Fuel cell for downhole power systems

#This invention relates to fuel cells, and in one embodiment, to fuel cells that are especially well suited for downhole use in oil and gas wells, and for subsea use in connection with offshore wells. The invention can also be useful for commercial energy generation, powering electric vehicles, and powering other equipment, for example, communication and control equipment located in remote areas away from commercially available power sources.

#Several types of equipment used downhole in oil and gas wells, or beneath the surface of the sea adjacent to offshore wells, are electrically operated or actuated. Examples of such equipment include certain wireline tools and remote well telemetry equipment. The electrical power required can be provided by connecting the device to a surface power source via electrical cables, or by placing a power source near the site of the device itself. Often it is not practical to use electrical cables running from the surface to the subterranean or subsea site of the electrically-powered device, because of the great distance involved, or because the cables can interfere with the passage of other equipment through the wellbore, and are vulnerable to being damaged during well operations.

#Batteries can be used as a local source of power for downhole and subsea electrical devices, but are subject to their own problems. For example, increasing the power and energy generation capacity of a battery generally requires a proportionate increase in the size of the battery, which can present difficulties given the space constraints that exist in wellbores. Also, batteries will typically need to be electrically recharged at some point, thereby often making it necessary to provide some type of recharging equipment in physical proximity to the battery.

#FIG. 1 is a cross-sectional drawing of a fuel cell apparatus of an embodiment of the present invention, comprising two fuel cells in a stack configuration.

#FIG. 2 is a schematic drawing showing a fuel cell in a wellbore.

#FIG. 3 is a schematic drawing showing a fuel cell positioned proximal a wellhead at the sea floor.

#Embodiments of the present invention provide a practical means of using fuel cells in downhole or subsea locations to power electrical devices that are used far below the surface of the well or the surface of the water. However, it should be understood that the fuel cells of the present invention can be used in other contexts as well, and the invention is not limited to subsea and downhole uses in or around oil or gas wells. In some applications, a fuel cell can supply more reliable and a greater cumulative quantity of power than alternative forms of energy, such as batteries. The greater energy and power density of a fuel cell over other alternatives can often decrease the weight and size of the overall power unit. The decrease in size of the fuel cell power unit can enable the use of instruments and tools requiring electrical power in applications where they could not be utilized before. Fuel cells are considered an environmentally clean energy source since the primary waste product generated from fuel cell usage is water (assuming a fuel source of hydrogen).

#FIG. 1 shows one embodiment of the present invention in cross-section. A fuel cell 10 comprises a fuel vessel 12, an oxidant vessel 14, and a reaction zone 16. It should be noted that although a single fuel vessel and oxidant vessel are mentioned throughout this application multiple fuel and oxidant vessels can be adapted for use by one skilled in the art.

#The fuel vessel 12 comprises a source of a fuel suitable for use in the fuel cell, such as hydrogen gas or a reformed hydrocarbon. In one embodiment, the fuel vessel comprises a metal hydride. This provides a high-density means for storing hydrogen. Hydrogen gas is released from the solid hydride, and flows through a fuel conduit 18 to the reaction zone 16. Alternatively, the vessel could comprise hydrogen gas under high pressure (e.g., 500 to 5000 psig). Utilizing a metal hydride for hydrogen storage has a number of advantages over a conventional high-pressure gas storage system. The metal hydride can provide more storage capability on a per unit volume basis and the lower pressure metal hydride can provide a safer mode of operation, especially in a high temperature environment. The fuel supply to the reaction zone 16 is controlled by a valve 64 that is typically a pressure control valve.