Abstract:
A technique facilitates generation of electric power in well environments. The technique involves combining a cooperating stator and rotor assembly to create an electromagnetic generator. The cooperating stator and rotor assembly utilize an electromagnet which works with a generator coil to create electrical power. Use of the electromagnet enables the electromagnetic field created during generation of electrical power to be selectively eliminated. Elimination of the electromagnetic field allows magnetic particles to be freely flushed from the electromagnetic generator.

Description:
BACKGROUND 
       [0001]    The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section. 
         [0002]    A variety of power generators are used in many types of well related applications to generate electric power for use downhole. In some well drilling and/or measurement applications, electricity is generated by power generators which have permanent magnets rotating about stator coils. Because of the permanent magnets, a permanent magnetic field exists in the region of the power generator, and this magnetic field can cause magnetic particle accumulation in an exposed generator design. If sufficient magnetic particles accumulate, components within the power generator are susceptible to damage and ultimate failure. For example, some power generators allow drilling mud to flow between the rotor and stator during the downhole application and this can lead to magnetic particle build up in areas susceptible to damage within the power generator. 
       SUMMARY 
       [0003]    In general, embodiments of the present disclosure comprise a system and methodology for generating electric power in well environments. The system and methodology employ a cooperating stator and rotor assembly to create an electromagnetic generator that may be positioned in a well environment. The cooperating stator and rotor assembly utilize an exposed electromagnet that works with a generator coil to create electrical power. Use of the electromagnet enables the electromagnetic field created during the generation of electrical power to be selectively eliminated. Elimination of the electromagnetic field allows magnetic particles to be freely flushed from the electromagnetic power generator. 
         [0004]    Other or alternative features will become apparent from the following description, from the drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Certain embodiments of the disclosure will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying drawings illustrate only the various implementations described herein and are not meant to limit the scope of various technologies described herein. The drawings are as follows: 
           [0006]      FIG. 1  is a schematic view of one example of a well system having an electromagnetic power generator, according to an embodiment of the present disclosure; 
           [0007]      FIG. 2  is a schematic illustration of one example of the electromagnetic power generator illustrated in  FIG. 1 , according to an embodiment of the present disclosure; and 
           [0008]      FIG. 3  is an enlarged section of the electromagnetic power generator illustrated in  FIG. 2 , according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    In the following description, numerous details are set forth to provide an understanding of various embodiments of the present disclosure. However, it will be understood by those of ordinary skill in the art that the embodiments of the present disclosure may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. In the specification and appended claims: the terms “connect”, “connection”, “connected”, “in connection with”, “connecting”, “couple”, “coupled”, “coupled with”, and “coupling” are used to mean “in direct connection with” or “in connection with via another element”; and the term “set” is used to mean “one element” or “more than one element”. As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and downwardly”, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the present disclosure. 
         [0010]    Embodiments of the present disclosure generally relate to a system and methodology for generating power in desired environments, such as downhole well environments. In one embodiment, an electromagnetic power generator is deployed downhole in a flow of fluid routed through a tubular housing in a wellbore. The flow of fluid can be used to power the rotation of a rotor assembly of the power generator so as to provide electrical power for downhole components. The power generator is designed with one or more electromagnets that reduce or negate the need for permanent magnets that would otherwise be used for enabling generation of electrical power. 
         [0011]    According to one example, the power generator is designed as an exposed fluid bearing style turbine generator in which the magnetic field acting in the turbine generator may be selectively turned on and off. As described in greater detail below, use of electromagnets enables control over the magnetic field by selectively controlling power to the electromagnets. Control over the magnetic field is helpful in enhancing the operation and longevity of the power generator. For example, when the magnetic field is turned off, magnetic particles may be flushed from the system, e.g. flushed from the gap between a stator and rotor assembly of the electromagnetic power generator. Additionally, use of electromagnets also enables easier regulation of electric power at lower current and voltage. 
         [0012]    The power generator is useful in numerous types of well applications. In a completion system, for example, the power generator may be used to extract hydraulic power from a flowing fluid and to convert that hydraulic power to usable electric power. By avoiding the use of permanent magnets, the power generator becomes much more amenable to long-term use in this type of relatively harsh environment. Selective elimination of the magnetic field acting in the power generator allows magnetic particles to be flushed from the power generator to avoid jamming rotational components due to particle buildup. Removal of magnetic particles also limits magnetic field degradation that would otherwise occur due to particle accumulation. Accordingly, many types of failure modes can be better controlled or eliminated which renders the power generator useful in permanent completion systems and in a variety of other well systems utilized downhole for substantial periods of time. 
