Patent Publication Number: US-9850897-B2

Title: Progressing cavity stator with gas breakout port

Description:
BACKGROUND 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     In order to meet consumer and industrial demand for natural resources, companies often invest significant amounts of time and money in finding and extracting oil, natural gas, and other subterranean resources from the earth. Particularly, once a desired subterranean resource such as oil or natural gas is discovered, drilling and production systems are often employed to access and extract the resource. These systems may be located onshore or offshore depending on the location of a desired resource. Further, such systems generally include a wellhead assembly mounted on a well through which the resource is accessed or extracted. These wellhead assemblies can include a wide variety of components, such as various casings, valves, pumps, fluid conduits, and the like, that control drilling or extraction operations. 
     In some instances, resources accessed via wells are able to flow to the surface by themselves. This is typically the case with gas wells, as the accessed gas has a lower density than air. This can also be the case for oil wells if the pressure of the oil is sufficiently high to overcome gravity. But often the oil does not have sufficient pressure to flow to the surface and it must be lifted to the surface through one of various methods known as artificial lift. Artificial lift can also be used to raise other resources through wells to the surface, or for removing water or other liquids from gas wells. Some forms of artificial lift use a pump that is placed downhole in the well, such as a progressing cavity pump having a stator that cooperates with a helical rotor to draw fluid up the well. 
     SUMMARY 
     Certain aspects of some embodiments disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below. 
     Embodiments of the present disclosure generally relate to progressing cavity devices, such as progressing cavity pumps. More specifically, in one embodiment a progressing cavity device includes a stator formed with a series of plates having apertures that define a rotor conduit of the device. The rotor conduit can be lined with a coating, such as a layer of elastomer provided over the edges of the plate apertures forming the rotor conduit. Left unchecked, gas trapped inside the stator (e.g., between the plates) could damage the coating and negatively impact the operation of the progressing cavity device. Accordingly, the stator includes a gas breakout port that allows gas between the plates to exit the stator. 
     Various refinements of the features noted above may exist in relation to various aspects of the present embodiments. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of some embodiments without limitation to the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of certain embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  generally depicts a production system having an artificial lift apparatus to draw fluid from a well to the surface in accordance with one embodiment of the present disclosure; 
         FIG. 2  is a block diagram of various components of the artificial lift apparatus of  FIG. 1 , including a progressing cavity device, in accordance with one embodiment; 
         FIG. 3  is a perspective view of a progressing cavity device provided in the form of a progressing cavity pump having a stator with gas breakout ports in accordance with one embodiment; 
         FIGS. 4 and 5  are cross-sections generally depicting certain features of the progressing cavity pump of  FIG. 3 , including a series of discs that form a stator core of the pump; 
         FIG. 6  is a perspective view of a progressing cavity pump similar to that of  FIGS. 3-5 , but in which the stator core is disposed in a housing between a pair of end plates in accordance with one embodiment; 
         FIGS. 7 and 8  depict an individual disc representative of the discs of the stator core depicted in  FIGS. 3-5 ; 
         FIG. 9  is a perspective view of the stator core of  FIGS. 3-5  before it is installed in a housing in accordance with one embodiment; and 
         FIG. 10  is a front elevational view of the stator core of  FIG. 9  and generally depicts how disc apertures overlap to form the gas breakout ports in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     Specific embodiments of the present disclosure are described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, any use of “top,” “bottom,” “above,” “below,” other directional terms, and variations of these terms is made for convenience, but does not require any particular orientation of the components. 
     Turning now to the present figures, a system  10  is illustrated in  FIG. 1  in accordance with one embodiment. Notably, the system  10  is a production system that facilitates extraction of a resource, such as oil, from a reservoir  12  through a well  14 . Wellhead equipment  16  is installed on the well (e.g., attached to the top of casing and tubing strings in the well). In one embodiment, the wellhead equipment  16  includes a casing head and a tubing head. But the components of the wellhead equipment  16  can differ between applications, and such equipment could include various casing heads, tubing heads, stuffing boxes, pumping tees, and pressure gauges, to name only a few possibilities. 
