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TECHNICAL FIELD 
       [0001]    The invention relates to an inductive coupler assembly including a first coupler and a second coupler, each having discrete ferromagnetic segments. 
       BACKGROUND 
       [0002]    To complete a well, various completion equipment is provided in a well. In many cases, the completion equipment includes electrical devices that have to communicate with an earth surface or downhole controller. Traditionally, electrical cables are run to downhole locations to enable such electrical communication. In other implementations, inductive couplers have been used for communicating power and/or signaling to electrical devices downhole in a wellbore and retrieving measurement information to surface. 
         [0003]    Typically, an inductive coupler includes two coil elements, a female coil element that is fixed in a downhole position, and a male coil element that is typically run with a tool for positioning adjacent the female coil element to enable inductive coupling between the female and male coil elements. In downhole applications, both the male and female coil elements of an inductive coupler are typically arranged in cylindrical structures. Each of the male and female coil elements includes a pole member (formed of a ferromagnetic material) that is cylindrically shaped. Each coil element has coil wiring that is wound along a circumference of the respective cylindrical pole member. 
         [0004]    A side sectional view of an example conventional inductive coupler  10  is depicted in  FIG. 1 , which shows a cylindrically-shaped female pole member  12  and a cylindrically-shaped male pole member  14 . Coil wiring  16  is provided in a circumferential groove  18  defined in the female pole member  12 , and coil wiring  20  is provided in a circumferential groove  22  defined in the male pole member  14 . Note that the cylindrically-shaped male pole member  14  has an outer diameter that is smaller than an inner diameter of the female pole member  12 , such that the male pole member  14  can be lowered into the inner bore of the female pole member  12  to enable inductive coupling between the male and female coil elements. Once the female and male coil elements are aligned, an electrical current is run through one of the coil wirings  16 ,  20 , which creates a magnetic field  24  to induce current to flow in the other of the coil wirings  16 ,  20 . 
         [0005]    An issue associated with using a conventional inductive coupler such as that depicted in  FIG. 1  is that it may be difficult or not cost-effective to make inductive couplers of different sizes for different applications. Cylindrically-shaped pole members made of certain types of ferromagnetic materials can be mechanically fragile, making the grinding process relatively difficult to achieve coupler elements of different sizes as well as making the inductive coupler easily susceptible to failure due to mechanical shocks or vibrations during deployment downhole or operation within the wellbore. Also, having to provide customized sizes and shapes to achieve coupler elements of different sizes is a time-consuming and labor-intensive process, which can drive up the costs of well operation. Also, an issue associated with conventional inductive couplers is that the ferromagnetic core and the coil element are exposed to well bore fluids which result in corrosion and reduced life span. 
       SUMMARY 
       [0006]    In general, according to an embodiment, an inductive coupler assembly includes a first coupler having a first support structure and plural discrete ferromagnetic segments supported by the first support structure, and a second coupler to inductively couple to the first coupler, where the second coupler has a second support structure and plural discrete ferromagnetic segments supported by the second support structure. 
         [0007]    In another embodiment, a ferromagnetic material core and coil can be immersed in a clean fluid chamber and the oil is separated and pressure compensated to the surrounding fluid. 
         [0008]    Other or alternative features will become apparent from the following description, from the drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  illustrates a conventional inductive coupler assembly. 
           [0010]      FIG. 2A  illustrates a side sectional view of an inductive coupler assembly according to an embodiment. 
           [0011]      FIG. 2B  shows a portion of the inductive coupler assembly of  FIG. 2A  in greater detail. 
           [0012]      FIG. 3  is a cross-sectional view of the inductive coupler assembly of  FIG. 2A . 
           [0013]      FIG. 4  illustrates formation of a magnetic field using an inductive coupler assembly, according to an embodiment. 
           [0014]      FIG. 5  illustrates inductive coupling achievable even when inductive coupler elements are slightly misaligned, in accordance with an embodiment. 
           [0015]      FIG. 6  is a side sectional view of an alternative implementation of a coupler. 
           [0016]      FIG. 7  is a side sectional view of another implementation of a coupler. 
