Abstract:
A motor protection system that utilizes a motor protector in combination with a submersible motor. The motor protector allows for the free flow of an internal lubricating liquid therethrough to the connected submersible motor. The internal liquid prevents the migration of surrounding, environmental liquids to the interior of the motor while allowing the internal pressure of the motor to equalize with external pressure. Additionally, the design allows the use of a power cable connector that can be coupled to the submersible motor without being sealed with respect to the environmental fluids.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the protection of submersible motors that are utilized in systems, such as electric submersible pumping systems, that are submersed in a fluid during operation. 
     BACKGROUND OF THE INVENTION 
     A variety of systems are used in the production of fluid from subterranean locations, tanks and other structures that compel the use of submersible systems. For example, a variety of electric submersible pumping systems are used in wellbores to pump petroleum-based fluids. 
     In a typical system, a pump is powered by a submersible motor. A motor protector is coupled to the submersible motor to allow for pressure equalization between the interior of the motor and the exterior. For example, if the system is utilized deep within a wellbore, the pressure acting on the interior of the motor must be allowed to substantially equalize with the increasing external pressure incurred as the system is moved deeper into the wellbore. Conventional motor protectors utilize labyrinths, isolation chambers, expandable bags and other types of barriers that permit equalization of pressure without allowing external fluid to move into the motor. Thus, the motor is allowed to undergo pressure equalization without contamination of its internal lubricating oil 
     Apart from the motor protector, other potential avenues for entry of external fluids into the motor interior are blocked by seals. For example, a power cable typically is routed through an external housing of the motor to provide power to the motor. The power cable is routed through a connector that is securely sealed to the motor housing. Typically, elastomeric seals are used to facilitate sealing of these and other connections. However, elastomeric seals are susceptible to pressure differentials as well as to certain of the corrosive elements often found in locations wherein submersible pumping systems are utilized. 
     The present invention addresses these and other drawbacks of current systems. 
     SUMMARY OF THE INVENTION 
     The present invention relates generally to a motor protection technique. The technique utilizes a motor protector having a free flow path from an upper region of the motor protector to the interior of the submersible motor. Thus, a lubricating liquid may be placed inside the motor protector and allowed to freely flow into and throughout the interior of the submersible motor. The system obviates the need for complex obstructions or flow inhibiting passageways that prevent movement of external fluids to the interior of the submersible motor. A common fluid deployed within both the motor protector and the submersible motor is designed to prevent mixing or migration of the wellbore fluid through the motor protector to the submersible motor. 
     According to another aspect of the present invention, a power cable connector is coupled to the submersible motor to permit electrical coupling of a power cable to the motor. The power cable connector comprises a flow passage that permits the flow of liquid between motor protector, submersible motor and power cable connector. In one embodiment, the power cable connector comprises an isolation tube that extends along the motor protector. Although both the motor protector and the isolation tube are exposed to the external environment, the lubricating liquid disposed within prevents migration of environmental fluids to the interior of the submersible motor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
     FIG. 1 is a front elevational view of an exemplary pumping system deployed in an exemplary environment, according to one embodiment of the present invention; 
     FIG. 2 is a partial cross-sectional view taken generally along the axis of an exemplary motor protector and the top of a submersible motor, similar to those illustrated in FIG. 1; and 
     FIG. 3 is a view similar to FIG. 2 illustrating one exemplary approach to filling the system with a desired lubricating liquid. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Although the present invention is described with reference to a specific embodiment utilized in a specific environment, this description should not be construed as limiting. The motor protection system can be utilized with a variety of pumping systems as well as other systems that may be powered by or benefit from the incorporation of a submersible motor. Similarly, the technique can be used in a variety of environments other than the exemplary subterranean, wellbore environment described. The specific embodiment and environment illustrated and described is used to facilitate an understanding of the invention rather than to limit the invention. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims 
     Referring generally to FIG. 1, an exemplary electric submersible pumping system  10  is illustrated. The exemplary system comprises at least a submersible pump  12 , such as a centrifugal pump, a submersible motor  14  and a motor protector  16 . 
