Abstract:
Anchoring of a pack-off assembly of an oil well pump is improved by the provision of a tapered conical sleeve as a wedge for a friction seating ring which is forced outwardly against the inner surface of the pump barrel upon advancement of a nut carried on the end of the pack-off assembly. In addition, downward movement of the pack-off assembly in response to fluid pound is limited by the provision of the pump barrel as two separate pieces joined together with a coupling which includes a tapered section slightly reducing the cross section of the barrel but which permits passage of the lower piston by compressing spring-type seals carried by the piston as it passes through the reduced cross section.

Description:
INCORPORATION BY REFERENCE 
     This application incorporates material by reference, namely to U.S. Pat. No. 3,945,774, issued on Mar. 23, 1976. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention: 
     The present invention relates to well pump apparatus, and in particular to an anchorable pack-off assembly and a method for seating the assembly for use within the tubing of a well, in particular an oil well, and to well pump apparatus in which the effects of fluid pound are countered. 
     2. Description of the Prior Art 
     My U.S. Pat. No. 3,945,774, which is fully incorporated herein by this reference, discloses an anchorable pack-off assembly for use in the well tubing of an oil well, in which the tubing constitutes an outer pump casing (pump barrel). The pack-off assembly is included in a structure in which first and second one-way valves are provided in the tubing at opposite ends of the pump structure. A hollow member having an outer diameter less than the inner diameter of the tubing is disposed within the tubing and connected to a string of sucker rods for reciprocation. The hollow member is sealed to the inner surface of the tubing by a pack-off assembly which divides the volume between the upper and lower plungers into separate pumping chambers. The hollow member includes fluid passages above the pack-off assembly to provide fluid communication with the upper chamber so that during an up stroke fluid is drawn through the first valve into the lower chamber and, during a down stroke, fluid is expelled by way of the second valve carried on the upper plunger, from the lower chamber through the hollow member and from the upper chamber via the fluid passages and upward through the second valve and into the tubing above the second valve. 
     During installation, the pack-off assembly is pushed into the tubing by the upper plunger and sealed thereto by the way of annular friction seating rings on the body seating member of the body of the anchorable pack-off assembly. At times, it was found, that there was a difficulty in installation. The sizing of the friction seating rings on the body of the anchorable pack-off assembly is particularly critical. If these rings are a few thousandths of an inch too small, the pressure of the upper plunger pumping thereagainst during operation of the pump would displace the assembly. If the friction seating rings are a few thousandths of an inch too large, the assembly cannot be forced into the barrel. This problem is compounded by the American Petroleum Institute&#39;s allowable tolerance of the sizing of working barrels, which is the nominal size, +0.005&#34;, thus making a tolerance range of 0.010&#34;. 
     SUMMARY OF THE INVENTION 
     The object of the present invention, therefore, is to provide an improved anchorable pack-off assembly which overcomes the aforementioned installation problems, and to provide a method for seating the pack-off assembly. 
     According to the present invention, the above objects are achieved by the addition of a slidable tapered cone below the bottom seating ring. The tapered cone comprises a sleeve tapered to a sharp edge and constitutes an annular wedge installed on the anchorable pack-off assembly body with the smaller end up. Also, the lower end of the anchorable pack-off assembly body is provided with a left-hand thread and a left-hand threaded nut thereon. The lower edge of the nut includes two notches 180° apart. A coupling on top of the lower plunger, which couples the plunger to the hollow rod, is made with two lugs on its top end 180° apart. 
     To install the improved anchorable pack-off assembly, as before, the assembly on the hollow rod between the two plungers is lowered via the string of pump sucker rods down into the pump barrel where the upper plunger engages and forces the anchorable pack-off assembly into the barrel and pushes it into a desired anchoring location. The friction seating rings are tight enough against the anchorable pack-off assembly body and the barrel to cause interim anchoring to maintain the anchorable pack-off assembly in place. The string of pump sucker rods are raised until the lugs on top of the lower plunger come into contact with the bottom of the left-hand threaded nut at the bottom of the anchorable pack-off assembly body. By turning the string of pump sucker rods, from above ground, in a right-hand direction (counter-clockwise as viewed into the well bore), the lugs on the coupling engage the notches on the lower end of the nut causing the nut to turn and advance on the threads and push the tapered cone upwardly with its tapered smaller end entering between the lower friction seating ring and the seating member of the anchorable pack-off assembly body and causing the friction ring to be radially expanded circumferentially thereabout and wedging it more tightly against the barrel, thus effecting increased anchoring forces. 
