US3912420A

US3912420A - Positive pull-down non-pounding oil well pump for use with flexible pumping strand

Info

Publication number: US3912420A
Application number: US443931A
Authority: US
Inventors: Robert H Gault
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1974-02-19
Filing date: 1974-02-19
Publication date: 1975-10-14
Anticipated expiration: 1992-10-14

Abstract

A positive pull-down oil well pump is provided with a check valve and packing to seal off the middle chamber of the pump above the lower plunger during the downstroke of the pump. A partial vacuum is thus induced in the middle chamber during the downstroke which vacuum is transferred to the lower chamber by opening of the lower traveling check valve associated with the lower plunger of the pump. The opening of the lower plunger check valve prevents pounding of the pump and increases the force of the downstroke of the pump due to the positive pull-down action of the pump by reducing the pressure in the middle and lower pumping chambers of the pump. An upper plunger is provided through which a positive pull-down force is attained in the operating pump which is dependent only upon the area of the plunger and the overlying hydrostatic head of oil well fluid in the well and independent of the size of the lower producing plunger.

Description

Oct. 14, 1975 1 POSITIVE PULL-DOWN NON-POUNDING OIL WELL PUMP FOR USE WITH FLEXIBLE PUMPING STRAND [75] Inventor: Robert H. Gault, Midland, Tex.

[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

[22] Filed: Feb. 19, 1974 [21] Appl. No.: 443,931

[52] U.S. Cl. 417/260 [51] Int. Cl. F04B 3/00 [58] Field of Search 417/554, 259, 260, 546

[56] References Cited UNITED STATES PATENTS 191,448 5/1877 Lewis 417/260 767,454 8/1904 Taylor.... 417/260 2,160,811 6/1939 Adams 1 417/260 3,136,265 6/1964 Chenault.... 417/448 3,140,667 7/1964 Anderson.. 417/546 3,175,512 3/1965 Sutliff 417/259 3,267,872 8/1966 Bloudofi 417/259 3,479,958 11/1969 Anderson et a1. 417/554 Primary E.taminerWi1liam L. Freeh Attorney, Agent, or FirmJoseph .1. OKeefe; Charles A. Wilkinson ABSIRACT A positive pull-down oil well pump is provided with a check valve and packing to seal off the middle chamber of the pump above the lower plunger during the downstroke of the pump. A partial vacuum is thus induced in the middle chamber during the downstroke which vacuum is transferred to the lower chamber by opening of the lower traveling check valve associated with the lower plunger of the pump. The opening of the lower plunger check valve prevents pounding of the pump and increases the force of the downstroke of the pump due to the positive pull-down action of the pump by reducing the pressure in the middle and lower pumping chambers of the pump. An upper plunger is provided through which a positive pulldown force is attained in the operating pump which is dependent only upon the area of the plunger and the overlying hydrostatic head of oil well fluid in the well and independent of the size of the lower producing plunger.

1 Claim, 5 Drawing Figures lee U.S. Patent Oct. 14, 1975 Sheet 1 of2 3,912,420

POSITIVE PULL-DOWN NON-POUNDING OIL WELL PUMP FOR USE WITH FLEXIBLE PUMPING STRAND 7 BACKGROUND OF THE INVENTION This invention is directed to pumps for use in the bottoms of oil wells and particularly to improved pumps which are both non-pounding and adapted for long stroke pumping with flexible pumping strand.

Oil well pumps at the bottom of oil wells have traditionally been in most oil fields operated by a mechanical connection to a pumping mechanism or prime mover at the surface at the well head. The mechanical connection has customarily comprised a string of socalled sucker rods, which are essentially steel rods screwed together at both ends. An oil well may be several thousand feet in depth and each sucker rod is only a limited number of feet in length due to the necessity for convenience in fabrication of the sucker rods in a shop and assembly of the individual sucker rods into a sucker rod string in the field. It is consequently necessary in placing or running a sucker rod string into an oil well or removing the sucker rod string from the well in order to remove the pump or other devices from the well for repair of changing, to thread together or unthread a large number of sucker rods, all of which requires a great deal of time and expense. The use of socalled flexible pumping strands, i.e. strands formed from a plurality of steel wires, in place of conventional sucker rods has been known in relatively shallow substantially non-corrosive wells in the eastern portion of the United States. The use of a single long length of flexible pumping strand formed from a plurality of steel wires stranded together precludes the necessity for mechanically coupling together a plurality of short lengths of conventional sucker rod such as is the current practice and thus can save considerable time and labor in inserting or withdrawing a sucker rod string from a well. The use of flexible pumping strands has until recently, however, not proved practical in deep oil wells in which severely corrosive conditions are present such as for example so-called sour brine wells and the like. While the use of flexible pumping strands would be more convenient from a handling viewpoint the use of solid sucker rods with their more restricted surface area available for attack by corrosive substances in the well has remained necessary because of the corrosive nature of large numbers of oil wells. Recently, however, several types of corrosion resistant flexible pumping strands have been invented for use in corrosive oil wells. The use of these strands can considerably decrease the equipment and time required to withdraw a pumping string from or replace a pumping string in a deep well. Flexible pumping strand, however, because of its nature and construction has presented several problems of its own. One of these problems is related to the inherent stretchability of ahelically wound flexible pumping strand. A minor degree of stretchability of such strand over a unit length may when spread over a long length of strand result in a fairly sizable differential between the movement of the end of the strand induced at the surface by a prime mover and the movement of the end of the strand which is attached to the pump at the bottom of the Well. A short stroke pumping mechanism at the surfacemay, therefore, sometimes not be adequate to properly operate a pump at the bottom of the well. A second-disadvantage of a flexible pumping strand is that such strand, because of its flexibility, does not readily exert the weight of its overlying portions against the bottom portions of the strand even when positioned vertically in a well. Thus, while the weight of a long string-of conventional sucker rods can be used to push the plunger of an oil pump at the bottom of a well down against the oil which collects at the bottom of the pump and the sucker rods can also thrust the pump plunger down through the positive action of the surface pumping mechanism transmitted through compression of the'solid sucker rods, a flexible pumping strand can neither transfer any downward force from the surface pumping mechanism to the pump at the bottom of the well nor even effectively exert its own weight against the pump during a downstroke of the pumping mechanism. So called positive pull-down pumps have been used in the past wherein the weight of the column of oil in the well tubing is taken advantage of to exert a downward force against the plunger of the pump at the bottom of the well to aid in forcing the pump plunger down. Such pumps have often been subject to rather severe pounding, however, particularly in the many oil wells where the flow of oil from the surrounding geological strata is not rapid.

As might be expected the use of a positive pull-down pump has become even more desirable in an oil well using flexible pumping strand than it has been in deep wells using solid sucker rods. Prior positive-pull down pumps have, however, not only been subject to socalled pounding in many instances, but have also not been as efficient as could be desired. While various means have been used to alleviate pounding in other types of pumps, they have not been applied to positive pull-down pumps and the positive pull-down pumps available have not been as effective as necessary to efficiently operate a down-hole pump by the use of positive pull-down pressure alone.

SUMMARY OF THE INVENTION The previous drawbacks of known positive pull-down pumps have now been obviated by the pump of the present invention which is especially adapted for operation with flexible pumping strand. In accordance with the present invention there is provided a pump having an upper and a lower plunger. There is an upper pumping chamber above the top plunger, a lower pumping chamber below the lower plunger and a middle pumping chamber located between the upper and the lower plungers. Unlike more conventional positive pull-down pumps in which an upper plunger serves to transfer pressure in the upper portion of the barrel of the pump derived from the head of oil contained in the well tubing above the pump to the lower plunger in order to aid in forcing the lower plunger down into the body of oil in the lower pumping chamber, the improved pump of the invention has a packing surrounding the middle plunger tube and a check valve between the middle pumping chamber and the upper pumping chamber which packing and check valve together serve to isolate the middle pumping chamber from the upper pumping chamber except during an upstroke of the plunger assembly when the check valve between the upper and the lower pumping chamber opens. The middle plunger tube packing divides the space between the upper plunger and the lower plunger into two variable sized chambers, the lower of which is open only to the lower and upper pumping chambers through appropriate one-way check valves and which chamber constitutes the middle pumping chamber, and the upper chamber of which is a chamber which is open through appropriate orifices to the outside of the pump in the casing annulus to allow free passage of oil well fluid back and forth between the chamber and the annulus.

