Abstract:
A system that is usable with a subterranean well includes a winding, a member and a circuit. The winding is located downhole in the well, and the member moves relative to the winding in response to vibration occurring in the well to cause a signal to be generated on the winding. The circuit is coupled to the winding to respond to the signal to provide power to operate a component located downhole in the well.

Description:
BACKGROUND  
       [0001]     The invention generally relates to harvesting vibration for downhole power generation.  
         [0002]     A typical subterranean well includes various devices that are operated by mechanical motion, hydraulic power or electrical power. For devices that are operated by electrical or hydraulic power, control lines and/or electrical cables typically extend downhole for purposes of communicating power to these tools from a power source that is located at the surface. A potential challenge with this arrangement is that the space (inside the wellbore) that is available for routing various downhole cables and hydraulic control lines may be limited. Furthermore, the more hydraulic control lines and electrical cables that are routed downhole, the higher probability that some part of the power delivery infrastructure may fail. Other risks are inherent in maintaining the reliability of any line or cable within the well&#39;s hostile chemical, mechanical or thermal environment and over the long length that may be required between the surface power source and the downhole power operated device.  
         [0003]     Thus, some subterranean wells have tools that are powered by downhole power sources. For example, a fuel cell is one such downhole power source that may be used to generate electricity downhole. The subterranean well may include other types of downhole power sources, such as batteries, for example.  
         [0004]     A typical subterranean well undergoes a significant amount of vibration (vibration on the order of Gs, for example) during the production of well fluid. In the past, the energy produced by this vibration has not been captured. However, an emerging trend in subterranean wells is the inclusion of devices to capture this vibrational energy for purposes of converting the energy into a suitable form for downhole power.  
         [0005]     Thus, there is a continuing need for better ways to generate power downhole in a subterranean well.  
       SUMMARY  
       [0006]     In an embodiment of the invention, a system that is usable with a subterranean well includes a winding, a member and a circuit. The winding is located downhole in the well, and the member moves relative to the winding in response to vibration occurring in the well to cause a signal to be generated on the winding. The circuit is coupled to the winding to respond to the signal to provide power to operate a component located downhole in the well.  
         [0007]     Advantages and other features of the invention will become apparent from the following description, drawing and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic diagram of a well according to an embodiment of the invention.  
         [0009]      FIG. 2  is a flow diagram depicting a technique to generate downhole power according to an embodiment of the invention.  
         [0010]      FIGS. 3, 4 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11 ,  12 ,  13  and  14  depict mechanisms to enhance the generation of downhole vibrational energy according to an embodiment of the invention.  
         [0011]      FIG. 15  depicts a system located on a sandscreen to aid in the generation of downhole power according to an embodiment of the invention.  
         [0012]      FIG. 16A  is a flow diagram depicting a technique to power wireless tags according to an embodiment of the invention.  
         [0013]      FIG. 16B  depicts a system to deploy wireless tags according to an embodiment of the invention.  
         [0014]      FIG. 17  is a schematic diagram of a wireless tag according to an embodiment of the invention.  
         [0015]      FIG. 18A  is a block diagram of a system to harness and store vibrational energy downhole according to an embodiment of the invention.  
         [0016]      FIG. 18B  depicts a piezoelectric material based vibration energy converter.  
         [0017]      FIG. 19A  is a block diagram of an electromagnetic based system to harness and store vibrational energy downhole according to an embodiment of the invention.  
         [0018]      FIG. 19B  depicts an electromagnetic based vibration energy converter.  
         [0019]      FIGS. 20A, 20B  and  20 C are schematic diagrams of vibrational energy harvesting mechanisms according to an embodiment of the invention.  
         [0020]      FIG. 21  is a schematic diagram of a portion of a drilling string according to an embodiment of the invention.  
         [0021]      FIG. 22  is a schematic diagram of a subsea well according to an embodiment of the invention.  
         [0022]      FIG. 23  is a flow diagram depicting a technique to power a downhole tool according to an embodiment of the invention.  
         [0023]      FIG. 24  is a flow diagram depicting a technique to use vibration in a cementing operation according to an embodiment of the invention.  
