A system for cableless bidirectional data transmission in a well for an extraction of formation fluids comprising: - a plurality of rods (11, 12) connected to each other in succession so as to form a rod string, which extends from a surface to a bottom of said well, said rod string being associable with a plurality of sensors configured for continuously detecting a plurality of parameters relating to a fluid circulating in the well and to a rock formation surrounding the well and/or to safety devices or other remote-controlled well instrumentation; - a plurality of communication modules applied at predefined distances along said rod string and configured for a transmission of signals from and towards the bottom of the well; - each of said communication modules comprising: - at least one metal plate selected from: - a transmitting metal plate; - a receiving metal plate; - a transceiver metal plate; - an electronic processing and control unit configured for processing signals to be transmitted by means of said at least one metal plate (21, 35) or signals received by means of said at least one metal plate (22, 35); - one or more supply batteries for feeding said metal plates (21, 22, 35) and said electronic processing and control unit; characterised in that, the transmission of said signal to be transmitted from a first communication module of said plurality of the communication modules (20, MC1) to a second communication module of said plurality of the communication modules (20, MC2) occurs by injecting into the fluid surrounding the rod string, by means of said at least one metal plate (21, 35) of said first communication module (20, MC1), an electric current that carries an information signal, at least a part of said injected electric current, that has propagated through at least said fluid, being received by means of said at least one metal plate (22, 35) of said second communication module (20, MC2). - a plurality of rods (11, 12) connected to each other in succession so as to form a rod string, which extends from a surface to a bottom of said well, said rod string being associable with a plurality of sensors configured for continuously detecting a plurality of parameters relating to a fluid circulating in the well and to a rock formation surrounding the well and/or to safety devices or other remote-controlled well instrumentation; - a plurality of communication modules applied at predefined distances along said rod string and configured for a transmission of signals from and towards the bottom of the well; - each of said communication modules comprising: - at least one metal plate selected from: - a transmitting metal plate; - a receiving metal plate; - a transceiver metal plate; - at least one metal plate selected from: - a transmitting metal plate; - a receiving metal plate; - a transceiver metal plate; - a transmitting metal plate; - a receiving metal plate; - a transceiver metal plate; - an electronic processing and control unit configured for processing signals to be transmitted by means of said at least one metal plate (21, 35) or signals received by means of said at least one metal plate (22, 35); - one or more supply batteries for feeding said metal plates (21, 22, 35) and said electronic processing and control unit; characterised in that, the transmission of said signal to be transmitted from a first communication module of said plurality of the communication modules (20, MC1) to a second communication module of said plurality of the communication modules (20, MC2) occurs by injecting into the fluid surrounding the rod string, by means of said at least one metal plate (21, 35) of said first communication module (20, MC1), an electric current that carries an information signal, at least a part of said injected electric current, that has propagated through at least said fluid, being received by means of said at least one metal plate (22, 35) of said second communication module (20, MC2).