           [0017]      FIGS. 8A ,  8 B, and  9  illustrate a further embodiment of an inductive coupler assembly. 
           [0018]      FIG. 10  illustrates an example completion system that uses an embodiment of an inductive coupler assembly. 
           [0019]      FIGS. 11-14  illustrate other embodiments of inductive coupler assemblies in which clean oil chambers can be employed to protect inductive coupler elements, according to some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible. 
         [0021]    As used here, the terms “above” and “below”; “up” and “down”; “upper” and “lower”; “upwardly” and “downwardly”; 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 invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or diagonal relationship as appropriate. 
         [0022]    An inductive coupler assembly according to an embodiment includes first and second couplers, where the first coupler can be considered a male coupler, and the second coupler can be considered a female coupler (in some implementations). The first and second couplers can also be referred to as first and second coil elements that are able to communicate by inductive coupling. However, instead of using concentrically arranged cylindrically-shaped or contiguous ferromagnetic pole members in the couplers, as conventionally done, discrete ferromagnetic segments are employed in each of the first and second couplers. Using discrete ferromagnetic members enables an operator to easily manufacture inductive couplers of different sizes or shapes by using different combinations of discrete ferromagnetic segments. The ability to conveniently provide robust and reliable inductive couplers of different sizes (or shapes) is useful because it allows for a more effective and cost-efficient well operation and provides a means to communicate wellbore measurements and equipment control commands that enable operators to monitor and optimize production operations and reservoir recovery. 
         [0023]      FIGS. 2A ,  2 B, and  3  depict an inductive coupler assembly  100  according to an embodiment.  FIG. 2A  is a side-sectional view of the inductive coupler assembly  100 , whereas  FIG. 3  is a top cross-sectional view of the inductive coupler assembly  100 . The inductive coupler assembly  100  includes a male coupler  102  and a female coupler  104 . As depicted in  FIGS. 2A and 3 , an annular gap  130  is defined between the male and female couplers. The male coupler  102  includes a support structure  106 , which can be a steel mandrel or other type of support structure. The support structure  106  is a generally cylindrically-shaped support structure. “Generally cylindrical” means that the structure is not perfectly cylindrical, but rather has a shape that is roughly cylindrical based on tolerances and accuracies of equipment used to manufacture the structure. 
         [0024]    A circumferential groove  108  is formed in an outer surface of the support structure  106 , where the groove  108  extends generally around the outer circumference of the support structure  106 . 
         [0025]    In accordance with some embodiments, discrete ferromagnetic segments  110  can be provided in the circumferential groove  108 . In one embodiment, the ferromagnetic segments  110  are ferromagnetic bars. The discrete ferromagnetic bars are further depicted in the cross-sectional view of  FIG. 3 , which shows a number of ferromagnetic bars  110  provided in the groove  108  of the male coupler support structure  106 . Note that the number of discrete ferromagnetic segments  110  can be varied for different applications. In some applications, for example, the ferromagnetic segments  110  can be provided all the way around the circumferential groove  108 . 
         [0026]    Coil wiring  112  is provided to extend circumferentially around the circumferential groove  108  (and also to extend around the discrete ferromagnetic segments  110 ). A first non-conductive ring  114  is provided between the top ends of the ferromagnetic segments  110  and the support structure  106 , and a second non-conductive ring  116  is provided between the lower ends of the ferromagnetic segments  110  and the support structure  106 . The non-conductive rings  114 ,  116  do not conduct electricity. 
         [0027]    Also, a cylindrically-shaped sleeve  118  is provided to sealably cover the groove  108  to isolate wellbore fluids (which can be harsh or corrosive) from the coil wiring  112  and the ferromagnetic segments  110 . The sleeve  118  can be sealably attached to the support structure  106  to provide a fluid-tight seal. In the depicted embodiment, the coil wiring  112  is positioned between the ferromagnetic segments  110  and the sleeve  118   
