Patent Publication Number: US-7905714-B2

Title: Progressing cavity pump assembly and method of operation

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to progressing cavity pumps driven by a rotating rod driven by a motor at surface or a well bore. More particularly, the present invention relates to an apparatus and method for axially positioning the rotor within the stator. 
     BACKGROUND OF THE INVENTION 
     A progressing cavity pump (PCP) is a well known pump, frequently called a “Moineau” pump, that has an elastomeric outer element or stator has a helical inner surface. A metal rotor having a helical exterior inserts within the stator. 
     Progressing cavity pumps of this type are used for many purposes, particularly, for pumping viscous liquids. These pumps are also used as oil well pumps. When used as an oil well pump, the stator is secured to the lower end of the well tubing and lowered into the casing of the well with the well tubing. The rotor is secured to the lower end of the drive rod and lowered through the tubing to a position inside the stator. The drive rod is rotated by means of a rotary power source at the surface or within the wellbore. 
     U.S. Pat. No. 7,201,222 (Kanady et al.) teaches a tag shoulder above the helical passage of the stator. The tag shoulder is more restrictive than a passage through the tubing. A pump rotor has a stop located above the rotor. The stop will freely pass through the tubing, but will not pass through the tag shoulder. The rotor is lowered on the rods until the stop lands on the tag shoulder and then the rotor is lifted to accommodate for expected stretch during operation. The stop is dimensioned so that it will orbit without contact with the tag shoulder. 
     It is, therefore, desirable to provide a progressing cavity pump assembly that provides improved axially positioning the rotor within the stator. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to obviate or mitigate at least one disadvantage of previous apparatus and method for axially positioning a PCP rotor within the PCP stator. 
     During the spacing out of a progressing cavity pump, when run-in on the rod string the rotor must be landed in the correct working location within the stator. In order to do this, some method of tagging and confirming the location of the rotor at the surface is needed. Traditionally, this has been through the use of a tagging pin or plate below the stator. The present invention provides a top-tag coupling assembly which includes a rotor head which is larger than the rotor helix, to tag on a narrowing shoulder section of a tubing string collar or coupling above the stator. 
     The tag-coupling may be aligned radially (timed) with the stator using a jig. Due to the helical shape of each rotor and the double helix opening in each stator a unique path or trajectory is traced by the rotor as it is threaded into the stator. Even small interferes with this path may hinder the run-in of the rotor or the operation of the pump. The present invention provides a narrowing tag shoulder which closely approximates this path allowing smooth run-in and operation. Apart from this, a top-tag coupling is similar to a typical collar normally threaded to the output end of a stator. Once threaded on hand tight, there is still thread enough to time the tag shoulder to end up in close proximity to the entrance of the stator helix, reducing inherent binding. The present invention provides a top-tag coupling to fit a group of pumps and once timed are welded to maintain the proper orientation of top-tag coupling to stator. 
     The elimination of the pin, plate, or bar below the pump, restrictions on fluid intake are lessened, production may be increased, and it is possible to coil monitoring or other equipment pas the rotor without obstruction. As well, production and assembly are somewhat streamlined. 
     In a first aspect, the present invention provides a PCP assembly, having a housing with a stator, having a stator bore, the housing adapted to receive a rotor within the stator bore, a collar assembly, having an inside diameter upset, the collar assembly adapted to connect the housing and a tubing string, and the rotor having a rotor head axially spaced from a rotor helix, the rotor head having an outer diameter forming a stop, the stop adapted to land on the inside diameter upset, the rotor head adapted to connect with a drive string. 
     Preferably, the housing and the collar assembly are axially and/or rotationally movable until the collar assembly and housing are timed. After they are timed, preferably they are welded. Preferably, the connection between the housing and the collar assembly is a slip fit or threaded connection. The housing and the collar assembly may be integral. 
     Preferably, the collar assembly is a coupling. The coupling may form a swage. The housing may have a greater diameter than the diameter of the tubing string. The diameter of the housing may be less than the diameter of the tubing string. The diameter of the housing and the diameter of the tubing string may be substantially equal. 
     Preferably, the collar assembly and the housing are proximate. Preferably, the collar assembly and the housing are adjacent. 