         [0024]      FIG. 25  is a flow diagram depicting a technique to evaluate potential blockage of a downhole pipe according to an embodiment of the invention.  
         [0025]      FIG. 26  is a flow diagram depicting a technique to communicate with a downhole tool according to an embodiment of the invention.  
         [0026]      FIG. 27  is a schematic diagram depicting a system in which vibrational energy is used to communicate with downhole tools according to an embodiment of the invention.  
         [0027]      FIGS. 28, 29  and  30  are schematic diagrams of mechanisms to harness vibrational energy to generate electrical power according to embodiments of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0028]     Referring to  FIG. 1 , an embodiment  10  of a well in accordance with the invention includes a tubular string  14  (a production string, for example) that extends into a wellbore of the well  10 . The tubular string  14  may include a central passageway  29  that communicates a flow  27  from a subterranean formation zone  32  (or to a formation zone in the case of an injection well). The zone  32  represents one out of many possible zones of the well  10 . The zone  32  may be defined (i.e., isolated from other zones) by one or more packers  30  (one being depicted in  FIG. 1 ).  
         [0029]     The flow  27  is a primary source of vibrational energy downhole, and this vibrational energy is captured by a vibrational energy harvesting mechanism  20  (of a power generation tool  18 ) for purposes of converting the vibrational energy into downhole electrical power. This electrical power, in turn, may be used to power one or more downhole power-consuming components, such as sleeve valves, ball valves, motors, actuators, sensors, sound sources, electromagnetic signaling sources, or equipment to fire “smart bullets” into a well casing, perforating gun firing heads, controllers, microprocessors, Micro Electrical Mechanical Sensors (MEMS), telemetry systems (transmitters or receivers), etc., depending on the particular embodiment of the invention.  
         [0030]     In some embodiments of the invention, the string  14  includes one or more features to enhance the generation of vibrational energy, referred to generally herein as a “vibration enhancement mechanism  16 .” More specifically, the flow  27  enters the mechanism  16  that, in some embodiments of the invention, produces a locally more turbulent flow  31  that flows uphole. The creation of this more turbulent flow, in turn, amplifies the vibrational energy, thereby leading to the increased production of downhole power. The vibrational harvesting mechanism  20  may be located in proximity to (within ten feet, for example) to the vibration enhancing mechanism  16 , in some embodiments of the invention. Various embodiments of the vibration enhancing mechanism are described below.  
         [0031]     Thus, referring to  FIG. 2 , in some embodiments of the invention, a technique  40  may be used to harvest vibrational energy downhole. More specifically, in accordance with the technique  40 , the downhole vibration is enhanced (block  42 ) such as by the vibration enhancement mechanism  16 , as further described below. Next, pursuant to the technique  40 , the downhole vibration is converted (block  44 ) into downhole power to power one or more downhole power-consuming devices.  
         [0032]     As a more specific example,  FIG. 3  depicts a cross-section of a vibration enhancing mechanism  50  in accordance with an embodiment of the invention. The device  50  may be formed from a section of the string  14  having an interior wall  15  that constricts the central passageway  29  of the string  14 . More specifically, in some embodiments of the invention, the section has a circular cross-section of varying diameter; and in some embodiments of the invention, the section forms a Venturi-type flow path. This flow path, in turn, converts the entering flow  27  into a more turbulent flow  31  for purposes of creating more vibration. The flow path of the device  50  thus creates vibrational energy that is harvested by the power generator tool  18 .  
         [0033]     Other types of vibration enhancing mechanisms may be used in other embodiments of the invention. For example, referring to a cross-section depicted in  FIG. 4 , in some embodiments of the invention, a cantilevered member  56  may extend from the interior wall  15  of the string  14  into the central passageway  29 . The member  56  introduces an obstruction in the flow path  27  to create the more turbulent flow  31 .  
         [0034]     As another example,  FIG. 5  depicts a cross-sectional view of a vibration-enhancing mechanism  60  that contains a flexible member  62  that has one end that is attached to the interior wall  15  of the tubular string  14  and another free end that extends into the central passageway  29 . Due to this arrangement, the flexible member  62  moves in response to the flow  27  to create the more turbulent flow  31  and thus, enhance the generation of vibrational energy.  
