US2884861A

US2884861A - Free piston pump

Info

Publication number: US2884861A
Application number: US650438A
Authority: US
Inventors: Renic P Vincent; Earl R Jennings
Original assignee: Pan American Petroleum Corp
Current assignee: Pan American Petroleum Corp
Priority date: 1957-04-03
Filing date: 1957-04-03
Publication date: 1959-05-05
Anticipated expiration: 1976-05-05

Description

R. P. VINCENT ET AL FREE PISTON PUMP 4 Sheets-Sheet 2 Filed April 3, 1957 m E I m w mm f m a I m n a I p g y m M M I 9 M J/ 1 3 7 V 6 7 4 mm W. 5 l 8 w 2 Q 8 4 2 J x8 ,7 7 #x W 7 f 4. 2 g a I u III I II Z Z w Q/ p I. IINNN /./V K%A/ 4%9 WA: Q 2 8 8 W 0 0 8 7 FIG. 3

INVENTORS EARL R. JENNINGS RENIC P. VINCENT R. P. ViNCENT ET AL 2,884,861

May 5, 1959 FREE PISTON PUMP 4 Sheets-Sheet 3 Filed April 5, 1957- FIG. 4

INVENTORS EARL R. JENNINGS RENIC P. VINCENT A T TORNEY &

May 5, 1959 'R. P. VINCENT ET AL FREE PISTON PUMP 4 Sheets-Sheet 4 Filed April 5, 1957 lll FIG. 5

FIG.6

INVENTORS EARL R. JENNINGS RENIC P.VINCENT A T TOR/V5 Y United States Pat FREE PISTON PUMP Renic P. Vincent and Earl R. Jennings, Tulsa, Okla, assignors to Pan American Petroleum Corporation,

This invention relates generally to an improved free piston pumping system and, more particularly, it pertams to an improved apparatus for catching a free piston at the surface and for reversing a free piston at the upper and lower endsof its travel through a well tubing.

In the past, a free piston has been caused to reciprocate in the well tubing and pump liquid, scrape paraffin and the like from the walls of the tubing by making certain changes in the free piston at the upper and lower ends of its travel. Such changes involve generally either varying the diameter of a packer on the outside of the free piston or opening a fluid bypass through the free piston, or both varying the diameter of the packer and controlling flow through, the free piston. A metallic packer adapted to seal the space between the free piston and the tubing wall is sometimes expanded automatically at the bottom end of the free piston travel or a bypass valve in the free piston is closed so that, when a fluid pressure is exerted, below, fluid will not pass the free piston and it will be raised by this fluid to the surface. At the surface the packer is again contracted or the valve opened so that the free piston falls freely through the tubing and the packer is not worn by pressure contact with the tubing. This expansion and contraction of the packer and the opening and closing of the valve have been accomplished in a number of ways including stopping one element of the free piston and permitting the inertia of the other member to move the valve or one end of the packer; Pressure chambers, which are sensitive to the differences in pressure at the bottom and top of the well and which have been used to expand the packer at the bottom and to contract the packer at the surface, have also been used for this purpose. The difference between the top and the bottom temperatures of the well has likewise been used to cause control or reverse the direction of travel of a free piston. In certain instances each of these methods for bypassing: fluid through or around a free piston to permit the free piston to fall and then for closing the bypass to. cause the free piston to rise has been satisfactory but each method is not completely satisfactory in every instance so that a more dependable means for controlling or reversing the direction of travel of a free piston is desirable.