     The system  10  also includes an artificial lift apparatus  18 . In one embodiment generally depicted in  FIG. 2 , the artificial lift apparatus  18  includes a progressing cavity device  22  that operates as a downhole pump in the well  14 . The progressing cavity device  22  includes a rotor  24  and a stator  26 . In the presently depicted embodiment, in which the progressing cavity device  22  operates as a pump of the artificial lift apparatus  18 , the rotor  24  rotates with respect to the stator  26  to pump fluid through the device  22  and from the reservoir  12  to the surface through the well  14 . 
     The apparatus  18  also includes a prime mover  28  that cooperates with a drive head  30  to rotate a drive string  32  that extends downward through the well  14  to the progressing cavity device  22 . The prime mover  28  and the drive head  30  can be provided at the surface—mounted to the wellhead equipment  16 , for example. The prime mover  28  can be provided in any suitable form, such as a diesel engine, a gas engine, or an electric motor. The drive head  30  can include a gear box to reduce rotational output from the prime mover  28  so that the drive string  32  (e.g., a sucker-rod string) rotates at a speed appropriate for operating the progressing cavity device  22 . 
     One example of a progressing cavity device  22  is depicted in  FIGS. 3-5  in the form of a progressing cavity pump  36 . The stator  26  of the pump  36  includes a stator core  38  installed within a housing  40 . In at least some embodiments, the stator core  38  and the housing  40  are both formed from metal. In the presently illustrated embodiment, the stator core  38  includes a series of plates (here depicted as discs) with elongated apertures, and the housing  40  is a hollow tube that receives the plates of the stator core  38 . It will also be appreciated that other arrangements could instead be used. For example, the plates could be provided in some other (non-disc) shape, the housing  40  could be provided in a different shape, or the housing  40  could be omitted from the pump  36 . 
     The rotor  24  includes a helical profile  42  (which may also be considered to include a spiraled tooth for engaging the stator  26 ) positioned within a rotor cavity or conduit  44  of the stator core  38 . As described in greater detail below, the rotor conduit  44  is formed by elongated apertures in the plates of the stator core  38 . Individual plates of the stator core  38  are rotationally offset with one another such that the apertures of the series of plates form a helically wound rotor conduit  44  for receiving a contoured portion of the rotor  24  having the helical profile  42 . 
     The rotor  24  and the stator  26  may be connected to other equipment in any suitable manner. For instance, the rotor  24  depicted in  FIG. 3  includes a threaded connection end  46  that facilitates coupling to an input shaft (e.g., the drive string  32  in a wellbore environment). The stator  26  could be attached to a production tubing string in the well  12  in some embodiments, such as by threading an end  48  of the stator  26  and connecting it to the production tubing string with a threaded collar or sub. But the stator  26  could be secured within the well  12  in other ways. And while the pump  36  is presently described in connection with downhole applications, it will be appreciated that the pump  36  could be used outside of a wellbore. 
     Operation of the pump  36  may be better understood with reference to the cross-sections depicted in  FIGS. 4 and 5 . As shown in these figures, the stator core  38  includes a series of discs denoted with reference numeral  56 . One example of such discs is generally depicted in  FIGS. 7 and 8 , although the discs or other plates of the stator core  38  could take different forms in other embodiments. The discs of the series  56  are rotationally offset with respect to one another such that the ends of the elongated apertures in the discs generally define two teeth or ridges (corresponding to opposite sides of the discs about their apertures) that wind through the stator core  38  in the form of a double helix. In the presently depicted embodiment, in which a single-toothed rotor  24  cooperates with a double-toothed stator  26 , the pump  36  is a single-lobe pump. But the pump  36  could be provided as a multiple-lobe pump in other embodiments. 
     With reference to  FIG. 4 , the winding rotor conduit  44  of the stator  26  includes a stator pitch  58 . In the present single-lobe arrangement, the helical profile  42  of the rotor  24  includes a rotor pitch  60  that is half that of the stator pitch  58 . The stator  26  is depicted here as having a length three times that of the stator pitch  58 , but could be of any desired length in other embodiments. 