         [0035]     As another example,  FIG. 6  depicts a cross-sectional view of a vibration-enhancing mechanism  66  that, similar to the Venturi-type flowpath of the mechanism  50  ( FIG. 3 ), includes a restricted flow path  68  for purposes of increasing vibration downhole. In some embodiments of the invention, the flow path  68  has a circular cross-section section that varies in diameter.  
         [0036]     It has been discovered that a production string (a possible embodiment of the tubing string  14  ( FIG. 1 )) has a fundamental vibration mode in which the cross-section of the production string expands and contracts in two orthogonal cross-sectional directions. For example, as depicted in a cross-section of a production tubing section in  FIG. 7 , during the flow of fluid through a production tubing string, the string may include a cross-section that expands in the positive and negative Y directions while the cross-section of the production tubing contracts in the positive and negative X directions. Next, pursuant to the fundamental vibration mode, the cross-section of the production tubing expands in the positive and negative X directions and contracts in the positive and negative Y directions. This process repeats to establish the fundamental vibration mode.  
         [0037]     As depicted in  FIG. 7 , in some embodiments of the invention, the thickness of the wall of the production string  70  may be radially varied to select the axis and otherwise enhance the fundamental vibration mode. More specifically, the cross-section of the string may include thinner portions  72  that extend along the X-axis and thinner portions  74  that extend along the Y-axis. The remaining portions  76  of the cross-section are thicker. Thus, due to this arrangement, the flexing of the production string  70  in the above-described cross-sectional directions is enhanced due to the thinning of the production tubing string cross-section in orthogonal directions. Increasing the flexing of the production tubing string, in turn, enhances the vibrational energy that is generated by the flow of fluids through the production tubing string. Thus, the arrangement that is depicted in  FIG. 7  enhances the vibrational energy that is converted into electrical energy downhole.  
         [0038]     As another example of a mechanism to enhance vibrational energy downhole,  FIG. 8  depicts a mechanism  80  that includes a spring  81  that may be attached to, for example, the interior wall  15  of the string  14  and extend into the central passageway  29 . In yet another embodiment of the invention, a vibration enhancing mechanism  84  (a cross-section of which is depicted in  FIG. 9 ) includes a wedge-shaped flow diverter  86  that is inserted into the flow path  27  for purposes of creating a more turbulent flow. As depicted in  FIG. 9 , regions  88  exist between the diverter  86  and the wall of the string  14  for purposes of allowing fluid to pass therethrough. However, the flow diverter  86  introduces additional turbulence into the flow  27 , thereby creating additional vibration downhole.  
         [0039]     In some embodiments of the invention, a piece of downhole equipment that may already be located downhole may be strategically placed near the power generation tool  20  ( FIG. 1 ) for purposes of enhancing vibration near the tool  20 . For example, referring to  FIG. 10 , a multiphase mixer  86  may be placed in close proximity (within ten feet for example) to the power generation tool  20 . The multiphase mixer  86 , as its name implies, typically is used in production to blend various phases of well fluid together. The mixer  86  may include, for example, an opening  102  that receives the flow  27 . The mixer  86  may also include an internal chamber  99  that includes various orifices  100  through which the flow may proceed to flow upstream and produce the flow  31  through the central passageway  29 .  
         [0040]     In other embodiments of the invention, a vibrational energy-enhancing mechanism  108  (a cross-section of which is depicted in  FIG. 11 ) may be used. The mechanism  108  includes a blind T  112  that is inserted into the flow path  27 . The blind T  112  is surrounded by openings  110  that permit the flow of the fluid around the blind T  112 . However, the inclusion of the blind T  112  in the flow path  27  creates turbulence that, in turn, enhances the vibrational energy downhole.  
         [0041]     Referring to  FIG. 12 , in some embodiments of the invention, a vibration-enhancing section  120  of the string  15  may include a spiral or helical groove  124  that extends along the inner surface of the wall  15  of the string  14 . As depicted in  FIG. 12 , the longitudinal axis of the groove  124  is concentric with the longitudinal axis of the string  14 .  
