Abstract:
A motor protector for use in protecting an electric motor in a subterranean environment. The motor protector utilizes a dual, flexible bladder system. One of the expandable bladders provides for the expansion and contraction of motor oil. The other expandable bladder contains a supply of neutralizing solution. The bladder filled with neutralizing solution cooperates with the bladder filled with motor oil to maintain the expandable bladder bathed in neutralizing solution. This prevents migration of corrosive agents into the motor oil.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to motor protectors for protecting submergible motors, such as those used in raising fluids from petroleum wells, and particularly to a system and method that utilizes a neutralizing agent to neutralize corrosive agents before they can damage the internal components of a submergible motor. 
     BACKGROUND OF THE INVENTION 
     A variety of production fluids are pumped from subterranean environments. Different types of submergible pumping systems may be disposed in production fluid deposits at subterranean locations to pump the desired fluids to the surface of the earth. 
     For example, in producing petroleum and other useful fluids from production wells, it is generally known to provide a submergible pumping system for raising the fluids collected in a well. Production fluids, e.g. petroleum, enter a wellbore drilled adjacent a production formation. Fluids contained in the formation collect in the wellbore and are raised by the submergible pumping system to a collection point at or above the surface of the earth. 
     A typical submergible pumping system includes several components, such as a submergible electric motor that supplies energy to a submergible pump. The system further may include a variety of additional components, including a connector used to connect the submergible pumping system to a deployment system. Conventional deployment systems include production tubing, cable and coiled tubing. Additionally, power is supplied to the submergible electric motor via a power cable that runs along the deployment system. 
     Often, the subterranean environment, and specifically the well fluid, contains corrosive compounds that may include CO 2 , H 2 S and brine water. These corrosive agents can be detrimental to components of the submergible pumping system, particularly to internal electric motor components, such as copper windings and bronze bearings. 
     Submergible electric motors are difficult to protect from corrosive agents because of their design requirements that allow use in the subterranean environment. A typical submergible motor is internally filled with a fluid, such as a dielectric oil, that facilitates cooling and lubrication of the motor during operation. As the motor operates, however, heat is generated, which, in turn, heats the internal motor oil causing expansion of the oil. Conversely, the motor cools and the motor oil contracts when the submergible pumping system is not being used. 
     Accordingly, this type of submergible motor requires a motor oil expansion system able to accommodate the expanding and contracting motor oil. Also, the internal pressure of the motor must be allowed to equalize or at least substantially equalize with the surrounding pressure found within the wellbore. As a result, it becomes difficult to prevent the ingress of corrosive agents into the motor oil and internal motor components. 
     Numerous types of motor protectors have been designed and used in isolating submergible motors while permitting expansion and contraction of the internal motor oil. A variety of elastomeric bladders alone or in combination with labyrinth sections have been used as a barrier between the well fluid and the motor fluid. For example, expandable elastomeric bags or bladders have been used in series to prevent mixing of wellbore fluid with motor oil while permitting expansion and contraction of the motor oil. 
     In this latter design, the motor protector includes a pair of chambers that each have an elastomeric bladder. The first bladder is disposed in a first chamber of the pair of chambers and includes an interior in fluid communication with the motor. This fluid communication permits motor oil to flow from the motor into the elastomeric bladder during expansion and to flow from the elastomeric bladder back to the motor during contraction. 
     The second chamber also includes an expandable bladder, filled with motor oil, that is in fluid communication with the first chamber but external to the first elastomeric bladder. The second chamber also is vented or open to the wellbore environment. This permits fluid to flow between the second elastomeric bladder and the adjacent chamber as the first elastomeric bladder expands or contracts. Simultaneously, wellbore fluid is allowed to flow in and out of the second chamber, external to the second elastomeric bladder, to permit equalization of pressure as the second bladder expands and contracts. 
