Abstract:
A method of forming a motor winding wire for use in an oilfield application can include providing a conductive core; layering an insulating polymer layer about the core for electrical isolation thereof; adding an outer polymer layer about the insulating polymer layer to provide contaminant resistance; providing a sealable casing that comprises an oil-fillable space; disposing the motor winding wire within the oil-fillable space of the casing; filling the oil-fillable space with oil; and sealing the sealable casing to seal the oil in the oil-fillable space.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application is a Divisional of U.S. application Ser. No. 11/951,818 filed Dec. 6, 2007, now U.S. Pat. No. 7,714,231, which is claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser. No. 60/889,650, entitled Motor Winding Wires for Oilfield Application, filed on Feb. 13, 2007, which is incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described relate to equipment for placement within a hydrocarbon well. In particular, embodiments of equipment employing magnetized motor winding wires are described wherein the equipment may be configured for placement and relatively continuous use within the well over an extended period of time, perhaps between about 1½ and 5 years. 
     BACKGROUND 
     A variety of hydrocarbon applications involve the use of electrically powered equipment disposed within a hydrocarbon well for extended periods of time. For example, an electric submersible pump (ESP) may be positioned within a hydrocarbon well to promote the extraction of hydrocarbons from the well. In such circumstances it may be preferable to leave the pump in place and operating throughout the hydrocarbon production from the well. Thus, depending on the hydrocarbon reservoir itself and the parameters of the operation, the pump may be left operating and in place for up to about 5 years or longer. 
     Equipment such as the indicated ESP may include several components susceptible to damage upon exposure to the downhole conditions of the well. For example, the moisture content, chemical makeup, and pressure or temperature extremes of the downhole environment may tend to degrade certain components of the ESP over time. Components of the ESP susceptible to such exposure may include a power cable and motor parts such as motor windings or conductors. However, measures may be taken to help shield such components from the downhole environment. For example, in the case of the power cable, thick and robust, moisture resistant polymer layers may be extruded over an electrically conductive core. In this manner the core may remain substantially unaffected by downhole conditions so as to help ensure that the cable remains operation for an extended period. Alternatively, in the case of the motor and windings, they may be housed within an oil-filled and hermetically sealed casing isolated from the environment of the well. 
     Unfortunately, the oil filled casing noted above invariably fails to maintain complete isolation from the conditions in the surrounding downhole environment. For example, when left within the well for an extended period, moisture and chemical contaminants from the downhole environment are eventually able to seep through and penetrate the casing to some degree. Nevertheless, in the case of some parts of the motor, the fact that the casing remains predominantly oil-filled may be enough to avoid failure. For example, the moving parts of the motor may remain in the presence of sufficient lubrication to remain operational in spite of a degree of moisture and chemical contaminants. However, as described below, the direct exposure of the motor windings to the well contaminants, especially moisture, may be enough to render them ineffective, leading to malfunction of the entire ESP. 
     Unlike other parts of the motor, motor winding wires are not dependent upon the presence of sufficient oil concentration within the casing in order to remain operational. Rather, like the power cable, it is the substantial shielding of the motor winding wires from direct contact with downhole contaminants, especially moisture, which may be key to ensuring continued functionality of the wires. However, as indicated above, given enough time downhole, the casing is likely to be penetrated by such downhole contaminants leaving the wires directly exposed to contaminants. 
     In order to further shield the motor winding wires from direct exposure to downhole contaminants, polymer layers may be provided about the conductive core of the motor winding wires. Thus, in theory, the polymer layers may provide a degree of shielding to the motor winding wires similar to the power cable configuration noted above. Unfortunately, however, the dimensions and properties of the motor winding wires themselves render conventional polymer layering and shielding ineffective for prolonged protection of the wires from exposure to downhole contaminants. For example, a conventional motor winding wire may be magnetized wire core of no more than about 5 gauge copper wire, generally between about 16 and 50 gauge. Furthermore, the motor winding wire may be configured for relatively tight windings. As such, no more than between about 0.25 to 20 mil polymer layers may be effectively provided over the wires. In fact, for 30 gauge or so windings and smaller, as a matter of practicality it may be more effective to bypass extruding the polymer layer altogether and simply varnish the polymer over the wound wires to provide the shielding from downhole contaminants. Regardless, the polymer layer may be of limited thickness and effectiveness. 
