One of increasingly used methods for reducing carbon dioxide emission to atmosphere is CCS technology (Carbon Capture and Storage). The last element of sequestration technological chain, after capturing and transporting, is storage which is currently considered in: natural environment, oceans and geological structures – of which depleted gas reservoirs have high sequestrating potential mainly by virtue of proven record of geological recognition and high recovery factor, hence, great storage capacity. This paper is connected with first stage of storage in depleted gas reservoir i.e. flow of injected fluid inside the well. Conducted analysis was concerned about flow conditions inside the injection well in various stages of storage process, and furthermore, relation between reservoir pressure, injection rate, well diameter. Moreover, the thermodynamic conditions and its impact on changeability of PVT parameters and hence phase changes were also investigated.