     This type of expansion chamber works well in many environments, but certain of the corrosive agents found in at least some wellbore environments include corrosive gases that permeate the elastomeric bags or bladders. These corrosive agents eventually can work their way into the motor oil within the first elastomeric bladder and ultimately corrode and damage internal components of the electric motor. 
     It would be advantageous to utilize an expandable bladder system in a motor protector without the threat of corrosive agents migrating to the internal components of the electric motor. 
     SUMMARY OF THE INVENTION 
     The present invention features a device for protecting a submergible motor from corrosive agents found in a wellbore environment. The device also accommodates the expansion and contraction of the motor oil disposed within an interior of the submergible motor. The device comprises a housing having a first chamber and a second chamber. A first bladder is disposed in the first chamber and includes an interior region in fluid communication with the interior of the submergible motor. A second bladder is disposed in the second chamber and includes an interior region in fluid communication with the first chamber external to the first bladder. The second chamber is exposed to the pressure of the wellbore environment to permit equalization of pressures. Furthermore, a neutralizer is disposed for movement between the interior region of the second bladder and the first chamber external to the first bladder. 
     According to another aspect of the present invention, a system is provided for incorporation into a motor protector of the type used in protecting a submergible motor from corrosive agents found in a subterranean environment. The submergible motor has an interior filled with a motor oil that aids in cooling and lubrication of the motor. The system includes a bladder having an interior region. The bladder includes a port that permits fluid flow to and from the interior region. The port is connectable to the submergible motor such that motor oil may flow between the interior region of the bladder and the interior of the submergible motor. Also, a liquid neutralant barrier is disposed between the bladder and the subterranean environment to prevent contamination of the motor oil. 
     According to a further aspect of the present invention, a method is provided for protecting a submergible motor in a submergible pumping system from corrosive agents. The method also provides for the expansion and contraction of a motor oil disposed in the submergible motor. The preferred method comprises connecting a submergible motor with an expandable bladder to permit flow of motor oil between the submergible motor and the expandable bladder. The method further includes holding a supply of liquid neutralant in a neutralant bladder disposed intermediate the motor oil and potential corrosive agents. Further, the method includes neutralizing the corrosive agents before they are able to contaminate the motor oil. 
    
    
     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 a submergible pumping system positioned in a wellbore and including a motor protector, according to a preferred embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of a system, according to a preferred embodiment of the present invention, in which the motor oil is in an expanded state; and 
     FIG. 3 is a cross-sectional view similar to that illustrated in FIG. 2, but showing the motor oil in a contracted state. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring generally to FIG. 1, a submergible pumping system  10 , of the type utilized in pumping subterranean production fluids to the surface of the earth, is illustrated. Submergible pumping system  10  may comprise a wide variety of components depending on the particular application or subterranean environment in which it is used. However, system  10  typically includes at least a submergible pump  12  and a submergible electric motor  14 . 
     In the particular embodiment illustrated, additional submergible pumps  16  and  18  are connected in series with submergible pump  12 . Each submergible pump  12 ,  16  and  18  may comprise, for example, a centrifugal pump, a progressing cavity pump, or a gear pump. Similarly, in the exemplary embodiment illustrated, an additional submergible electric motor  20  is connected in series with motor  14 . At least one submergible electric motor and one submergible pump are used to pump production fluids to the earth&#39;s surface, but additional motors and pumps may be utilized, depending on the environment, type of production and depth of the well. 
     System  10  is designed for deployment in a well  22  within a geological formation  24  containing the desirable production fluids, such as petroleum. In a typical application, a wellbore  26  is drilled and lined with a wellbore casing  28 . The submergible pumping system  10  is deployed within wellbore  26  to a desired location for pumping of wellbore fluids. 
     As illustrated, submergible pumping system  10  typically includes other components. For example, system  10  is deployed in well  22  by a deployment system  30  that may comprise cable, coiled tubing, or production tubing  32 , as illustrated. Production tubing  32  provides a fluid path through which the production fluids are pumped to the surface. Deployment system  30  is connected to the string of pumping system components by a connector or head  34 . 
