Abstract:
A reinforcing interface between the stator and its housing in a progressing cavity pump is created from ribs extending inwardly into the stator from the housing inner wall that can be longitudinally oriented or spirally oriented. Alternatively, the housing wall can have grooves into the inner wall that are made more bulbous further into the housing wall from the groove inlets so that when filled with stator material a long and continuous grip is obtained with either the wall groove embodiment or the internal rib embodiment.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention is progressing cavity stators and more particularly devices that enhance adherence of the stator to its housing apart from interface adhesives. 
       BACKGROUND OF THE INVENTION 
       [0002]    Progressing cavity pumps (PCP) were invented in the 1930s by Moineau as seen in U.S. Pat. Nos. 1,892,217 and 2,028,407. 
         [0003]    A progressing cavity pump has a stator and a rotor. The stator typically comprises an elastomeric liner within a housing. The stator is open at both ends and has a multi-lobe helical passage extending through it. The rotor is normally of metal and has a helical exterior formed on it. Rotating the rotor causes fluid to pump through the stator. Progressing cavity pumps are used for a variety of purposes. 
         [0004]    As a well pump, progressing cavity pumps may be driven by a downhole electrical motor or by a string of rods extending to a motor located at the surface. With a rod driven pump, normally the stator is suspended on a string of tubing, and the drive rods are located within the tubing. When installing a rod driven progressing cavity pump, the operator first secures the stator to the string of tubing and runs the tubing into the well to a desired depth. The operator then lowers the rotor through the tubing on the string of rods and into the stator. 
         [0005]    To operate the pump at desired capacity, the rotor must be at the desired axial spacing within the stator and the rods must be in tension. If the lower end of the rotor is spaced above a lower end of the stator during operation, then a lower portion of the stator will not be in engagement with the rotor and the pumping capacity will suffer. The operator thus needs to know when the rotor has fully entered the stator during installation. The operator can calculate how much the rods will stretch due to the hydrostatic weight of the column of well fluid in the tubing. With the anticipated stretch distance known and with the rotor at a known initial position in the stator, the operator can pull the rods and rotor upward a distance slightly greater than the anticipated stretch, so that during operation, the rotor will move back downward to the desired axial position relative to the stator. 
         [0006]    Stators are manufactured by insertion of a core into a tubular housing and capping the ends with the core properly positioned. The inside wall of the housing can have an adhesive coating before the material for the stator is injected through one of the end caps and forced under pressure to fill the annular space between the core and the housing inner wall. The adhesive was used in the past to help the stator body adhere to the surrounding housing. Depending on the size and the particular application, the housing could be over 10 meters long and could have an inside housing wall diameter smaller than 10 centimeters. 
         [0007]    As the industry develops, PCPs are being deployed in progressively hotter environments to the point where the commercially available adhesives reach their temperature service limit in the order of about 150° C. In an effort to allows stators to operate effectively at higher temperatures structures have been proposed to be supported from the housing inside wall and extend inwardly such that when the stator was created within the housing a core and injected rubber around it, the end result would be a better bond to the housing inside wall than just using adhesive by itself. Along those lines U.S. Pat. No. 7,407,372 suggests a ring structure with openings that allow the rubber to pass through during manufacturing and positioned in the stator housing with L-shaped rings  18  that are welded to the stator inside wall as shown in  FIGS. 2 and 3  of that patent.  FIGS. 4 and 5  show another embodiment of such a ring with openings and external grooves  52  that lead to openings  54  so that the rubber can hopefully envelope the ring structure  50 . The grooves are stated to be longitudinal or spiral and  FIG. 5  further shows L-shaped indents at opposed ends into the ring  50  from the inside that are stated to help seal the rubber to the ring structure  50 . 
         [0008]    There are several issues with this design. In a long housing it is expensive and difficult to secure the intermediate standoff supports  18  to the housing inner wall. The more substantial the tube for structural rigidity the less rubber can be used as the stator. On the other hand if the tube is too flimsy so as to maximize the rubber content it will be structurally weaker to the point that during stator manufacturing with the core in the housing and the ring held by supports, the delivery of rubber under very high pressures to fill all the void space between the housing inner wall and the core will result in flexing of the tube to the point where it will touch the core. When the core is then removed portions of the tube extend out of the stator and damage the rotor. 