     Pumping system  10  is designed for deployment in a well  18  within a geological formation  20  containing desirable production fluids, such as petroleum. In a typical application, a wellbore  22  is drilled and lined with a wellbore casing  24 . Wellbore casing  24  may comprise a plurality of openings  26 , commonly referred to as perforations, through which a production fluid  27  flows into wellbore  22  from the environment surrounding submersible motor  14  and motor protector  16 . Electric submersible pumping system  10  is deployed in wellbore  22  by a deployment system  28  that may have a variety of configurations. For example, deployment system  28  may comprise tubing  30  connected to pumping system  10  by a connector  32 . 
     Power is provided to submersible motor  14  via a power cable  34  which is coupled to submersible motor  14  by a power cable connector  36 . Connector  36  has an isolation tube  38  extending generally along the exterior of motor protector  16  towards an upper region of the protector. Once powered, motor  14  actuates submersible pump  12  which, in turn, draws production fluid  27  into wellbore  22  and through a pump intake  40 . The submersible pump  12  then produces the fluid to a desired location, e.g. the surface of the earth, via tubing  30 . 
     In the system illustrated, motor protector  16  and submersible motor  14  are filled to a desired level with a lubricating fluid that may freely flow downward through motor protector  16  and into an interior  42  of submersible motor  14 , as illustrated in FIGS. 2 and 3. Motor protector  16  is designed to provide a free flow path  43  through the interior of the motor protector to interior  42  of submersible motor  14 . Thus, submersible motor  14  and motor protector  16  may be filled simply by pouring the desired liquid into an upper region  44  of motor protector  16 . 
     Free flow path  43  also may be continued through power cable connector  36  and its isolation tube  38 . Thus, if a desired liquid is poured into upper region  44  of motor protector  16 , the liquid is free to move downwardly through motor protector  16  into interior  42  of submersible motor  14  and ultimately upwardly through power cable connector  36  and its isolation tube  38  until the fluid level in motor protector  16  and isolation tube  38  reaches a substantially equal level. Accordingly, it is not necessary to seal power cable  34  to submersible motor  14  as it enters motor  14  (at a point of entry location  46 ) through an outer housing  48  of submersible motor  14 . 
     Although a variety of components may be utilized in forming the motor protection system described above, the specifics of one exemplary design is described with reference to FIGS. 2 and 3. In this embodiment, a motor protection system  50  comprises motor protector  16  coupled to submersible motor  14  via a motor protector mounting end  52  attached to a motor coupling end  54  by, for example, appropriate fasteners  56 . Also, motor protection system  50  may comprise power cable connector  36  coupled to outer housing  48 . In this embodiment, power cable connector  36  is coupled to submersible motor  14  via an unsealed connection and without elastomeric seals. By way of example, the connector may be attached to outer housing  48  via a metal-to-metal connector  58 , such as a Swedgelock connector. Other exemplary forms of connection comprise formation of a welded or threaded connection between power cable connector  36  and submersible motor  14 . 
     The exemplary motor protector  16  comprises a shaft segment  60  that is coupled to a corresponding shaft segment (not shown) of submersible motor  14  as known to those of ordinary skill in the art. Shaft  60  is rotatably mounted in an upper protector head  62  via an upper bushing  64 . A shaft seal  66  prevents particulates and other solids from moving downwardly along shaft  60 . Additionally, a vent port  68  extends between upper region  44  and an isolation chamber region  70 . (It should be noted that region  44  is exposed to the environment surrounding motor protector  16  via appropriate parts or openings as with a conventional motor protector.) Isolation chamber  70  is formed as an annular space between an upper shaft tube  72  and an outlying upper isolation chamber housing  74  that forms an outer wall of motor protector  16 . 
