Abstract:
Systems and methods for providing seals around the motor leads and other conductors in ESP&#39;s. In one embodiment, elastomeric boot seals are positioned within annular spaces around motor leads in an ESP motor. When the motor is filled with dielectric oil, the elastomeric material of the boot seals absorbs some of the oil and swells. High temperatures may also cause the material of the seals to expand. Retainers which are not subject to swelling are positioned around the boot seals, thereby preventing the boot seals from expanding away from the leads. The retainers thereby maintain the seal of the boot seals against the motor leads.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates generally to power subsystems for downhole equipment such as electrical submersible pumps (ESP&#39;s), and more particularly to means for improving the effectiveness of sealing components in downhole equipment that are exposed to high temperatures and dielectric oils. 
         [0003]    2. Related Art 
         [0004]    Downhole equipment such as ESP systems are commonly installed in wells for purposes of producing fluids (e.g., oil) from the wells. Power suitable to drive the equipment is produced at the surface of the wells and is delivered to the equipment via power cables that extend into the wells. The power cables may have one or more electrical junctions, such as splices to motor leads and “pothead” connectors that couple the power cable to the downhole equipment. 
         [0005]    The motor of an electric submersible pump is commonly connected to the power cable through a pothead connection. The motor typically has one or more terminals which extend through an insulating block in the motor housing so that a pothead connector can be coupled to the terminals. On the interior of the motor, the terminals are connected to leads which are in turn connected to the windings of the motor. 
         [0006]    The interior of the motor is often filled with dielectric oil. This oil has lubricating, cooling and electrically insulating properties. Insulating boots are usually installed around the motor leads at the interior end of the insulating block. These boots provide a seal around the leads and prevent particles which are suspended in the oil from getting between the motor leads in the insulating block. The boots, however, are made of elastomeric materials that typically swell when exposed to their dielectric oil, resulting in gaps between the boots and the motor leads which impairs their functionality. 
         [0007]    It would be desirable to provide improved means for manufacturing and installing boot-type seals so that the problems associated with swelling of the elastomeric seals are reduced or avoided. 
       SUMMARY OF THE INVENTION 
       [0008]    Embodiments of the present invention include systems and methods for sealing around the motor leads and other conductors, wherein elastomeric boot seals are positioned within annular spaces, and retainers which are not subject to swelling resulting from exposure to the electric oil are positioned around or within the boot seals to prevent dimensional changes in the boot seals which would otherwise result in gaps between the boots and corresponding sealing surfaces. 
         [0009]    In one embodiment, an improved boot seal for use in downhole equipment is provided. In this embodiment, an annular boot seal is made of elastomeric material. The boot seal is configured to fit around an insulated conductor, so that the inner diameter of the boot seal fits snugly against the insulated conductor. The outer diameter of the boot seal is configured to fit snugly within an opening in a housing of the downhole equipment. A groove is provided in the outer diameter of the boot seal to accommodate a boot seal retainer. The boot seal retainer is made of a material that does not significantly expand when exposed to dielectric oil at high temperatures. When the boot seal is installed in a piece of downhole equipment and the equipment is operated, the elastomeric material of the seal may swell, but the boot seal retainer will provide hoop strength that prevents the inner diameter of the boot seal from expanding and leaving a gap between the boot seal and the insulated conductor around which it is installed. 
         [0010]    In an alternative embodiment, a motor for an ESP system is configured to enable a pothead connector to be attached to the motor. The motor housing includes a head portion that accommodates an insulation block in which a set of terminals are installed. The terminals are connected to motor leads that extend into the interior of the motor. On the interior side of the insulation block, an annular elastomeric boot seal is installed around each of the motor leads. An annular boot seal retainer is positioned around the boot seal to prevent the inner diameter of the boot seal from expanding away from the outer diameter of the motor lead when the elastomeric material of the boot seal swells from exposure to dielectric oil in the motor. 
         [0011]    Another alternative embodiment may comprise installing one or more elastomeric boot seals around insulated conductors in a motor for an ESP system, and installing boot seal retainers around each of the boot seals. The motor is then filled with dielectric oil and operated, wherein when the elastomeric material of the boot seals swells from exposure to dielectric oil in the motor at high temperatures, the boot seal retainers prevent the boot seals from expanding away from the insulated conductors. 
