Abstract:
A downhole electrical power generator. A downhole electrical power generating system includes a flow restricting device which variably restricts flow through an opening, the restricting device vibrating in response to flow through the opening and the restricting device thereby alternately increasing and decreasing flow through the opening; and an electricity generating device which generates electricity in response to vibration of the restricting device. Another downhole electrical power generating system includes a flow restricting device which vibrates in response to flow through an opening, the restricting device thereby alternately increasing and decreasing flow through the opening, a pressure differential across the restricting device variably biasing the restricting device to increasingly restrict flow through the opening, and the pressure differential alternately increasing and decreasing in response to respective alternate increasing and decreasing flow through the opening; and an electricity generating device which generates electricity in response to vibration of the restricting device.

Description:
TECHNICAL FIELD 
   The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a downhole electrical power generator. 
   BACKGROUND 
   A wide variety of downhole well tools may be utilized which are electrically powered. For example, flow control devices, sensors, samplers, packers, instrumentation within well tools, telemetry devices, etc. are available, and others may be developed in the future, which use electricity in performing their respective functions. 
   In the past, the most common methods of supplying electrical power to well tools were use of batteries and electrical lines extending to a remote location, such as the earth&#39;s surface. Unfortunately, some batteries cannot operate for an extended period of time at downhole temperatures, and those that can must still be replaced periodically. Electrical lines extending for long distances can interfere with flow or access if they are positioned within a tubing string, and they can be damaged if they are positioned inside or outside of the tubing string. 
   Therefore, it may be seen that it would be very beneficial to be able to generate electrical power downhole, e.g., in relatively close proximity to a well tool which consumes the electrical power. This would preferably eliminate the need for batteries, or at least provide a means of charging the batteries downhole, and would preferably eliminate the need for transmitting electrical power over long distances. 
   SUMMARY 
   In carrying out the principles of the present invention, a downhole electrical power generator is provided which solves at least one problem in the art. An example is described below in which flow through a tubular string is used to vibrate a flow restricting device, thereby displacing magnets relative to one or more electrical coils. 
   In one aspect of the invention, a downhole electrical power generating system is provided which includes a flow restricting device for variably restricting flow through an opening. The restricting device vibrates in response to flow through the opening, with the restricting device thereby alternately increasing and decreasing flow through the opening. An electricity generating device generates electricity in response to vibration of the restricting device. 
   In another aspect of the invention, a downhole electrical power generating system is provided which includes a flow restricting device which vibrates in response to flow through an opening, thereby alternately increasing and decreasing flow through the opening. A pressure differential across the restricting device variably biases the restricting device to increasingly restrict flow through the opening. The pressure differential alternately increases and decreases in response to respective alternate increasing and decreasing flow through the opening. An electricity generating device generates electricity in response to vibration of the restricting device. 
   These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic partially cross-sectional view of a downhole electrical power generating system embodying principles of the present invention; and 
       FIG. 2  is an enlarged scale schematic cross-sectional view of an electrical power generator which may be used in the system of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Representatively illustrated in  FIG. 1  is a downhole electrical power generating system  10  which embodies principles of the present invention. In the following description of the system  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present invention. The embodiments are described merely as examples of useful applications of the principles of the invention, which is not limited to any specific details of these embodiments. 
   As depicted in  FIG. 1 , a tubular string  12  (such as a production, injection, drill, test or coiled tubing string) has been installed in a wellbore  14 . An electrical power generator  16  is interconnected in the tubular string  12 . The generator  16  generates electrical power from flow of fluid (represented by arrow  18 ) through an internal flow passage  20  of the tubular string  12 . 
   The fluid  18  is shown in  FIG. 1  as flowing upwardly through the tubular string  12  (as if the fluid is being produced), but it should be clearly understood that a particular direction of flow is not necessary in keeping with the principles of the invention. The fluid  18  could flow downwardly (as if being injected) or in any other direction. Furthermore, the fluid  18  could flow through other passages (such as an annulus  22  formed radially between the tubular string  12  and the wellbore  14 ) to generate electricity, if desired. 