     The rotor  24  can be rotated (e.g., by the drive string  32  attached to a connection end  46  of the rotor  24 ) within the conduit  44  to draw fluids through the stator  26 . In operation, the rotor  24  seals against the inner surface of the stator  26  (more specifically, against a coating  50  as described below) to retain fluid within individual chambers or cavities  62  of the rotor conduit  44  between the rotor  24  and the stator  26 . These fluid cavities  62 , upon rotation of the rotor  24 , progress in winding fashion about the rotor  24  and through the stator  26  from an intake end  64  to a discharge end  66  such that fluid is drawn through the stator  26  at a rate that varies based on the rotational speed of the rotor  24  about its axis. In another embodiment, the pump  36  can be arranged such that the end  66  is the intake end and the end  64  is the discharge end. Although described herein as being able to convert rotation of the rotor  24  into fluid flow, the pump  36  could instead be arranged to perform the reverse—that is, to convert fluid flow into rotation of a component. In such a variation, the pump  36  could serve as a downhole mud motor or some other device. 
       FIG. 5  generally depicts the rotor  24  having been turned by 180 degrees from its position in  FIG. 4 . At both of these depicted positions of the rotor  24  within the stator  26 , the rotational axis of the rotor  24  differs from the central axis of the stator. As the rotor  24  is driven about its own axis (e.g., by drive string  32 ), it also rotates eccentrically with respect to the axis of the stator  26  due to engagement of the helical profile  42  with the inner surface of the stator  26 . It is also noted that while the pump  36  is configured as a right-handed device (with a right-handed helical profile of the rotor  24 ), other progressing cavity devices  22  could instead be configured as left-handed devices with rotors  24  having left-handed helical profiles that wind in a direction opposite that of the rotor  24  of pump  36 . 
     As generally depicted in  FIGS. 3-5 , the stator  26  includes a coating  50  provided on the edges of the plate apertures that form the rotor conduit  44 . The coating  50 , which may be provided as a layer of elastomer or other suitable material, can be a deformable layer that facilitates sealing engagement between the rotor  24  and the stator  26  to reduce slip during operation of the pump  36 . The coating  50  can also serve as a barrier layer between the interior of the rotor conduit  44  on the one hand and interstitial spaces between adjoining plates of the stator core  38  on the other. This allows the coating  50  to inhibit the flow of fluid from inside the conduit  44  (e.g., from progressing fluid cavities  62 ) to the interstices between the plates of the stator. 
     In some instances, however, pressurized gas inside the conduit  44  could penetrate through the coating  50 , allowing the gas to collect behind the coating  50  and between the plates of the stator core  38 . And if pressure were to then decrease in the conduit  44 , a pressure differential between gas behind the coating  50  and the fluid in the conduit  44  could cause blistering or other damage to the coating  50 . Consequently, the stator  26  includes gas breakout ports or conduits  52  that facilitate the egress of pressurized gas from the stator core  38 . 
     The gas breakout ports  52  can be formed in the stator core  38  in any suitable manner. For instance, in the depicted embodiment, the stator  26  includes two gas breakout ports  52  that wind helically about the rotor conduit  44  through the stator core  38  from one end of its discs to the other. These gas breakout ports  52  are spaced apart from the rotor conduit  44  and are in fluid communication with the interstitial spaces between the discs of the stator core  38 . This allows gas that penetrates through the coating  50  (as well as any other gas present in the stator core  38  behind the coating  50 ) to flow to the gas breakout ports  52  via the interstitial spaces between the discs and then exit the stator  26 , thereby enabling pressure balancing of the stator core  38  with the environment outside of the stator  26 . 
     Although the stator  26  is shown as having two gas breakout ports  52  in  FIG. 3 , other progressing cavity stators could have fewer or more gas breakout ports in accordance with the present technique. Further, in one embodiment the gas breakout ports  52  are formed by apertures in the discs of the stator core  38  that are offset from one another. But in other embodiments the gas breakout ports  52  could be formed in other ways, such as being machined in the assembled stator core  38 . 