         [0042]     In some embodiments of the invention, a free flowing part may be used to enhance the generation of vibrational energy downhole. For example, a vibration enhancing mechanism  130  (a cross-section of which is depicted in  FIG. 13 ) may include a chamber  132  (in the flow path  27 ) that contains a ball  140 . Analogous to a policeman&#39;s or an umpire&#39;s whistle, the ball  140  is trapped inside the chamber  132 , in that lower  139  and upper  135  openings in the chamber  132  are sized to permit fluid (but not the ball  140 ) to pass into and out of the chamber  132  and contact the ball  140 . The interaction of the fluid with the ball  140  creates vibrational energy that may be harvested for electrical power.  
         [0043]     In some embodiments of the invention, an electrical device that consumes harvested power downhole may also be used to generate vibrational energy used for purposes of power generation. For example, as depicted in  FIG. 14 , in some embodiments of the invention, a vibration-enhanced mechanism  150  may include an electrical pump  152  (a beam-type pump, a rod-type pump or an electrical submersible pump (ESP)), as just a few examples. The electrical pump  152  receives the flow  27  to produce the output flow  31 . The operation of and fluid flow through the pump  152  enhances the vibrational energy.  
         [0044]     Although the vibration-enhancing mechanisms and power generating mechanisms (such as the power generator tool  18 ) that are described above are generally located in the central passageway of the string  14 , it is noted that in other embodiments of the invention, these mechanisms may be located in other regions of the well. For example, in some embodiments of the invention, these mechanisms may be located on the outside of the string  14  or located in a side packet mandrel, as further described below in connection with  FIG. 22 .  
         [0045]     As a more specific example, referring to  FIG. 15 , in some embodiments of the invention, a vibration-enhancing mechanism  160  may be located on the outside of a sandscreen  158 . Thus, the mechanism  160 , which may be any of the above-described mechanisms, may be located in a flow path located between the exterior and the interior of the sandscreen  158 . In some embodiments of the invention, the mechanism  160  may be located inside the sandscreen  158 . Furthermore, in some embodiments of the invention, a power generator (not shown) to generate electrical power from vibrational energy may be mounted to the sandscreen  158  and may be located either on the outside or inside of the sandscreen  158 .  
         [0046]     Although in the embodiments described above, the power generation mechanism  20  is depicted ( FIG. 1 ) as being attached to the string  14 , in other embodiments of the invention, the power generation mechanism  20  may not be fixed in position relative to the string  14 . For example, in some embodiments of the invention, a wireless (a radio frequency (RF), for example) tag may be used to measure various properties in a subterranean well. These properties may include, for example, detection of water or chemical constituents, such as hazardous H2S, or measurement of pressure and temperatures at various positions in the well. The tag may be free-flowing, in that the tag may be released into the well and take a measurement at a particular depth in the well. Many variations are possible. For example, the tag may be activated at a particular depth, a particular temperature, a particular pressure, etc.  
         [0047]     For purposes of supplying power to the tag, the tag may derive its power from the vibrational forces that are experienced by the tag itself. Thus, instead of being attached to a static structure, such as the string  14 , for example, the tag is free-flowing and is imparted with vibrational energy as the tag flows in the well. This vibrational energy, is converted by a vibrational energy transformer of the tag into electrical power for the tag.  
         [0048]     Thus, referring to  FIG. 16A , in some embodiments of the invention, a technique  180  includes deploying (block  182 ) wireless tags in a subterranean well. Vibrational energy is used (block  184 ) to activate (i.e., power up and continue providing power to) the tags. Once activated, measurements are then performed (block  186 ) with the tags.  
         [0049]      FIG. 16B  depicts a subterranean well  200  in accordance with the technique  180 . As shown in  FIG. 16B , the well  200  may include a tubular string  204  (a production tubing, for example) into which several tags  220  have been placed into the central passageway of the well  200 . As an example, the well  200  may include a surface pump  206  that may control the flow of fluid through the well  200 . For example, the pump  206  may halt fluid flow through the string  204  to allow the tags  220  to descend into the well  200 . When the tags have collected the data, the pump  206  may then be re-activated to cause fluid to flow uphole and thus return the tags  220  toward the surface.  