         [0028]    Similarly, the female coupler  104  also includes a generally cylindrically-shaped support structure  120  in which a circumferential groove  122  is formed in the inner diameter of the female coupler support structure  120 . Discrete ferromagnetic segments  124  (which in one example are discrete ferromagnetic bars) are provided at least partially around the circumference of the groove  122  (as better depicted in  FIG. 3 ). Coil wiring  126  is wound around the groove  122 . A first non-conducting ring  140  is provided between the top ends of the ferromagnetic segments  124  and the support structure  120 , and a second non-conductive ring  142  is provided between the bottom ends of the ferromagnetic segments  124  and the support structure  120 . Also, a sleeve  128  is sealably attached to the female coupler support structure  120  to provide a seal to prevent wellbore fluids from entering the groove  122 . Note that in the depicted embodiment, the coil wiring  126  is between the ferromagnetic segments  124  and the sleeve  128 . 
         [0029]    The coil wiring  126  of the female coupler  104  can be wrapped (or wound in a spiral manner) around a bobbin  127  ( FIG. 2B ), which is made of a magnetically low-permeability and electrically non-conductive material such as Polyetheretherketones (PEEK7). The bobbin  127  is ring-shaped and is provided between the coil wiring  126  and the ferromagnetic segments  124 . The coil wiring  112  of the male coupler  102  can be directly wrapped around the ferromagnetic segments  110  or around a ring-shaped bobbin  113  ( FIG. 2B ), which is made of a low-permeability and non-conductive material such as PEEK. 
         [0030]    Examples of ferromagnetic materials for the ferromagnetic segments  110  and  124  that can be used include ferrite. Other ferromagnetic materials can also be used, such as soft iron magnetic alloys, mu-metal alloys, or other materials. A desired property for proper operation of the inductive coupler is that the desired magnetic path that couples the male and female couplers should pass through low-loss magnetic materials and the air gap (or wellbore fluid gap)  130  should be made relatively small. In some implementations, the ferromagnetic segments have a higher magnetic permeability than the adjacent metal alloy that is used for the support structures  106  and  120 . Moreover, a low-magnetic permeability material can be used between the support structures  106  and  120  and the ferromagnetic segments to help provide a path of least magnetic reluctance to the desired magnetic field that couples the male and female couplers. 
         [0031]    Instead of using bars, the ferromagnetic segments can be laminated bars or sheets, tape-wound sheets, rods, rings, ring segments, bricks, or other structures. 
         [0032]    In one embodiment, the ferromagnetic bars are coated with a thermoplastic material such as PEEK or packaged into Teflon® sleeves. This feature gives more protection of the ferromagnetic segments against vibrations and shocks. Also, it avoids any direct mechanical contact between adjacent ferromagnetic segments, which are easily chipped and it provides protection from corrosive well fluids. 
         [0033]    The sleeves  118  and  128  are formed of non-magnetic materials. The sleeves help mechanically support and protect respective ferromagnetic segments  110  and  124 , since the ferromagnetic segments can be fragile parts. Moreover, the sleeves have a low magnetic permeability; hence, they can help decrease magnetic flux losses into the surrounding metal structures by increasing the magnetic flux reluctance of the undesired magnetic paths. This helps to increase the overall efficiency of the inductive coupler  100 . 
         [0034]    The geometry of each ferromagnetic segment and each coil wiring can be selected to optimize the coupler efficiency. For example, a substantial length of the ferromagnetic segment can be provided above and below the bobbin  113 ,  127  to increase the mutual inductance between the male and female couplers  102  and  104 . 
         [0035]    Note that the coupler efficiency is not dependent at the first order upon the thickness of the ferromagnetic segments, provided that relatively high permeability materials are selected. As a result, relatively thin ferromagnetic segments can be provided to allow easier fitting into couplers of different geometries. 
         [0036]    The ferromagnetic segments  110  of the male coupler  102  and the ferromagnetic segments  126  of the female coupler  104  can be coupled electromagnetically (by inductive coupling) to cause the creation of a closed path of least resistance (or more precisely, least magnetic reluctance) for magnetic flux to flow. The size, number, and placement of the ferromagnetic segments are designed to ensure good electromagnetic coupling for any rotational orientation of the cylindrical support structures  106  and  120 . 
         [0037]    As depicted in  FIG. 4 , the inductive coupler can be considered as a magnetic circuit with ferromagnetic bars I  10 ,  124  and a gap space  130  between the ferromagnetic bars. The gap space  130  is filled with downhole fluids. The magnetic flux  0  is forced through each ferromagnetic bar and returns via the fluid gap  130 . Each ferromagnetic bar provides a relatively high permeability path that guides the flux, whereas the gap  130  has relatively low permeability. 
         [0038]    Mathematically, the operation of an inductive coupler may be described according to Faraday&#39;s law in the integral form: 
         [0000]    
       
