Abstract:
A chamber for use in a submersible pump assembly. The submersible pump assembly has a submersible motor which is connected to a power source and which will drive a submersible pump in the submersible pump assembly. A motor protector with expansion chamber is connected to the submersible motor. The expansion chamber and submersible motor are filled with motor oil. The expansion chamber has a housing and a reactant disposed in the housing interior for reacting with and reducing the concentration of contaminants present in the well fluid that are harmful to components of the motor protector.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a motor protector for oil-filled submersible electric motors and, more particularly, to a motor protector having a prolonged operational life and increased resistance to chemical attack. 
   A variety of fluids is pumped from subterranean zones with a variety of different types of pumps. In the production of petroleum, it is common to employ electric submersible systems for lifting the fluids collected in the well. Such systems generally include a submersible pump and a submersible oil-filled electric motor separated by a seal or protector assembly. The seal or protector functions, in part, to provide a reservoir of motor fluid in communication with the electric motor, to allow for thermal expansion and contraction of the motor fluid, and to keep the well fluid out of the motor. Well fluid generally comprises salt water, particulate solids and other contaminants that are deleterious to the motor. 
   There are two types of motor protectors commonly used in the field. One type is referred to as a bladder or bag protector. The bladder, positioned within the protector assembly housing, provides a positive barrier between the well fluid outside the bladder and the motor fluid within. It is made of an elastomeric material that flexes to provide a variable capacity chamber thus accommodating volume changes in the motor oil. Generally, a vent through the housing is utilized to allow entry and expulsion of well fluid between the housing interior and the well bore as required by the expansion and contraction of the elastomeric bladder. 
   The other common type of motor protector is normally referred to as a “labyrinth” type protector. The labyrinth design uses a series of cavities and vertical labyrinth paths to keep the well fluid and the motor fluid separated. The two fluids are in direct contact; therefore, the effectiveness of the device depends on the difference in specific gravity and the immiscibility between the well fluid and the motor fluid. The design allows for expansion and contraction of the motor fluid by providing a vent through the housing wherethrough well fluid can enter or be withdrawn from the adjacent cavity in response to changes in motor fluid volume. 
   The motor protectors are often used in combination. For example, one or more labyrinth-type protectors may be used above or below one or more bladder protectors. Usually, motor fluid in the bladder communicates directly with a passage to the motor. Therefore, a failure of the elastomeric material comprising the bladder creates a short path for well fluid subsequently penetrating the bladder to reach the motor. 
   The bladder is usually made of a high-temperature, high-performance elastomer that is resistant to the harsh conditions encountered downhole. However, there is still a need to reduce the chemical attack of well fluid contaminants or impurities on the elastomer and thus prolong the operational life of the bladder elastomer itself and ultimately the motor protector and submersible motor assembly. 
   SUMMARY OF THE INVENTION 
   The present invention is a motor protector for use in a submersible pumping system disposed in a well. The motor protector comprises a housing having a port therethrough for communicating a housing interior with the well. A reactant is disposed in the housing interior and will contact well fluid that is communicated into the housing interior. The reactant will react with the well fluid communicated into the housing interior. The motor protector may have an expansion chamber in communication with the motor to accommodate the expansion and contraction of the motor fluid in the motor. The expansion chamber may be defined by a barrier in the housing interior separating the well fluid from the motor fluid. Preferably the barrier is a flexible barrier, which may be referred to as a bladder, and more preferably the flexible barrier comprises an elastomer. The reactant may be, for example, but not limited to, a liner, preferably cylindrical, webbing, wool, mesh, and granules. Nonlimiting examples of suitable reactants include metallic copper, metallic zinc, elastomers and polymers. 
   Because the reactant is located in the housing such that the reactant is in contact with well fluid communicated into the housing, the reactant can react with or trap impurities in the well fluid that are harmful to, for example, the bladder before the impurities can migrate closer to the bladder. There are many impurities in the well fluid that are harmful to materials used in submersible pumping systems generally and to elastomeric bladder material particularly. Such impurities include hydrogen sulfide (H 2 S), amines, and dipolar gases such as carbon dioxide (CO 2 ). H 2 S aggressively corrodes most metal alloys and reacts with elastomeric bladder material to degrade the elastomer, eventually resulting in tearing or similar failure of the material. Amines, often intentionally added to the well fluid as a corrosion inhibitor, react with hydrofluorocarbon elastomers to produce a reactive grafted substitute that replaces the fluorine atoms. As a result, the chemical inertness of the fluoropolymer, and its ability to resist chemical attack, is reduced. In addition, important physical and mechanical properties can suffer. Dipolar gases such as CO 2  react similarly. 