         [0050]     In some embodiments of the invention, the well  200  may include a tag reader  230  to extract information from the tags  220  as the tags  220  return from downhole. As the tags  220  descend downhole, vibrational energy imparted on the tags  220  generate power on the tag  220  to activate the tag  220  so that the tag  220  may then take the appropriate measurement downhole.  
         [0051]     Referring to  FIG. 17 , in some embodiments of the invention, the tag  220  may have an architecture that is generally depicted in  FIG. 17 . This architecture may include, for example, a processor  248  that is coupled to a sensor  250  (a pressure or temperature sensor, for example) through a bus  248 . The processor  248  may execute instructions that are stored in a memory  244  (also coupled to the bus  249 ) as well as store data from the sensor  250  in the memory  246 . The architecture may include various other features, such as a transmitter to transmit to the reader  230  ( FIG. 16B ), depending on the particular embodiment of the invention.  
         [0052]     As depicted in  FIG. 17 , the tag  220  includes power generation circuitry that includes, for example, a vibrational energy converter  240 . As its name implies, the converter  240  produces a voltage (for example) in response to vibrational energy that occurs to the tag  220 . A DC-to-DC converter  242  converts this voltage into a regulated voltage that appears on voltage supply lines  246 . The voltage supply lines  246 , in turn, furnish power to the various components of the tag  220 , such as the sensor  250 , processor  248  and memory  246 , as just a few examples.  
         [0053]     In some embodiments of the invention, the tag  220  may include a reserve energy source, such as a battery  244 , that is coupled to the output terminals of the DC-to-DC converter  242 . The battery  244  serves as an energy buffer to store excess energy that is provided by the converter  240  so that this energy may be used to regulate the power that is provided to the power-consuming components of the tag  220 .  
         [0054]     In some embodiments of the invention, the power harvesting circuitry (whether on a wireless tag or affixed to the string  14 ) may have an architecture  260  that is generally depicted in  FIG. 18A . This architecture  260  includes a vibration responsive strain inducer  264 . As examples, the vibration responsive strain inducer  264  produces a mechanical force that, as its name implies, imparts a physical strain on a piezoelectric material  262 . A piezoelectric material, by its very nature, produces a terminal voltage responsive to the strain that is induced on the material. Therefore, in response to the strain produced by the inducer  264 , the piezoelectric material  262  produces a voltage that appears on a signal line  266 . This voltage, in turn, is regulated to a specific DC level by a DC-to-DC converter  268  to produce a regulated voltage that appears on a power supply  270 .  
         [0055]     Thus, the inducer  264 , piezoelectric material  262  and converter  268  form a basic power-harvesting generator  273  in accordance with an embodiment of the invention.  
         [0056]     Although depicted in  FIG. 18A  as producing DC power, it is noted that in other embodiments of the invention, the generator  273  may include an inverter for purposes of generating an AC voltage. Thus, other embodiments are within the scope of the following claims.  
         [0057]     Additionally, in some embodiments of the invention, a particular well may include several generators  273  that are connected in parallel to the voltage supply  270 . Furthermore, in some embodiments of the invention, a battery  272  may be coupled to the voltage supply line  272  for purposes of serving as an energy buffer to absorb and supply power, depending on the particular vibrational energy being experienced at the time.  
         [0058]     In accordance with an embodiment of the invention, the vibration responsive strain inducer  264  and piezoelectric material  262  may, in some embodiments of the invention, have a form  280  that is depicted in  FIG. 18B . More specifically, the arrangement  280  may include a piezoelectric material  282  that is located between fairly rigid members  286  and  284 . These members may be formed from, as examples, part of housing of the string  14  as well as explicit plates. A cantilevered mass  290  is connected to the plates  284  and  286  to exert a strain force on the piezoelectric material  282  in response to the vibrational energy sensed by the mass  290 . Thus, vibrational energy causes movement of the mass  290 , and this movement, in turn, induces stress to cause the piezoelectric material to generate a corresponding voltage.  