         
           
             
               
                 
                   
                     
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                       C 
                     
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                         E 
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                   = 
                   
                     
                       - 
                       
                          
                         
                            
                           t 
                         
                       
                     
                      
                     
                       
                         ∫ 
                         S 
                       
                        
                       
                         
                           B 
                           ρ 
                         
                         · 
                         
                           
                              
                             
                               S 
                               ρ 
                             
                           
                           . 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Eq 
                     . 
                     
                         
                     
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                     1 
                   
                   ) 
                 
               
             
           
         
       
     
         [0039]    In Eq. 1, B is the magnetic flux coupling the male and female couplers and S is the surface area defined by the inner diameter of the inner coil. Notice that this is a surface area over which the integral is computed. There is no requirement for this surface area to be completely filled by the magnetic material or that the magnetic material within the surface area to be comprised of one contiguous piece of ferromagnetic material. Likewise for the left side of Eq. 1, E is the electric field potential around the closed path, C, defined by the inductive coupling&#39;s outermost coils, and           is a line vector aligned with the wire as it goes around the closed path C. There is no requirement that the magnetic material within this line integral be continuous, contiguous, cylindrically connected, or symmetric. 
         [0040]    In  FIG. 4 , A g  notes the overlapping area (or gap longitudinal section area) between the two bars, and A c  notes the ferrite bar cross section area. 
         [0041]    The two ferromagnetic bars in the male and female couplers can tolerate misalignment as depicted in  FIG. 5 . In this case, Ae g  (≦A g ) notes the effective cross section area that is common between the two bars. Due to possible misalignment, this effective section is less or equal to the overall cross section as shown in  FIG. 4  when the two bars are perfectly aligned. The parameter Ae c  represents the effective cross-section of the ferromagnetic bar, which is equal to A c  in  FIG. 4 . 
         [0042]    The coupler mutual inductance can be computed using the expression of the reluctance of the various elements along the magnetic flux. R c  notes the reluctance of the ferromagnetic core, and R g  notes the reluctance of the fluid gap. As a first order approximation, the following is obtained: 
         [0000]        R   c =λ c /(μ c   *A   c ), 
         [0000]        R   g =λ g /(μ g   *A   g ).   (Eq. 2) 
         [0043]    In Eq. 2 The symbol μ c  is the magnetic permeability of the ferromagnetic bars or ferromagnetic material and μ g  is the magnetic permeability of the fluid gap. Magnetic permeability is measured in henries per meter, or newtons per ampere squared. It represents the degree of magnetization of a material that responds linearly to an applied magnetic field. 
         [0044]    The parameters λ c  and λ g  represent the length of magnetic lines in the ferromagnetic bars and in the gap  130 , respectively. The parameters λ c  and λ g  represent the magnetic permeability in the ferromagnetic bars and in the gap, respectively. 
         [0045]    Since the inductive coupler is constructed with a set of ferromagnetic bars, the effective reluctance includes the contribution of each bar in the male and female coupler. The contributions of each bar and corresponding fluid gap section are added. 
         [0046]    The reluctance in the ferromagnetic core section R c  and in the fluid gap R g  becomes: 
         [0000]        R   c =λ c /(μ c   *Ae   c ), 
         [0000]        R   g =λ g /(μ g   *Ae   g ).   (Eq. 3) 
         [0047]    The total flux is expressed as Φ=N 1 I/R c +R g ). N 1  notes the number of turns in the male coupler. 
         [0048]    Since the gap  130  is filled with air or fluid, μ g  is close to unity. The conditions μ c &gt;&gt;μ g  leads to: 
         [0000]      Φ˜N 1 I/R g =μ o N 1 IAe g /λ g .   (Eq. 4) 
         [0049]    The constant value μ 0  is known as the magnetic constant or the permeability of vacuum and it has the defined value μ 0 =4π×10 −7  Newtons per Ampere squared. 
         [0050]    The inductive coupling&#39;s mutual inductance is equal to the total flux divided by the coil current: 
         [0000]        M   12   =N   2   Φ/I,    (Eq. 5) 
         [0000]    where N 2  notes the number of turns on the secondary female coil. Based on Eq. 4, M 12  becomes: 
         [0000]        M   12   =μ   o   N   1   N   2   Ae   g /λ g ,   (Eq. 6) 
         [0051]    It is thus concluded that the mutual inductance depends largely upon the geometrical dimensions of the fluid gap. The mutual inductance depends mainly upon the gap thickness λ g  and effective overlapping area Ae g . These parameters are optimized to enhance the mutual impedance between the two couplers and consequently raise the coupler&#39;s efficiency. 
         [0052]    The coupler&#39;s efficiency can be optimized as follows. The coupler&#39;s efficiency increases when the gap thickness λ g  is reduced. This implies that the inner and outer diameters of the female and male couplers should be as close as possible. The coupler&#39;s efficiency also increases when the overlapping area Ae g  is raised. This can be achieved by increasing the length of ferromagnetic segments on both ends of the coupler. 
         [0053]    Alternatively, enhanced efficiency can be achieved also by increasing the number of ferromagnetic segments The coupler efficiency increases also with the wellbore size since the overall gap area is magnified while the gap length or spacing between male and female couplers remains about the same. 
         [0054]    The mutual inductance and therefore the coupler&#39;s efficiency is not dependant upon the ferromagnetic segment thickness, to a first approximation This allows selecting thin ferromagnetic bars. The above is true only if the permeability of the ferromagnetic segments is sufficiently high so that the condition μ c &gt;&gt;μ g  is valid. 
         [0055]    For optimum efficiency, it is also desired to minimize the interaction between the magnetic field and the metal of the support structures. For this reason, non-conductive rings ( 114 ,  116 ,  140 ,  142  in  FIG. 2 ) made of thermoplastic material such as PEEK can be placed on both ends of the ferromagnetic bars. These rings between the ferromagnetic bars and surrounding metallic structure reduce eddy current losses in the metal and consequently lead to a more efficient coupling between the two couplers. 
         [0056]      FIG. 6  is a longitudinal sectional view of a male coupler of a slightly different embodiment. As with the embodiment depicted in  FIGS. 1 and 2 , the male coupler  200  includes a support structure  202 , which can be a metal mandrel. A groove  204  is formed in the outer surface of the support structure  202 , in which discrete ferromagnetic segments  110  are provided. The coil wiring  206  is wrapped around the ferromagnetic segments  110 . Although a bobbin is not employed in  FIG. 6 , note that in other implementations, a bobbin can be provided between the coil wiring  206  and the ferromagnetic segments  110 . 
         [0057]    The coil wiring  206  can be properly coated to protect against elevated temperature and pressure. Examples of coatings that can be applied include Teflon, PEEK, a mix of polymers, and so forth. The ferromagnetic segments  110  may also be exposed to well fluids. In some cases, the ferromagnetic segments can also be coated with a protective layer. However, in other implementations, such as when the ferromagnetic segments  110  are implemented with a ferrite material, the protective coating may not be necessary since the ferrite material is relatively stable and does not react easily with mud or wellbore fluids. 
         [0058]    As further depicted in  FIG. 6 , non-conductive rings  208  and  2   1   0  are provided on the two ends of the ferromagnetic segments  110  to improve coupler efficiency and to reduce the interaction between the magnetic field and the metal of the support structure  202 . The rings  208  and  210  can be formed of a material having a relatively low magnetic permeability. 
         [0059]    As depicted in  FIG. 7 , for additional protection, a low magnetic permeability sleeve  212  is provided to cover the groove  204 , in another embodiment. In this embodiment, a clean oil (or other protective fluid) can be provided in a chamber  214  defined between the sleeve  212  and the support structure  202 A. The sleeve  212  is engaged with surfaces  216  and  218  of the support structure  202 A, where the surfaces have indentations  220  and  222  to receive seals  224  and  226 , such as  0 -ring seals, to provide a sealed engagement between the sleeve  212  and the support structure  202 A. Attachment rings  228  and  230 , such as metal rings, can be used to secure the sleeve  212  to the support structure  202 A. 