         [0012]    Numerous other embodiments are also possible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Other objects and advantages of the invention may become apparent upon reading the following detailed description and upon reference to the accompanying drawings. 
           [0014]      FIG. 1  is a diagram illustrating an exemplary ESP system in accordance with one embodiment. 
           [0015]      FIG. 2  is a diagram illustrating the structure of a pothead connection at the top of an ESP motor in accordance with one embodiment. 
           [0016]      FIG. 3  is a perspective view of the interior of a motor head showing boot seals with boot seal retainers installed around motor leads from the pothead connection. 
           [0017]      FIG. 4  is a cross-sectional view of the structure of the male terminal assembly of the pothead connection of the motor head. 
       
    
    
       [0018]    While the invention is subject to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and the accompanying detailed description. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular embodiment which is described. This disclosure is instead intended to cover all modifications, equivalents and alternatives falling within the scope of the present invention. Further, the drawings may not be to scale, and may exaggerate one or more components in order to facilitate an understanding of the various features described herein. 
       DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0019]    One or more embodiments of the invention are described below. It should be noted that these and any other embodiments described below are exemplary and are intended to be illustrative of the invention rather than limiting. 
         [0020]    In one embodiment, a motor for an ESP system is configured to enable a pothead connector to be attached to the motor, thereby providing an electrical path for power to be supplied to the motor. The motor housing includes a head portion that is configured to accommodate an insulation block. The insulation block has a set of terminals installed therein which are configured to mate with corresponding terminals of a pothead connector. The terminals are connected to motor leads that extend to the windings of the stator within the motor housing. On the interior side of the insulation block (the side exposed to the interior of the motor housing), an elastomeric boot seal is installed around each of the motor leads. Each boot seal is generally annular, and is positioned in a gap between the corresponding motor lead and the insulation block. An annular boot seal retainer is positioned around the boot seal to prevent the inner diameter of the boot seal from expanding away from the outer diameter of the motor lead. 
         [0021]    Referring to  FIG. 1 , a diagram illustrating an exemplary ESP system in which one embodiment of the present invention may be installed is shown. In this embodiment, an ESP system is installed in a well for the purpose of producing oil, gas or other fluids. An ESP  120  is coupled to the end of tubing string  150 , and the ESP and tubing string are lowered into the wellbore to position the ESP in a producing portion of the well (as indicated by the dashed lines at the bottom of the wellbore). Surface equipment that includes a drive system  110  is positioned at the surface of the well. Drive system  110  is coupled to ESP  120  by power cable  112 , which runs down the wellbore along tubing string  150 . Tubing string  150  and power cable  112  may range from less than one thousand feet in a shallow well, to many thousands of feet in a deeper well. 
         [0022]    ESP  120  includes a motor section  121 , seal section  122 , and pump section  123 . ESP  120  may include various other components. Motor section  121  is operated to drive pump section  123 , thereby pumping the oil or other fluid through the tubing string and out of the well. Drive system  110  produces power (e.g., three-phase AC power) that is suitable to drive motor section  121 . This output power is provided to motor section  121  via power cable  112 . 
         [0023]    Power cable  112  extends downward along the tubing string from the drive unit at the surface of the well to a point near the ESP. At this point (typically 10-50 feet above the ESP), the primary cable is connected to the motor lead by a splice  111 . The motor lead extends from the primary cable to the motor, and is connected to the motor by a pothead connector  113 . Pothead connector  113  is mated with a set of power terminals of the motor, and the pothead connector is secured to the motor housing. 
         [0024]    Referring to  FIG. 2 , a cutaway view of the motor at the pothead connection is shown. The illustrated structures are exemplary, and may differ from one embodiment to another. In this embodiment, motor lead  210  is coupled to pothead connector  220 , which is secured to motor head  230 . A single one of the conductors of motor lead  210  is depicted in the figure. 
         [0025]    The insulated conductor  215  passes through the body of pothead connector  220  and is connected to a conductive female terminal  222 , which is positioned at a lower or motor end of the pothead connector. Female terminal  222  is configured to mate with a male terminal  231 , which is installed in an insulating block  233  which is installed in motor head  230 . Male terminal  231  is electrically coupled to internal motor lead  232  of the motor. A boot seal  234  is installed around motor lead  232  in a gap between insulating block  233  and motor head  230 . 