   The generator  16  is illustrated in  FIG. 1  as being electrically connected to various well tools  24 ,  26 ,  28  via lines  30  external to the tubular string  12 . These lines  30  could instead, or in addition, be positioned within the tubular string  12  or in a sidewall of the tubular string. As another alternative, the well tools  24 ,  26 ,  28  (or any combination of them) could be integrally formed with the generator  16 , for example, so that the lines  30  may not be used at all, or the lines could be integral to the construction of the generator and well tool(s). 
   The well tool  24  is depicted in  FIG. 1  as being an electrically set packer. For example, electrical power supplied via the lines  30  could be used to initiate burning of a propellant to generate pressure to set the packer, or the electrical power could be used to operate a valve to control application of pressure to a setting mechanism, etc. 
   The well tool  26  could be any type of well tool, such as a sensor, flow control device, sampler, telemetry device, etc. The well tool  26  could also be representative of instrumentation for another well tool, such as a control module, actuator, etc. for operating another well tool. As another alternative, the well tool  26  could be one or more batteries used to store electrical power for operating other well tools. 
   The well tool  28  is depicted in  FIG. 1  as being a flow control device, such as a sliding sleeve valve or variable choke. The well tool  28  is used to control flow between the passage  20  and the annulus  22 . Alternatively, the well tool  28  could be a flow control device which controls flow in the passage  20 , such as a safety valve. 
   Although certain types of well tools  24 ,  26 ,  28  are described above as being operated using electrical power generated by the generator  16 , it should be clearly understood that the invention is not limited to use of the generator  16  with any particular type of well tool. The invention is also not limited to any particular type of well installation or configuration. 
   Referring additionally now to  FIG. 2  an enlarged scale schematic cross-sectional view of the generator  16  is representatively illustrated. The generator  16  is shown apart from the remainder of the system  10 , it being understood that in use the generator would preferably be interconnected in the tubular string  12  at upper and lower end connections  32 ,  34  so that the passage  20  extends through the generator. 
   Accordingly, in the system  10  the fluid  18  flows upwardly through the passage  20  in the generator  16 . The fluid  18  could flow in another direction (such as downwardly through the passage  20 , etc.) if the generator  16  is used in another system. 
   The passage  20  extends through a generally tubular housing  36  of the generator  16 . The housing  36  may be a single tubular member or it may be an assembly of separate components. 
   Note that the housing  36  includes a flow diverter  38  in the form of a venturi in the passage  20 . As the fluid  18  flows through the diverter  38 , a pressure differential is created, in a manner well understood by those skilled in the art. Pressure in the passage  20  upstream of the diverter  38  will, therefore, be greater than pressure downstream of the diverter. 
   The housing  36  also includes openings  40  formed through its sidewall downstream of the diverter  38 , and openings  42  formed through its sidewall upstream of the restriction. An annulus  44  formed between the housing  36  and an outer housing  46  is in communication with each of the openings  40 ,  42 . Thus, instead of flowing directly through the diverter  38 , a portion of the fluid  18  is induced by the pressure differential in the passage  20  to flow through the openings  42  upstream of the diverter  38  to the chamber  44 , and from the chamber through the openings  40  back into the passage  20  downstream of the diverter. 
   Note that it is not necessary for the diverter  38  to include a restriction in the passage  20  in order to divert the portion of the fluid  18  to flow through the annulus  44 . For example, the diverter  38  could instead include an enlarged flow area (such as, provided by an annular recess) in the passage  20  at the openings  40 , so that a pressure reduction is created in the annulus  44  via the openings  40 , thereby drawing fluid into the chamber from the passage via the openings  42  upstream of the enlarged flow area. In this manner, the pressure differential may be created in the passage  20  without restricting flow or access through the passage. 
   A flow restricting device  48  is positioned in the chamber  44 . The device  48  operates to variably restrict flow through the openings  40 , for example, by varying an unobstructed flow area through the openings. The device  48  is illustrated as a sleeve, but other configurations, such as needles, cages, plugs, etc., could be used in keeping with the principles of the invention. 
   As depicted in  FIG. 2 , the openings  40  are fully open, permitting relatively unobstructed flow through the openings. If, however, the device  48  is displaced upwardly, the flow area through the openings  40  will be increasingly obstructed, thereby increasingly restricting flow through the openings. 
