Subsurface Pump Holddown Apparatus

Abstract

A lower mandrel threadedly connected to a subsurface pump barrel at its lower end is threadedly connected to an upper mandrel and through which a rod assembly adapted to reciprocate a pump piston through such barrel is adapted to be lowered from the earth's surface by the rod assembly to a restricted diameter tubing seal located within a tubing string in an earth borehole. A collected tubular member adapted to rotate about the lower mandrel is caused to deflect inwardly in passing through the tubing seal ring and further movement of the apparatus through the seal ring causes it to be locked in place within the tubing string. The single split collet entails a lower split shoulder which can deflect through the sealing ring with a second upper shoulder tapered to fit the taper on the top of the seal ring after passing through the ring, the lower shoulder of the collet being allowed to expand out to lock against the bottom of the sealing ring and hold the upper shoulder of the collet locked against the upper shoulder of the ring to thereby obtain a fluid seal between them.

Description

BACKGROUND OF THE INVENTION

This invention relates in general to apparatus for locking a subsurface pump in place within an earth borehole, and specifically to an apparatus for locking a subsurface pump within a string of tubing within an earth borehole.

It is well known in the art to lower a pump, for example, as with a rod assembly, through a string of tubing to the depth within an earth borehole at which pumping action is required. In lowering the pump through the tubing to its desired location, it has also been well known to lock a portion of the pump, for example, the barrel of the pump, in place within the tubig string so that the piston can be reciprocated within the barrel by action of the rod.

One known apparatus for locking the pump barrel in place within the tubing string is exemplified by the API standard part No. 11AX-S21. In this prior art apparatus, a box housing is positioned within the tubing string and the pump assembly is lowered through the box and a tubing seal ring located immediately beneath the box until a circumferential set of open ended spring-like fingers pass through the seal ring to thus lock the pump in place within the tubing string. This type of pump lock assembly requires a multiplicity of parts having critical distances between tapered faces of separate parts which results in extremely expensive manufacturing costs. It has also been commonplace when using such prior art apparatus that the yield strength of the materials used in the fingers is exceeded by the forces needed to cause such fingers to go through the seal ring. Thereafter, the apparatus will not reset and hold the same load as previously attainable.

Such prior art apparatus is also hampered by the reduction in flow around the rod because the multiple part assembly requires more space and thus less fluid passage.

It is therefore the primary object of the present invention to provide a new and improved assembly for locking a pump in place within a tubing string;

It is yet another object of the present invention to provide a new and improved pump holddown assembly having improved operating characteristics;

It is yet another object of the invention to provide an improved pump holddown assembly having a reduced number of parts;

It is still another object of the invention to provide a new and improved pump holddown assembly which will positively lock and seal with a predetermined force and yet be reset without changing the holddown force;

It is also an object of the invention to provide a new and improved pump holddown assembly having increased fluid passage around the valve rod; and

It is also an object of the present invention to combine within a pump holddown assembly the holding mechanism and seal within a single unit.

The objects of the invention are accomplished, generally, by an apparatus attachable to a rod assembly and having at its lower end means for attaching a subsurface pump, such apparatus including a split double-ended collet adapted to be engaged with, locked into place within and sealed with a ring within the tubing string.

These and other objects, features and advantages of the present invention will be more readily understood from a reading of the following detailed specification and drawing, in which:

FIG. 1 is an elevational view in cross section of an apparatus according to the prior art;

FIG. 2 is an elevational view, partly in cross section and partly in pictorial illustration, of an apparatus according to the present invention;

FIG. 3 is an elevated view in cross section of a mandrel forming a part of the apparatus according to the present invention;

FIG. 4 is a plan view through the section A--A of FIG. 3; and

FIG. 5 is an elevated view in cross section of a tubular member adapted to encircle the mandrel illustrated in FIG. 3 according to the invention.

Referring now to the drawing in more detail, especially to FIG. 1, there is illustrated a prior art pump holddown assembly 10 in its locked position within a tubing string 11 which is itself within the interior of a casing 12 in an earth borehole. A rod assembly 13 passes through the interior of the holddown apparatus 10 and the barrel 14 of a pump assembly used for pumping fluids from earth boreholes, for example, oil and gas wells. Although not illustrated, it should be appreciated that the rod 13 is connected to a plunger within the pump barrel 14 and is adapted to reciprocate within the pump barrel to produce a pumping action. It should also be appreciated that the tubing 11, the casing 12 and the rod assembly 13 extend from the earth's surface.

A tubing seal ring 15 is inserted between the threaded sections 16 and 17 of the tubing string 11, the seal ring 15 having an internal diameter slightly smaller than the circumferential spring-like fingers 18 and 19 mounted on the apparatus 10. A holddown seal ring 20 is mounted on the apparatus 10 and is in a metal-to-metal sealing arrangement with the tubing seal ring 15 when the apparatus 10 is locked in place within the tubing string 11.