In operation, during the upstroke the operation of the pump is essentially the same as in a conventional pump in that the oil in the middle and upper pumping chambers is lifted by both plungers and forced into the well tubing above. Meanwhile oil is admitted from the well to the lower pumping chamber through the lower standing check valve. The upstroke of the pump is activated or powered by the upstroke of the pumping mechanism at the surface through a flexible pumping strand comprised of a wire strand coated with a protective plastic jacket.

On the downstroke of the pumping mechanism the tension in the flexible pumping strand is relieved and the column of oil in the well tubing exerts its weight against the upper surface of the upper plunger and against the check valve between the upper pumping chamber and the lower pumping chamber. The plunger assembly is consequently forced downwardly in the pump casing. Oil well fluid between the bottom of the upper plunger and the middle plunger tube packing is expelled through the orifices in the pump casing into the well. Meanwhile as the lower plunger descends in the pump casing the middle pumping chamber between the middle plunger tube packing and the upper surface of the lower plunger increases in size. Since this middle pumping chamber is isolated from the upper pumping chamber by a check valve which is held closed by the weight of the overlying oil in the well tubing as the middle pumping chamber increases in size, there is engendered in the middle chamber a decreasing pressure which quickly causes the establishment ofa partial vacuum in this chamber. The increasing partial vacuum in the middle pumping chamber quickly reaches a value at which gas and oil vapor pressure above the oil in the body of oil contained in the lower pumping chamber is great enough to force open the usual lower traveling valve associated with the lower plunger. The opening of the lower traveling valve serves two functions. First. it serves to exhaust vapor from the lower pumping chamber to the upper pumping chamber so that the partial vacuum in the middle pumping chamber is transferred to the lower pumping chamber above the surface ofthe oil body in this chamber and secondly the opening of the lower traveling valve decreases the initial resistance of the lower plunger so that when the lower surface of the lower plunger strikes the surface of the oil in the lower pumping chamber the oil is immediately admitted through the traveling valve and pounding ofthe plunger against the oil is avoided. The partial vacuum in the lower chamber and also in the middle pumping chamber meanwhile serves to reduce back pressure in the lower portions of the pump so that the downward movement of the lower plunger during the initial portion of the downstroke is facilitated and the pressure engendered by the head of oil in the well tubing more effectively serves to push the plunger as sembly down and imparts a downward momentum to the plunger assembly which is effective to increase the power of the downward stroke ofthe pump. Release of pressure from beneath the lower plunger prevents a pressure build-up in the lower pumping chamber during the down-stroke which build-up would oppose the effective downward stroke of the pump plungers. The preopening of the lower traveling valve meanwhile serves to prevent the momentum of the plunger assembly from being dissipated in striking the surface of the oil in the lower pumping chamber with resultant pounding. It will be understood from the foregoing description that normally the pump of this invention will be operated at a sufficient rate of speed to prevent complete filling of the lower pumping chamber on each pumping stroke. prevention of pounding in the pump under such conditions is very important because a flexible pumping strand not only is not effective to place a compressive weight upon the underlying pump. but is also very easily damaged if placed in compression by even a momentary hesitation of the downward travel of the pump plunger assembly such as occurs when a pump pounds. When a flexible pumping strand is placed in compression the resultant slight untwisting of the strand is very destructive over a period to the individual wires of the strand.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of a pump operating assembly according to the present invention.

FIG. 2 is a diagrammatic sketch of the longitudinal cross section of one simplified version of the pump of the present invention.

FIGS. 3, 4 and 5 are diagrammatic longitudinal cross sections of a second simplified version of the pump of this invention wherein FIG. 3 shows the pump in resting condition or not in operation. FIG. 4 is an illustration of the operation of the pump during an upstroke and FIG. 5 an illustration ofthe pump during a downstroke of the pumping mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is shown a diagrammatic view of an oil well using a flexible pumping strand and pump assembly according to the present invention. In FIG. 1 there is shown an oil well 11 including a well casing 13, a well tubing 15 through which the oil is pumped to the surface and a positive pull-down pump 17 according to the present invention seated in the lower end of the tubing 15 at the bottom of the well. The pump 17 extends into the strata at the bottom of the well and pumps the oil up through the well tubing 15 to the well head 19 where it passes out the pipe 21. A flexible pumping strand 23 comprised of individual steel wires 25 and a plastic protective jacket 27 covering the strand passes at the well head 19 through the usual packing 29 protected at this point by a so-called hollow polished rod 31 which is secured to the strand and reciprocates in the packing 29 as the flexible pumping strand 23 is reciprocated by the movements of a horsehead 33 operated at the surface by a motor 35 through a connecting rod 37 operatively connected to flyweight arm 38. The individual wires 25 of the flexible pumping strand 23 may or may not be protected by individual plastic coatings or jackets, not shown. The reciprocation of flexible pumping strand 23 serves to operate pump 17. The flexible pumping strand is operatively attached to the pump 17 through a swaged fitting 39 or the like. a shear release 41 and preferably a series of conventional sinker bars 43 which serve to add some extra weight to the pumping assembly to aid in moving the pump plunger assembly on the downstroke, and particularly during the initial pumping strokes when the pump initially begins pumping and before a full head of oil has been built up in the well tubing to aid in forcing the plunger assembly of the pump downwardly during a downstroke. A pony rod or pump rod connects the sinker bars 43 to the pump 17. It will be understood that the well shown in FIG. 1 may be several thousand feet deep and will be filled with crude oil or a mixture of crude oil and other well fluids. Hollow polished rod 31 and the strand 23 may be preferably supported from the horsehead 33 by a carrier bar 47 through bridles 49. Excessive pumping strand 23 is reeled on a reel 51 secured to the supporting framework 53 upon which the horsehead 33 is pivoted. A well packing 55 may be used at the bottom of the well to pack off the casing above the pump from the surrounding strata. Not all wells use such packing.

It will be readily understood that the pumping arrangement shown in FIG. 1 is not the only one which could be used to reciprocate the flexible pumping strand pump assembly of the invention as various other types of pumping apparatus such as drum type strand reciprocating apparatus and the like could be used.

In HO. 2 there is shown a simplified diagrammatic sketch of the pump of the invention. A pump 61 is seated in a well tubing 63 by a diagrammatically shown pump seat holddown 64. Within the barrel 67 of the pump there is accommodated an upper or first plunger 69 and a lower or second plunger 71 connected together into an overall plunger assembly designated generally as 72 by a'middle plunger tube 73 which passes through a middle plunger packing 75 mounted in the barrel of the pump and dividing the area between the first plunger 69 and the second plunger 71 into two portions, an upper portion 82 and a lower portion which comprises a middle pumping chamber 83 of the pump. A series of openings 84 in the barrel 67 of the pump provide access from the upper chamber 82 to the casing annulus surrounding the pump and allow free access for well fluid between the inside and outside of the pump so that movement of the first plunger is not restricted by a build-up of pressure between the middle plunger packing 75 and the bottom the first plunger 69. The first plunger is provided with a traveling first ball check valve 77 which serves to seal off the space above the first plunger 69 from the middle plunger tube. The second plunger 71 is provided with a second traveling valve 79 in the form of a ball check valve which on the upstroke of the plunger assembly 72 closes to prevent backward flow of oil from the middle pumping chamber 83 to the lower or entrance chamber 85 of the pump. A standing ball check valve 87 serves to admit oil from the well into the lower chamber 85 during the upstroke'of the plunger assembly. A flexible pump strand 91 is diagrammativally shown extending from a pony rod 93 which is shown attached to a yoke 95 secured to the upper portion of the plunger assembly 72. Likewise the middle plunger tube 73 is attached to the lower plunger 71 through a yoke 97. The several pumping chambers of the pump may be designated as an upper or first pumping chamber 81, a middle or second pumping chamber 83 and a lower or third pumping chamber 85. Alternatively the chambers may be numbered in the sequence in which oil well fluid enters them so that the lower chambers is considered to be the first chamber, the middle pumping chamber to be the second chamber and the upper pumping chamber to be the third chamber.

in operation of the pump shown in FIG. 2 during an upstroke of the plunger assembly 72 the upper or first traveling ball check valve 77 opens and the lower or second traveling ball check valve 79 closes as oil is forced throughthe middle plunger tube 73 into the upper or first pumping chamber of the pump above the first plunger 69 and once into the upper chamber is lifted farther up the tubing by the first plunger 69. At the same time the standing ball check valve 87 opens to admit fresh crude oil to the lower or third pumping chamber 85 of the pump. On the downstroke of the pumping apparatus the upper or first traveling ball check valve 77 and the lower or second traveling ball check valve 79 initially close to prevent back flow of oil. The upper or first ball check valve 77 remains closed throughout the downstroke so the entire weight of the head of oil accumulated in the well tubing 63 above the upper plunger 77 is exerted upon the upper surface of the plunger 69 and the ball check valve 77 and serves to force the entire plunger assembly 72 downwardly. As the middle pumping chamber 83, which on the upstroke is almost emptied of oil, expands on the downstroke due to the downward movement of the lower or second plunger 71, the pressure within the middle or second pumping chamber 83 is progressively decreased and a partial vacuum is engendered within the chamber 83. After the pressure is sufficiently reduced in the middle or second pumping chamber 83 the pressure of gas and oil vapor in the lower pumping chamber 85 will force open the lower or second traveling ball check valve 79 sufficiently to substantially equalize the pressure between the two chambers 83 and 85. The unseating and partial opening of the lower or second traveling valve is sufficient so that when the bottom surface of the lower or second plunger 71 contacts the surface of the body of oil in the lower or third pumping chamber 85 the oil can immediately pass through the valve without pounding. In addition, the reduced pressure within the lower chamber 85 occasioned by relief of pressure from the lower chamber through the lower or second traveling valve 79 into the middle pumping chamber 83 increases the effect of the weight of the head of oil in the well tubing 63 in pressing down the entire plunger assembly 72 and ultimately forcing the plunger 71 into the oil accumulated in the lower pumping chamber. In a conventional positive pull-down pump, on the other hand, the lower traveling valve is kept closed by the pressure of the overlying oil in the well tubing until the bottom surface of the lower plunger contacts the upper surface of the body of oil in the lower chamber. This results not only in pounding of the plunger against the surface of the oil with resultant repeated shock to the pump structure and the overlying sucker rods or flexible pumping strand, but also causes a progressive build-up of pressure in the lower pumping chamber, which pressure resists the downward movement of the plunger assembly and loss of momentum of the plunger assembly. This loss of momentum due to the resistance of the gas and vapor in the lower pumping chamber is particularly objectionable in a flexible pumping strand pumping arrangement where the weight of the strand cannot be effectively added to the plunger and the positive pull down effect of the head of oil above the pump is the main motivating force upon the pump on the downward stroke.

The operation of the pump of the invention is further illustrated in FIGS. 3, 4, and which show a simplified diagrammatic representation of a somewhat different embodiment of the pump of the invention which is in some respects an improvement over the simplified embodiment shown in FIG. 2. Similar designating numerals are used in FIG. 2 and FIGS. 3, 4, and 5 as an aid to understanding the differences and similarities between the pumps. The letter designation (1 is applied to each designating numeral in FIGS. 3, 4, and 5 to distinguish from the numerals in FIG. 2. Thus in FIG. 3, which is a general view of the second pump in nonoperating condition, the overall pump is designated as 61a. The barrel 67a of the pump 610 has a plunger assembly 72a mounted for up and down movement in the barrel 67a. The assembly 720 comprises an upper or first plunger 69a, a lower or second plunger 71a and a middle plunger tube 73a through which oil passes from the middle pumping chamber 820 above the lower plunger 71a to the upper pumping chamber 81a above the upper plunger 69a. A middle plunger packing 75a divides the space between the upper plunger and the lower plunger into two sections or chambers comprising an upper portion or chamber 82a and a middle pumping chamber 83a. A cage 86a serves to connect a pony rod 93a to the upper portion of the middle plunger tube 73a and serves also to admit oil from the middle plunger tube to the upper pumping chamber 81a. A standing ball check valve 870 at the bottom of the pump serves to admit oil from the casing of the well or the area below the casing into the lower pumping chamber 85a during theup-stroke of the pump while a lower traveling valve 79a serves to isolate the middle pumping chamber 83a from the lower pumping chamber 8541 during the up-stroke of the pump. An upper traveling ball check valve 77a serves to isolate the upper pumping chamber 81a from the middle pumping chamber 83a during the downstroke of the pump. It will be noted that the upper traveling ball valve 77a is located in the embodiment of the pump assembly of the invention shown in FIGS. 3, 4, and 5 in the lower portion of the middle plunger tube 73a rather than at the top of the plunger tube as in the pump embodiment shown in FIG. 2. Location of the valve 77a in the lower portion of the middle plunger tube is a preferable and improved location as it prevents the fluid contents of the middle plunger tube 730 from draining into the middle pumping chamber 83a during the downstroke of the pump and thus, since the lower plunger 71a can closely approach the middle plunger packing 75a, and the portion of the pump structure which carries the packing, on the up-stroke to expel almost all of the oil contained in the middle pumping chamber by the end of the up-stroke, on the subsequent downstroke the pressure in the middle pumping chamber 83a decreases very rapidly causing an early opening of the lower traveling valve 79a so that the resistance of the lower plunger to downward movement is quickly lessened. Thus the positioning of the upper traveling valve 77a as close to the middle pumping chamber 83 u as possible very effectively increases the positive pull-down of the pump on its downstroke by assuring a minimum resistance of the lower plunger 71a to downward movement during the downstroke of the pump. The orifices 84a in the barrel of the pump provide free access of oil from the interior of barrel 67 of the pump to the exterior, i.e., from the chamber 82a during the downstroke of the pump, and from the exterior of the casing to the interior chamber 82a during the upstroke of the pump to prevent interference with the free movement of the upper plunger on either stroke.

The operation of the improved pump shown diagrammatically in FIGS. 3, 4 and 5 is the same as the operation of the pump shown in FIG. 2. That is to say that on the downstroke of the pump the weight of the head of oil in the well tubing above the pump forcefully closes the upper traveling ball check valve 77a so that a full positive downward pressure of the overlying oil is exerted upon the top of the upper plunger 6941 and the valve 77a to quickly and efficiently force the plunger assembly 72a downwardly. As the lower plunger descends a reduced pressure or partial vacuum is quickly induced in the middle pumping chamber and the lower traveling ball check valve 79:! quickly opens as shown in FIG. 5 to a degree effective to release gas and oil vapor pressure from the lower pumping chamber to the middle pumping chamber whereby a reduced pressure is established in both chambers which considerably aids in attaining an effective downstroke. As the plunger 71 continues to descend any excess pressure in the lower pumping chamber is continuously released into the middle pumping chamber so that no excess pressure can be built up below the lower plunger to counteract the positive pull down action of the head of oil above the pump. Furthermore. continued movement of the plunger downwardly and release of excess gas through the valve 79a maintains the valve 79a partially unseated so that when the lower plunger 71:! fr nally contacts the surface of the oil reservoir in the lower pumping chamber a the oil in the lower pumping chamber 85a is immediately released through the lower traveling valve 79a and the pump does not pound. Damage to the pump structure and overlying flexible pumping strand which might be occasioned by such pounding is thus avoided.