   The device  48  has an outwardly extending annular projection  50  formed thereon which restricts flow through the chamber  44 . Because of this restriction, another pressure differential is created in the chamber  44  between upstream and downstream sides of the projection  50 . As the fluid  18  flows through the chamber  44 , the pressure differential across the projection  50  biases the device  48  in an upward direction, that is, in a direction which operates to increasingly restrict flow through the openings  40 . 
   Upward displacement of the device  48  is resisted by a biasing device  52 , such as a coil spring, gas charge, etc. The biasing device  52  applies a downwardly directed biasing force to the device  48 , that is, in a direction which operates to decreasingly restrict flow through the openings  40 . 
   If the force applied to the device  48  due to the pressure differential across the projection  50  exceeds the biasing force applied by the biasing device  52 , the device  48  will displace upward and increasingly restrict flow through the openings  40 . If the biasing force applied by the biasing device  52  to the device  48  exceeds the force due to the pressure differential across the projection  50 , the device  48  will displace downward and decreasingly restrict flow through the openings  40 . 
   Note that if flow through the openings  40  is increasingly restricted, then the pressure differential across the projection  50  will decrease and less upward force will be applied to the device  48 . If flow through the openings is less restricted, then the pressure differential across the projection  50  will increase and more upward force will be applied to the device  48 . 
   Thus, as the device  48  displaces upward, flow through the openings  40  is further restricted, but less upward force is applied to the device. As the device  48  displaces downward, flow through the openings  40  is less restricted, but more upward force is applied to the device. Preferably, this alternating of increasing and decreasing forces applied to the device  48  causes a vibratory up and down displacement of the device relative to the housing  36 . 
   An electrical power generating device  54  uses this vibratory displacement of the device  48  to generate electricity. As depicted in  FIG. 2 , the generating device  54  includes a stack of annular shaped permanent magnets  56  carried on the device  48 , and a coil  58  carried on the housing  36 . 
   Of course, these positions of the magnets  56  and coil  58  could be reversed, and other types of generating devices may be used in keeping with the principles of the invention. For example, any of the generating devices described in U.S. Pat. No. 6,504,258, in U.S. published application no. 2002/0096887, or in U.S. application Ser. Nos. 10/826,952 10/825,350 and 10/658,899 could be used in place of the generating device  54 . The entire disclosures of the above-mentioned patent and pending applications are incorporated herein by this reference. 
   It will be readily appreciated by those skilled in the art that as the magnets  56  displace relative to the coil  58  electrical power is generated in the coil. Since the device  48  displaces alternately upward and downward relative to the housing  36 , alternating polarities of electrical power are generated in the coil  58  and, thus, the generating device  54  produces alternating current. This alternating current may be converted to direct current, if desired, using techniques well known to those skilled in the art. 
   Note that the generator  16  could be used to produce electrical power even if the fluid  18  were to flow downwardly through the passage  20 , for example, by inverting the generator in the tubular string  12 . Thus, the invention is not limited to the specific configuration of the generator  16  described above. 
   It may be desirable to be able to regulate the vibration of the device  48 , or to stop displacement of the device altogether. For example, damage to the generating device  54  might be prevented, or its longevity may be improved, by limiting the amplitude and/or frequency of the vibratory displacement of the device  48 . For this purpose, the generating device  54  may include one or more additional coils or dampening devices  60 ,  62  which may be energized with electrical power to vary the amplitude and/or frequency of displacement of the device  48 . 
   The electrical power to energize the dampening devices  60 ,  62  may have been previously produced by the generating device  54  and stored in batteries or another storage device (not shown in  FIG. 2 ). When energized, magnetic fields produced by the dampening devices  60 ,  62  can dampen the vibratory displacement of the device  48  and, if strong enough, even prevent such displacement. 
   Note that, instead of the annulus  44  being formed between the housing  36  and outer housing  46 , the annulus  44  could be the annulus  22 , in which case the outer housing  46  may not be used at all. Thus, the portion of the fluid  18  could be diverted from the passage  20  to the annulus  22  via the openings  42 , and then return to the passage via the openings  40 . As another alternative, the fluid  18  could flow from the annulus  22  into the passage  20  via the openings  40 , without first being diverted from the passage to the annulus via the openings  42 . In this alternative, the diverter  38 , openings  42  and outer housing  46  would not be used, and the device  48  would create a pressure differential in the annulus  22  due to the fluid  18  flowing past the projection  50  in the annulus. 
   Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents.