Wells – Processes – Electric current or electrical wave energy through earth for...
Reexamination Certificate
1999-08-05
2001-07-03
Tsay, Frank (Department: 3672)
Wells
Processes
Electric current or electrical wave energy through earth for...
C166S065100, C204S421000
Reexamination Certificate
active
06253847
ABSTRACT:
This invention concerns downhole power generation within a borehole and relates to downhole power generation apparatus for use within the borehole and also to an associated method of generating power downhole.
BACKGROUND OF THE INVENTION
For downhole power generation, various methods of transmitting power from the surface to devices within the borehole have been proposed, such as placing cables in an annulus formed between the borehole and casing placed within the borehole, or use of electrical conduction through the casing. The use of sea water batteries, being isolated cells which are placed on the sea floor to provide local power generation for sub-sea production systems, is also known. However the use of batteries within boreholes is a problem as there is only space for small batteries within boreholes, and these batteries have a current generating lifetime of only a few days, due to the high temperatures downhole.
It is one aim of the present invention to provide downhole power generation method and apparatus with an extended life time for generating electricity.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided downhole power generation apparatus comprising a first electrode, a second electrode and an electrolyte, wherein the first electrode comprises a casing within a borehole. The use of a metal casing, such as that cemented into place within a borehole to provide zonal isolation, is of advantage as in this way the usually detrimental process of corrosion of the casing which occurs naturally within a borehole can be utilized to generate electrical power in situ.
Preferably the first electrode is a cathode and the second electrode is the anode. This is of advantage as very little material forming the casing will be removed as a result of current flow and as current flow is typically limited by the reaction of oxygen at a cathode, the large area of the casing will ensure that a large current flow is achieved.
Preferably the first electrode and the second electrode are formed from dissimilar metals and by appropriate selection of the two dissimilar metals, the casing will function as the cathode electrode. Thus typically the first electrode is formed from a steel casing and the second electrode is of zinc. The first and second electrodes may also be provided by metal alloys.
Desirably the second electrode is provided on an insulated connector joining at least two sections of casing. For such a second electrode, power is extracted in an electrical load connected between the casing and the second electrode.
However as an alternative the second electrode may be provided by a sacrificial electrode placed at the bottom of the borehole and in electrical communication via a load to the first electrode.
The electrolyte may be provided in a variety of ways as long as sufficient oxygen is available for use in the electrolytic reaction at the electrodes. Therefore one preferred electrolyte is flowing water produced by a well. Oxygen concentrations as low as 1 ppm are sufficient to allow the water to function as the electrolyte.
Alternatively where a cement holds the casing in place within the borehole, it may serve as the electrolyte. To this end, the cement may be provided with additives, such as NaCl, to improve its conductivity.
The electrodes may be provided with coatings of compounds to mediate the electrolytic reactions occurring. Thus preferably the first electrode is provided with oxide coatings to mediate electrolytic reaction at the cathode. A desirable coating is iron (III) oxide, with oxygen for the cathode reaction being provided by the reduction of iron (III) oxide to iron (II) oxide. The iron (III) oxide is preferably incorporated into the first electrode by pre-rusting the first electrode before it is inserted downhole.
In accordance with another aspect of the invention, a method of generating electrical power down a borehole comprises positioning at least one hollow cylinder made from a first material within a borehole, placing a dissimilar second material within the borehole, the first and second materials both communicating with a common electrolytic medium, thereby to form an electrolytic cell, and connecting an electrical load to the first and second materials to complete an electrical circuit and allow a current to flow through the load.
Preferably the method also comprises placing a plurality of hollow cylinders made from the first material within a borehole, and connecting successive hollow cylinders via an insulated connector bearing the dissimilar second material.
The method may also further comprise providing an electrical load on the insulated connector, electrical communication between the first and second materials being via the load.
According to a further aspect of the invention, a system for generating an electrical current for powering an electrical device down a borehole comprises first and second electrodes of dissimilar materials located in proximity downhole, but electrically separated, an electrolytic first medium in the vicinity of the electrodes, to form with the electrodes an electrolytic cell, and conductor means to conduct electric current from one electrode via an electrical device, to the other electrode.
These and other features of the invention, preferred embodiments and variants thereof, possible applications and advantages will become appreciated and understood by those skilled in the art from the detailed description and drawings following below.
REFERENCES:
patent: 3876471 (1975-04-01), Jones
patent: 4060988 (1977-12-01), Arnold
patent: 5099918 (1992-03-01), Bridges et al.
patent: 5656140 (1997-08-01), Oesterle et al.
patent: 5839508 (1998-11-01), Tubel et al.
Galletti, R., Citi, G., and Battaia, C. Sea Water Batteries Application to the Luna 27 Autonomous Well Society of Petrolium Engeineers 36940, European Petroleum Conference, Oct. 22-24, 1996, Milan, Italy, pp. 591-597.
Batzer William B.
Schlumberger Technology Corporation
Tsay Frank
Wang William L.
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