It is, therefore, an object of this invention to provide an improved free piston pumping system. Another object of this invention is to provide an improved free piston. A more specific object of this invention is toprovide an improved apparatus for holding and for co-ntrolling or reversing the direction of travel of a free piston in a vertical conduit. Other objects of this invention will be apparent from the following description. In. this description reference will be made to the accom panying, drawingsv in which:

Figure 1 is, a view partly in cross section of a Well tubing including a well head with a free piston therein.

and; showing the reversing mechanism of the free piston.

in a position to permit thefree, piston to fall in the tubing;

Patented May 5, 1959 Figure 2 is a cross-sectional view of the free piston shown in Figure l, the reversing mechanism being in a position to cause the free piston to rise when pressure is applied beneath it;

Figures 3 and 4 are cross-sectional views (Figure 4 being a lower extension of Figure 3) of a preferred embodiment of a tubing head particularly adapted for use with a preferred embodiment of a free piston which is also shown in cross section in its upper position in the tubing head;

Figure 5 is a crossasectional view of one type of a free piston having a modified apparatus for reversing the direction of travel of the free piston and expanding the packer on that type of free piston; and

Figure 6 is across-sectional view of another embodiment of atubing head adapted for use in a free piston pumping system of the type herein described.

This invention in brief may be described as an apparatus for controlling and particularly for reversing the direction of travel of a freepiston, an important feature being in use of the energy of the lifting fluid for such control. In the preferred embodiment a packer on the periphery of a free piston is expanded and contracted to cause the free piston to rise and fall, respectively. The packer is contracted at the surface and, in a modification, a large part of the energy. necessary for expanding the packer when the free piston returns to the bottom of the tubing is obtained by utilizing the excess energy in the lifting gas following a slug of liquid.

Referring now to Figure l for a more detailed, description of this invention, a well pumping system including the upper end of a casing 10, a tubing head 11, and a tubing 12 located, within the casing, are shown schematically. Pumping systems of this type, as is known in this art, may utilize a free piston to increase the lifting efficiency of a solution gas lift system, or lifting gas may be injected through a gas inlet 13 into the casing continuously, but preferably intermittently, to supplement the solution gas and lift the free piston and a slug of liquid above it to the surface. A master or control valve 14 is generally provided in the tubing above the tubing head 11 to shut the well in and to catch the'free piston 15 when it is. at the, surface. The tubing-is typically connected at the upper end by a flow T or the like to a flow line 1 6v by which the pumped liquid is delivered to storage such as a tank battery. The tubing is closed at the top with a cap 17 which may be connected as by threads to the upper end of the tubing so that it can be removed for access to the inside of the tubing, e.g., for installing and removing the free piston 15. An upper free piston stop 18 is resiliently connected via spring 19 with this tubing cap, the spring being connected to the cap through a spring anchor 21 and to the upper stop 18 by a similar spring anchor 22. The upper free piston stop has a fluid passage 23 through it, preferably axially, so that well fluids raised by the free piston can pass through to the flow line 16. Peripheral packing 24 may be provided between the upper free piston stop and the tubing so that well fluids are forced to flow through the passage 23. Spring 19 suspends the upper stop 18 resiliently a substantial distance below the tubing outlet into flow line 16 so that when the stop isv raised by the free piston, due to inertia of the free piston or the pressure beneath the free piston, the stop is still below the tubing outlet to the flow line.

The elements of one type of free piston include an elongated body 25 on which is mounted a peripheral sealing element or packer 26 which may be metallic, or it maybe resilient rubber or the like. The upper end of the body comprising a valve member 27 which is adapted to seat against the annular bottom of the upper free piston stop 18 and close the passage 23. A sleeve valve 28, having ports 29 in its walls, is disposed within the body providing a flow passage through the free piston and around the packer when the sleeve valve 28 is in an upper position and ports 29 are in communication with ports 31 in the body. The sleeve valve is resiliently held in one of two positions, an upper or open position and a lower or closed position, by an external annular cam 32 on the lower end of the valve body and by a snap ring 33. The split snap ring 33, which is disposed within and of smaller diameter than an internal annular groove 34 in body 25, has a smaller, unstressed internal diameter than the maximum diameter of annular cam 32. Thus, the sleeve valve is initially held in its upper position with the snap ring 33 in groove 35 when the free piston is dropped into the well so that a fluid passage is maintained through

ports

29 and 31 until the free piston reaches a bottom stop 36 within the tubing. When the free piston strikes this bottom sto the body is stopped immediately and the sleeve valve is carried by its inertia into its lower position in the body 25 with the passing the snap ring 33 and the snap ring falling into upper groove 37. This movement thus closes the fluid passage through

ports

29 and 31 as indicated in Figure 2 so that the free piston forms an impermeable plug in the tubing with no fluid bypass and is, therefore, lifted through the tubing when a force is applied on the bottom. The snap ring 33 is held in position by an annular ring 38 threaded into the bottom of the body 25.

Referring now to Figures 3 and 4 for a more detailed description of a preferred embodiment of this invention, the packers 26, of which there are preferably at least two, are mounted at their lower ends on the elongated tubular body 25 of the free piston. This body, which extends generally from the top of the free piston to the bottom, has a centering device or guide 39 afiixed to the lower end. A piston '41, having a packing such as a piston ring 42, is connected by a piston rod 43 to the guide 39. The center shaft or control rod 44, which extends through the tubular body, is connected to and actuates the expansion and contraction of the packers. Pins 45, which extend through slots 46 in the body, connect the control rod to the upper ends of the packers. These pins are anchored in holes 47 in the control rod and in holes 48 in the upper brackets 49 of the packers and are held in place by sleeves 51. These sleeves also hold the anchored end 52 of each of the packer segments 53. These segments are held in the brackets for lateral or radial rotation about the anchored ends by providing an annular groove 54 and a shoulder 55 on each of the brackets which cooperate with a knob on the anchored ends 52 so that the free end 56 of each segment can expand and contract to change the diameter and crosssectional area of the packer. The knobs on the anchored ends are resiliently held against shoulders 55 by compression springs 57 anchored against the shoulders 58 in each of the brackets. A longitudinal slot 59 in the control rod 44 is provided for a snap-acting device which includes a toggle fork 61. This fork is mounted in the slot 59 on a transverse pin 62. Rollers 63 are mounted in the fork ends and are adapted to expand when the fork is unstressed so that the outer oppositely disposed surfaces are spaced a distance substantially equal to or greater than the internal diameter of the tubular body. Toggle blocks 64, having an internal or minimum spacing less than the normal unstressed spacing of the active outer surfaces of rollers 63, are oppositely disposed in the tubular body in the same plane as the rollers. This snap-acting device, as will be explained in greater detail of the control rod contains a cylinder 65 which is open cylinder is typically filled with an expansible fluid such as gas to provide means, as shown for example in U.S. Patent 2,688,928, for expanding the packers at the bottom of a well when the pressure on the outside is substantially greater than the gas pressure in the cylinder 65. Piston 41 thus provides a movable wall in the cylinder and varies the volume of the enclosed gas chamber as the external pressure is varied. A spring 66, which may be calibrated to adapt the free piston for use in wells of different bottom hole pressures and to cause the free piston to fall to different depths in a well, is placed in compression between guide 39 and the lower end of the control rod 44. Calibration washers 67 may be added or removed, as desired, to change the calibration of this spring 66. It will be apparent that springs having different spring constants may also be used to change the operating characteristics and particularly the bottom hole pressure at which the direction of the free piston is reversed.

The sealing elements or packers are each divided into upper and lower halves as shown in greater detail in copending application Serial Number 561,467, now Patent No. 2,850,339. The upper half is connected to and operated by the control rod 44 as indicated above. The lower half is connected to the body 25. This latter connection is made by attaching an anchoring ring 68 to the body with set screws 69 or by welding or the like. Compression springs 71, placed between each of these anchoring rings and the lower brackets 72, urge the lower half of each packer upward and into resilient engagement with the upper half of the respective packer when the packers are expanded. It will be apparent that, while each of the segments is preferably resiliently held in the

brackets

49 and 72 by springs 55 to provide for some deflection between individual segments in each group, each of the segments may if desired be either non-resiliently hinged to the brackets or individually resiliently mounted in the brackets so that any one segment can be deflected when it encounters an obstruction without affecting the position of any other segment in the group. Typically, there are four or more of the segments 53 in each group. The lower brackets 72, in which the packer segments are rotatably anchored, slide on the body and, when the packers are expanded against the inside of the cylinder or tubing in which the free piston operates, springs 71 are slightly compressed to maintain a radial force outwardly against the cylinder or tubing wall. This force is produced by the frusto-conical surfaces 73 and 73' reacting against cams or rings 74. These rings are slidably sealed on the body with, for example, 0 rings 75 which permit the rings to move axially along the body at an equilibrium position where the frusto-conical surfaces 73 and 73' intersect. The lower and upper external surfaces of the rings 74 are desirably sloped at the same angle as the angle of the frusto-conical surfaces 73 and 73' when the segments are expanded to the nominal diameter of the tubing and the periphery preferably comes to a point 76. Where expansion of a packer is accomplished as in the illustrated embodiment by movement of only one of its upper or lower halves of each of the packing elements, then the ring 74 is preferably movably sealed to the outside surface of the body so that it is relatively free to move axially and thus displace upper and lower segments radially by substantially the same amount. The lower segments being resiliently mounted, as shown in the drawings, and the rings 74 being movably sealed on the body, it can be seen that when the upper halves are lowered to expand each of the packers, thc frusto-conical surface 73 on the segments of the upper halves first contacts the rings 74. This forces the free ends 56 of these upper segments out against the inside tubing wall. When these segments cannot be further expanded, the rings are moved downward along the body until they contact the frusto-conical surfaces 73 on the segments of the lower halves of the packers,

forcing these segments to expand radially. Since there is practically always some variation in the internal diameter of the tubing in which the free piston operates, the axial movement of the control rod in the bodycannot always be adjusted initially to provide the proper external diameter on the packers. Accordingly, this initial axial movement of the control rod in the body is typically greater than the movement required to expand the packers to the nominal or mean diameter of the tubing. After expanding the packers to the area of the tubing, any extra movement of the control rod is transmitted through the segments, moving the rings 74 and the lower brackets 72 axially downward on the body. This places springs 71 in compression and) provides means to expand the packers. diametrically when they encounter a point in the tubing having an enlarged diameter or area. At a point in the tubing where the minimum diameter is in creasing, both the rings 74 and the lower brackets 72 with their respective segments are accordingly moved upward by the forces of springs 71. Similarly, when the tubing diameter is decreasing, the packer segments are forced radially inward, moving both rings 74 and the lower brackets 72 axially downward and compressing springs '71. In either case, the, axial movement of the rings 74 is obviously only about one-half of the axial movement of the lower brackets 72. Insome cases both the upper and lower halves of the packers may be oppositely actuated to open and close symmetrically on each of the rings 74 so that the rings, if desired, can be fixed to the body.

Each of the segments 53 of the packers is adapted to form a seal on the periphery with the inside tubing wall and. with the adjacent oppositely disposed segments and, at the same time, form a seal on the frusto-conical surfaces 73 and 73' with the rings 74 so that the fluid passage between the body 25 and the inside of the tubing is completely sealed. The construction of the individual segments to accomplish a complete seal in this area is described in substantially greater detail in the abovementioned copending application Serial Number 561,467. While the packets are preferably thus made of such segments and are metallic for greater resistance to wear, other types of packing elements such as rubber sleeves or the like may be substituted in some cases to accomplish the same or similar results.