         [0059]     Referring both to  FIGS. 19A and 19B , in some embodiments of the invention, the power harvesting circuitry (whether on a wireless tag or affixed to the string  14 ) may have an architecture  260  that is generally depicted in  FIG. 19A . This architecture  260  includes a vibration responsive strain inducer  264 . As examples, the vibration responsive strain inducer  264  produces a mechanical force that, as its name implies, imparts a physical strain on an electromechanical energy conversion, or generator, that is depicted, as an example, in  FIG. 19B . An electromagnetic energy converter, by its very nature, produces a terminal voltage induced by an electrical conductor, or coil, moving in a magnetic field that is maintained by a suitable ferro-magnetic material, permanent magnet. Therefore, in response to the strain or motion produced by the inducer  264 , the electromagnetic converter produces a voltage that appears on a signal line  266 . This voltage, in turn, is regulated to a specific DC level by a DC-to-DC converter  268  to produce a regulated voltage that appears on a power supply  270 .  
         [0060]     In the various embodiments of the invention, the mass that induces the strain on the piezoelectric material may not be a cantilevered mass but alternatively, may be another type of strain inducer that generates a strain on the piezoelectric material in response to vibrational energy. For example, in some embodiments of the invention, the wall of the tubular string  14  (see  FIG. 1 ) may be lined with a piezoelectric coating  304 , as depicted in  FIG. 20A . More specifically, the piezoelectric material lining  304  may completely or partially coat the interior wall of the tubular string  14 , according to the particular embodiment of the invention. Due to the above-described fundamental mode of vibration of the tubular string  14 , this vibration induces a strain on the piezoelectric material coating  304  to generate a corresponding voltage across the material  304 .  
         [0061]     Although not depicted in  FIG. 20A , in some embodiments of the invention, a thin insulation layer may be interposed between the lining  304  and the interior surface of the tubing string wall for purposes of isolating the terminal voltage appearing on the coating  304  from the tubing string  14 .  
         [0062]     As another example of a strain-inducing mechanism in accordance with the invention,  FIG. 20B  depicts a mechanism  304  that includes a flexible flow member  62  (see  FIG. 5 ) that has a piezoelectric electric coating  308  lining the flexible member  62 . Thus, the motion of the flexible member  62  induces a strain on the material  308  to generate a voltage on the material  308 .  
         [0063]     Thus, as can be seen, the piezoelectric coating may be applied to various downhole components that are subject to vibration, in that the vibration induces a strain on the piezoelectric coating, and this strain induces a voltage that may be converted into downhole power. As yet another example,  FIG. 20C  depicts the blind T  112  (see  FIG. 11 ) that is at least partially covered by a piezoelectric coating  311 . Thus, other variations are possible and are within the scope of the appended claims.  
         [0064]     Due to the generation of electrical power downhole, various control lines and electrical cables do not need to be extended from the surface of the well. Furthermore, generating electrical power downhole may be advantageous for purposes of reducing cabling between downhole components. For example,  FIG. 21  depicts a drill string  320  that includes a mud motor  324  and a drill bit  328 . The drill string  320  may include sensors  326  that are used for purposes of monitoring operation of the drill string  320  and monitoring general operation of the drilling. The sensors  326  typically are located close to the drill bit  328 . A particular challenge with this arrangement is that the sensors  326  may be located away from a power source and thus, electrical cables may have to span across the mud motor  324  for purposes of delivering power to the sensors  326 . However, in accordance with embodiments of the invention, the sensors  326  may be in close proximity to power generation circuitry  324  that generates electrical power from the vibration of the drill string  320 , such as the vibration that occurs during operation of the mud motor  324 . Due to this arrangement, cabling does not have to be extended across the mud motor  324  for purposes of delivering power to the sensors  326 .  
         [0065]     Referring back to  FIG. 1 , as another example of the reduction of cabling due to the generation of power downhole, the well  10  may include an intelligent completion, a completion that contains circuitry that automatically controls downhole equipment independently from any commands that are communicated from the surface of the well. For example, the string  14  may be a production string and include a valve  21  (a sleeve valve or ball valve, as examples) that is electrically operated by power that is produced by the power generator tool  18 . An intelligent controller  23  of the string  14  may, for example, use a sensor  111  (also of the string  14 ) to detect one or more characteristic(s) of the flow  27 . The sensor  111  may include one or more of a pressure sensor, a temperature sensor, a fluid composition sensor and a Micro Electrical Mechanical Sensor (MEMS), depending on the particular embodiment of the invention.  