     Preferably, the inside diameter upset comprises a tag shoulder. The tag should may have an axial profile. The profile may be straight or planar. Preferably, the profile includes a taper, a chamfer, or a fillet. 
     Preferably, the inside diameter upset comprising a coupling tag bore, the coupling tag bore adapted to allow the threading of the rotor through the coupling tag bore. Preferably, the coupling tag bore timed to the stator bore to allow insertion of the rotor. 
     Preferably, the coupling tag bore and the stator bore forming a pathway, the pathway adapted to movably receive the rotor. Preferably, the pathway is adapted to receive the rotor in a rotating threading motion. 
     In a further aspect, the present invention provides a method of operating a PCP assembly, comprising providing a tubing string, providing a housing comprising a stator, a collar assembly, timed to the stator, connected with the housing, the collar assembly having an inside diameter upset, connecting the tubing string and the housing, installing the tubing string and the housing into a wellbore, providing a drive string, providing a rotor having a rotor head axially spaced from a rotor helix, the rotor head having an outer diameter forming a stop, connecting the rotor and the drive string, installing the rotor and the drive string into the wellbore by rotatably threading the rotor into the stator through the collar assembly until the stop lands on the inside diameter upset, and lifting the rotor a selected distance by lifting the drive string from surface. 
     Preferably, the method includes rotating the drive string, thereby rotating the rotor within the stator to pump fluids from the wellbore up the tubing string. 
     In a further aspect, the invention provides a method of timing a progressing cavity pump assembly by providing a housing comprising a stator, having a stator bore, providing a collar assembly, the collar assembly having an inside diameter upset, movably connecting the collar assembly and the housing, providing a timing piece, the timing piece having a timing helix adapted to fit the stator bore, selectively adjusting the relative position of the collar assembly and/or the housing to form a pathway substantially corresponding to the timing helix, providing a rotor having a rotor head axially spaced from a rotor helix, the rotor head having an outer diameter forming a stop, and installing the rotor into the housing by threading the rotor into the stator through the collar assembly until the stop lands on the inside diameter upset, and fixing the relative position of the collar assembly and/or the housing. 
     Preferably, the timing piece is a timing jig or the rotor. 
     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
         FIG. 1   a  is a vertical cross-section view of a PCP assembly in accordance with the present invention, showing the rotor being threaded into the stator; 
         FIG. 1   b  is a vertical cross-section view of the PCP assembly of  FIG. 1   a , showing the stop landed on the inner diameter upset; 
         FIG. 2   a  is a vertical cross-section view of a PCP assembly in accordance with the present invention, showing the rotor being threaded into the stator; 
         FIG. 2   b  is a vertical cross-section view of the PCP assembly of  FIG. 2   a , showing the stop landed on the inner diameter upset; 
         FIG. 3   a  is a detail top view of a collar of the present invention, showing a collar adapted for a housing and a tubing string of approximately the same diameter; 
         FIG. 3   b  is a detail vertical cross-section view of the collar of  FIG. 3   a;    
         FIG. 4  is a perspective cross-section view of a collar assembly of the present invention, showing a coupling adapted for a housing diameter greater than the tubing string diameter; 
         FIGS. 5   a - d  are perspective views of a PCP assembly in accordance with the present invention, showing the timing of the collar and stator; and 
         FIG. 6  is a vertical cross-section of a PCP assembly in accordance with the present invention, showing a housing having a diameter greater than the tubing string. 
     
    
    
     DETAILED DESCRIPTION 
     Generally, the present invention provides a method and apparatus for providing a top tag system for a progressing cavity pump (PCP). 
     Referring to  FIGS. 1   a - b  and  2   a - b , a PCP assembly  10  of the present invention provides a housing  20  having a stator  30 , the stator  30  having a stator bore  40 . 
     A collar assembly  50  joins the housing  20  and a tubing string  60 . The joint may be threaded or slip on. A weld  70  or other bond (such as adhesive) fixes the joint in place. The weld  70  may be a tack weld or seal welded. Alternatively, the collar assembly  50  may be integral with the housing  20 . The collar assembly  50  has an inner diameter upset  80  in the form of a tag shoulder  90  having a coupling tag bore  100 . The collar assembly  50  is timed to the stator bore  40  such that a pathway  110  is formed by the coupling tag bore  100  and the stator bore  40 . 
