The present invention relates to progressing cavity pumps and motors, and more particularly relates to improvements in downhole progressing cavity pumps or motors which facilitate reliable operation at relatively high temperatures and/or pressures.
Operating temperatures and pressures for progressing cavity downhole pumps and motors have been generally considered to be limited by the adhesive used to bond the polymeric sleeve to the stator tube or housing. A seal gland of the type disclosed in U.S. Pat. No. 7,407,372 in a downhole pump or motor operates well in steam and high sand content wells where conventional bonding of the polymeric layer to the stator has failed.
Axial grooves in the inside wall of a cylindrical stator tube have been proposed to prevent rotation of the polymeric sleeve due to torque. These grooves are large relative to the stator tube, and were often a quarter or more of the tube width. Other manufacturers have sought to retain the polymeric sleeve on the tube by molding a flange on the end of the sleeve.
Relevant patents include U.S. Pat. Nos. 6,309,195, 7,131,827 and 7,407,372. Other patents of interest include U.S. Pat. Nos. 5,474,432, 4,313,717, 4,029,443, and 7,192,260. Asymmetric contouring of the polymeric liner is disclosed in U.S. Pat. No. 7,083,401.
The disadvantages of the prior art are overcome by the present invention, an improved progressing cavity pump/motor is hereinafter disclosed.
In one embodiment, a progressing cavity pump/motor comprises a rigid stator housing which has an interior surface, a polymeric layer within the stator housing and having has a radially outer surface in engagement with the stator housing and radially interior profiled surface, and a rotor within the polymeric layer for rotation relative to the stator housing and the polymeric layer. A plurality of circumferentially spaced and axially extending grooves are formed in the interior surface of the stator housing and receive polymeric material therein, the plurality of grooves including one of the necked grooves and intersecting grooves. At least one seal gland adjacent an end of the polymeric layer maintains sealing between the stator housing and the polymeric layer, with the seal gland including a lip axially extending toward a central portion of the polymeric layer.
These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.
Improvements concerning the bonding between the polymeric layer and the stator housing are disclosed. More particularly, a combination of one or more seal glands and grooves in the inner surface of the stator housing reliably grip the elastomer to the stator housing to prevent the elastomer from “peeling” away from the housing. This problem is significantly acute for downhole applications wherein the pump/motor is subjected to high temperature, high pressure, or a combination of high temperature and high pressure. In some applications, the ability of the polymeric layer to withstand high forces is also adversely influenced by the type of downhole fluids and solids (sand) which flow through the pump/motor.
Referring now to
The feature of intersecting grooves is shown more clearly in
The stator housing may be manufactured from a single, heavy wall tube. The concepts disclosed herein may be used on a unitary stator housing manufactured from steel or other materials, including composite materials. For a uniform polymeric thickness application, the desired profile or contour may be cut directly into the stator housing interior wall. A polymeric sleeve of an even rubber thickness may be bonded to the housing to form the stator. The concepts disclosed herein may also be used with a cylindrical stator housing and a polymeric sleeve which has a varying thickness. Also, the concepts disclosed may be used on stator housings with non-circular outer configurations, including a spiraling configuration with an exterior stator surface matching the interior stator profile for 1:2 geometry (1 rotor lobe: 2 stator lobes) since the grooves and the seal glands may still be used to secure the polymeric layer to the stator housing. A seal gland matching the stator profile rather than circular seal gland may thus be provided at an end of the polymeric layer. The features of the present invention may be used with various bonding materials so that the combination of grooves, seal glands, and bonding materials create a mechanical lock between the tube and the polymeric sleeve.
In one embodiment, a plurality of axially extending grooves are each aligned with the stator helix, i.e., the grooves are each shaped in a spiral or helical configuration. A helical groove provides support for the sleeve around the entire perimeter of the stator housing and may maximize resistance of the polymeric sleeve to movement of the housing. A conventional “tapered” groove may be used which has an opening throat which is the same or wider than the radially outer (deeper) portion of the groove. A “necked” groove is a groove wherein the throat adjacent the inner surface housing is narrower than a radially outer (deeper) portion of the groove, so that the groove itself provides mechanical locking of the elastomer to the stator housing. The use of grooves also increases the bonding area between the elastomer and the stator.
In one embodiment, axial movement of the sleeve relative to the stator tube is prevented with the use of grooves which intersect at one or more locations. Intersection can be achieved by the use of different or variable pitch length grooves, grooves with an opposite direction of lead, or grooves generally concentric about the tube axis intersecting axially extending, spiraling grooves. Necked grooves or tapered grooves may be used, particularly with intersecting grooves.