         [0009]    Other references relating to PCP stator construction are: U.S. Pat. Nos. 3,280,753; 5,318,416; 7,131,827; JP 61180512; DE 3322095; US 2009/0152009; 2009/0169404; 2002/0153141; 2009/0129937; U.S. Pat. Nos. 7,299,873; 7,201,222; 6,868,912 and 6,705,402. 
         [0010]    What is needed and provided by the present invention is a simple way to enhance grip of the stator to its housing that is structurally sound against torsional stresses and offers in some embodiments the ability to stiffen the stator. This is accomplished with modifications to a tubular housing for the stator that can have elongated ribs extending inwardly from the housing inner wall disposed longitudinally or in a spiral array. The spiral array can have ribs spiraling all in one direction or with one or more ribs spiraling in the opposite direction forming an overlapping pattern of ribs. These ribs are formed as an integral part of the housing either by extrusion, machining, or welding such that they cannot move with respect to the housing during injection of the stator rubber or due to torsional stresses during operation. The reverse of inwardly extending ribs can also be used in the form of wall grooves in the stator housing interior wall that preferably have a bulbous region further into the wall from a narrower inlet so that a grip is created when the internal groove structure is filled with injected rubber to form the stator. These and other aspects of the present invention will become more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is defined by the literal and equivalent scope of the appended claims. 
       SUMMARY OF THE INVENTION 
       [0011]    A reinforcing interface between the stator and its housing in a progressing cavity pump is created with ribs extending inwardly into the stator from the housing inner wall that can be longitudinally oriented or spirally oriented. Alternatively, the housing wall can be formed to have grooves into the inner wall that are made more bulbous further into the housing wall from the groove inlets so that when filled with stator material a long and continuous grip is obtained with either the wall groove embodiment or the internal rib embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a section view of a stator housing showing the elongated groove disposed in the housing wall and the form that has a narrow entrance leading to a bulbous or a larger region; 
           [0013]      FIG. 2  of a single groove such as shown in  FIG. 1 ; 
           [0014]      FIG. 3  is an alternative embodiment using ribs shown in an end view of a stator housing; 
           [0015]      FIG. 4  is an internal view of a longitudinally oriented rib within a stator housing; 
           [0016]      FIG. 5  is the rib of  FIG. 4  showing a spiral orientation; 
           [0017]      FIG. 6  is a stator tube before insertion of the stator retention device of  FIG. 7 ; 
           [0018]      FIG. 7  is a coiled spring brought to a reduced diameter for insertion into the stator housing shown in  FIG. 6 ; and 
           [0019]      FIG. 8  is the spring uncoiled in the stator housing so that it is fixed by radially outward spring force against the inner wall of the stator housing to retain the stator to the housing after the stator is formed in the housing. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]      FIG. 1  shows a section through a stator housing  10  showing the stator  12  developed in the housing  10  using known injection techniques with a core placed into the housing  10 . An assortment of grooves  14 ,  16 ,  18  and  20  are shown disposed within the wall  22 . They can be configured in several ways. Groove  14  is square or rectangular with parallel sides  24  and  26  so that the entrance  28  is as wide as the groove  14  for the entire depth. Not shown but may be present in groove  14  as well as any other groove shown in  FIG. 1  is an adhesive bonding material that helps adhere the stator  12  to the walls of groove  14 . The number of grooves such as  14  can vary keeping in mind the structural need for the housing  10  as well as the capabilities of an extrusion process that can be used to form the grooved housing  10  as a seamless tube cut to the desired length for a particular application. In the preferred embodiment and for reason of cost of manufacturing among other reasons, the groove  14  is continuous. It can be completely straight along its length while oriented to parallel to the longitudinal axis of the housing  10  or it can be in a helical or spiral format with one or more grooves  14  circumferentially equally spaced or unequally spaced at any given cross-section. One or more of the spiral groves may spiral in the opposite direction of the other groves. While square or rectangular groove profiles such as used in groove  14  resist torsional stresses from rotation of the rotor (not shown) within the stator  12  thus reducing such forces acting on the adhesive bond between the stator  12  and the inner wall  30  of housing  10 , the other illustrated configurations add resistance to mechanical separation in a radially inward direction toward the center of the housing  10  that is not found in the configuration of groove  14 . 
