reservoir engineering study such as analogical calculation is conducted. A 3-d numerical stimulation model is established in the Ren-11 gas storage on the basis of the existing recognition and conclusions. Based on the detailed history matching, the indexes for the important basic parameters including the storage capacity and the dissolved gas are predicted. The result shows that the capacity of the gas storage in Ren-11 reservoir after being rebuilt can reach as high as three billion cubic meters. 