Patent Application
20110103989
The field of the invention is Moineau progressing cavity pumps for subterranean use and more particularly to a feature that facilitates rotor alignment with the stator where the tag shoulder is a reinforced upper section of the stator.
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.
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.
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. 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.
In the prior art, prior to running the tubing, the operator secures or welds a tag bar across the bottom of the stator. During installation, downward movement of the rods will stop when the lower end of the rotor contacts the tag bar at the bottom of the stator. Upon tagging the bar, the operator pulls the rod string back toward the surface by the calculated amount of rod stretch. During operation, as well fluid fills the tubing, the rod stretches, allowing the rotor to move back downward until in full engagement with the stator. If installed properly, once the rods have stretched fully, the lower end of the rotor will be spaced above the tag bar and the rods will be in tension.
While this method works well enough, tag bar creates an obstruction at the bottom of the pump. The obstruction prevents the operator from lowering tooling or instruments through and below the pump for logging, tagging fill, and other monitoring related purposes. Other problems with this approach are the obstruction to flow during operation, and the tendency of sand and well debris to accumulate around the tag bar and clog the intake.
U.S. Pat. No. 7,201,222 teaches of a tag method in which the tag location is an interference shoulder above the pump. The tag shoulder is located above the stator in a reduced diameter collar connected to the tubing, while the rotor tag is connected to the rod string above the rotor. When the rotor is lowered down and reaches its appropriate location relative to the stator, the stop on the rotor rod string interferes with the reduced diameter collar located above the stator in the tubing string, preventing the rotor from progressing further into the stator. While some of the above issues were overcome with this method, there was still the issue of proper placement of the tag bar with respect to the stator. To avoid the eccentric rotation of the rotor, proper distance had to be placed between the tag area and the top of the stator. As the tag location on the collar has to match up directly with the tag location on the rotor rod string, long precision equipment would be required, as well as specialized equipment to prevent the stop on the rotor rod string from damaging the tubing as the rod string rotated. In addition, this method would present more flow obstruction problems, now moved from below the pump to above the pump.
Similarly, U.S. Publication 2009/0136371 suggests a method that lowers the tag surface to just above the stator, by shaping the pass through hole in the tag collar located in the tubing string above the stator or integral with the stator, in such a way that the rotor eccentric motion would not cause the rotor to contact the through hole. More simply, the opening is shaped like the stator helical cavity, so as the collar is placed directly above the stator and timed correctly using a timing jig, the rotor should operate freely in the collar. The rotor tag would then locate on what would be the minor diameter of the collar through hole. To avoid damage from heat if welding was used to secure the tag bar above the stator, there still needed to be a substantial spacing between the stator top and the tag bar. If connections that were threaded were used instead placement issues could exist. A threaded connection was difficult to properly torque while still winding up with the needed alignment of the oblong openings. If the thread had to be backed up after being torqued to align the stator and collar openings then the torque for the connection was reduced, which risked the connection getting subsequently undone while the pump was in service.
Also relevant to issues of rotor placement are U.S. Pat. Nos. 5,209,294 and 5,725,053.
The present invention addresses the issues with top tag systems of the past by removing the need for an additional collar or timing equipment, by simply reinforcing the rubber in the upper section of the stator helix to the point that the rubber will not “give way” to an increased shoulder in the rod string. This also reduces, if not eliminates, the possible cavity between the tag surface and the top of the stator. What allows this to happen is that the upper section of the stator is reinforced in some way, such that when the rotor is delivered on rods its travel stop lands on the reinforced upper stator so that proper alignment is obtained. The rotor is then lifted the requisite amount and the pump is ready to run. These and other advantages of the present invention will be more readily understood by those skilled in the art from a review of the specification describing the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.
In one embodiment of this invention, the upper section of the rubber stator helix is reinforced with reinforcement tags. The reinforcement tags are secured inside a stator housing through holes in the housing wall. An adhesive can be applied to the housing inner wall. The stator core is then inserted in the stator housing with the reinforcement tag segments secured. By inserting the reinforcing tags prior to rubber injection, the core can be aligned with the tags, eliminating the need for later timing devices. Also, the core can be inserted prior to the tags being placed. End caps are placed over the core and rubber or other resilient material is injected into the annular space between the core and the housing inner wall until the space is filled as noted when the resilient material exits the end caps. The end caps and core are removed leaving the reinforcement tags embedded in the stator helix. The rotor advances until it lands on the rubber just above the reinforcement tags and in alignment with the stator.
Alternatively, the stator helix composition can be chemically altered in the location where the tags would otherwise go so as to integrate the tags into the stator and properly locate this harder segment with respect to the core to eliminate the need for subsequent timing devices.
a is a section along lines 2a-2a of
a is a detailed view of a part of
In the manufacturing method, the core 30 is placed inside the housing 10 after the housing inside wall 32 and/or the reinforcing tags 12 and 14 are coated with an adhesive. The reinforcing tags 12 and 14 are placed in the housing 10 prior to or after the core 30 is inserted, fixed to the inside wall 32, and the core 30 is rotated to center the helical profile between the reinforcing tags 12 and 14. With the core 30 and reinforcing tags 12 and 14 in the housing 10, the end caps 34 and 36 are attached to the core 30 to center it in housing 10. The annular space 38 is filled with rubber or some other resilient material while the reinforcing tags 12 and 14 are in the annular space 38. The injected material bonds to the adhesive on the inner wall 32 and the top tags 12 and 14 that were in the annular space 38. Except for the presence of the reinforcing tags 12 and 14 in the annular space 38 the remaining steps to form the stator 28 in its housing 10 are well known to those skilled in the art.
Referring to
In
As
It should also be noted that the fasteners 16 and 18 can be retained with lock nuts, pins or snap rings to keep them from backing out when the stator 28 is manufactured. If the connection to the housing 10 interior wall 32 is with threads then snap rings or set screws can also be used to hold the tags 12 and 14 in position. Preferably the tags 12 and 14 are embedded in the stator helix 28 so that in use leak paths do not develop to any holes for fasteners in the housing 10 or behind the stator helix 28 and in the housing 10. The presence of the tags 12 and 14 gives strength to the top of the stator helix 28 so that it can support the rotor stop 70 when it lands as shown in
As alternative embodiments to embedded and preferably metallic tags 12 and 14 being disposed in the stator helix 28, the tags 12 and 14 can be non-metallic discrete structures from helix 28 or they can actually be integrated into the structure of the helix 28. For example, the stator helix 28 can be a composite of discrete rubber shapes with the tags 12 and 14 being a harder rubber that is initially placed and secured in the housing 10 before the stator helix 28 is formed in the manner described above. Alternatively, as the stator helix 28 is formed, the rubber formulation can be changed so that the upper end winds up being stiffer or harder to the point where the stator helix assembled in this manner as a unitary rubber, for example, structure can act as a travel stop to the rotor 68.
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.