A stator housing or tube for a progressing cavity pump/motor preferably includes axially extending grooves on its inner surface, which may be spiraling grooves which follow the contour of the stator lobes. The stator housing may have a circular cross-sectional configuration, a spiraling oval cross-sectional configuration, or a multi-lobed cross-sectional configuration. In such cases, the stator housing will have a nominal or “standard” wall thickness. The groove depth preferably is from 5% to 25% of the wall thickness, which provides a sizable cross-sectional cavity for the elastomer to hold the elastomer in place, while not significantly reducing the strength of the stator housing.
The grooves on the inner surface of the stator housing are also elongated in that each groove has a length significantly greater than its width. Continuous grooves may be formed along substantially the entire length of the stator housing, or a foot long axially extending groove may be formed, followed by several inches of no groove, followed by a continuation foot long axially extending groove, etc. Grooves in the interior surface of the stator may have a dovetailed cross-sectional configuration, with the sidewalls projecting outward from the groove centerline so that the throat of the groove is less than a deeper, wider part of the groove. The groove alternatively may have one outwardly slanted side wall, and a “straight” side wall which is substantially perpendicular to the interior surface of the stator. In another alternative, both the side walls of the groove may be tapered outwardly, but at different angles relative to a centerline of the groove. In yet another embodiment, the groove has a generally truncated oval configuration, so that the throat is narrower than the widest part of the grooves, and the sidewalls of the groove extend downward and away from the groove centerline to form a curvilinear groove bottom with matching side walls.
Either axially extending grooves which do not match the contour of the stator lobes or intersecting grooves within a plane substantially perpendicular to a central axis of the stator may be a substantially uniform depth from a centerline of the pump/motor. In the case of the intersecting groove positioned within a plane perpendicular to centerline of the pump/motor, for example, each groove may cut through peaks of the stator lobes and “run out” before encountering the deep valley between the lobes, so that intersecting grooves may be provided on each side of a lobe, but not in the valley between the lobes. Similarly, axially extending grooves which do not match the profile of the stator may have a substantially uniform depth from the central axis of the pump/motor. In this case, the groove may extend axially downward in a spiraling manner and cut through a right side, a top, and a left side of the stator lobe, and the groove simply runs out onto the stator interior surface so that it is not formed in the deep valley between the lobes. A groove in the deep valley may be easily formed as an axially extending groove which matches the profile of the stator interior.
The circumferential spacing between the grooves is relatively short, and the lands between the grooves (interior surface of stator housing not having a groove) for a preferred embodiment may occupy from one to four times the surface area of the groove throats. This allows grooves to fill with the elastomer about a large portion of the circumference of the stator, thereby firmly securing the polymeric material in place.
A currently preferred groove geometry along the interior surface of the stator housing may conform to the following parameters: (1) a cross-section of the stator in a plane perpendicular to the central axis at the pump/motor may include two or more grooves in the valley between the stator lobe peaks, so that at least two grooves will be present in each valley to hold the elastomer in place; (2) a preferred ratio of groove throat to the widest part of the necked groove is between 45:100 and 95:100; and (3) the angle formed between a symmetrical or nonsymmetrical groove sidewall relative to the cross-section groove centerline between the groove throat and widest part of the groove is between 0° and 26°.
The technology presented herein improves the bond strength between the polymeric sleeve and tube (stator housing) by increasing the bond surface area between the sleeve (polymeric layer) and tube, and increasing the mechanical locking forces between the sleeve and tube. This groove technology preferably locks the polymeric sleeve to the tube by increasing the adhesive contact surface and thus the bond strength between the sleeve and the tube. The addition of helical grooves on the tube interior increases the resistance of the sleeve to move axially relative to the tube. The addition of intersecting grooves on the tube increases the resistance of the sleeve to move axially relative to the tube. The addition of helical grooves on the tube increases the resistance of the sleeve to rotate relative to the tube. The addition of intersecting grooves on the tube increases the resistance of the sleeve to rotate relative to the tube. The addition of helical grooves on the tube increases the resistance of the sleeve to move in the radial direction relative to the tube. The addition of intersecting grooves on the tube increases the resistance of the sleeve to move in the radial direction relative to the tube. The addition of helical necked grooves on the tube increases the resistance of the sleeve to move in the radial direction relative to the tube. The addition of intersecting necked grooves on the tube increases the resistance of the sleeve to move in the radial direction relative to the tube. This groove technology mechanically locks the sleeve to the tube by providing continuous, intersecting groove locking mechanism about the internal surface of the tube and maintaining a retention force normal to the tube surface even when this force does not act through the axis of the tube, i.e., even when the tube surface is not cylindrical. The mechanical lock design disclosed herein eliminates the need for adhesive while retaining the field proven ERT tube design, although an adhesive may still be used. The thermal, mechanical, and chemical limitations of the stator housing are now functions of only the elastomer.
The term “polymeric” as used herein for the layer 14 is intended to include polymeric and/or plastic materials suitable for use as the layer molded to the housing 12 of a pump/motor.
Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.
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Number | Date | Country | |
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20120156078 A1 | Jun 2012 | US |