     In addition to the limited thickness, the effectiveness of the polymer layer as a shield from downhole contaminants may be further limited by the particular types of polymers available for use with motor winding wires. That is, given the small dimension and the conductive nature of motor winding wire, materials disposed thereabout may be of an electrically insulating character to ensure proper wire operation. These materials may include polyimide, polyester, polyamide, poly-ether-ether-ketone and other conventional electrical insulators. Unfortunately, however, such insulators are prone to hydrolytic degradation or moisture absorption upon prolonged direct exposure to even a small degree of moisture and other downhole contaminants. As a result, the motor winding wire as well as the entire ESP or other equipment employing such winding wire is prone to fail, generally well in advance of about 5 years. In fact, smaller ESP motors positioned downhole for continued use often display a lifespan of no more than about 1 year. Furthermore, efforts to overcome polymer shielding limitations via over-wrapping or enamel layer configurations remain insufficient to prevent such hydrolytic degradation and moisture absorption. 
     SUMMARY 
     A motor winding wire is provided for an application in a hydrocarbon environment such as the downhole environment of a well. The wire includes a conductive core with an electrically insulating polymer layer thereabout. A moisture resistant outer polymer layer is provided about the electrically insulating polymer layer for shielding it from moisture in the environment. 
     In one embodiment, a tie layer may be disposed between the electrically insulating polymer layer and the moisture resistant outer polymer layer. The tie layer may include a polymer of one of the outer polymer layer and the electrically insulating polymer layer along with an adhesive functional group to provide bonding between the outer and electrically insulating polymer layers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cross-sectional view of a well with an embodiment of an electrically driven assembly disposed therein. 
         FIG. 2  is an enlarged cross-sectional view of an electric motor of the assembly and the well of  FIG. 1 . 
         FIG. 3  is an enlarged cross-sectional view of an embodiment of a motor winding wire of the electric motor of  FIG. 2 . 
         FIG. 4  is cross-sectional view of an alternate embodiment of a motor winding wire. 
         FIG. 5  is an enlarged view of the motor winding wire of  FIG. 4  taken from  5 - 5 . 
         FIG. 6  is a partially cross-sectional overview of an embodiment of an electrically driven assembly within a well at an oilfield. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are described with reference to certain types of motor winding wires for use with electrical equipment for hydrocarbon applications. In particular, focus is drawn to equipment in the form of electric submersible pumps employed within hydrocarbon wells. However, a variety of electrical equipment may employ embodiments described herein, particularly where the equipment is intended for long term and/or continuous use while exposed to a harsh or moisture rich hydrocarbon environment. 
     Referring now to  FIGS. 1 and 2 , an embodiment of an electrically driven assembly  100  is depicted disposed within a hydrocarbon well  180 . The well  180  is defined by a casing  150  through a formation  190  at an oilfield. In the embodiment shown, the assembly  100  is electronically driven equipment in the form of an electric submersible pump (ESP). However, other types of electrically driven equipment may be employed within such a well  180 . As shown, the ESP assembly  100  includes an extraction line  160 , a pump  140 , and an intake region  130 , as well as a motor  125  powered by a cable  175 . The ESP assembly  100  may operate by rotation of a motor assembly  200  within a casing  225  of the motor  125 . The motor  125  may be employed to power the pump  140  to draw in hydrocarbon fluids from the environment of the well  180 . Such fluids may then be driven up the extraction line  160  to the well surface. 
     The above-noted assembly  100  may be disposed within the well  180  for continuous operation over an extended period of time. For example, an ESP assembly  100  may be disposed within the well  180  as shown for substantially continuous use throughout the productive life of the well  180 . In most cases, this may be between about 2 and 5 years, or longer. For this period, the assembly  100  may be subjected to harsh well conditions such as extreme temperatures or pressures, and exposed to contaminants  110  such as moisture and corrosive chemicals. Nevertheless, the assembly  100  may remain functional throughout the substantial duration of the productive life of the well  180 . In particular, as detailed below, motor winding spools  210  of the assembly  100  may be sufficiently shielded from contaminants  110  of the well  180  so as to avoid operational failure of the assembly  100  during the productive life of the well  180 . 
     Continuing with reference to  FIGS. 1 and 2 , the assembly  100  is directly exposed to the environment of the well  180  which includes the above-noted contaminants  110 . With reference to  FIG. 2 , a casing  225  of the motor  125  may be hermetically sealed to provide a degree of protection from the indicated contaminants  110 . Nevertheless, at some point during the life of the well  180 , contaminants  110  may reach an oil-filled space  250  within the casing  225 . Thus, the rotable motor assembly  200  being located within the oil-filled space  250  may be directly exposed to such contaminants  110 . Of particular note, motor winding wire  201  of motor winding spools  210  may come into direct contact with contaminants  110  such as moisture. However, as detailed below, the electrical conductivity of the motor winding wire  201  may remain substantially unaffected by contact with moisture contaminants  110 . Thus, failure of the motor  125  and thus, the entire ESP assembly  100  may be avoided. Furthermore, while the spools  210  are shown disposed within an ESP assembly  100 , other motorized assemblies may employ motor winding wire  201  as noted below. Such assemblies may include downhole tractor assemblies, powered centralizers, perforation guns, sampling tools and a host of other assemblies that may be motorized. 