     The depicted stator  26  also includes additional ports or conduits  54  that connect the gas breakout ports  52  to the exterior environment. Gas within one of the gas breakout ports  52  can escape the stator  26  by traveling to the end of the gas breakout port  52  or by passing through one of the additional conduits  54 . To prevent pumped fluid exiting a discharge end of the pump  36  from returning to the intake end through the gas breakout ports  52  in the stator  26 , the gas breakout ports  52  can be plugged or capped in any suitable manner. For example, in some embodiments the discs of the stator core  38  are disposed in the housing  40  between end plates  68 , as generally depicted in  FIG. 6 . The additional conduits  54  allow gas within the gas breakout ports  52  to escape from the stator core  38  even when the end plates  68  block the ends of the gas breakout ports  52 . The conduits  54  can also be formed in any suitable number and way, such as by boring holes through the housing  40  and into the stator core  38  to connect with the gas breakout ports  52 . 
     One example of an individual disc  70  of the stator core  38  is illustrated in  FIGS. 7 and 8 . As shown in these figures, each individual disc  70  includes a body  72  having a circumferential edge  76  and an elongated aperture  74 . In the presently depicted embodiment, the aperture  74  is provided as a central aperture in the shape of an oval through the disc  70 . The discs  70  also include additional apertures  78 . The apertures  74  and  78  can be cut from the body  72  via laser cutting in some embodiments, or can be formed through any other suitable manufacturing techniques (e.g., stamping). 
     By way of further example, the stator core  38  is depicted in greater detail in the perspective and front elevational views of  FIGS. 9 and 10 . As shown here in  FIG. 9 , as well as in  FIGS. 4 and 5 , the stator core  38  has a length that is three times the stator pitch  58 , although the stator core  38  could have any desired length as noted above. With a stator length equal to three times the stator pitch  58 , each disc  70  of the stator core  38  is rotationally offset with respect to its neighbor to cause the rotor conduit  44  to wind through three full turns (one turn per stator pitch length). This rotational offset also causes the apertures  78  of adjacent discs  70  to overlap one another and form the gas breakout conduits  52 , as generally depicted in  FIG. 10 . The apertures  74  and  78  of the foremost disc  70  of the stator core  38  are fully shown in  FIG. 10 , with the apertures  74  and  78  of the next two discs  70  in the stator core  38  partially drawn in phantom (where obscured by the foremost disc  70  and the coating  50 ) to generally illustrate the rotational offset of these neighboring discs. 
     In one embodiment the stator core  38  includes seventy-two individual discs  70  per stator pitch length, with the discs  70  rotationally staggered at five-degree intervals and each having a thickness of one-sixteenth of an inch (about 1.6 mm). But the dimensions of the discs or plates, as well as the number of such discs or plates per stator pitch length (along with the amount of rotational offset), could differ in other embodiments. 
     It will be appreciated that the stator core  38  can be installed in the bore of the housing  40  and retained in any suitable fashion. For example, the series  56  of discs  70  could be bonded to the housing  40 , retained by an interference fit, or retained by end caps (e.g., end plates  68 ) coupled to the housing  40 . Additionally, the discs can also be joined to one another prior to installation in the housing  40 , such as through welding or bonding. After the stator core  38  is installed in the housing, the conduits  54  depicted in  FIG. 3  can be formed, such as by boring holes through the housing and into the stator core  38  as described above. 
     The coating  50  can be formed on the edges of the apertures  74  in various ways. For example, the coating  50  can be applied via injection molding (e.g., by inserting a mold inside the cavity  44  and feeding the material of the coating  50  to fill the space between the mold and the edges of the apertures  74 ). The rotor  24  can then be inserted into the assembled stator  26  as generally depicted in  FIG. 3 . 
     While the aspects of the present disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. But it should be understood that the invention is not intended to be limited to the particular forms disclosed. The presently disclosed techniques may be applied to other progressing cavity devices, such as to mud motors or other devices that use fluid flow to drive rotation of a component rather than driving rotation of the rotor to cause fluid flow. The invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.