Compressed air energy storage, as a new energy storage technology, plays an important role in peak shaving and valley filling. Based on the compressed air energy storage with abandoned oil wellbores, a pipeline-wellbore gas storage chamber, that is, the storage space was composed of above ground pipelines and underground wellbores, was proposed. Its inflation process was simulated, with a focus on analyzing the thermodynamics and flow characteristics of the internal gas. The results showed that with compressed gas flowed into the pipeline wellbore gas storage chamber, the gas temperature rapidly increased under the heating effect of the high-temperature wellbore wall. Subsequently, the temperature of the gas became slightly higher than that of the wall, at this point, a heat release of the gas to the wall. The gas temperature and heat dissipation tended to remain stable until the gas storage pressure rose to about 3 MPa. Due to the presence of geothermal gradient, there were significant differences in gas characteristics in different areas of the underground wellbore during the inflation process. As the depth of the wellbore increased, gas flow rate, density, and frictional resistance decreased. With the increase of the gas storage pressure, the differences in the gas flow rate and frictional resistance in different areas diminished. The results of this study provide significant theoretical insights that can effectively inform the practical application of compressed air energy storage systems, particularly those that employ underground wellbores as the repository for gas storage.