         [0013]    Referring generally to  FIG. 1 , one example of a well system  20  is illustrated as deployed in a wellbore  22  that extends generally from a surface location  24 . In many applications, wellbore  22  extends downwardly from a wellhead  26  or other surface structure. In the example illustrated, well equipment  28 , e.g. a completion system, is deployed downhole as part of a well string  30 . The well string  30  may be formed as a tubing string or other suitable string designed for a given a well operation. Regardless, a power generator  32  is employed as part of or in cooperation with the well equipment  28  to provide electrical power to specific components  34  of well equipment  28 . 
         [0014]    In some applications, well equipment  28  may be part of a drill string in which one of the components  34  is a drill assembly  36  used to drill wellbore  22 . During the drilling operation, a flow of drilling mud is moved past drill assembly  36 , and this flow of drilling mud is used to hydraulically power generator  32  to enable production of electric power for one or more of the components  34 . It should be noted, however, that a variety of fluid flows may be used to provide hydraulic power to generator  32  in many types of well operations. For example, flows of production fluid, injection fluid, and other types of applicable fluid flows may be used to facilitate creation of electric power with power generator  32 . 
         [0015]    Referring generally to  FIG. 2 , an example of power generator  32  is illustrated. In this example, power generator  32  is a turbine type power generator deployed in a tubular structure  38 , such as a tubing used in well string  30 . A flow of fluid, as represented by arrow  40 , moves within tubular structure  38  and past power generator  32  to impart hydraulic power to the generator  32   
         [0016]    In the embodiment illustrated, power generator  32  comprises a rotor assembly  42  that moves relative to a stator  44  along a film of fluid between the two components, e.g. rotates about stator  44 . By way of example, stator  44  may be stationary and formed with a stationary core  46  about which rotor assembly  42  is rotatably guided via a bearing assembly  48 . The rotary assembly  42  may also rotate around the stator  44  via a hydrodynamic fluid film without any guidance from a bearing assembly. In this embodiment, rotor assembly  42  comprises impeller members  50 , e.g. blades, which extend generally radially outward from a base structure  52  of rotor assembly  42  toward the surrounding tubular structure  38 . As the flow of fluid  40  moves past impeller members  50 , the energy of the flowing fluid impacting on impeller members  50  causes the rotor assembly  42  to rotate about stator  44 . A nose cone  54  may be mounted at the upstream end of stator  44  and rotor assembly  42  to direct the flowing fluid  40  past impeller members  50 . This generator would also work with an upstream stator assembly to shape the flow before spinning the rotor. 
         [0017]    Referring again to  FIG. 2 , rotor assembly  42  comprises one or more electromagnets  56  that may be positioned along a radially inward surface of base structure  52 . As illustrated, the electromagnet  56  is formed from a conductive coil  58  that creates the desired magnetic field upon receipt of an electric current. The electromagnet  56  cooperates with a power generation coil  60  that forms part of stator  44 . The power generation coil  60  is positioned radially inward of electromagnet  56  across a separation gap  62 , as further illustrated in  FIG. 3 . As the flow of fluid  40  moves past impeller members  50 , rotor assembly  42  is moved relative to stator  44  which, in turn, moves the electromagnet  56  past power generation coil  60 . If current is supplied to coil  58  of electromagnet  56  to create a magnetic field, the relative movement causes power generation coil  60  to output electric power. 
         [0018]    In the illustrative embodiment, separation gap  62  is part of a flow channel  64  through which a portion of flowing fluid  40  is directed, as represented by arrows  66 . Any accumulation of magnetic particles within gap  62  or along other regions of rotor assembly  42  and stator  44  may be cleared by fluid flows  40 ,  66  when the magnetic field created by electromagnet  56  is eliminated or removed. The magnetic field is easily and selectively eliminated simply by cutting the flow of electric current to electromagnet  56  that is otherwise used to create the electromagnetic field necessary for the production of electrical power via generation coil  60 . 
         [0019]    The design of power generator  32  enables use of the power generator in applications that do not require any special seals. Consequently, contaminated fluids are allowed to pass along the power generator and through the gap  62  between rotor assembly  42  and stator  44 . The ability to remove the magnetic field enables flushing of the system, which increases the life of the power generator  32  by eliminating or reducing premature failure and/or degradation of the magnetic fields that would otherwise have occurred due to magnetic particle buildup. 
         [0020]    The specific arrangement of electromagnets and power generation coils can be changed to accommodate specific applications, size envelopes, power requirements, types of fluid flow, and other factors. For example, electromagnet  56  could be placed on a stationary portion while the power generation coil  60  is moved, because it is the relative movement between the two that generates the desired electrical power. Additionally, the electrical power/current supplied to electromagnet  56  to create the magnetic field also may be supplied via a variety of systems and components. 