An upper cylinder 77 at the upper end of the free piston body 25 has a port 78 near the bottom by which fluid pressure surrounding the upper end of the free piston is transmitted to the under side of a plunger 79 on the upper end of control rod 44. This plunger moves axially in the upper cylinder 77 and is sealed with the cylinder wall by a packing 81 to prevent fluid bypass around the plunger. The upper end of the cylinder 77 is open through an axial bore 82 in a fishing neck or head 83. The upper end of the body has a tapered shoulder or valve member 27 adapted, as described in greater detail hereinafter, to seat against the bottom end of an upper free piston stop 18. The control rod is urged downwardly in the body by a reset spring 86 placed between the plunger 79 and a shoulder 87 in the upper end of the body. While this reset spring counter acts some of the force produced by spring 66 which is stronger and which urges the control rod upwardly in the body, the control rod normally is held in the position shown with the rollers 63 of the snap-acting device at the upper end of the toggle blocks 64. The action of the lower spring 66 is confined by a wa her 88 which strikes a shoulder 89 on the free piston body so that any movement of the control rod above the position shown merely compresses the reset spring 86. This movement of the control rod above the normal position maintained by the two

springs

66 and 86 is produced when a differential pressure is developed across plunger 79 and the ditferential force on the lower side of the plunger is greater than the force of reset spring 86. This differential pres- 6 sure raises the control rod, including the toggle fork and the cylinder 65 relative to the body, the piston 41 and the piston ring 42. As they are thus raised, the port 91 in the chamber wall is raised above the piston ring 42 allowing the pressure in the cylinder 65 to equalize with the well or tubing pressure below the bottom packer 26. When this differential pressure across the plunger 79 is removed, reset spring 86 returns the control rod 44 to its normal position as shown in the drawing with the lower end of the control rod resting on the washer 88.

While this preferred embodiment of a free piston may be used in a tubing head of the type shown in Figure l where the upper free piston stop 18 is located below a single outlet to the flow line 16, a modified tubing head as shown in Figures 3 and 4 is preferred. In this preferred tubing head, two tubing outlets are provided. The lower tubing outlet to flow line 16 is spaced by a nipple 92- and the upper free piston stop housing 93 from a second tubing outlet 94 by a distance which permits the bottom f-ree piston packer 26 to be stopped by the upper free piston stop 18 substantially at the upper end of the tubing 12. The upper free piston stop comprises generally an open-ended cylinder which may be reciprocated in the housing 93. It is urged downward by one or more bumper springs 19 which are placed in compression between the upper end of the stop and the cap 17. The lower end of the upper free piston stop has a valve seat 95 on which the valve member 27 seats to provide a seal so that fluid cannot pass from the tubing into the upper tubing outlet 94 when the free piston is in its uppermost position. The annular space between the upper free piston stop and the housing 93 is desirably sealed as by an O ring packing 24. The upper free piston stop may float freely in the housing 93 as in the embodiment shown in Figure l, but in a preferred embodiment its downward movement is confined by a ring 97 placed between the ends of nipple 92 and housing 93 in collar 98. The upper tubing outlet 94 may be connected to any line, for example the flow line 16, downstream from a choke 99 so that the pressure at the outlet 94 will be maintained lower than the normal tubing pressure when the free piston is at the upper end of its travel and valve member 27 is in position in the valve seat 95 in upper free piston stop 18 to provide a fluid seal between these two areas. This upper tubing outlet is used to control the operation of the free piston as will be explained in greater detail hereinafter.

In operation, a free piston as shown in Figures 3 and 4 is lowered into the well tubing by, for example, removing the nipple 92 from the flow T 100. As the free piston is lowered or dropped into the tubing, the packers are in a contracted position as shown with the rollers 63 on the upper edges of the toggle blocks 64. The packers being contracted, the free piston will fall freely through the tubing and any fluid which may be moving upwardly therein until the free piston strikes a lower stop in the tubing or until the hydrostatic head on the free piston is great enough to force piston 41 into chamber 65 and cause the toggle rollers 63 to jump the toggle blocks 64. This snap-acting device, as is well-known, initially restrains movement of the piston 41 into the chamber 65 until the differential pressure across the piston 41 is great enough to compress spring 66 and allow the toggle rollers to completely pass the toggle blocks. When the control rod moves and the toggle rollers pass the toggle blocks, the packers are simultaneously expanded. After the free piston is thus lowered or dropped into the well, the nipple 92 and upper stop mechanism are again attached to the flow T 100. Injection of lifting gas is typically timecontrolled and delayed until the liquid production of the well and buildup of liquid head in the tubing above the free piston is great enough to actuate the snap-action of the control rod and the expansion of the packers. After such a delay gas is injected into the tubing below the free piston, as for example through the lower end of the tubing, causing the free piston to rise and displace the well liquids above it through the tubing.