         [0026]    Referring to  FIG. 3 , a perspective view of the interior of the motor head is shown. Motor head  230  is viewed from the lower end, and is shown disconnected from the remainder of the motor housing. It can be seen in this figure that the three motor leads (e.g.,  232 ) extend from insulating block  233  into the interior of motor head  230 . Each of the motor leads (e.g.,  232 ) has a corresponding boot seal (e.g.,  234 ) installed around it, between the motor lead and motor head  230 . 
         [0027]    Referring to  FIG. 4 , a cross-sectional view of the structure of the terminal assembly is shown in more detail. As noted above, insulation block  233  is installed in an opening in motor head  230 . An annular external seal  228  is positioned between insulation block  233  and motor head  230  at the exterior of the motor head. Boot seal  234  is installed at the interior of the motor head. Boot seal  234  is positioned around insulated conductor  232  and extends between insulation block  233  and motor head  230 . 
         [0028]    The interior ( 420 ) of the motor is filled with dielectric oil. As the motor is operated, the presence of the dielectric oil and the elevated temperatures within the motor cause some of the oil to be absorbed by the elastomeric material of boot seal  234 , which results in swelling of the elastomeric material. In conventional systems, the swelling of the elastomeric material causes the inner diameter of the boot seal to increase. Because the outer diameter of insulated conductor  232  does not expand in the same manner as the boot seal, the swelling of the boot seal can create a gap between the boot seal and the insulated conductor, allowing the dielectric oil and particles within the oil to get between the boot seal and the insulated conductor. This can cause increased wear and degradation of the insulation around the conductor, which reduces the effective lifetime of the motor. 
         [0029]    In the present systems and methods, a boot seal retainer is provided to prevent the boot seal from expanding outward, away from the insulated conductor. In the embodiment of  FIG. 4 , an annular boot seal retainer  430  is installed around the portion of the boot seal that extends beyond the interior surface  421  of the motor head. In this case, boot seal  234  extends approximately ½ to 1 inch into the interior of the motor head from surface  421 . A groove is provided on the exterior of boot seal  234  to accommodate boot seal retainer  430 . In alternative embodiments, boot seal retainer  430  may be formed integrally with boot seal  234 . 
         [0030]    Boot seal retainer  430  is made of a material that does not swell or expand significantly in the presence of the dielectric oil and high temperatures within the motor. Boot seal retainer  430  provides increased hoop strength to boot seal  234 . In one embodiment, boot seal retainer  430  is made of a substantially rigid plastic, but other materials may be used in alternative embodiments. 
         [0031]    Because boot seal retainer  430  does not expand to a significant degree, it constrains the expansion of boot seal  234  away from insulated conductor  232  and thereby prevents a gap from forming between these components. In fact, because the elastomeric material of boot seal  234  cannot expand outward, the swelling of the material actually causes the inner diameter of the boot seal to shrink (the material expands inward). By preventing a gap from forming between boot seal retainer  430  and the insulated conductor  232 , the boot seal retainer helps to prevent debris in the dielectric oil from damaging the insulated conductor and/or insulation block  233 . 
         [0032]    As noted above, the foregoing embodiments are exemplary, and there may be many alternative embodiments of present invention. The alternative embodiments may have variations of the features described above. For instance, while the boot seals and retainers described above are installed in an ESP motor, they may be installed in other types of equipment as well. The boot seals and retainers may be installed around individual leads or groups of leads/conductors. Similarly, the steps of the methods disclosed herein may be varied (e.g., performed in an alternative order) in alternative embodiments. Numerous other variations may be made in other embodiments. 
         [0033]    The benefits and advantages which may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the claims. As used herein, the terms “comprises,” “comprising,” or any other variations thereof, are intended to be interpreted as non-exclusively including the elements or limitations which follow those terms. Accordingly, a system, method, or other embodiment that comprises a set of elements is not limited to only those elements, and may include other elements not expressly listed or inherent to the claimed embodiment. 
         [0034]    While the present invention has been described with reference to particular embodiments, it should be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions and improvements fall within the scope of the invention.