     The above improvement per se works well in high fluid level wells that remain high fluid wells. Sometimes, however, in a well where, after a time, the fluid level has been lowered to a point where both chambers of the pump do not completely fill at the end of the up stroke of the pump, there is a condition known as &#34;fluid pound&#34;. When this condition exists, the plungers on the down stroke hit fluid and before the upper ball can be forced off the seat, sufficient pressure must be generated to overcome approximately 400 pounds of pressure per square inch of the plunger area per 1000 feet of well depth. This severe pounding, jarring, or hammering effect makes it difficult to maintain anchoring of the anchorable pack-off assembly. It is therefore another object of the invention to provide a pump structure for an anchorable pack-off assembly which overcomes the problem of fluid pound, and a method for installing such a pump structure. 
     According to the invention, this object of overcoming the problem of fluid pound is achieved in that, instead of using a one-piece barrel, two shorter barrels are used and connected with a coupling. The holes that were formally in the barrel are now provided in the coupling. Near the center of the coupling is a tapered reduced inner diameter area. This area is a few thousandths of an inch smaller than the inner diameter of the barrel, for example 0.008&#34;-0.009&#34; smaller. Spring-type plunger rings are used on the lower plunger, which rings are known in the art as Flexite rings or pressure-actuated rings. These rings are made of a hard, springy composition. By making the slotted nut on the bottom of the anchorable pack-off assembly a few thousandths of an inch, for example, 0.004&#34;-0.005&#34; smaller than the barrel, but larger than the reduced diameter of the pump barrel provided by the coupling, the lower plunger can be lowered through the coupling. The spring-type plunger rings will compress a few thousandths of an inch while passing through and spring back to original size against the inner surface of the pump barrel. After the pump is placed into service, if at any time the well fluid is lowered to a point where a fluid pound exists sufficiently to move the anchorable pack-off assembly downwardly, the nut will move against the reduced diameter in the coupling and stop, because of the few thousandths of an inch difference in diameter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the invention, its organization, construction and operation will be best understood from the following detailed description, taken in conjunction with the accompanying drawings, on which: 
     FIG. 1 is a schematic elevation of a pumped oil well of the type which may incorporate the present invention; 
     FIG. 2 is a longitudinal sectional view taken through an oil well pump constructed and operating in accordance with the present invention, shown at the initiation of an up stroke; 
     FIG. 3 is a sectional view similar to that illustrated in FIG. 1 at the initiation of, or at least during, a down stroke of the pump; 
     FIG. 4 is a sectional view taken substantially along the parting line IV--IV of FIG. 2; and 
     FIG. 5 is a sectional view taken substantially along the parting line V--V of FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, oil well pump apparatus is generally illustrated at 10 in which a well bore 14 is located in the ground 12 and includes therein a tube 16 constructed of a plurality of hollow well tubing which, as is well known in the art, is normally constructed of a plurality of end-to-end connected tubes. Forming a part of the tube 16 and located below ground at a desired pumping location is a pump 18. The pump 18 is a reciprocating pump which is reciprocated by a reciprocating member 22. The reciprocating member 22 is, as is well known in the art, a series of end-to-end connected sucker rods known as a string of sucker rods. The reciprocating member 22 is reciprocated by a rocking boom 24, as indicated by the double-headed arrow 23. The boom 24 is rocked or pivoted by a prime mover 26, which is usually an electric motor or an internal combustion engine driving an eccentric mechanism, as shown. 
     Referring to FIGS. 2 and 3, the pump 18 is illustrated as comprising a hollow rod 28 mounted for reciprocation in a pump barrel 30. The hollow rod 28 includes a plurality of bores 29 therethrough for supporting a flow of fluid between the interior and the exterior of the rod 28, as specifically set forth and described in the aforementioned U.S. Pat. No. 3,945,774 which is relied on here for a description of the pumping action for reasons of simplicity and clarity in that the pumping action forms no part of the present invention. 
     The hollow rod 28 carries, at its lower end, a plunger or piston 32 which is fluid sealed to the inner surface of the barrel 30 by way of a pair of seal rings 42, the lower piston 32 being positioned above a first one-way valve 34 which is mounted in the barrel 30. At its upper end, the hollow rod 28 carries an upper plunger or piston 36 which is fluid sealed to the inner surface of the barrel 30 by way of a pair of seal rings 40. The upper plunger or piston is connected to the string of sucker rods 22 for reciprocation by way of a second one-way valve 38. 