     Upper isolation chamber housing  74  is attached to protector head  62  by, for example, threaded engagement and/or an appropriate weldment. At a lower end, isolation chamber housing  74  is similarly coupled to an intermediate support body  76  by, for example, appropriate threaded and/or welded engagement. 
     Intermediate support body  76  rotatably receives shaft segment  60  and supports the shaft via an internal bushing  78 . Additionally, a shaft tube support ring  80  is positioned to couple upper shaft tube  72  to intermediate support body  76 . A communication port  82  extends generally longitudinally through intermediate support body  76  to permit fluid flow through support body  76  between upper isolation chamber  70  and a lower isolation chamber  84 . 
     Lower isolation chamber  84  generally comprises an annular chamber defined between a lower shaft tube  86  and an outlying lower isolation chamber housing  88 . As described above with respect to upper isolation chamber housing  74 , lower isolation chamber housing  88  is connected to intermediate support body  76  and extends downwardly to a lower support body  90 . Housing  88  is connected to support body  90  by, for example, an appropriate threaded and/or welded connection. 
     Lower support body  90  rotatably receives shaft segment  60  and supports rotation of the shaft via a bushing  92 . Additionally, a lower shaft tube support ring  94  couples lower shaft tube  86  to an upper portion of support body  90 , as illustrated. Lower support body  90  also comprises a generally longitudinal communication port  96  that allows the free flow of liquid therethrough. A breather-stand tube  98  may be coupled to lower support body  90  in fluid communication with communication port  96  and extending upwardly therefrom. Breather tube  98  inhibits the ability of particulate matter to migrate through lower support body  90  to lower components. Thus, if sand or other particulate matter manages to move into lower isolation chamber  84 , the particulates tend to collect along the upper surface of lower support body  90  instead of passing through communication port  96 . 
     In the embodiment illustrated, a thrust bearing system  100  is disposed below lower support body  90 . According to one exemplary embodiment, thrust bearing system  100  comprises a thrust bearing locking ring  102  positioned between lower support body  90  and an upthrust bearing  104 . A thrust bearing runner  106  is disposed below upthrust bearing  104 , and a downthrust bearing  108  is disposed between thrust bearing runner  106  and a lower protector base  110 . Thrust bearing system  100  can be any of a variety of thrust bearing types that are commonly used in submersible pumping components. 
     Lower protector base  110  rotatably receives shaft segment  60  and supports the shaft segment via a bushing  112 . Additionally, a communication port  114  extends through lower protector base  110  from thrust bearing system  100  to motor protector mounting end  52 . Communication port  114  permits the flow of internal liquid into interior  42  of submersible motor  14 . It should be noted that the flow of liquid is not restricted through thrust bearing system  100 , so liquid is permitted to freely flow from communication port  96  through thrust bearing system  100  and then downwardly into submersible motor  14  via communication port  114 . Thus, a free flow passage is formed from upper region  44  of motor protector  16  through vent port  68 , isolation chamber  70 , communication port  82 , lower isolation chamber  84 , communication port  96 , thrust bearing system  100  and communication port  114  to interior  42  of submersible motor  14 . 
     Depending on the specific design of motor protection system  50 , the free flow of internal liquid may be allowed to continue through power cable connector  36  and its isolation tube  38 . In the illustrated embodiment, power cable  34  is secured within power cable connector  36  via an epoxy  116  or other comparable material to anchor the power cable and to provide strain relief with respect to its connection to submersible motor  14 . However, a breather tube  118  extends longitudinally through epoxy  116  to permit the flow of liquid therethrough. Isolation tube  38  includes an upper open end or port  120  that permits direct communication between the interior of isolation tube  38  and the environmental fluid that surrounds submersible motor  14  and motor protector  16 . 
     To prevent potentially deleterious environmental fluids from reaching interior  42  of submersible motor  14 , motor protection system  50  is filled to an operational level with a desired internal liquid  122 . Internal liquid  122  is selected for its ability to prevent migration of environmental fluid, such as wellbore fluids, through motor protector  16  and/or power cable connector  36  to the interior of submersible motor  14 . Otherwise, the wellbore fluids could cause excessive wear and other to damage internal components of the motor. 