   In one embodiment, the reactant comprises metallic copper and/or zinc. Metallic copper is well known for reacting with impurities such as hydrogen sulfide (H 2 S) to produce copper sulfide precipitate. 
   In another embodiment the reactant comprises a polymer or elastomer. Preferably, the elastomer or polymer is one that offers little resistance to amines, dipolar gases and H 2 S. In this manner, the elastomer or polymer can react with or consume the contaminant before it reaches the elastomer bladder. Reaction with even a portion of the contaminants will help to protect the motor and the bladder separating the motor oil from the well fluid. 
   The present invention can also be defined as a method for protecting a motor fluid of a motor submersed within a well from a well fluid, the method comprising separating the well fluid from the motor fluid and positioning the reactant in the housing interior so that it will react with and reduce the concentration of harmful contaminants in the well fluid. 
   The foregoing and other objects, advantages and features of the present invention will become apparent upon reading the following detailed description in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically shows a submersible pump assembly in a well. 
       FIG. 2  is a cross section of a motor protector of the current invention. 
       FIG. 3  is a cross section of another embodiment of the current invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings,  FIG. 1  schematically shows a production string  10  lowered into a well  12 . Well  12  typically includes a casing  14  cemented within a well bore  16 . An annulus  18  is defined between the casing  14  and the production string  10 . Well  12  intersects a subsurface producing formation  20  that may be communicated with the well  12  in any manner known in the art. In the embodiment shown, fluid  22  is produced from subsurface formation  20  and is communicated with the well  12  through perforations  24  in casing  14 . 
   Production string  10  may include production tubing  26  with a submersible pump assembly  28  connected to a lower end thereof. Submersible pump assembly  28  includes electric submersible pump  30  driven by an electric submersible motor  32 . 
   Electric submersible pump assembly  28  further includes an intake  34  connected at a lower end of submersible pump  30 . The current invention includes a motor protector  36  which in the embodiment shown is connected between intake  34  and electric submersible motor  32 .  FIG. 1  shows a typical placement of the motor, which is below the pump; however, it is sometimes desirable to locate the motor above the pump, in which case the motor protector will be positioned below the motor. 
   Referring to the drawings,  FIG. 2  shows a cross section of a motor protector for an electric submersible motor wherein the motor protector  36  comprises a bladder-type variable capacity chamber  38 , which may be referred to as an expansion chamber. The motor protector comprises a housing  40  defining a housing interior  42 . Housing  40  has an upper end  44  adapted to be connected to, for example, an intake  34  and a lower end  46  adapted to be connected to, for example, a submersible motor  32 . It is understood and well known in the art that the motor can also be positioned above the pump with motor protectors on either or both sides of the motor, and that the electric submersible pump  30  will be driven by the electric motor  32  with a shaft such as shaft  48 . Such submersible motors are filled with motor lubricating oil, which may be referred to as motor fluid. 
   Expansion chamber  38  comprises a bladder  52  in housing interior  42 . Bladder  52  defines a bladder interior  54  which contains motor fluid communicating with the motor. Bladder  52  acts as a barrier separating the motor fluid from the well fluid and is usually made of an elastomer. During operation, as the motor heats causing the motor oil to expand, the motor oil is communicated into bladder interior  54  causing the flexible elastomer bladder  52  to expand. As the motor oil cools and contracts, bladder  52  contracts communicating a portion of the motor fluid back to the motor. 
   As is known in the art, a fluid passage exists between the interior of motor  32  and the bladder interior  54  and generally will accommodate the expansion and contraction of motor oil and will also allow for the filling of the motor protector  36 . To accommodate expansion and contraction of the bladder, well fluid is communicated through port  56  out of and into housing interior  42 . The well fluid often contains contaminants that are harmful to the motor and to the elastomer that generally comprises bladder  52 . The concentration of these contaminants is reduced by causing at least a portion of the contaminants to contact and react with a reactant such as a cylindrical reactant liner  58 . The reactant can be located anywhere within the housing interior where it can contact the well fluid when well fluid is communicated into the housing. In this way the reactant can react with and reduce the concentration of contaminants before they reach, and harm the elastomer bladder and ultimately migrate toward the motor if the bladder degrades or is perforated. 