As the well liquids reach the surface, part of the liquid flows through the flow line 16 and part of it flows through the upper tubing outlet 94. A choke 101 may be placed in the upper tubing outlet 94 to restrict the amount of well liquids flowing through the upper outlet and thus tend to cushion the free piston when it arrives at the surface and the upper end passes the flow T 100. In any case, when the well liquids have been displaced from the tubing above the free piston, the free piston is stopped by the valve member 27 striking seat 95 in the upper stop 18. The inertia of the free piston remaining after the free piston thus strikes the stop is absorbed by the bumper springs 19 and by the displacement of liquid through the orifice or choke 101. Since the fluid pressure beneath the bottom free piston packer is greater than the flow line pressure, the free piston is held in this upper position until the packers are contracted. Contraction of the packers may be delayed any desired length of time by closing the upper tubing outlet 94. This may be done manually as by closing a valve 102 or such valve may be closed and opened automatically as by a time clock so that the predetermined period of the free piston can be automatically timed. That is, with the upper tubing outlet 94 closed, the fluid pressure in the housing 93 will be substantially the same as the fluid pressure in the tubing below the packers. These pressures being about equal, there is insuflicient differential pressure across plunger 79 to make the toggle rollers 63 jump the toggle blocks 64 so the control rod is held in its lower position in the body and the packers remain expanded. When the valve 102 is opened to relieve the pressure in the housing 93 above the valve member 27 and seat 95, the pressure on the top side of plunger 79 is less than the pressure on the bottom side of the plunger and this diflerential pressure raises the control rod 44 in the body 25 compressing reset spring 86, causing the toggle roller 63 to pass the toggle blocks 64 and thus contracting the packers. At the same time that the control rod is thus raised in the body, the differential pressure across plunger 79 carries the toggle rollers 63 substantially above the toggle blocks 64, thus raising the cylinder 65 relative to the piston 41 such that the orifice 91 is above the piston ring 42 and is in com munication with the fluid in cylinder 65. By thus exposing the fluid in cylinder 65 to the well head pressure once each cycle, any liquid leaking into the cylinder during submersion of the free piston in the well liquids is drained off at the bottom of the enclosed chamber and the pressure within that chamber is re-established at well head pressure. When the packers are contracted and the differential pressure across the fluid seal at valve member 27 and seat 95 is equalized or substantially equalized, the weight of the free piston causes it to drop away from the top stop and fall again through the well tubing. If not otherwise sufliciently equalized, this pressure may be equalized by closing valve 102 or in some cases it may be desirable to place an equalizing line 103, having a bypass valve 104, across the upper stop or to otherwise build up the pressure in the housing above the upper free piston stop so that the force produced by the ditferential pressure across the valve member 27 is less than the weight of the free piston.