     Internal liquid  122  may be selected for its lack of affinity with the surrounding environmental fluids. In the example illustrated, motor protector system  50  is utilized in a wellbore environment for the production of oil-based fluids. Accordingly, internal liquid  122  may be selected for its inability or limited ability to mix with oil-based fluids. Additionally, internal liquid  122  typically is selected with a greater specific gravity than the surrounding fluids. For example, wellbore fluids may have a specific gravity of approximately 0.8 or less. Accordingly, internal liquid  122  is selected such that its specific gravity is greater than approximately 1.0, and for many applications the specific gravity is greater than approximately 1.5. Thus, the internal liquid  122  is substantially heavier than the surrounding environmental fluids, and the surrounding environmental fluids are unable to move downwardly through isolation tube  38  or motor protector  16  to submersible motor  14 . 
     By way of specific example, internal liquid  122  may be a relative heavy polytetrafluoroethylene (PTFE)-based liquid. Such liquids do not mix with the typical fluid components found in a wellbore environment. A specific example of such a liquid is a PTFE-based liquid referred to as Uniflor available from Nye Lubricants Company. The liquid is a lubricating liquid rated ISO 500 with a specific gravity of approximately 1.9. This type of liquid is substantially heavier (i.e., a greater specific gravity) than the surrounding oil-based fluids. Also, because the lubricant is not oil-based, the wellbore fluids do not mix with the internal liquid  122 . 
     In an exemplary application, internal liquid  122  is poured into upper region  44  of motor protector  16  and the liquid flows downwardly through motor protector  16 . The liquid fills interior  42  of submersible motor  14  and rises through power cable connector  36  until the system is filled to a desired level, labeled with reference numeral  124  in FIG.  3 . The remainder of motor protector  16  and isolation tube  38  may be filled with a less expensive, sacrificial liquid that is typically lost during deployment and initial startup of the system. However, internal liquid  122  also could be used to fill motor protector  16  and isolation tube  38  to a higher level. Once motor protector  16  is filled to desired level  124 , the remaining components of electric submersible pumping system  10  are connected and the submersible pumping system  10  is deployed to a desired location within wellbore  22 . Both the natural heat of the subterranean location and the heating of motor during initial operation causes internal liquid  122  to heat and expand to a higher level, labeled  126  in FIG.  3 . Excess liquid, e.g. a sacrificial liquid, is expelled through upper open end  120  of isolation tube  38  and/or upper region  44  of motor protector  16  into the surrounding environment. 
     When submersible motor  14  is shut down, the heavier internal liquid  122  cools and the fluid level moves downwardly to an intermediate level, labeled as level  128  in FIG.  3 . Thus, even though internal liquid  122  is free to flow through the entire extent of motor protector  16  and submersible motor  14 , deleterious environmental fluids are not able to migrate into submersible motor  14 . If power cable connector  36  is utilized, a free flow path  43  is created throughout motor protector  16 , submersible motor  14 , and power cable connector  36 , including isolation tube  38 , without incurring migration of unwanted fluids into submersible motor  14 . The use of this system allows not only the elimination of complex flow inhibiting devices within motor protector  16 , but also the elimination of elastomeric seals otherwise used to form fluid-tight seals at various junctions, such as at the juncture of power cable  34  with submersible motor  14 . 
     It will be understood that the foregoing description is of exemplary embodiments of this invention, and that the invention is not limited to the specific forms shown. For example, the motor protection system may be utilized with a variety of motor types, in a variety of applications and submerged within various environmental fluids. Additionally, the size and shape of the motor protector, submersible motor and power cable connector can be changed according to the specific application or desired design parameters. The number and configuration of support bodies, longitudinal ports, bushings and other components internal to the motor protector also can be changed. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims.