Abstract:
A submersible pump housing with seal bleed ports is provided. In an implementation, a pump housing for electric submersible pumps (ESPs), such as a centrifugal ESP, has end seals that are located inside or further inboard toward the high thrust pressure generated by the pump, than the threaded ends of the pump housing. The inboard seals contain and seal off the pump pressure and spare the threaded regions that are more pressure-vulnerable from the pump&#39;s high pressure interior, thereby increasing the pressure rating of the entire housing. Leak ports or bleed ports are provided further outboard of the end seals to relieve fluid seeping from inside the submersible pump housing past each end seal. A plate may be added to direct small amounts of fluid escaping from the end seals away from the wellbore casing in which an ESP is situated.

Description:
RELATED APPLICATIONS 
     This patent application claims the benefit of priority to U.S. Provisional Patent No. 61/678,101 to Eslinger, filed Aug. 1, 2012 and entitled, “Submersible Pump Housing With Seal Bleed Holes,” which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     An electric submersible pump (ESP) is often used in well settings to artificially lift subsurface resources such as hydrocarbons and water to the Earth&#39;s surface. Conventionally, the maximum pressure rating of a given ESP housing is limited by the stresses in the threaded end portion of the ESP housing. In a conventional centrifugal pump housing (diffuser), for example, the housing is sealed at the head and at the base with an O-ring seal located at the end of the housing and outboard of the end threads. Conventional arrangement of the end seals in an ESP causes the circumferential or hoop stresses of the housing in the threaded region to be the sum of the hoop stresses due to the thread radial forces resulting from axial loads on the thread flank angle, and the internal pressure differential from inside to outside the housing. The sum of these hoop stresses determines the maximum pressure rating of a conventional housing. Some conventional ESP housings have end seals both inboard and outboard of the threaded ends of the conventional housings. However, there is no fluid path from inside to outside the housing between these two seals. Thus, this conventional arrangement can trap the high internal pressure between the two seals and render the conventional inboard seal ineffective. 
     SUMMARY 
     A submersible pump housing with seal bleed ports is described. In an implementation, the submersible pump housing includes a housing, an interior compartment of the housing for fluid at high thrust pressure, a threaded end region of the housing, an inboard end seal to seal off the threaded end region from the interior compartment; and at least one bleed hole or port outboard of the end seal for allowing leakage of fluid from the interior compartment past the end seal to escape radially through the housing. An example centrifugal pump housing may include a diffuser for directing high thrust fluid accelerated by an impeller, an end seal inboard of each threaded end of the centrifugal pump housing, and at least one leak port outboard of each end seal to relieve a fluid seeping from inside the centrifugal pump housing past each end seal. An example method includes locating an end seal inboard of a threaded portion of a centrifugal pump housing to seal internal pressure from the threaded portion, and locating a radial bleed port outboard of the end seal to relieve pressure of seepage past the end seal. This summary section is not intended to give a full description of submersible pump housings with seal bleed ports. A detailed description with example embodiments follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an example electric submersible pump (ESP) section with inboard end seals and seal bleed ports. 
         FIG. 2  is a diagram of a second example ESP section with inboard end seals and seal bleed ports. 
         FIG. 3  is a diagram of an example ESP section with inboard end seals, seal bleed ports, and a lockplate protector. 
         FIG. 4  is a flow diagram of an example method of increasing the pressure rating of a submersible pump housing. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure describes submersible pump housings with seal bleed ports. Features, systems, and methods associated with submersible pump housings with seal bleed ports represent possible implementations and are included for illustration purposes and should not be construed as limiting. Moreover, it will be understood that different implementations can include all or different subsets of aspects described below. Furthermore, the aspects described below may be included in any order, and numbers and/or letters placed before various aspects are done for ease of reading and in no way imply an order, or level of importance to their associated aspects. 