The operation of the pump during the upstroke of the plunger assembly 7211 is illustrated in FIG. 4. In this FIGURE the opening of the lower standing valve 87a to admit oil from the exterior of the pump to the lower pumping chamber 85a can be seen as can the opening of the upper traveling valve 77:! to allow oil or oil well fluid to pass from the middle pumping chamber 830 to the upper pumping chamber 81a. The lower traveling valve 79a, is, as shown in FIG. 4, closed during the upstroke of the plunger assembly 72a.

The operation of the pump during the downstroke of the plunger assembly is clearly shown in FIG. 5 wherein the tightly closed condition of the upper traveling valve 77a is shown and the unseating or partial opening of the lower traveling valve 79a is illustrated whereby pressure in the lower pumping chamber 85a is relieved into the partial vacuum of the middle pumping chamber 83a as the lower plunger 71:! descends.

By the arrangement and construction of the pump of this invention a much more efficient positive pull down action is attained in the pump than could be attained before and in addition pounding of the pump is avoided.

It is customary to overproduce or operate many wells at a greater rate than that at which the lower chamber of the pump can fill with oil in order to assure that all possible fluid is removed from the well as quickly as possible even though such a procedure leads in the usual pump to fluid pounding and accelerated component failure. The increased costs of rod, pump and pumping unit failure caused by this practice are, however, often offset by the increased revenues derived from maximum production. The pump of the invention is ideally suited for such practices since it does not pound under these conditions and the efficiency of its operation due to increased pull down effect is also considerably increased. Since the pump of the invention does not pound component failure is very much decreased under accelerated pumping conditions. In those cases where the well would not normally be pumped so vigorously or overproduced with conventional equipment, the well will, of course, be pumped in an accelerated manner when using the pump of the invention in order to take advantage of the improved operating characteristics and efficiency of the new pump.

Since the entire pressure of the head of oil well fluid in the oil well tubing is exerted against the upper plunger in the pump of the invention and is isolated from the pumping chambers below during a downstroke so that a reduced pressure is engendered in the lower chambers, the pull down force is dependent only upon the area of the upper plunger times the hydrostatic head in the well tubing. The positive pull-down force is independent of the lower or producing plunger size.

The relative size or areas of the upper and lower plungers may be varied as desired for particular operating conditions rather than being substantially similar in size as shown. in such cases the cross section of the pump barrel or casing in the area in which each plunger operates will also be varied. This feature allows the pump construction to be readily varied depending upon the use to which the pump is to be put. For example where a large head of oil is available as in a deep well a smaller upper plunger may be used to operate a large lower plunger to thereby attain increased pumping capacity. Where only a small head of oil is available, on the other hand, the upper plunger may be made proportionately larger.

it should also be noted that the pump of the invention pump cannot be gas locked, i.e. attain a condition where the pumping chamber becomes substantially completely filled with gas and the pump compression ratio is inadequate to force the gas into the well tubing, yet the gas pressure is too high to allow oil to enter the pump. Since transfer occurs from the lower chamber to the upper chamber the pump acts somewhat like a two stage compressor and some gas or liquid must be transferred on each stroke of the pump ensuring that gas lock will not occur except under the most unusual conditions.

I claim:

1. An improved long stroke positive pull-down oil well pump for use with flexible pumping strand comprising:

a. an extended pump barrel adapted for mounting at the bottom of a well tubing in an oil well,

b. a standing valve at the bottom of said pump barrel,

c. a plunger assembly reciprocally mounted in said pump barrel and comprised of i. an upper plunger in sealing relation with the barrel of the pump,

ii. a lower plunger in sealing relation with the barrel of the pump,

iii. a middle plunger tube operatively connecting said upper and lower plungers,

d. a central plunger packing positioned in the barrel of said pump and through which the middle plunger tube passes,

e. a series of interconnected pumping chambers comprising:

i. an upper pumping chamber between the upper plunger and the outlet of the pump into the well tubing,

ii. a middle pumping chamber between the central plunger packing and the lower plunger,

iii. a lower pumping chamber between the lower plunger and the standing valve,

f. passage means extending through said middle plunger tube and interconnecting said upper pumping chamber and said middle pumping chamber,

g. a traveling one way valve means operative to close said passage means through said middle plunger tube with respect to passage of fluid from said upper pumping chamber to said middle pumping chamber but not from said middle pumping chamber to said upper pumping chamber,

h. a traveling one way valve means operative to close passage means through said lower plunger between said middle pumping chamber and said lower pumping chamber with respect to passage of fluid from said middle pumping chamber to said lower pumping chamber but not with respect to liquid passing between said lower pumping chamber to said middle pumping chamber,

i. an upper chamber positioned below the said upper plunger and above the central plunger packing, said upper chamber having openings through the barrel of the pump for passage of fluid into and out of the upper chamber from the well,

said well pump being arranged and constructed such that on the upstroke of said pump the standing valve at the bottom of the pump will open and the upper traveling valve will open and during the downstroke of the pump the standing valve will close and the upper traveling valve will close while the lower traveling valve will be initially closed during the beginning of the pump downstroke and will then open as pressure builds up in the lower pumping chamber of the pump and external pressure is decreased in the middle pumping chamber as said chamber increases in size whereby the pump mechanism does not pound when the pump is operated at a rate such that the'lower pumping chamber does not fill completely with well fluid during the upstroke of the lower plunger and prior to the beginning of the downstroke of the lower plunger and the closing of the standing valve and the lower plunger during its downward movement forceably contacts a free surface of a body of well fluid trapped above the standing valve in the lower pumping chamber.

Claims

1. An improved long stroke positive pull-down oil well pump for use with flexible pumping strand comprising: a. an extended pump barrel adapted for mounting at the bottom of a well tubing in an oil well, b. a standing valve at the bottom of said pump barrel, c. a plunger assembly reciprocally mounted in said pump barrel and comprised of i. an upper plunger in sealing relation with the barrel of the pump, ii. a lower plunger in sealing relation with the barrel of the pump, iii. a middle plunger tube operatively connecting said upper and lower plungers, d. a central plunger packing positioned in the barrel of said pump and through which the middle plunger tube passes, e. a series of interconnected pumping chambers comprising: i. an upper pumping chamber between the upper plunger and the outlet of the pump into the well tubing, ii. a middle pumping chamber between the central plunger packing and the lower plunger, iii. a lower pumping chamber between the lower plunger and the standing valve, f. passage means extending through said middle plunger tube and interconnecting said upper pumping chamber and said middle pumping chamber, g. a traveling one way valve means operative to close said passage means through said middle plunger tube with respect to passage of fluid from said upper pumping chamber to said middle pumping chamber but not from said middle pumping chamber to said upper pumping chamber, h. a traveling one way valve means operative to close passage means through said lower plunger between said middle pumping chamber and said lower pumping chamber with respect to passage of fluid from said middle pumping chamber to said lower pumping chamber but not with respect to liquid passing between said lower pumping chamber to said middle pumping chamber, i. an upper chamber positioned below the said upper plunger and above the central plunger packing, said upper chamber having openings through the barrel of the pump for passage of fluid into and out of the upper chamber from the well, said well pump being arranged and constructed such that on the upstroke of said pump the standing valve at the bottom of the pump will open and the upper traveling valve will open and during the downstroke of the pump the standing valve will close and the upper traveling valve will close while the lower traveling valve will be initially closed during the beginning of the pump downstroke and will then open as pressure builds up in the lower pumping chamber of the pump and external pressure is decreased in the middle pumping chamber as said chamber increases in size whereby the pump mechanism does not pound when the pump is operated at a rate such that the lower pumping chamber does not fill completely with well fluid during the upstroke of the lower plunger and prior to the beginning of the downstroke of the lower plunger and the closing of the standing valve and the lower plunger during its downward movement forceably contacts a free surface of a body of well fluid trapped above the standing valve in the lower pumping chamber.