     The hollow rod 28 reciprocates in the pump barrel through a pack-off assembly 44 which divides the pump barrel into upper and lower chambers. The pack-off assembly 44 comprises an elongate hollow body 54 which mounts a plurality of packing members 46 for sealing with respect to the hollow rod 28. The elongate body 54 also comprises a reduced diameter section terminated at its upper extent by a shoulder 56 against which a series of alternating seals 48 and spacers 50 is disposed. 
     As mentioned above, an object of the present invention is to provide an improved method and structure for seating the pack-off assembly. To this end, the lower end of the elongate hollow body 54 comprises a threaded section 56 having a nut 58 threaded thereon against a lower end 62 of an annular wedge or conical sleeve 60 which tapers to a sharp upper end 64. As will be appreciated from the drawing, advancement of the nut 58 upwardly against the end 62 of the annular wedge 60 causes the sharp end 64 to enter between the lowest annular seal ring 48 and further entry of the wedge 60 causes expansion of the lowest annular seal ring 48 radially about its entire circumference to tightly wedge against the inner surface of the barrel 30. 
     Inasmuch as the pump is well below ground, and the internal components of the pump are moved into a desired location in a &#34;loose&#34; condition from above ground in which the hollow rod 28 carrying the upper and lower pistons is lowered down into the tube 16 and into the pump barrel 30 carrying the pack-off assembly 44 therewith, and as the upper piston is employed to push the pack-off assembly 44 into the desired location, some structure must be provided for advancing the nut 58 after the pack-off assembly has been pushed to the desired location. This structure includes the string of sucker rods 22, the upper oneway valve 38, the upper piston 36, the hollow rod 28 and the lower piston 32. 
     Attention is invited that the lower end of the nut 58 includes a pair of recesses 66 for receiving corresponding lugs 68 which are provided on the upper surface of the lower piston 32. Therefore, after the pack-off assembly 44 has been placed in the desired location, the string of sucker rods is raised until the upper surface of the piston 32 contacts the lower end of the nut 58. Then, upon rotation of the string of sucker rods, while maintaining an upward tension on the string of sucker rods, the lugs 68 are received in the recesses 66 to turn the nut 58. Inasmuch as it is normal to provide right-hand threads for connection of the other components of the pump, as viewed from above, a corresponding rotation of the sucker rods, as viewed from below, would be risky with respect to loosening or detachment, the threaded section 56 and the nut 58 are therefore provided with left-hand threads and the sucker rods are rotated to the right, above ground, as indicated by the arcuate arrow 70. As pointed out above, advancement of the nut 58 causes the annular wedge or conical sleeve 60 to expand the lower seal ring 48 and provide an improved anchoring over that heretofore known. 
     With respect to fluid pound conditions, as mentioned above, which could hammer the pack-off assembly 44 downwardly, a further improvement is provided for limiting the downward movement of the pack-off assembly. This improvement resides in the provision of the pump barrel 30 as a two-piece structure including an upper barrel section 70 and a lower barrel section 72 which are coupled together by way of a coupling 74 which includes a plurality of holes 78 therethrough which are equivalent to the openings 128 and 130 of the aforementioned U.S. Pat. No. 3,945,774 for lubrication of the lower piston 32 and breathing of the pump apparatus. The coupling 74 includes a central portion of reduced diameter and a tapered surface 76, which tapers outwardly away from the central axis, the bores 78 being provided through the portion of reduced diameter. Upon the occurrence of a fluid pound condition, the pack-off assembly can only be minimally moved in that the tapered section acts as a lower limit for the nut 58 due to the reduced internal diameter of the pump at this location. 
     Inasmuch as the lower plunger or piston 32 must reside below the openings 78, the same must pass through the reduced diameter section. This is accomplished by the provision of the diameter of the piston 32 slightly less than the diameter of the reduced diameter section and by providing the seal rings 42 as spring-type or pressure-actuated rings. As the piston is moved downwardly into the pump barrel, the spring-type seal rings 42 will engage and yield to the tapered surface 76 to permit the piston 32 to pass through the reduced diameter section and then, after such passage, expand again against the inner surface of the lower pump barrel section 72. 
     In order to enable initial compression of the spring-type rings 42 for assembly or for maintenance of the pump, it should be noted that entry to the reduced area section from either direction is by way of a respective arcuate shoulder 80, 82. 
     Although I have described my invention by reference to particular illustrative embodiments thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. I therefore intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.