     Also, a power cable  36  generally is disposed along or through deployment system  30 . Power cable  36  is connected to the electric motor or motors, i.e. submergible electric motors  14  and  20 , to power the entire pumping system  10 . 
     Other components may include a gas separator  38 , a pressure and temperature sensing instrument  40  and one or more motor protectors  42 ,  44  and  46 . Gas separator  38  separates out components of the production fluid that are in gaseous form prior to their entering submergible pump  12 . Pressure and temperature sensing instrument  40  is designed to detect a variety of parameters in the downhole, subterranean environment. Motor protectors  42 ,  44  and  46 , on the other hand, are designed to protect submergible electric motors  14  and  20  from corrosive agents found in the production fluid and wellbore environment while permitting equalization of internal and external pressures. Motor protectors may also be designed to absorb the downthrust from the submergible pump or pumps, as is well known to those of ordinary skill in the art. 
     Motor protectors  42 ,  44  and  46  may be a mixture of different types of motor protectors that each include, for instance, labyrinth sections, bag sections or combinations of these different types of sections that help isolate electric motors  14  and  20 . One or more of the illustrated motor protectors may incorporate the system of the present invention. For example, motor protector  42 , motor protector  44  or both can be modified according to the description provided below. 
     An exemplary motor protector that can be modified according to the present invention, is a modular protector incorporating an expandable bag or bladder, such as the Reda BSB type protector available from the Reda Pump Company of Bartlesville, Okla. This type of protector has a dual bag or dual bladder system readily utilized with the current invention. 
     Referring now to FIGS. 2 and 3, a preferred embodiment of the present invention can be explained. An outer motor protector housing  48  includes an outer wall  50  that preferably is tubular in shape. A plurality of dividers or bulkheads  52 ,  54  and  56  are disposed within outer wall  50  generally transverse to outer wall  50 . This arrangement creates a first chamber  58  and a second chamber  60  within outer motor protector housing  48 . 
     An expandable bladder  62  is disposed in first chamber  58 . First expandable bladder  62  preferably comprises an elastomeric bag or elastomeric material that permits an interior region  64  to be filled with a motor oil  66  as the motor oil in motors  14  and/or  20  expands during operation. The elastomeric materials may comprise AFLAS, HSN or neoprene, but other materials, such as metallic materials, e.g. flexible monel, potentially can be used to form bladder  62 . 
     First expandable bladder  62  also includes a fluid flow-through port  68  that is connected to a fluid passageway  70  which extends through bulkhead  52  and ultimately to an interior region  72  of submergible electric motor  14 . Thus, as the internal motor oil  66  is heated by the electric motor, it expands and flows through fluid passageway  70  and flow-through port  68  into interior  64  of first expandable bladder  62 . This causes expansion of bladder  62 , as illustrated in FIG.  2 . When the motor oil  66  begins to cool, e.g. during motor shutdown, the motor oil contracts and flows from interior  64  through flow-through port  68  and fluid passageway  70  back to interior region  72  of the electric motor. This causes a contraction of first expandable bladder  62 , as illustrated in FIG.  3 . Also, first expandable bladder  62  includes a pressure relief valve  99  that vents motor oil to first chamber  58  if the oil pressure rises to an undesirable level, e.g. a level that could damage bladder  62 . 
     To accommodate the expansion and contraction of first expandable bladder  62  a neutralant or neutralizer  74  is disposed in first chamber  58  external to first expandable bladder  62 . Neutralizer  74  preferably is in liquid form and in fluid communication with a neutralizer bladder or second expandable bladder  76  disposed in second chamber  60 . Preferably, second expandable bladder is similar to first expandable bladder  62  in design and in the materials utilized in its formation. 