     Referring now to  FIG. 3 , with added reference to  FIG. 2 , embodiments of motor winding wire  201  may be configured and constructed so as to avoid contaminant  110  contact with a conductive core  300  of the wire  201 . In this manner, the conductive nature of the core  300 , generally magnetized copper, may remain unaffected by contaminants  110  otherwise prone to diminish conductivity. In particular, the conductive core  300  may be shielded by a tailored combination of polymer layers  350 ,  375  as described below. 
     In order to provide corona discharge resistance and electrically isolate the conductive core  300 , an insulating polymer layer  350  may be provided thereabout. The insulating polymer layer  350  may be of a variety of polymer types conventionally used for electrically insulating winding or magnet wires and provided in a variety of manners. For example, where the motor winding wire  201  is larger than about 18 gauge, the insulating polymer may be extruded to more than about 2 mils in thickness over the core  300  to form the layer  350 . Alternatively, for smaller winding wire  201 , an enamel coating or varnishing process may be employed to provide less than about 2 mils of insulating polymer over the core  300 , thereby forming the insulating polymer layer  350 . Additionally, other techniques for providing the layer  350  may be employed such as use of an adhesive tape form of the insulating polymer, with the adhesive type selected based on downhole temperature extremes likely to be encountered within the well  180 . 
     Materials for the insulating polymer layer  350  when provided by extrusion or in the form of a polymer tape may include a polyimide, polyester, polyesterimide, polyamide-imide, polyamide, poly-ether-ether-ketone, polyethylene terephthalate, polyphenylene sulfide, and a self-reinforced polyphenylene. Alternatively, where the above described technique of varnishing is employed, the insulating polymer layer  350  may more preferably be a polymeric imide, ester, ester-imide, ester-amide, amide-imide, urethane or an epoxy. Additionally, the polymeric or epoxy material may be filled with nano-scale particles configured to improve durability and/or insulating characteristics of the insulating polymer layer  350 . 
     Continuing with reference to  FIG. 3 , with added reference to  FIGS. 1 and 2 , the insulating polymer layer  350  may provide sufficient electrical insulation and corona discharge protection. However, an additional moisture resistant outer polymer layer  375  may be provided over the insulating polymer layer  350  so as to prevent contaminants  110  such as moisture from reaching the insulating polymer layer  350 . In this manner, an insulating polymer may be selected for the underlying insulating polymer layer  350  without significant concern over contaminants  110  within the well  180 . In particular, the material for the insulating polymer layer  350  may be selected without significant concern over hydrolytic degradation thereof. That is, the outer polymer layer  375  may be configured to shield the insulating polymer layer  350  from moisture within the well  180 . Thus, electrically insulating polymers, perhaps even those otherwise susceptible to hydrolytic degradation upon exposure to moisture, may nevertheless be employed in forming the insulating polymer layer  350 . As a result, a greater degree of flexibility may be exercised in selecting the proper insulating polymer for electrical isolation of the underlying core  300 . 
     In addition to shielding the underlying insulating polymer layer  350 , the outer polymer layer  375  may be configured without significant regard to providing electrical insulation to the core  300 . Thus, polymers for the outer polymer layer  375  may be selected with focus on moisture resistance, corrosive chemical resistance or other contaminant shielding characteristics. 
     In one embodiment, the outer polymer layer  375  may be particularly configured based on downhole temperatures within a well  180  such as that of  FIGS. 1 and 2 . For example, the outer polymer layer  375  may be configured to withstand high-temperature downhole conditions exceeding about 300° C. In such an embodiment, the outer polymer layer  375  may be configured of a fluoropolymer. For example, an ethylene-tetrafluoroethylene copolymer may be employed, perhaps amended with an adhesive functional group to promote adhesion to the insulating polymer layer  350  may be employed. Maleic anhydride, acrylic acid, carboxyl acid, or silane, may serve as such an adhesive group. Other suitable high temperature resistant materials for the outer polymer layer  375  may include polychlorotrifluoroethylene or ethylene chlorotrifluoroethlyene which may similarly be amended with an adhesive group as described. Additionally, perfluoroalkoxy resin, fluorinated ethylene propylene copolymer, polytetrafluoroethylene, expanded-polytetrafluoroethylene (ePTFE), and any improved fluoropolymers may be employed to form the outer polymer layer  375 . 
     In another embodiment, the outer polymer layer  375  may be configured for lower temperature applications at below about 300° C. and of a polyolefin such as polyethylene, polypropylene, ethylene-propylene copolymer, poly(4-methyl-1-pentene), and a polyolefin elastomer. Again, these materials may be amended with maleic anhydride, acrylic acid, carboxyl acid, silane or other suitable material to promote adhesion to the underlying electrically insulating polymer layer  350 . 
     As with the insulating polymer layer  350 , a variety of techniques may also be employed to deliver the outer polymer layer  375 . That is, depending on wire sizing, the outer polymer layer  375  may be extruded, perhaps even co-extruded with the insulating polymer layer  350 . In one embodiment the outer polymer layer  375  is processed down to about 1 mil following the extrusion. Alternatively, the outer polymer layer  375  may be sintered over the insulating polymer layer  350  by conventional techniques. Additionally, an adhesive tape form of the outer polymer may be employed to provide the outer polymer layer  375  over the insulating polymer layer  350 . 