One of the particular advantages of this apparatus is in the utilization of the blow-down gas following the free piston to contract the packers and recock the toggle fork at the surface. Otherwise, as is well-known in the operation of a free piston, the piston often arrives at the surface at a velocity so low that, in those free pistons utilizing the forces of inertia to contract the packers, the energy available is inadequate and the operation of the free piston is sometimes not dependable. The energy of the blowdown gas, on the other hand, is many times more than adequate to provide the necessary operating forces to contract the packers and otherwise recock the mechanism so that the packers can be again expanded easily at the lower end of the free piston travel. In one embodiment of this invention this excess energy available in the blowdown gas is stored in a spring so that when a minor amount of threshold energy is supplied, as by contact of the free piston with a bottom stop in the tubing, the energy stored in the spring is released to expand the packers. Such an embodiment is shown in Figure 5. The trigger mechanism shown here or various alternates may in some cases be substituted for the pressure-sensitive apparatus shown in the lower part of the free piston illustrated in Figures 3 and 4. In this case the lower end of the body 25 is connected to a shoe instead of the guide 39. A compression spring 106 is placed between shoulder 89' on the body and a collar 108 on the lower end of control rod 44 so that the control rod is normally urged downwardly with respect to the body with a force great enough when released to expand the packer 26. The upper bracket 49 of the packer is in this case, as in the embodiment described above, connected to the control rod by pins 45 and the lower bracket 72 is connected to the body so that this axial movement of the control rod relative to the body expands and contracts the packer 26 in the same manner. Additionally, the movement of the control rod opens and closes a fluid passage through the

ports

29 and 31. When the free piston with this release mechanism is dropped into the tubing, the spring 106 is under compression and the control rod 44' is held up (in the position shown in Figure 5) with respect to the body by the dogs 109 which are anchored on shoulders 110 of the shoe. These dogs are flexibly hinged at the upper end 111 to the lower end of the control rod and are held out ward on these shoulders by the cam 112 on latch 113 acting against the rollers 114. The latch is normally held in its lower position with the rollers 114 on the cam 112 by its own weight or by a suitable spring. When the lower end of the latch strikes a bottom stop in the tubing, the latch is raised displacing cam 112 from between rollers 114 so that the dogs 109 are displaced or deflected by the downward force of spring 106 off of the tapered shoulders 110. Compression spring 106 then forces the control rod downwardly, closing the fluid passage through

ports

29 and 31 and expanding the packer. The angle or taper of shoulders 110 is preferably great enough so that the force of spring 106 urges the dogs 109 inward when the trigger 113 is raised and the cams 112 are removed from between the rollers 114. If lifting gas is injected below the free piston after the fluid passage is closed and the packer is thus expanded by striking a bottom stop in the tubing, the free piston is lifted through the tubing as in the embodiment above described. After the well liquids above the free piston are discharged from the top of the tubing, the valve member 27 is again seated in the upper stop 18 and, with the housing above this stop open via the tubing outlet 94 to a low pressure area, pressure is applied by the blow-down gas to the bottom side of plunger 79. The force produced by the differential pressure across the plunger raises the control rod into the position shown in Figure 5, opening the fluid bypass through

ports

29 and 31, the control rod and the ports 115 in the shoe, contracting the packer, compressing spring 106 and lifting dogs 109. When the lower end of these dogs is above shoulders 110, cam 112 drops down between the rollers 114, driving the dogs 109 apart so that they will rest on shoulders 110 when the difierential pressure is removed, thus cocking the control rod with spring 106 in a compressed state so that when a minor amount of threshold energy is again applied to the end of trigger 113, i.e., when the trigger again strikes a bottom stop in the tubing, the energy in spring 106 is again released to close the fluid bypass through the free piston, expand the packer, etc.

Another particular advantage of the free piston pumping system herein described is that it may be adapted for use in a well equipped with well head or surface connections that are larger than the well tubing. Such a well head is illustrated in Figure 6. In this apparatus the tubing 12, which is typically of a standard size, terminates in the well below the tubing head 11 at a reducing coupling 121 and from this reducing coupling an enlarged tubing section 12' extends upwardly through the tubing head. Wells are often completed with larger surface connections of this type for a number of reasons. One reason is that it is often desirable at a later date, due to increased fluid production or the like, to increase the size of the main part of the tubing without changing the surface fittings. When the main part of the tubing is thus changed, the tubing is of uniform size from top to bottom and a free piston can be used in this enlarged tubing in the same manner as described above. Prior to the installation of the enlarged tubing, however, a free piston small enough to operate in the main part of the tubing but too small to seal in the enlarged tubing section 12' in the well head can be used by resiliently mounting the upper free piston stop 18 at or near the lower end of the enlarged tubing section 12 as shown in Figure 6. The upper end of spring 19, which is used to absorb the shock when the free piston 15 arrives at the surface, may be anchored at any place in the enlarged tubing section above the upper free piston stop 18. As indicated in the drawing, the upper end may desirably be anchored to the cap 17.