         [0060]    The clean oil in the chamber  214  protects the coil wiring  206  from corrosion and reduces the risk of short-circuit in the electrical connections due to presence of water or other corrosive or electrically conductive wellbore fluids. Elastic deformation of the sleeve  212  compensates for expansion and contraction of the oil at various temperatures and pressures. Consequently, the sleeve  212  can be used as a membrane to compensate for changing volume of the system due to variation in temperature and pressure. Protective layers can be provided on the sleeve  212  to protect the sleeve  212  from damage when running a tool including the coupler  200  in the well. The protective layers can be strips, plates, or sheets of metallic materials that do not form a closed electrically conductive loop to avoid short-circuiting the magnetic circuit or redirection of the magnetic field path through the protective layers. 
         [0061]    In other implementations, other techniques for compensation for expansion and/or compression of the oil in the chamber  212  can be used, including a pressure compensation bellows, a dynamic O-ring, a compensating piston, and so forth. 
         [0062]    The chamber  214  shown is filled with clean oil and compensated for pressure and temperature variation to protect ferromagnetic material segments and coil wiring. However, the same protection method could be used for cylindrical ferromagnetic core and coil wiring (such as that depicted in  FIG. 1 , for example), toroidal shaped ferromagnetic core, or any other shaped ferromagnetic core and coil wiring. 
         [0063]    As depicted in  FIGS. 8A ,  8 B, and  9 , instead of providing the ferromagnetic segments as discrete segments in the circumferential direction, as depicted above, the ferromagnetic segments can also be discrete in the longitudinal direction. Thus, as depicted in  FIG. 5A , a longer length ferromagnetic segment  300  and a shorter length ferromagnetic segment  302  can be provided, where the ferromagnetic segments  300  and  302  can be stacked in the longitudinal direction as depicted. The stacked arrangement of the ferromagnetic segments  300 ,  302  is referred to as a set  304 . Multiple sets  304  of ferromagnetic segments are arranged in the circumference, as depicted in  FIG. 8A . In the implementation depicted in  FIG. 8A , some of the sets  304  have the longer length ferromagnetic segment  300  stacked on top of the shorter length ferromagnetic segment  302 , while other sets  304  have the shorter length ferromagnetic segment  302  stacked on top of the longer length ferromagnetic segment  300 . The two different arrangements are provided in alternating fashion, as depicted in  FIG. 8A , such that an alternating arrangement of ferromagnetic segments  300 ,  302  is provided. 
         [0064]    The arrangement of ferromagnetic segments,  300 ,  302  in  FIG. 8A  can be part of the male inductive coupler. As further depicted in  FIG. 8B , a bobbin  306  is provided around the outer surfaces of the ferromagnetic segments  300 ,  302 , and coil wiring  308  is provided around the bobbin  306 . 
         [0065]    A similar arrangement of longer length and shorter length ferromagnetic segments  310  and  312  are also provided for the female inductive coupler, as depicted in  FIG. 9 . The ferromagnetic segments  310 ,  312  are arranged in alternating fashion. A bobbin  314  is placed inside the ferromagnetic segments  310 ,  312 , with the female coupler coil wiring  316  arranged around the bobbin  314  inside the bobbin. 
         [0066]      FIG. 10  shows an example completion system deployed in a wellbore  400 . The completion system includes an upper completion section  402 , and a lower completion section  404 . The upper completion section  402  includes a tubing  406  (e.g., production tubing). A male inductive coupler  408  is provided at the lower end of the tubing  406 . The lower completion section  404  has a female inductive coupler  410  that is electrically connected over a cable  412  to electrical devices  414  (e.g., sensors and/or control devices). 
         [0067]    The inductive coupler assembly including the couplers  408  and  410  form an inductive coupler assembly, and the couplers  408  and  410  can be arranged as discussed above in the various embodiments. The upper completion section  402  is run into the wellbore  400  and engaged with the lower completion section  404 . Once engaged, the male coupler  408  is positioned adjacent the female coupler  410  to enable the couplers to communicate. 