     In the preferred embodiment shown, the collar assembly  50  forms a swage  115 , the tubing string  60  having a greater diameter than that of the housing  20 . 
     A rotor  120 , having a rotor head  130  axially spaced from a rotor helix  140  is received in the stator bore  40  through the pathway  110 . The rotor head  130  incorporates an outer diameter  150  forming a stop  160 . The rotor  120  is rotatably threaded into the stator bore  40  through the pathway  110  on a drive string  170 . 
     The stop  160  of the rotor  120  lands on the inner diameter upset  80  in the form of a tag shoulder  90 . 
     Referring to  FIGS. 3   a - b , the collar assembly  50  provides an inner diameter upset  80  in the form of a tag shoulder  90 , having a coupling tag bore  100 . The coupling tag bore  100  is substantially timed to the stator bore  40  to allow the insertion of the rotor  120  with reduced interference. The tag shoulder  90  has an axial profile  180  to land the stop  160  of the rotor  120 . The axial profile has a taper  190  at an angle  200 . The angle  200  preferably is within a range of about 0 to 90 degrees. Preferably, the angle  200  is between about 15 degrees and about 75 degrees. Preferably, the angle  200  is about 45 degrees. Preferably, the tag shoulder  90  includes a conical ledge  92 . Preferably, tag shoulder  90  has a beveled edge  94 . 
     Referring to  FIG. 4 , the collar assembly  50  in the form of the coupling  115  provides an inner diameter upset  80  in the form of a tag shoulder  90 , having a coupling tag bore  100 . The swage  115  is adapted to receive the tubing string  60  (see  FIGS. 1   a - 1   b ) having a diameter greater than that of the housing  20  (see  FIGS. 1   a - 1   b ), in this case, the coupling  115  being a swage. 
     The tag shoulder  90  has an axial profile  180  to land the stop  160  of the rotor  120 . The axial profile has a taper  190  at an angle  200 . The angle  200  preferably is within a range of about 0 to 90 degrees. Preferably, the angle  200  is between about 15 degrees and about  75  degrees. Preferably, the angle  200  is about  45  degrees. 
     Referring to  FIGS. 5   a - d , the housing  20  has the stator  30  having the stator bore  40 . The corresponding collar assembly  50  is attached to the housing  20  by a threaded or slip on connection. The axial and rotational position of the collar assembly  50  is selectively adjusted to approximate the pathway  110  through the coupling tag bore  100  and the stator bore  40  for the rotor  120 . 
     The rotor  120  or a timing jig  125 , referred to generally as a timing piece  127  having a timing helix  129  adapted to fit the stator bore  40  is threadably (axially and rotatably) inserted through the coupling tag bore  100  and the stator bore  40 . In the case of the rotor  120 , it may be inserted until the stop  160  lands on the tag shoulder  90 . The position of the collar assembly  50  is selectively adjusted relative to the housing  20  to reduce or minimize the interference between the timing piece  127  (whether it is the rotor  120  or the timing jig  125 )  140  and the pathway  110  to allow the smooth insertion and/or removal of the rotor  120 . The collar assembly  50  may then be fixed to the housing  20  by a weld  70 . A timing jig  125  or a ‘core’, known to one skilled in the art, is in the form of a double stator (as shown). Preferably, the timing jig  125  is used to tag the rotor  120  as described. 
     In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments of the invention. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the invention. 
     As used herein tubing string may include conventional jointed tubing or endless or coiled tubing or a combination thereof. 
     As used herein drive string may include conventional jointed sucker rod, continuous sucker rod, jointed drive rod, continuous drive rod or a combination thereof. 
     The present invention has been described generally in terms of a one (1) lobe rotor, two (2) lobe stator for simplicity. One skilled in the art recognizes that the present invention is applicable to PCP pumps generally, which includes two (2) lobe rotor/three (3) lobe stator, three (3) lobe rotor/four (4) lobe stator, four (4) lobe rotor/five (5) lobe stator, seven (7) lobe rotor/eight (8) lobe stator, or generally n lobe rotor/n+1 lobe stator. The corresponding timing jig  125  having n+1 lobes. As shown in  FIG. 5 , the timing jig  125  has two lobes. 
     The above-described embodiments of the invention are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.