         [0021]    Groove  18  for example has a dovetail shape with a flat groove bottom  32  and a pair of converging side walls  34  and  36  in the direction from the bottom  32  to the center of the housing  10 . This shape leads to a groove inlet  38  that is considerably smaller in width than bottom  32 . Still the inlet  38  cannot be overly minimized because while doing so increases resistance to pullout of the stator  12  in a radial direction, the decreased width will reduce the resistance of the stator  12  at the inlet  38  to shear force from torsional reaction forces imparted from rotation of the rotor (not shown) and the fluid moving through the stator  12 . 
         [0022]    Groove  20  is similarly configured to groove  18  except rather than an angled dovetail shape it is more bulbous and somewhat elliptical while groove  40  shows a more circular bulbous configuration with a smaller entrance  42 . Groove  16  shows generically a rectangular or quadrilateral shape within the groove again with a narrower entrance  44 . 
         [0023]      FIG. 2  shows in section a single groove  20  that the interior width D is larger than the entrance width d. In the preferred embodiment the ratio of D/d is greater than 2. 
         [0024]      FIG. 3  shows an alternative embodiment of ridges  46  that extend radially inwardly from interior wall  30  and preferably extend for the length of the housing  10  as shown in the alternative interior views of  FIGS. 4 and 5 . The ridges  46  can be straight and oriented parallel to the longitudinal axis of the housing  10  or spiraling as shown in  FIG. 5 . The spacing can be equal or unequal and the ridges can be continuous or discontinuous. The number of ridges will depend on space limitations of the inside diameter of the housing  10 . While shown as a quadrilateral shape in  FIG. 3  as being a cost effective design to produce by extrusion when making a seamless housing  10  other shapes are contemplated. Because of the radial extension from the wall  30  it is preferable to avoid minimizing the transition width of each ridge at the wall intersection at  30  so that the result of a flimsy cantilevered structure that flexes too much is avoided. However, use of a partial circular or rounded shape or a trapezoidal or elliptical or other bulbous shape that has its largest dimension at the interface of wall  30  is one suitable approach to preserving structural rigidity against torsional moments created when the rotor (not shown) is rotating in the stator (not shown in  FIG. 3  so that the ridges can be seen going into housing  10 ). Alternatively the dimension at the wall  30  interface can be somewhat smaller than the top  48  of any particular ridge while still retaining enough rigidity against torsional stresses. 
         [0025]    While the shape of the grooves or ridges are preferably created as the housing  10  is extruded, ridges  46  can be attached after the housing tube is fabricated and welded or otherwise affixed to the interior wall  30 . Alternatively, the grooves can be made separate from the extrusion process into a seamless tube wall using other techniques such as wire EDM for example. 
         [0026]    Grooves and ridges the same or different shapes can also be combined in a single housing. The groove or ridge can extend continuously or discontinuously for the substantial length of the housing  10  with substantially meaning at least for half the length of the housing  10 . When extending discontinuously the segments need not be axially or circumferentially aligned but can be offset. 
         [0027]      FIGS. 6-8  show a stator housing  50  and a coiled spring  52  rotated to a reduced diameter so that it can be inserted into the housing  50  and set loose to snap against the inner wall  54  of the housing  50  for position fixation. The core (not shown) is then inserted in the housing  50  and the annular space in between is injected with the material that will form the stator  12  which will be anchored in place by the radial spring force of the coils in spring  52  pushing against the wall  54  for fixation above and beyond any bonding forces of the stator  12  or any adhesive applied to the wall  54  before forming the stator with injected material. Spring or springs  52  can be used with grooves  14  or ridges  46  or by themselves. Ridges can be combined with grooves or springs. All permutations of the three elements in groups of three two or one are envisioned When used with ridges  46  such ridges can have gaps to allow the spring to sit against the housing inner wall so that the ridge breaks help to fixate the spring or springs  52 . The spring  52  can also be considered as a ridge. 
         [0028]    The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.