         [0068]      FIGS. 11-14  illustrate other embodiments of inductive coupler assemblies in which clean oil (or other fluid) chambers are provided to protect inductive coupler elements. As depicted in  FIG. 11 , a female coupler  500  and a male coupler  502  are provided adjacent each other. The female coupler  500  includes a ferromagnetic core  504 , and the male coupler  502  includes a ferromagnetic core  506 . Coil wiring  508  is provided around the ferromagnetic core  504  of the female coupler  500 , and coil wiring  510  is provided around the ferromagnetic core  506  of the male coupler  502 . 
         [0069]    As further depicted in  FIG. 11 , an elastic sleeve  512  is sealably attached to a housing  514  of the female coupler  500 , with a sealed chamber  516  containing a clean oil defined between the sleeve  512  and the housing  514 . The sleeve  512  can be formed of PEEK, for example. Also, optionally, a PEEK coating  518  can be provided around the ferromagnetic core  504  and the coil wiring  508 , and another PEEK coating  519  can be provided around the ferromagnetic core  506  and the coil wiring  510 . 
         [0070]    Similarly, an elastic sleeve  520  (which can be made of PEEK, for example) is sealably attached to a housing  522  of the male coupler  502  to define a chamber  524  containing a clean oil between the sleeve  520  and the housing  522 . 
         [0071]      FIG. 12  shows an inductive coupler assembly that is similar to the inductive coupler assembly of  FIG. 11 , except that compensating pistons  530  (in the female coupler  500 ) and  532  (in the male coupler  502 ) are provided. The compensating pistons  530  and  532  are moveable to compensate for expansion and compression of the clean oil in respective chambers  516  and  524 . 
         [0072]    As depicted in  FIG. 12 , the piston  530  is movable in a space between the sleeve  512  and housing  514  of the female coupler  500 . One end of the piston  530  is exposed to the chamber  516 , while the other end of the piston  530  is exposed to another chamber  534 . A port  536  is provided in the sleeve  512  to allow for fluid communication between the chamber  534  and an exterior space outside the female coupler  500 . 
         [0073]    Similarly, the piston  532  is movable in a space between the sleeve  520  and the housing  522  of the male coupler  502 . One end of the piston  532  is exposed to the chamber  524 , while another end of the piston  532  is exposed to another chamber  538  that communicates with a port  540  to an external space outside the male coupler  502 . 
         [0074]      FIG. 13  illustrates use of a different compensating mechanism in the inductive coupler assembly. The inductive coupler assembly of  FIG. 13  is similar to the inductive coupler assembly of  FIGS. 11 and 12  except that moveable O-ring seals are used to provide compensation for expansion of clean fluids in respective chambers  516  and  524 . O-ring seals  550  and  552  are provided in the female coupler  500  and male coupler  502 , respectively, with the  0 -ring seals  550  and  552  exposed through respective ports  554  and  556  to an external space outside the inductive coupler assembly. The O-ring seals  550  and  552  are moveable to compensate for expansion and compression of fluids in respective chambers  516  and  524 . 
         [0075]      FIG. 14  shows another embodiment of an inductive coupler assembly that includes the female coupler  500  and male coupler  502 . The inductive coupler assembly of  FIG. 14  is similar to the inductive coupler assembly of  FIG. 11 , except that the ferromagnetic cores  504  and  506  and coil wirings  508  and  510  of the respective couplers  500  and  502  are potted (provided in protective vessels  560  and  562 ) to protect the ferromagnetic cores and wiring coils from corrosive well fluids. The potting (protective vessels  560  and  562 ) can be formed of any non-electrically conductive potting material that is compatible with the insulated coil wirings. Example potting materials include epoxy, a thermoplastic such as PEEK, an elastomer, and so forth. 
         [0076]    While the invention has been disclosed 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 such modifications and variations as fall within the true spirit and scope of the invention.

Summary:
An inductive coupler assembly has a first coupler having a first support structure and plural discrete first ferromagnetic segments supported by the first support structure, and a second coupler to inductively couple to the first coupler, the second coupler having a second support structure and plural discrete ferromagnetic segments supported by the second support structure.