     Second expandable bladder  76  also has a flow-through port  78  connected to a fluid passageway  80 . Flow-through port  78  and fluid passageway  80  allow neutralizer  74  to flow back and forth between first chamber  58 , external to first expandable bladder  62 , and an interior  82  of second expandable bladder  76 . Thus, when first expandable bladder  62  fills with motor oil  66  and expands, the liquid neutralizer  74  is forced through bulkhead  54 , via fluid passageway  80  and flow-through port  78 , into interior  82  of second expandable bladder  76 . This causes second expandable bladder  76  to expand in second chamber  60 , as illustrated in FIG. 2. A pressure relief valve  100  protects bladder  76  from over-expansion and is configured to exhaust neutralizer into second chamber  60  in the event the fluid pressure rises to an undesirable level. Conversely, when the motor oil  66  contracts, first expandable bladder  62  also contracts and pulls the neutralizer  74  from interior  82  of second expandable bladder  76  into first chamber  58 , as illustrated best in FIG.  3 . 
     Second expandable bladder  76  may freely expand and contract within second chamber  60 , because second chamber  60  is vented to the well. A vent or opening  84  provides a fluid flow path between wellbore  26  and second chamber  60 , external to second expandable bladder  76 . Thus, wellbore fluids may flow in and out of second chamber  60  to permit expansion and contraction of second expandable bladder  76 . Vent  84  also permits equalization of the internal pressures of pumping system components, e.g. submergible electric motors  14  and  20 , with the external pressure in the well. 
     The use of a liquid neutralizer  74  in the second expandable bladder  76  provides a strong barrier to corrosive agents that, otherwise, might permeate second expandable bladder  76  and first expandable bladder  62 . Once the corrosive agents, e.g. corrosive gasses, permeate the bladders, they ultimately migrate through motor oil  66  and damage internal components of the electric submergible motors. In the preferred system, the only point of exposure to wellbore fluids is through vent  84 . However, once potential corrosive agents enter second chamber  60 , they are blocked or neutralized by the neutralizer  74  disposed throughout interior  82 , fluid passageway  80  and the portion of first chamber  58  external to first expandable bladder  62 . 
     An exemplary preferred neutralizer  74  is a liquid neutralizer comprising a solution of amines and methanol. For example, a liquid neutralizer, referred to as ATC 707-A (hydrogen sulfide scavenger) may be purchased from Alberta Treating Chemicals, Ltd. of Calgary, Alberta, Canada. The concentration of methanol and amines may need to be adjusted depending on the environment in which submergible pumping system  10  is utilized. For example, it may be desirable to lower the concentration of methanol to approximately 10% to 30% (a specific example is approximately 20% methanol base) and/or it may be desirable to raise the concentration of amines to approximately 80% concentration. The liquid neutralizer  74  is injected into first chamber  58  and ultimately into second expandable bladder  76  via a fluid passageway  88  and a ball check valve  90  that provide a fluid fill path from the outside of outer housing  48 . 
     As known to those of ordinary skill in the art and as apparent from the exemplary Reda BSB type modular protector, first expandable bladder  62  and second expandable bladder  76  may be mounted to the appropriate bulkheads  52 ,  54  and  56 . Additionally, a rotatable shaft  92  typically is disposed along the longitudinal axis of outer motor protector housing  48 , and through bulkheads  52 ,  54  and  56  as well as bladders  62  and  76 . The shaft section  92  may be rotatably mounted in bulkheads  52 ,  54  and  56  via appropriate bearings  94  and mechanical seals  96 . 
     It will be understood that the foregoing description is of a preferred exemplary embodiment of this invention, and that the invention is not limited to the specific form shown. For example, a variety of neutralants may be used depending on the environment; the bladders may be made from a variety of materials and in a variety of configurations; the arrangement of submergible pumping system components can vary substantially; and the arrangement of flexible bladders can be changed. For example, the first expandable bladder  62  potentially can be disposed inside of second expandable bladder  76 . This configuration would still provide a barrier to corrosive agents via the neutralizer disposed within the outer expandable bladder but external to the internal bladder containing motor oil. 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.