In the operation of the apparatus according to FIG. 1, the apparatus 10 is attached to the rod assembly 13 and is lowered within the tubing string 11 from the earth's surface (not shown). It should be appreciated that the apparatus 10 has limited movement along the length of the rod assembly 13 depending upon the stroke of the piston (not illustrated) within the pump barrel 14. The pump barrel 14 is sized to pass through the tubing seal ring 15. By placing additional weight on the rod assembly, the spring-like fingers 18 and 19 are forced to contract and are passed through the tubing seal ring 15. In this locked position, the holddown seal ring 20 prevents the apparatus 10 from traveling further down the borehole through the tubing string 11 and the fingers 18 and 19 prevent the assembly from going back uphole. Thus, the assembly 10 is locked in place within the tubing string 11. Thereafter, by reciprocating the rod assembly 13, the piston attached to the rod assembly is reciprocated within the pump barrel 14 and a pumping action occurs of the fluids within the borehole. A metal-to-metal seal occurs between the tapered upper face of the seal ring 15 and the lower tapered face of the holddown ring 20.

With such a prior art apparatus 10 as is illustrated and described with respect to FIG. 1, the pulrality of spring-like fingers must be compressed a considerable amount in order to enable the pump locking operation of the apparatus. In so doing, the yield strength of the material from which the fingers 18 and 19 are constructed is often exceeded and thus an element of uncertainty is introduced as to the force necessary to set and to unlock the apparatus. Likewise, it should be appreciated that because of the multiplicity of parts involved with the apparatus 10, there necessarily is a reduced amount of fluid which can flow internal to the apparatus 10 and around the exterior of the rod assembly 13. It should also be appreciated that the fingers 18 and 19, illustrated as being only a pair of fingers, usually comprises a larger number of fingers, for example, seven or eight of such fingers. In manufacturing the apparatus 10 according to the prior art, the exact distances between tapered faces of the several parts are extremely critical and are difficult and expensive to manufacture and to fabricate.

Referring now to FIG. 2, the apparatus according to the present invention, referred to generally by the numeral 30, is attached to a subsurface pump having a pump barrel 34 in a similar manner as was described with respect to the apparatus of FIG. 1. The apparatus 30 and the subsurface pump is connected to a rod assembly 33, the apparatus 30 being adapted to be lowered into an earth borehole through a tubing string 31 which is inside of the casing 32 within the borehole. A tubing seal ring 35 identical to the seal ring 15 of FIG. 1 is secured within a tubing string 31 between the threaded sections 36 and 37 of the tubing string 31. The apparatus 30 according to the present invention has an upper mandrel 40 having one or more ports 41 providing a means of fluid communication between the pump and the annulus of the tubing string 31 above the apparatus 30. The apparatus 30 also has a lower maandrel 42 and a tubular sleeve 43 which is locked in place against rotation around the lower mandrel 42 by means of the groove 44 in the lower mandrel 42 and the extension 45 forming a part of the sleeve 43. It should be appreciated that there are a pair of such grooves and extensions 180.degree. apart around the circumference of the mandrel 42 and the sleeve 43, each of which is illustrated in greater detail in FIGS. 3, 4 and 5.

Referring again to FIG. 2, the colleted sleeve 43 has a centralized recess area 50 which is adapted to mate with the tubing seal ring 35 whenever the apparatus 30 is locked in place within the tubing string 31.

The recessed area 50 is formed by a lower split shoulder 52 which deflects through the seal ring 35 and having an upper shoulder 53 tapered to fit the taper of the top portion of the seal ring 35.

In the operation of the apparatus according to FIG. 2, the apparatus 30 and the subsurface pump is lowered through the tubing string 31 until such time as the collet passes through the seal ring 35. The split shoulder area 51 deflects inwardly to pass through the seal ring 35 and the shoulder 53 is then in engagement with the top tapered section of the seal ring 35. After passing through the seal ring 35, the lower shoulder 52 of the collet is allowed to expand out to lock against the bottom tapered surface of the seal ring 35 and hold the upper shoulder 53 of the collet locked against the upper shoulder of the seal ring 35 to obtain a fluid seal between the shoulder 53 and the seal ring 35. The raised area 51 of the colleted surface has a third shoulder 54 which first engages the seal ring 35 as the apparatus 30 is being lowered through the tubing string 31. The sleeve 43 has a plurality of openings 55 and 56 which enable the sleeve 43 to be depressed and thus pass through the seal ring 35.

Referring now to FIG. 3, the lower mandrel 42 is illustrated in greater detail. The mandrel 42 is essentially tubular in shape and has an upper threaded section 60 adapted to threadedly engage the upper mandrel section 40 of FIG. 2. The lower mandrel 42 has an internal threaded box lower end 61 which is adapted to be threadedly connected to a pump barrel 34 illustrated in FIG. 2. The lower mandrel 42 also has a reduced diameter portion 62 which enables the colleted tubular section 43, illustrated in greater detail in FIG. 5, to be depressed when passing through the seal ring 35 within the tubing string. A pair of grooves 44 and 44', only one of which can be seen in FIG. 2, are formed 180.degree. apart around the periphery of the lower mandrel 42, the grooves 44 and 44' being formed at the interface of the reduced diameter section 62 and the raised portion 63 of the lower mandrel 42. An intermediate diameter portion 64, being approximately the same diameter as the internal diameter of the tubular member 43, is arranged to provide a surface 65 upon which the tubular member 43 can rotate.

Referring now to FIG. 4, a cross-sectional view through the section A--A of FIG. 3 illustrates in greater detail the grooves 44 and 44' and the surface 65 upon which the tubular member 43 can rotate.

Referring now to FIG. 5, the tubular member 43 is illustrated having a lower extension 45 which is adapted to lock in place in the groove 44 in the lower mandrel 42 when properly rotated. It should be appreciated that there is a corresponding lower extension 45' (not shown) which mates with the other groove 44'. It should also be appreciated that the tubular member 43 can rotate in either direction into the locking position around the mandrel 42. As further illustrated in FIG. 4, the shoulder 52 is preferably of a sharper angle than that of the shuolder 54 whereby a lesser force is required to lock the assembly in place on the seal ring 35 than the force required to unlock the device. Thus, in a typical installation, the apparatus might be set in place around the seal ring 35 with approximately 500 or 600 pounds for the locking step whereas approximately 2,000 pounds might be required to unlock the apparatus from the seal ring 35.

A pair of grooves 70 and 71 are formed in the upper section of the tubular member 43 for receiving a pair of 0-rings 72 and 73, respectively, to provide a fluid seal between the tubular member 43 and the upper increased diameter section 74 of the mandrel 42 in FIG. 3.

Thus, it should be appreciated that there has been illustrated and described herein the preferred embodiments of a new and improved holddown apparatus for locking a subsurface pump within a tubing string in an earth borehole. Because of the reduction of the number of parts and the overall simplicity of the apparatus described herein, the apparatus is far easier and less expensive to fabricate than those apparatus of the prior art. As a special feature of the invention, it should be appreciated that because of the reduction of the number of parts, additional room is provided for fluid to pass through the apparatus and around the rod assembly 33 which passes therethrough. Likewise, it should be appreciated that the apparatus according to the present invention enables a means for locking and for sealing the apparatus to the sealing ring within the tubing string from a single assembly and does not depend upon a holding ring for sealing purposes as does the prior art apparatus as is illustrated in FIG. 1.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for holding a rod-actuated subsurface pump in place within a tubing string having a seal ring therein, comprising:

a tubular mandrel attached to said pump;

a tubular sleeve having a double-ended, split-shoulder collet portion enclosing and locked against longitudinal movement on said mandrel, said portion having an external diameter larger than the internal diameter of said seal ring and adapted to compress and pass through said seal ring upon the application of a predetermined force to said mandrel by a rod assembly from the earth's surface; and,

sealing shoulder means on said tubular sleeve adapted to engage said tubing seal ring in sealing engagement upon engagement of said collet portion in said seal ring.

2. The apparatus according to claim 1, including in addition thereto, fluid seal means between said mandrel and said sleeve.

3. The apparatus according to claim 1, including in addition thereto, means to lock said sleeve against rotation around said mandrel.

4. The apparatus according to claim 1, said collet portion being further characterized by a first shoulder locking said apparatus against a lower tapered shoulder on said seal ring and thus against upward movement in the borehole and a second shoulder locking said apparatus against an upper tapered shoulder on said seal ring and thus against downward movement in the borehole, said second shoulder and said seal ring providing a fluid seal therebetween.

5. The apparatus of claim 4 wherein said tubular sleeve has an annular raised shoulder ring passing circumferentially around said sleeve and containing said first shoulder on the upper side thereof and a third shoulder on the lower side thereof for camming against said seal ring shoulders when passing therethrough.

6. The apparatus of claim 5 wherein said first shoulder is at a relatively abrupt angle with the central longitudinal axis of said sleeve; said third shoulder is at a less abrupt angle with said axis thereby providing a slanted camming surface for ease in lowering through said seal ring; and said first surface provides a greater resistance to upward movement of said shoulder ring through said seal ring.

7. The apparatus of claim 1 wherein said tubular mandrel further comprises an upper raised shoulder portion having a cylindrical exterior sealing surface; a recessed expansion area interior of said tubular sleeve collet portion and spaced concentrically inward therefrom; and a lower abutment means having an intermediate rotation shoulder therein for receiving said tubular sleeve in abutting relationship and maintaining said sleeve spaced concentrically from said recessed area while preventing downward movement of said sleeve on said mandrel.