   The reactant may also be present as a webbing, wool, mesh or granules. In some forms, such as a webbing, wool or granules, it may be necessary to include a screen or support above and below the reactant to fix the reactant position and keep it from migrating from the desired position. 
   Contaminants that are particularly troublesome include hydrogen sulfide (H 2 S), amines, and dipolar gases such as carbon dioxide (CO 2 ). It is well known that H 2 S reacts with metals such as copper and zinc to form the respective metal sulfide precipitate. For example, during water treatment, dissolved hydrogen sulfide can be removed from the water by passing the water through granules of metallic copper, zinc or a copper-zinc alloy. Also, in the winemaking process, dissolved hydrogen sulfide is often removed from wine by passing the wine through a metallic copper wire screen or even by inserting several pennies in the wine-processing container. In both examples the dissolved hydrogen sulfide gas reacts with copper to gain electrons (reduction) while metallic copper from the reactant medium loses electrons (oxidation). The reaction product is a black copper sulfide precipitate which is harmless and easily removed from the water or wine. In the present invention, these metals are positioned within the motor protector as a liner, or another form as described above, in order to reduce the concentration of H 2 S in the well fluid contacting the elastomer bladder. 
   The concentration of amines, CO 2 , and other impurities harmful to the elastomer bladder material can be reduced using a sacrificial elastomer or polymer. Preferably the sacrificial elastomer or polymer is also in a form and location as described above. Although any polymer or elastomer can be used, those that are not recommended for typical use in environments with amines and polar compounds such as CO 2  will provide better sacrificial material. Any reduction in the concentration of these impurities will prolong the operating life of the bladder and ultimately the electric motor. Nonlimiting examples of commercial elastomers that can be used to trap amines and polar compounds such as CO 2  are nitrile rubber, polyacrylate, ethylene-propylene terpolymers and fluorocarbon elastomers. Preferably a polyacrylate or fluorocarbon elastomer is used. 
     FIG. 3  shows a cross section of a motor protector  59  comprising a labyrinth-type expansion chamber  60  within a housing  51 . During expansion, motor fluid is communicated from the motor into the motor protector through a lower inlet tube  62 . The motor fluid will pass upwardly through a flow tube  64 , a connecting conduit  66  which has an upper end  68  and a relief conduit  70 . Relief conduit  70  is open at upper end  72  and connected to a port  74  in the motor protector. 
   When the motor fluid expands during operation of the motor, motor fluid from the motor is communicated into lower inlet tube  62  through flow tube  64  and connecting conduit  66  and will be urged outwardly to port  74  through relief conduit  70 . When motor fluid contracts, well fluid will be drawn in through port  74  and fluid relief conduit  70 . 
   The housing interior  42  is divided into an upper labyrinth portion  76  and a lower labyrinth portion  78 . Because the well fluid will be heavier than the motor fluid in the housing interior, well fluid will settle in the lower labyrinth portion  78 . So long as the well fluid level in lower portion  78  remains below the level of the upper end  68  of the connecting conduit  66 , well fluid will not pass into a lower motor protector section  80  and potentially contaminate the motor. 
   However, since the motor fluid and well fluid are in direct contact at the interface, impurities in the well fluid can partition into the motor fluid according to equilibrium conditions. Such equilibrium partitioning is proportional to the concentration of impurities in the respective fluids. Inclusion of a reactant as previously described causes a reduction in the concentration of impurities due to reaction with the reactant. Reduction of the impurity level in the well fluid adjacent the motor fluid causes an equilibrium reduction of the impurity level in the motor fluid, and this results in a prolonging of the operating life of the submersible motor. 
   The reactant can be located anywhere within the housing interior where the reactant contacts well fluid. Preferably, the reactant is located as a liner  82 , or another form, such that the reactant is in contact with well fluid when well fluid is communicated into the housing in, for example, the labyrinth upper portion  76  or the housing interior  42  generally. 
   It is understood by those skilled in the art that expansion chambers and motor protectors can be modified from those described above and can be used singly or in series in any combination. Also the motor may be positioned above the protectors rather than below as was described. When multiple expansion chambers are used above the motor, the reactant is preferably located within the top expansion chamber since this chamber will generally have a port receiving well fluid; however, designs can vary. Preferably the reactant is positioned in a space within the motor protector that is normally filled with well fluid. 
   Thus, it is seen that the apparatus and methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for purposes of the present disclosure, numerous changes in the arrangement and construction of parts and steps may be made by those skilled in the art, which changes are encompassed within the scope and spirit of the present invention as defined by the appended claims.