       FIG. 1  shows a section of an example electric submersible pump (ESP)  100  of the centrifugal type. The illustrated section shows a base-end portion of the centrifugal ESP  100 . An impeller region  102  inside the pump housing generates high thrust pressure as the impeller accelerates fluid radially outward and axially upward, or toward a wellhead of an ESP installation. At the periphery of the pump housing, the fluid in the interior high pressure compartment  104  that includes the impeller region  102  extends to a location at which the end seal  106  is situated to seal off the high thrust pressure and highly mobilized fluid from flowing out to the exterior of the pump housing or from flowing out to the next component in a stack of components. 
     In the example centrifugal ESP  100  with seal bleed ports  108 , the end seals  106  are inboard of the threaded end regions  110  of the pump housing in order to contain the high pressure compartment  104  and prevent the threaded end region  110  from participating in the interior high pressure compartment(s) of the ESP  100 . This arrangement of having the end seals  106  inboard of the threads  110  increases the maximum pressure rating of the pump housing, because the threaded end regions  110  of conventional pumps are subject to increased stresses over the non-threaded regions of conventional pump housings when subjected to interior pump pressures. In  FIG. 1 , the bleed ports  108  or vent ports are located just outboard of the end seal  106  to provide a leak path for fluid that seeps or blows by the end seal  106 . The terms “port” and “hole” as used herein, are used representatively to mean a fluid path, passageway, port, hole, lumen, channel, vent, etc., enabling the movement of fluid from one location to another. The vent ports do not have to be “holes,” such as a round, straight passages as drilled by a bit. For example, the term bleed ports  108  can mean a vent passage that is a milled castellation(s) in the end face of either the housing or end cap (base or head). 
     In an implementation, the vent passage, leak path, or seal bleed ports  112  may be located outboard of the threaded end region  110 , instead of just outboard of the end seal  106  as seal bleed ports  108  are. Locating the bleed ports  112  outboard of the threads  110  utilizes the threads  110  to dissipate leakage fluid pressure and minimize jetting velocity of fluid that has escaped the end seal  106 . 
     The term “outboard” or “outboard of” as used herein, means “outside” or “on the other side of” a designated feature that is closer to, or more “inboard,” to the pump&#39;s high thrust pressure compartments or to the fluids being accelerated by the pump. Correspondingly, “inboard,” as used herein, means “inside of,” in first contact with, or in closer contact with the high thrust pressure generated by the pump than a designated feature that is therefore more “outboard.” 
       FIG. 2  shows an example centrifugal ESP  200  with cutaway housing  202 . The illustrated section shows a head-end portion of the example centrifugal ESP  200 . The example centrifugal ESP  200  includes one or more impeller regions  204  in a high thrust pressure compartment. An end seal  206  is positioned inboard of one or more fluid bleed ports  208 . The end seal  206  is also positioned inboard of a threaded end region  210 . The illustrated bleed ports  208  are radially-directed to form a leak path from outboard of the end seal  206  to the exterior of the housing  202 . In this manner, an internal pressure differential caused by the pumping action of the example centrifugal ESP  200  is sealed off from the end threads  210 , and the hoop stresses in the same threaded region  210  are significantly reduced to enable a higher maximum pressure rating for the overall housing  202  of the example centrifugal ESP  200 . Any fluid leakage that does seep past the end seal  206  on account of the high pressure that is inboard of the end seal  206  is allowed to escape the housing  202  without building up at the threaded region  210 . 
     The bleed ports  208  form a leak path that is situated from inside to outside the housing  202  just outboard of the end seal  206 . The leak path can be implemented so that a very small leakage of fluid past the end seal  206  does not pressure the space or volume that may exist between the end seal  206  and the contact face between the head (or the base) and the centrifugal pump housing  202 . If this volume is pressured, then the same undesired stress state that exists in conventional housings occurs. In an implementation, the leak path can be created by drilling small radial holes in the housing  202  just downstream (outboard) of the end seal(s)  206 . In an implementation, the seal bleed ports  214  may be located to form a leak path outboard of the threaded end region  210 , instead of just outboard of the end seal  206  as seal bleed ports  208  are. Locating the bleed ports  214  outboard of the threads  210  utilizes the threads  210  to dissipate leakage fluid pressure and minimize jetting velocity of fluid that has escaped the end seal  206 . The head-end of compression ring (CR) style pumps also requires a bleed path, such as port  212 , for weepage that may occur past the compression ring-to-head seal. 
       FIG. 3  shows a centrifugal pump housing  302  with inboard seal  306 , bleed port  308 , and an example housing lockplate protector  310 . The lockplate protector  310  covering the bleed port  308  shown in  FIG. 3  can be used to protect the well casing from any damage due to fluid leaking from the radial bleed port  308  in the housing  302 . The lockplate protector  310  can be a standard lockplate except that the housing-facing side of the lockplate can be stepped to allow bleed fluid to be deflected axially along the housing  302  rather radially toward the bore of the well casing. 
     In an implementation, an example submersible pump includes a housing, an interior compartment of the housing for fluid at high thrust pressure, a threaded end region of the housing, an inboard end seal to seal off the threaded end region from the interior compartment, and at least one bleed port or hole outboard of the end seal for allowing leakage of fluid from the interior compartment past the end seal to escape radially from the end seal through the housing. 
     The example submersible pump may comprise a centrifugal electric submersible pump (ESP) for the oil and gas industries. The housing may comprise a diffuser of the centrifugal ESP. The inboard end seal protects the threads to increase the pressure rating of the housing. The at least one bleed port can relieve a pressure between the end seal and a contact face between the submersible pump housing and a head or a base connecting to the submersible pump. 
     A lockplate protector over the bleed port can protect a well casing from the leakage of fluid from the interior compartment past the end seal. The lockplate protector can be stepped to deflect fluid axially along the housing instead of radially toward a bore of the well casing. 
     When the submersible pump is a compression ring (CR) style pump, a leak port can be used for weepage past a compression ring-to-head seal. 
     A centrifugal ESP may operate at temperatures of up to approximately 149 degree Celsius and pressures of up to approximately 6,000 pounds per square inch or approximately 41 megapascals in a downhole environment of up to approximately 12,000 feet or 3.7 kilometers deep. The centrifugal ESP can use up to approximately 1000 horsepower or 750 kilowatts of power and has a speed of rotation of a rotor of up to approximately 4000 revolutions per minute. Even in such harsh conditions, the end seal protects the threaded end region from the fluid at high thrust pressure in the interior compartment of the centrifugal ESP. 
     In an implementation, a centrifugal pump housing includes a diffuser for directing high thrust fluid accelerated by an impeller, an end seal inboard of each threaded end of the centrifugal pump housing, and at least one leak port outboard of each end seal to relieve a fluid seeping from inside the centrifugal pump housing past each end seal. Each leak port can relieve a pressure between a respective end seal and a contact face between the centrifugal pump housing and a head or a base. 
     A lockplate protector can be used over the leak port. The lockplate protector protects the well casing from a fluid leaking from the leak port. The lockplate protector can be stepped to deflect fluid axially along the centrifugal pump housing instead of allowing the fluid to escape radially toward a bore of the well casing. 
     Example Method 
       FIG. 4  shows an example method  400  of increasing the pressure rating of a submersible pump housing. In an implementation, the submersible pump can be a centrifugal ESP. In the flow diagram, operations are shown in individual blocks. 
     At block  402 , an end seal is located inboard of the threaded portion of a submersible pump housing to seal internal pressure from the threaded portion. 
     At block  404 , radial bleed ports are located outboard of the end seal to relieve pressure of small blow-by or seepage past the end seal. 
     The example method enables an internal pressure differential of the submersible pump to be sealed from the end threads, and the hoop stresses in the threaded region of the housing to be significantly reduced, achieving a higher pressure rating for the example submersible pump housing. 
     CONCLUSION 
     Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the subject matter. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.