Abstract:
A liquid well pumping arrangement, especially for oil wells, comprising a pair of adjacent downhole reciprocating pumps each having a barrel, a piston rod connected to a piston slidable within the barrel, and valves adapted to cause liquid to flow from a lower inlet of the barrel to an upper outlet from the barrel when the piston is reciprocated in the barrel. The arrangement includes a well head pumping mechanism for applying reciprocating movement to sucker rods to cause movement of the pistons, the well head pumping mechanism being arranged to reciprocate each of the pistons at the same cyclic rate but with the motions of the two pistons being out of phase by 180°. A single delivery tube is connected to both of the outlets from the barrels such that, with the pumping mechanism operating, a substantially continuous flow of liquid can be produced from said delivery tube.

Description:
BACKGROUND OF THE INVENTION. 
     1. Field of the Invention 
     The present invention relates to fluid pumping arrangements for wells, intended to give an increased rate of recovery and/or better efficiency in pumping. The invention is particularly valuable for oil wells, but may be used for other liquids such as water. 
     2. Prior Art 
     Presently, most oil is pumped from oil wells using down-hole reciprocating pumps. Such a pump has a well head pumping mechanism causing reciprocating movement of a sucker rod which operates the down hole pump. The latter pump has a piston rod operating a piston slidable within a barrel, and has valve means in the piston and barrel which cause the oil to be lifted on each upstroke of the sucker rod. With a single-acting pump of this kind the rod operates almost entirely in tension. Such single acting pumps cannot maintain a steady flow of oil, and the need to accelerate a long column of oil in the well with each stroke is a major factor in the energy required for pumping oil or other liquids. 
     Another source of losses in conventional reciprocating pumps is the frictional resistance between the sucker rods and the column of liquid in which they move, which may be substantial given that the column of liquid may be hundreds of feet long. 
     Proposals have been made for double acting pumps which could give a more even delivery of oil by producing an output both on the upstroke and the downstroke; such proposals are shown for example in the following U.S. patents: 
     U.S. Pat. No. 6,585,049, issued Jul. 1, 2003 to Lenick, Sr., and 
     U.S. Pat. No. 5,873,411, issued Feb. 23, 1999 to Prentiss. 
     Proposals such as these, for double acting pumps, are either complicated, as in the Prentiss patent, or, as with the Lenick, Sr. patent, they require the sucker rods or their equivalent to apply downwards forces, which means these rods either have to be rigid, or have to be heavily weighted at the bottom so that they are not subjected to significant compressive forces. Compressive forces are normally avoided or minimized since these rods may be very long. 
     Another form of downhole pump is a rotary auger-type pump, sometimes termed a “progressive cavity pump”, as manufactured by Moyno Oilfields Products of Tulsa, Okla., which can give a substantially constant output. However, such pumps are less efficient than is desirable. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to overcome these drawbacks of the prior art by retaining generally conventional, high efficiency, single-acting, reciprocating pumps, but using them in tandem and connecting them in such a way that they operate in an out-of-phase manner and together provide a generally continuous flow of oil, or other liquid, at the well head, thus reducing the energy requirements relative to the amount of liquid being pumped. 
     According to one aspect of the present invention, a liquid well pumping arrangement comprises: 
     a pair of adjacent downhole reciprocating pumps each having a barrel, a piston rod connected to a piston slidable within the barrel, and valve means adapted to cause liquid to flow from a lower inlet of the barrel to an upper outlet from the barrel when the piston is reciprocated in the barrel; 
     sucker rod means attached to the piston rod of each pump; 
     a well head pumping mechanism for applying reciprocating movement to each of the sucker rod means to cause movement of the pistons; 
     wherein said well head pumping mechanism is arranged to reciprocate each of said sucker rod means at the same cyclic rate but with the motions of the two sucker rod means being out of phase by 180°; 
     and wherein there is provided a single delivery tube connected to both of the outlets from the barrels such that, with the pumping mechanism operating, a substantially continuous flow of liquid can be produced from said delivery tube. 
     The two pump barrels may be arranged side-by-side, or may be arranged at different levels. In the latter case, the pair of pumps may be arranged to occupy minimal overall cross-sectional area of the well bore by having an upper pump barrel located wholly above a lower pump barrel, with said upper pump barrel having an axis which is off-set from that of the lower pump barrel but which, when projected, lies within the boundaries of the lower pump barrel. The term “adjacent”, as applied to the pumps, includes both the side-by-side arrangement and the off-set arrangement at different levels; it means that the pumps are in the same bore and receiving liquid from essentially the same source. 
     Preferably the two pumps are identical, having the same diameter and stroke. 
