A process performed by an underwater vehicle for transporting extraction fluids, such as, for example, natural gas, oil or water, wherein the underwater vehicle comprises one or more containment tubes for containing said extraction fluid and a main structure comprising a plurality of structural tubes and a plurality of transverse frames positioned substantially transversal to the one or more containment tubes and to the plurality of structural tubes, said plurality of transverse frames supporting and holding the one or more containment tubes and the plurality of structural tubes, said process comprising the following operations: a) hydraulically connecting the underwater vehicle to the head of an extraction well; b) transferring and storing the extracted fluid, such as, for example, natural gas, oil or water, on the vehicle, subjecting said fluid to one or more of the following processes operations performed by plants installed onboard the same vehicle; b.1) mechanical, electrical or chemical separation; b.2) separation of the gases or more volatile fractions of the extracted fluid; b.3) separation of predetermined phases or substances from the rest of the extracted fluid; b.4) extraction and elimination of acid gases, such as, for example, carbon dioxide or hydrogen sulphide; b.5) re-injection into geological formations; wherein the vehicle also comprises a first removable module containing at least part of the motors, pumps, fluid, electric or electronic circuits for the power or signalling of one or more of the plants onboard for effecting one or more of the process operations b.1-b.4, or compressing or liquefying the extraction fluid loaded on the vehicle itself, and the removable module being designed for being reversibly removed from and reinstalled on the vehicle for example, for programmed overhauling or maintenance operations, wherein fluid circuits onboard the removable module are provided with rapid connection systems to the parts of fluid circuit that remain permanently fixed on the rest of the vehicle; c) transporting the extracted fluid(s) subjected to one or more of the processes operations b.1 - b.4, causing the submerged underwater vehicle to advance. a) hydraulically connecting the underwater vehicle to the head of an extraction well; b) transferring and storing the extracted fluid, such as, for example, natural gas, oil or water, on the vehicle, subjecting said fluid to one or more of the following processes operations performed by plants installed onboard the same vehicle; b.1) mechanical, electrical or chemical separation; b.2) separation of the gases or more volatile fractions of the extracted fluid; b.3) separation of predetermined phases or substances from the rest of the extracted fluid; b.4) extraction and elimination of acid gases, such as, for example, carbon dioxide or hydrogen sulphide; b.5) re-injection into geological formations; wherein the vehicle also comprises a first removable module containing at least part of the motors, pumps, fluid, electric or electronic circuits for the power or signalling of one or more of the plants onboard for effecting one or more of the process operations b.1-b.4, or compressing or liquefying the extraction fluid loaded on the vehicle itself, and the removable module being designed for being reversibly removed from and reinstalled on the vehicle for example, for programmed overhauling or maintenance operations, wherein fluid circuits onboard the removable module are provided with rapid connection systems to the parts of fluid circuit that remain permanently fixed on the rest of the vehicle; b.1) mechanical, electrical or chemical separation; b.2) separation of the gases or more volatile fractions of the extracted fluid; b.3) separation of predetermined phases or substances from the rest of the extracted fluid; b.4) extraction and elimination of acid gases, such as, for example, carbon dioxide or hydrogen sulphide; b.5) re-injection into geological formations; c) transporting the extracted fluid(s) subjected to one or more of the processes operations b.1 - b.4, causing the submerged underwater vehicle to advance.