         [0021]    One example of an excitation system  68  for supplying electric current to excite coil  58  of electromagnet  56  is best illustrated in  FIG. 3 . In this example, excitation system  68  comprises an excitation coil assembly  70  that receives power from a power storage device  72  positioned at a desirable location, e.g. within stationary core  46  of stator  44 . Power storage device  72  may comprise a battery, such as a rechargeable battery, or another suitable power source. In some applications, electric current may be routed downhole to the excitation coil assembly  70 . 
         [0022]    As illustrated, power storage device  72  is electrically coupled with an inner excitation coil  74  of excitation coil assembly  70  via a suitable electric line  76 . Electric current flows from power storage device  72  to inner excitation coil  74  to excite excitation coil assembly  70 , as represented by arrow  78 . In the example illustrated, the inner excitation coil  74  is located in the stationary stator  44  and cooperates with an outer excitation coil  80 . The outer excitation coil  80  is located in rotor assembly  42  at a position radially outward of inner excitation coil  74  across separation gap  62 . 
         [0023]    The primary operation of power generator  32  begins with excitation coil assembly  70  receiving electrical power from power storage device  72 . The excitation coils  74 ,  80  are small so the current and voltage supplied by power storage device  72  is minimal. In operation, the electrical power flows to inner excitation coil  74  via electric line  76  and the electromagnetic field created is received by the rotating outer excitation coil  80  in rotor assembly  42 . The outer excitation coil  80  is directly coupled to a generator coil assembly  82  that comprises outer coil  58  (of electromagnet  56 ) and power generation coil  60 . For example, the outer excitation coil  80  may be electrically coupled with the outer generation coil  58  via a conductive link  84 . 
         [0024]    During rotation of rotor assembly  42  about stationary stator  44 , the flow of electric current from power storage device  72  to inner excitation coil  74  creates the magnetic field that acts on the rotating outer excitation coil  80 . The magnetic field causes outer excitation coil  80  to produce an electric current that flows to outer generation coil  58  via conductive link  84 . The outer generation coil  58  then effectively becomes the electromagnetic  56  that creates the power generating magnetic field. The power generating magnetic field, in turn, acts on power generation coil  60  to create electrical power for powering desired downhole devices. The electric current may be directed to desired downhole devices via one or more suitable electric lines  86  designed to deliver the electric power, as represented by arrow  88 . At least some of the power generated by power generation coil  60  may be directed back to power storage device  72  via electric line  90  to recharge the power storage device. 
         [0025]    In this type of system, the power input by power storage device  72  to excitation coil assembly  70  is amplified because the size of the coils in the generator coil assembly  82  is substantially larger than the coils in the excitation coil assembly  70 . In addition, the excitation coil assembly  70  may function to regulate the magnetic field strength and therefore may be used to regulate the output voltage. The voltage regulation aspect of this configuration of the excitation coil assembly  70  of power generator  32  is typically not provided in this form in known generators and alternators. 
         [0026]    With the type of system described above, the magnetic field may be selectively turned off and on even as rotor assembly  42  is rotated by flowing fluid  40 . The ability to selectively eliminate the magnetic field facilitates cleaning of generator  32  by enabling flushing of magnetic particles from the power generator. For example, the magnetic field may be periodically eliminated, e.g. turned off, to allow the flowing fluid  66  moving through flow channel  64  to remove magnetic particles from the gap region  62  between stator  44  and rotor assembly  42 . By flushing the system, product life is increased and premature failure and/or degradation of magnetic fields due to particle buildup is reduced or eliminated. 
         [0027]    The magnetic field may be selectively eliminated by a variety of techniques and mechanisms. For example, delivery of excitation power to excitation coil assembly  70  from power storage device  72  may be controlled by enabling interruption of electric power delivered via electric line  76 . In one example, a remotely controlled switch  92  may be used to control the flow of electric power between power storage device  72  and excitation coil assembly  70 . However, other devices, systems and techniques may be utilized to effectively control the excitation energy and the creation of magnetic fields in power generator  32 . 
         [0028]    Well system  20  may be constructed in a variety of configurations for use with many types of well applications and environments. The power generator may be deployed in various types of tubular structures, such as well tubing, or in other tubular structures used to conduct a flow of fluid. Additionally, the power generator may be deployed in tubular structures disposed within a wellbore or disposed at other locations for use in facilitating a given well application. Also, the size and arrangement of the excitation coils and power generation coils may be adjusted according to the parameters of a specific well application. The excitation energy source may be supplied by a battery or by other types of power sources located in the stator or at other suitable locations. Depending on the application and the power requirements, the size, materials, and configuration of the power generator may be adjusted as desired to accomplish the goals of a given well application. 
         [0029]    Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The term “or” when used with a list of at least two elements is intended to mean any element or combination of elements. 
         [0030]    Although only a few illustrative embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.