     A preferred liquid well pumping arrangement in accordance with the invention, comprises: 
     a pair of adjacent downhole reciprocating pumps each having a barrel, a piston rod connected to a piston slidable within the barrel, and valve means adapted to cause liquid to flow from a lower inlet of the barrel to an upper outlet from the barrel when the piston is reciprocated in the barrel, 
     said pumps including an upper pump and a lower pump, the upper pump barrel being located wholly above the barrel of the lower pump, with said upper pump barrel having an axis which is off-set from that of the lower pump barrel but which, when projected, lies within the boundaries of the lower pump barrel, first and second sucker rod means attached respectively to the piston rods of the upper pump and lower pump, said second sucker rod means including a pair of rods which are connected to the piston rod of the lower pump and which are spaced apart so as to straddle a portion of the upper pump barrel, 
     a well head pumping mechanism for applying reciprocating movement to each of the sucker rod means to cause movement of the pistons; 
     said well head pumping mechanism being arranged to reciprocate each of said sucker rod means at the same cyclic rate but with the motions of the first sucker rod means being out of phase with motions of the second sucker rod means by 180°; 
     and wherein there is provided a single delivery tube connected to both of the outlets from the pump barrels such that, with the pumping mechanism operating, a substantially continuous flow of liquid can be produced from said delivery tube. 
     The outlets from the pump barrels preferably have angled sections which merge smoothly together into the delivery tube, and the piston rods pass out of these angled sections via sealing sleeves which prevent escape of the pressurized liquid. Thus the main length of the sucker rods pass beside the delivery tube, so that, unlike with a conventional reciprocating pump, there is no contact, and therefore no frictional resistance, between the sucker rod means and the liquid being pumped. 
     Also, the fluid friction resistance within the delivery tube is significantly reduced because the high fluid pressure normally produced with each upward lift of the oil column, in a conventional single pump arrangement, may be greatly reduced; i.e. the fluid pressure may be far lower and more even with two pumps than with the conventional single pump. This is in addition to the advantage of having the delivery tube offset from the polished rods so that no pressure seals are required at the well head. 
     The well head pumping mechanism may include a pair of pump jacks arranged head-to-head and conventional adjacent to each other, and linked together either by electrical control means or by a mechanical connection. The mechanical connection may be a flexible member such as a chain or toothed belt having each of its ends connected to one of the horse heads and having its intermediate length passing over a pulley held above the two horse heads. Preferably however the pumping mechanism includes a rotatable crankshaft having two cranks off-set from each other at 180°, and connecting rods connecting a first of said cranks to a first of the sucker rod means and also connecting a second of said cranks to a second of the sucker rod means. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS. 
       Preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which; 
         FIG. 1   a  shows a front view of a well head pumping mechanism in accordance with one aspect of the invention; 
         FIG. 1   b  shows a front view of a pair of tandem pumps, such as may be connected to the various well head pumping mechanisms described herein; 
         FIG. 1   c  shows a cross-sectional view of the same pump arrangement, taken on lines  1   c - 1   c  of  FIG. 1   b;    
         FIG. 1   d  shows a front view of a well head pumping arrangement similar to that of  FIG. 1 , but with a mechanical connection between the horse heads; 
         FIGS. 2   a  and  2   b  show front views of upper and lower parts, respectively, of a pumping arrangement suitable for connection to the various well head mechanisms described herein; 
         FIGS. 3   a  and  3   b  show side views of the pumping arrangement of  FIGS. 2   a  and  2   b;    
         FIG. 4  shows a cross-section through the pumping arrangement, taken on lines  4 - 4  of  FIG. 2   a.    
         FIG. 5   a  shows a front view of a preferred form of well head pumping mechanism such as may be connected to the various pumping arrangements shown herein; 
         FIG. 5   b  shows a side view of the pumping mechanism of  FIG. 5   a;    
         FIG. 6   a  shows a front view of an alternative form of pumping mechanism, and 
         FIG. 6   b  shows a side view of the  FIG. 6   a  pumping mechanism. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1   a  shows a tandem arrangement of two conventional oil well head pumping mechanisms or pump jacks  10   a  and  10   b  of the type each having a walking or rocking beam  12   a ,  12   b  mounted on respective samson posts  14   a ,  14   b  and each having a cable track or horse head  16   a ,  16   b  carrying cables  17   a ,  17   b  connected to polished rods  18   a ,  18   b . The pumping mechanisms are arranged head to head so that the polished rods  18   a ,  18   b  are close together, probably no more than a few inches apart. Also, means are provided, which may be mechanical or may be electrical control means, to ensure that the pumping units operate at the same rate but are 180° out of phase with each other. 
     Each polished rod  18   a ,  18   b  is connected via a sucker rod (not shown) to a piston rod  20   a ,  20   b , seen in  FIG. 1   b . As shown in the latter figure, each piston rod operates one of two conventional pump units  22   a ,  22   b , arranged close together in a well bore B. As indicated in  FIG. 1   b , each pump has a piston  24  with a one-way valve  25 , and operates between a bottom inlet  26  with valve  27 , and a top outlet  28  with valve  29 , all these parts being conventional. As also indicated in  FIG. 1   b , the outlets  28  of both pumps are connected to outlet conduits  30  which slope towards each other and merge together a short distance above the top pump outlets, so that when both pumps are operated in a 180E out of phase manner a mostly steady flow of oil is provided up a delivery tube  33 . The delivery tube  33  is offset to a side of the pumps so that the pumps and tube  33  form a triangular arrangement as seen in cross section in  FIG. 1   c.    
     As shown in  FIG. 1   b , the outlet conduits  30  have inwardly upwardly sloping outer side walls provided with bushings  31  through which the piston rods  20   a  and  20   b  pass, seals  32  being provided on the inner ends of these bushings to prevent oil leaking out of the conduits at these points. The provision of these seals avoids the usual need for seals around the polished rods  18   a ,  18   b . Also, the fact that the sucker rods are outside the delivery tube avoids the usual friction between the sucker rods and the liquid being pumped. 
       FIG. 1   d  shows a modification of the well head pumping mechanism of  FIG. 1   a , in which the horse heads  16   a ,  16   b  have a mechanical-connection to ensure that they remain 180° out of phase. For this, the horse heads  16   a ,  16   b  are connected at  40   a ,  40   b  to opposite ends of chain or toothed belt  42 , and the intermediate part of this belt passes over pulley  44  which is carried by bearing  46  mounted on frame  48  at a position above the horse heads and centrally positioned with respect to these horse heads and to the polished rods  18   a ,  18   b.    
       FIGS. 2   a ,  2   b ,  3   a  and  3   b  show a preferred form of pump arrangement in which the pumps are arranged at upper and lower levels and nested together so as to fit into a bore B′ of an oil well that is narrower than the bore B of  FIG. 1   b  needed by the side-by-side pumps. 
     As shown in  FIGS. 2   a ,  2   b ,  3   c ,  3   d  and  4 , the pump arrangement includes lower pump  140   a  and upper pump  140   b , operated respectively by sucker rods  136   a  and  136   b . Each pump has a barrel  142   a  and  142   b , these barrels being vertically separated by a substantial height which is greater than the barrel length, and being laterally off-set but sufficiently close that, as seen in  FIG. 4 , the axis of the lower pump, which corresponds to the axis of rod  136   a  if extended, lies within the circumference of the upper pump barrel  142   b . Each pump has the usual piston  146   a ,  146   b  acting between a lower valved inlet  148   a  and  148   b  and an upper valved outlet  150   a ,  150   b.    
     The upper pump piston  146   b  has its piston rod  147   b  connected directly to the sucker rod  136   b  in the usual way, and draws liquid up the well casing through passages which pass beside the lower pump. The lower pump draws liquid directly from the bottom of the well casing, and in this case the piston  146   a  has its piston rod  147   a  connected indirectly to the sucker rod  136   a  to avoid interference with the upper pump barrel  142   b . For this purpose the sucker rod  136   a  terminates above the upper pump barrel  142   b , where it is connected to an upper cross-head  152  which, in turn, connects to two depending, parallel rods  154  spaced to straddle, and lie just outside of, the upper pump barrel  142   b , as best shown in  FIG. 4 . Lower ends of these rods  154  are connected to a lower cross-head  156 , the center of which holds lower piston rod  147   a  which in turn is connected to the lower pump piston  146   a . By these means the axes of the two pumps can be close together, while allowing the lower pump to be operated without interference from the upper pump. 
     As shown in  FIGS. 2   a ,  2   b  and  4 , the upper pump  140   b  has its outlet connected to an outlet pipe  160  which is co-axial therewith, while the lower pump  140   a  has its outlet connected to an outlet pipe  162  of roughly semi-circular cross section which extends up from the top of the lower pump beside the upper pump barrel, at the side of the pump arrangement opposite the upper pump outlet pipe  160 . This outlet pipe  162  meets the outlet pipe  160  shortly above the upper pump  140   a , where both these pipes  160  and  162  are smoothly merged into a main delivery tube  164  which has its axis off-set to one side of the pipes  160  and  162 , and which carries the oil to the surface. As in the previous embodiment, the piston rods  147   a  and  147   b  of the lower and upper pumps pass out of the liquid delivery tubes  162  and  160  via bushings  163   a  and  163   b , escape of liquid being prevented by associated seals  163   a ′ and  163   b ′, so that the sucker rods are outside the liquid column, and no polished rod seals are required at the well head. 
     The various pump parts, outlet tubes, and delivery pipe are held together by rigid interconnections between the parts, such as the outlet tubing and the delivery tubes, and there is no need for an outer casing. 
     A third arrangement of pumps would use upper and lower pumps, as in the previously described embodiment, having slightly increased distance between centrelines, such that the piston rod of the lower pump, with attached suction rod, would bypass the upper pump barrel. This means that the dual bypass rods and cross heads would not be required. Of course, this arrangement, although simpler in design, would result in slightly smaller diameter pumps in any given well, and oil output would be less than in the previous embodiment. 
       FIGS. 5   a  and  5   b  show one embodiment of a preferred form of pumping mechanism at the well head. This includes a gear case  114  provided, near its base, with a drive motor (not shown), and carrying a fixed horizontal chain case  115  at its upper end, the outer end of chain case  115  in turn being attached to a depending, vertical support  116 . The driven end of chain case  115  has journals supporting a horizontal shaft  118  with sprocket wheel  119  driven from the drive motor by sprocket chains  120  which pass along the chain case and are connected, by a further sprocket wheel  121  and a chain carried thereby, to the drive motor in the gear case  114 . The shaft  118  carries two circular side plates  122   a ,  122   b  located on opposite sides of chain case  115 , and which provide thin strong plates for mounting connecting rods to be described. 
     The outer sides of the side plates  122   a ,  122   b  each have a crank pin  124   a ,  124   b , these crank pins being located at diametrically opposed positions on the side plates. Each crank pin  124   a ,  124   b  is connected by a connecting rod  126   a ,  126   b  to a cross head  128   a ,  128   b . Each cross head is vertically slidable on a pair of vertical, parallel rods  130   a ,  130   b , each pair of rods being associated with one side of the vertical support  116 . As best seen in  FIG. 5   b , each of these cross heads is connected to a polished rod  132   a ,  132   b , these being reciprocated vertically at the same rate but 180° out of phase with each other. 
     The polished rods  132   a ,  132   b  could be used to operate the two pumps  22   a ,  22   b  described with reference to  FIGS. 1   b  and  1   c , as well as to operate sucker rods  136   a ,  136   b , of the preferred pump arrangement shown in  FIGS. 2   a ,  2   b ,  3   a ,  3   b , and  4 , as described. 
       FIGS. 6   a  and  6   b  show yet another embodiment of the preferred form of well head pumping mechanism using a wheel with diametrically opposed cranks. This includes a gear case  214  carrying one end of a horizontal beam  217  the other end of which beam is carried by a support  216 . The gear case  214  is provided, near its base, with a drive motor (not shown) which drives a sprocket chain connected to an upper sprocket wheel  221 . This latter sprocket wheel is located at one end of a fixed horizontal chain case  215 , the outer or driven end of chain case  215  having journals supporting a horizontal shaft  218  with sprocket wheel  219  driven from the drive motor by sprocket chains which pass along the chain case and are connected, by the upper sprocket wheel  221 , to the drive motor in the gear case  214 . The shaft  218  carries two circular side plates  222   a ,  222   b  located on opposite sides of chain case  215 , and which provide thin strong plates for mounting connecting rods to be described. 
     The outer sides of the side plates  222   a ,  222   b  each have a crank pin  224   a ,  224   b , these crank pins being located at diametrically opposed positions on the side plates. Each crank pin  224   a ,  224   b  is connected by a connecting rod  226   a ,  226   b  to a cross head  228   a ,  228   b . Each cross head is horizontally slidable on a horizontal slideway constituted by a pair of horizontal, parallel rods  230   a ,  230   b  supported by the beam  217 , and each cross head is connected to one end of a sprocket chain  231   a ,  231   b , these chains undergoing a 90° change of direction by passing over sprocket pulleys  233   a  and  233   b  held on an axle  234  above the vertical support  216 . As best seen in  FIG. 6   b , a vertically hanging, outer end portion of each of these chains  231   a ,  231   b  is connected to a polished rod  232   a ,  232   b , so that the polished rods are reciprocated vertically at the same rate but 180° out of phase with each other. Other flexible members such as cables or flat belts can be substituted for the chains. 
     In the embodiments of  FIGS. 5 and 6  the sucker rod strings fully balance each other; i.e. the design is fully balanced and there is no need of counterweights as with the conventional pumping jacks of  FIG. 1 .