A gas injection system suitable for use in a geothermal plant comprising at least one reinjection well which enables the geothermal fluid received from a geothermal energy source via at least one production well to be delivered again to the geothermal energy source after being treated, comprising: - at least one exchanger to which non-condensable gases from the plant are delivered and which allows decreasing temperature of said gases; - at least one storage to which said gases, temperatures of which are decreased by said exchanger, are delivered and stored therein; - at least one compressor which is provided at an outlet of said storage and allows increasing pressure of the gases received from the storage; - at least one pump which allows increasing pressure of at least one part of the reinjection water received from said plant; - at least a first line in which reinjection water, which is received from said pump and the pressure of which is increased, and gases from said compressor, the pressure of which are increased, are gathered and delivered to the reservoir by said reinjection well; - at least a first delivery line which enables to deliver the gas, the pressure of which is increased, to said first line; - at least a second delivery line which enables to deliver the reinjection water, the pressure of which is increased, to said first line; - at least a first outlet line which is in communication with said first line on at least one side, at least another side of which communicates with a lower part of the reinjection well, and which enables to deliver the reinjection water, received from the first line and the pressure of which is increased, and the gases, the pressure of which are increased, to said lower part of the reinjection well; - at least one water delivery line to allow receiving non-pressurized part of the reinjection water from said plant; and - at least a second outlet line which enables to deliver the relatively low-pressure reinjection water that is received from the water delivery line to the reinjection well. - at least one exchanger to which non-condensable gases from the plant are delivered and which allows decreasing temperature of said gases; - at least one storage to which said gases, temperatures of which are decreased by said exchanger, are delivered and stored therein; - at least one compressor which is provided at an outlet of said storage and allows increasing pressure of the gases received from the storage; - at least one pump which allows increasing pressure of at least one part of the reinjection water received from said plant; - at least a first line in which reinjection water, which is received from said pump and the pressure of which is increased, and gases from said compressor, the pressure of which are increased, are gathered and delivered to the reservoir by said reinjection well; - at least a first delivery line which enables to deliver the gas, the pressure of which is increased, to said first line; - at least a second delivery line which enables to deliver the reinjection water, the pressure of which is increased, to said first line; - at least a first outlet line which is in communication with said first line on at least one side, at least another side of which communicates with a lower part of the reinjection well, and which enables to deliver the reinjection water, received from the first line and the pressure of which is increased, and the gases, the pressure of which are increased, to said lower part of the reinjection well; - at least one water delivery line to allow receiving non-pressurized part of the reinjection water from said plant; and - at least a second outlet line which enables to deliver the relatively low-pressure reinjection water that is received from the water delivery line to the reinjection well.