         [0066]     Based on the detected characteristic(s), the controller  23  operates a valve  21  (a sleeve valve or ball valve, as examples) to control the flow  27 . For example, the controller  23  may determine the flow  27  has a high water content level and close the valve  21  to shut off flow from the zone  32 . As another example, the controller  23  may also control the valve  21  to regulate a pressure in the well. The controller  23 , sensor  11  and valve  21 , in some embodiments of the invention, receive power from the power generator tool  18 . In some embodiment of the invention, the controller  23 , sensor  111  and valve  21  receive all of their operating power from the power generating tool  18 .  
         [0067]     As another example of a power consuming device that may rely on energy derived from vibrational energy downhole,  FIG. 22  depicts a subsea well  400  that extends beneath a sea floor  402 . The subsea well  400  includes a subsea well tree and wellhead  404 ; and a tubular string  406  that extends into a wellbore of the well. A robot  414  may be located inside the tubular string  406 . The robot  414  may generally be autonomous in that the robot  414  does not rely on a tethered connection for purposes of operating in the subsea well to perform an intervention, for example. Thus, for purposes of generating power, robot  414  may dock to power connectors that are electrically coupled to a power generation mechanism  410  that generates downhole electrical power from vibrational energy.  
         [0068]     As an example, the power generation mechanism  410  may be located in a side pocket mandrel  412  that is formed in the tubing  406 . As shown in  FIG. 2 , due to the inclusion of the power generating mechanism  410  and the side pocket mandrel  412 , the central passageway of the tubing string  406  is unobstructed for purposes of operating the robot  410 , performing an intervention with other tools, producing well fluid, etc.  
         [0069]     The subsea well  400  may include other components that are powered by the power generating mechanism  410 , such as, for example, telemetry circuitry  420  that is located on the sea floor  402  and is used to communicate (via acoustic, optical or electromagnetic communication, as examples) with a surface platform (not shown in  FIG. 22 ). The power generating mechanism  410  may also deliver power (via communication lines  425 ) to electrical storage  424  (a battery, for example) that is located on the sea floor  402 .  
         [0070]     The above-described arrangements rely on the vibrational forces that are produced either by downhole equipment or by the flow of well fluid in contact with a particular vibration-enhancing mechanism. However, in some embodiments of the invention, vibrations may be intentionally introduced into a fluid or slurry that is introduced downhole from the surface.  
         [0071]     For example,  FIG. 23  depicts an embodiment of a technique  430  in accordance with the invention, which uses vibrations in a gravel pack flow for purposes of communicating vibrational energy downhole that may be used to produce downhole power. More specifically, in accordance with the technique  430 , vibrations are induced in a gravel packed flow, as depicted in block  432 . For example, these vibrations may be induced by pressure pulses that are applied to a slurry flow as well as less regulated vibrational energy that is applied to the flow. Regardless of the specific form of the vibrational energy, the vibrational energy is applied at the surface of the well and is communicated downhole via the flow. Pursuant to the technique  430 , this vibrational energy is used (block  434 ) to generate downhole power, such as for a downhole tool to be used during or after the completion of gravel packing (for example).  
         [0072]     Referring to  FIG. 24 , other types of downhole flows may be used for purposes of communicating vibrational energy downhole. For example,  FIG. 24  depicts a technique  444  for purposes of communicating vibrational energy via a cement flow. Pursuant to the technique  444 , a vibration is introduced in the cement flow, as depicted in block  446 . Similar to the gravel packed flow discussed in connection with  FIG. 23 , vibrational energy may be imparted to the cement flow by, for example, pulses or other types of vibrational energy. This vibrational energy is then used to generate power downhole (as depicted in block  450 ) for one or more downhole tools.  