     Referring now to  FIG. 4 , an alternate embodiment of a motor winding wire  400  is depicted. Of particular note is the fact that the wire  400  includes an additional tie layer  465  disposed between its outer polymer layer  480  and its insulating polymer layer  450 . The tie layer  465  may be employed to serve as an adhesive layer between the outer polymer layer  480  and underlying insulating polymer layer  450  so as to ensure adequate bonding therebetween. As detailed below, the tie layer  465  may be particularly advantageous in maintaining such a bond given the different types of materials employed for the outer polymer layer  480  versus the underlying insulating polymer layer  450 . Ensuring adequate bonding in this manner may be beneficial to the performance and life of an electric motor  125  in a harsh downhole environment such as that of  FIG. 1 . 
     Continuing with reference to  FIG. 4 , the insulating polymer layer  450  may be configured for electrically insulating a conductive core  425  of the wire  400 . Thus, the insulating polymer layer  450  may be made of materials such as those detailed above for the insulating polymer layer  350  of the motor wire  201  of  FIGS. 2 and 3 . Additionally, the outer polymer layer  480  may be configured to provide contaminant resistance to the underlying portions of the wire  400 , for example, to moisture. Thus, again, the materials employed for the outer polymer layer  480  may be those detailed above with reference to the outer polymer layer  375  of the wire  201  of  FIGS. 2 and 3 . However, given the generally different purposes of the insulating polymer layer  450  as compared to the outer polymer layer  480 , the tie layer  465  may be provided to ensure adequate bonding of the layers  450 ,  465 ,  480  to one another. 
     Continuing with reference to  FIG. 5 , an enlarged view of section  5 - 5  of  FIG. 4  is depicted. In particular, the tie layer  465  is shown between the outer polymer layer  480  and the insulating polymer layer  450  as described above. So as to ensure compatibility and bonding to both the other layers  450 ,  480 , the tie layer  465  is made up of a main chain or base polymer of one of the adjacent layers  450 ,  480  with a functional group  500  disbursed therein having an adhesive character relative to the other of the layers  450 ,  480 . In this manner, the base polymer of the tie layer  465  may provide for adhesion of one adjacent layer  450 ,  480  to the tie layer  465  while the functional group  500  provides adhesion to the other. 
     A variety of base polymers may be employed for the tie layer  465  depending on the materials of the adjacent insulating polymer layer  450  and outer polymer layer  480 . For example, polyethylene, polypropylene, ethylene-propylene copolymer, poly(4-methyl-1-pentene), ethylene-tetrafluoroethylene copolymer, ethylene fluorinated ethylene-propylene terpolymers, polychlorotrifluoroethylene, ethylene chlorotrifluoroethlyene, as well as a host of other fluoropolymers may be employed as the base polymer of the tie layer  465 . Maleic anhydride, acrylic acid, carboxyl acid, silane or other suitable functional group  500  may similarly be employed to serve as an adhesive relative to one of the layers  450 ,  480  adjacent the tie layer  465 . 
     By way of example, with reference to the above listed material choices for the tie layer  465 , one embodiment of a motor winding wire  400  as depicted in  FIG. 4  may include an electrically insulating polymer layer  450  of polyamide material whereas the contaminant resistant outer polymer layer  480  may be of ethylene-tetrafluoroethylene copolymer. In such an embodiment, the tie layer  465  may be made up of ethylene-tetrafluoroethylene copolymer as its base polymer for adhesion to the outer polymer layer  480 . In this example a functional group  500  of, for example, maleic anhydride may be present throughout the tie layer  565  as depicted in  FIG. 5  to provide adhesion to the underlying insulating polymer layer  450 . 
     Continuing with reference to  FIGS. 4 and 5 , manufacture of the depicted motor winding wire  400  may be according to techniques described above relative to the insulating polymer layer  450  and the outer polymer layer  480 . Providing of the intervening tie layer  465  is preferably achieved by extrusion. In fact, in one embodiment each of the layers  450 ,  465 ,  480  is simultaneously co-extruded about the conductive core  425  to form the wire  400 . 
     Referring now to  FIG. 6 , an embodiment of a contaminant resistant electrically driven assembly  600  in the form of an ESP is depicted within a well  680  at an oilfield  645 . The well  680  is positioned below conventional surface equipment  625  at the oilfield  645  and equipped with a casing  650  traversing various portions  655 ,  660  of a formation. The well  680  ultimately provides access to a production region  675  where the ESP assembly  600  may be positioned for long term operation exceeding about 2 years and perhaps throughout the productive life of the well  680 . 
     Resistance to moisture, harsh chemicals, and other potential contaminants  610  is provided to motor winding wires of the ESP assembly  600  according to configurations and techniques detailed above. Thus, in spite of the potentially harsh moisture rich downhole conditions, embodiments of the ESP assembly  600  may be left in place without undue concern over the possibility of pump failure. In this manner, expenses associated with well shut down and pump replacement may generally be avoided. 
     Embodiments described hereinabove include motor winding wires, which, in spite of limited dimension, may be provided with adequate electrical insulating along with sufficient polymer shielding so as to allow for their direct exposure to moisture and other hydrocarbon contaminants without undue risk of premature failure. In fact, equipment employing such motor winding wires may be positioned downhole in a hydrocarbon well and operated continuously for the substantial life of the well without serious concern over equipment breakdown due to motor winding wire failure. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 High Strength Toughened 
               