         [0073]     Not only may the vibrational energy be used to produce downhole power, other uses of the vibrational energy may be used, in accordance with particular embodiments of the invention. For example,  FIG. 25  depicts a technique  470  for purposes of using vibrational energy to detect problems with tubular passageways (production tubing passageways, gravel packing shunt tubes, etc.) downhole. In this manner, pursuant to the technique  470 , vibrational energy is detected (block  472 ) downhole and then used to evaluate (block  474 ) possible blockage in response to the detected energy. The vibrational energy may be generated downhole (in response to a fluid flow, for example) and/or may be communicated downhole by a flow (a cement or gravel packing flow, as examples) from the surface of the well. As a more specific example, in some embodiments of the invention, a circuit may analyze the spectral components of the produced vibrational energy and based on comparing the computed spectral energy to reference patterns, may determine whether or not a blockage exists in a particular downhole member.  
         [0074]     As yet another example of the use of vibrational energy to perform a function other than solely being converted into downhole power, a technique  481 , depicted in  FIG. 26 , uses vibrational energy for purposes of communicating with the downhole tool. More specifically, pursuant to the technique  481 , vibrational energy is detected (block  482 ) downhole, and this detection is used (block  484 ) to handshake, that is to communicate commands and/or measurements with a specific downhole tool.  
         [0075]     As a more specific example,  FIG. 27  depicts a well  500  in accordance with the invention that includes a tubular string  582  that extends into a wellbore of the well  500 . The string  582  includes gas lift valves  584  that may be used for purposes of injecting gas for purposes of lifting production fluid uphole. A circuit  590  on the surface of the well  500  monitors vibrational energy that is generated by the gas lift valves  584  for purposes of determining when a particular gas lift valve  584  has been activated. In this regard, in some embodiments of the invention, each gas lift valve  584  may be designed to have a unique and identifiable resonant frequency when activated. This vibrational frequency, in turn, is detected by the circuit  590  for purposes of identifying when the gas lift valve  584  has activated.  
         [0076]     Alternatively, in some embodiments of the invention, each gas lift valve  584  may be designed to release tags that contain a unique and identifiable code that can be communicated to a suitable circuit at the surface located as  590  in  FIG. 27 .  
         [0077]     Other embodiments are within the scope of the following claims. For example, many other techniques may be used to generate electric power from vibrational energy downhole. For example, in some embodiments of the invention, a capacitor may be used that has at least one plate that is mounted to a spring. A voltage may be stored on the capacitor so that by variation of the distance between the plates of the capacitor, a varying voltage is produced. This varying voltage, in turn, may be converted into power for a particular downhole tool.  
         [0078]     As another example of a mechanism to generate power from downhole vibrational energy,  FIG. 28  depicts, as a variation on the electromagnetic energy converter depicted in  FIG. 19B  a mechanism  600  that includes a coil  602  that generally circumscribes a magnetically-charged ferrous material  610 . The material  610 , in turn, may be mounted on springs  606  to move longitudinally along the axis of the coil  602 , as depicted in  FIG. 28 . This movement of the material  610 , in turn, produces a voltage on the coil  602  and this voltage may be converted into downhole power. In some embodiments of the invention, the coil  602  may be embedded in a mandrel  604  that generally circumscribes the ferrous material  610 .  
         [0079]     In another variation,  FIG. 29  depicts a power generation mechanism  620  in which the mandrel  604  (that contains the coil  602 ) moves instead of the ferrous material  610 . More specifically, the ferrous material  610  may be relatively stationary; and the mandrel  604  is mounted on springs  624 . Thus, vibration causes movement of the mandrel  604  (and coil  602 ) with respect to the ferrous material  610 . This movement, in turn, induces a voltage on the coil  602 , and this voltage may be used to generate power downhole. It is noted that many other variations are possible in the various embodiments of the invention. For example,  FIG. 30  depicts a mechanism  650  similar to the mechanism  600  except that the ferrous material  610  is mounted via springs  651  so that the ferrous material  610  moves laterally with respect to the coil  602 . This lateral movement, in turn, changes the magnetic permeability of the path inside the coil  602  to change the voltage that appear on the coil&#39;s terminals. As depicted in  FIG. 30 , in some embodiments of the invention, the spring  651  may couple the ferrous material  610  to the inner side-walls of the mandrel  604 .  
         [0080]     Other variations are possible. For example, in other embodiments of the invention, the ferrous material  610  may be distributed on a dynamo that rotates inside the coil  602  to generate voltage on the coil&#39;s terminals. The rotational speed of the dynamo increases with the level of vibration in the well.  
         [0081]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.