               
                   
                 Polyimide (PI) 
                 Fluoropolymer (ePTFE) 
               
               
                   
                 enameled wire on 
                 coating over PI enameled 
               
               
                 Test* 
                 31 AWG copper 
                 wire on 31 AWG copper 
               
               
                   
               
             
             
               
                 Outer Diameter, inch 
                 0.011″ 
                 0.012″ 
               
               
                 Wall thickness (PI/HSTF)  
                 (0.001″ PI wall) 
                 (0.001″ PI/0.0005″  
               
               
                   
                   
                 HSTF wall) 
               
               
                 Breakdown voltage in 5% 
                 70 VAC 
                 1000 VAC 
               
               
                 Salt in Water Solution 
                   
                   
               
               
                 Cut through resistance, N 
                 33 
                 33 
               
               
                 Scrape abrasion, cycles 
                 118 cycles 
                 218 cycles 
               
               
                   
               
               
                 *Test results for 6 specimen average value 
               
             
          
         
       
     
     The preceding description has been presented with reference to presently preferred embodiments. However, other embodiments not detailed hereinabove may be employed. For example, a motor winding wire constructed of materials and according to techniques detailed hereinabove may be employed in conjunction with powering of a downhole tractor, powered centralizer, perforation gun, sampling or other oilfield tools aside from an ESP. Persons skilled in the art and technology to which these embodiments pertain will appreciate that still other alterations and changes in the described structures and methods of operation may be practiced without meaningfully departing from the principle, and scope of these embodiments. Furthermore, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.