The operation of this alternative embodiment is substantially identical to the operation of the embodiment shown in Figure 1. When the cap 17 and the attached spring and upper free piston stop are removed, the free piston 15 may be dropped into the tubing with the packer contracted and/or the flow passage through ports 31 open so that it falls freely to the bottom of the tubing. At the bottom of the tubing the packer is expanded and/ or the flow passage through the port 31 is closed so that the free piston is raised by the well fluids or by a lifting gas injected into the well. The well fluids above the free piston are displaced through the tubing outlet to the flow line 16. When the free piston then arrives at the upper end of the regular tubing 12, the valve member 27 contacts the lower end of the upper free piston stop 18, closing the flow passage 23 therethrough. With this flow passage closed, a differential pressure is developed across the free piston, as above described, shifting the control rod 44 or valve member 28 and causing the direction of travel of the free piston to be reversed, i.e., allowing the free piston to fall through the tubing again on a return cycle.

From the foregoing description of certain preferred embodiments of this invention it can be seen that this invention is susceptible of a wide variety of embodiments. This invention should, therefore, be construed not to be limited to the embodiments actually described, but should be construed to be limited only by the scope of the appended claims.

We claim:

1. A free piston pump for a well including a tubing in said well, a fluid outlet in the upper end of said tubing, an upper free piston stop in said tubing below said outlet, a flow passage through said stop, a free piston in said tubing below said upper free piston stop, bypass means on said free piston to permit fluid to flow past said free piston so that said free piston will fall in said tubing, closure means on said free piston to close said bypass means when said free piston is at the lower end of its travel and prevent fluid from passing said free piston so that said free piston can be lifted through said tubing by fluid pressure beneath said free piston, means on said free piston to close said flow passage through said stop and create a differential pressure across said stop when said free piston is lifted by said fluid pressure and contacts said stop, and means on said free piston actuated by said diflerential pressure to open said bypass means so that said free piston will fall on a return cycle in said tubing.

2. A free piston pump according to claim 1 in which said free piston includes a body and snap-acting means 10 between said body and said closure means to cause said closure means to delay opening and then open rapidly and to delay closing and then close rapidly.

3. A free piston pump for a well including a tubing in said well, a fluid outlet in the upper end ofsaid tubing, an upper free piston stop in said tubing below said outlet, 9. flow passage through said stop, a free piston including a free piston body in said tubing below said upper free piston stop, means to inject gas below said free piston in said tubing, a packer on said free piston to form a fluid seal with said tubing, a fluid bypass through said free piston to permit said free piston to fall through fluid in said. tubing, means to close said fluid bypass when said free piston is at the lower end of its travel in said tubing so that said free piston can be lifted through said tubing by said gas, means on said free piston to close said flow passage through said stop and create a differential pressure across said stop when said free piston is lifted by said gas and contacts said stop, and means actuated by said differential pressure to open said fluid bypass so that said free piston will fall on a return cycle in said tubing.

4. A free piston pump for a well including a tubing in said well, a fluid outlet in the upper end of said tubing, an upper free piston stop in said tubing below said outlet, a flow passage through said stop, and a free piston including a free piston body for reciprocation in said tubing below said upper free piston stop, a packer on said free piston expansible to form a fluid seal with said tubing, means to expand said packer when said free piston is at the lower end of its travel so that fluid cannot pass said free piston and it will be lifted through said tubing by a fluid pressure beneath said free piston, valve means on said body to close said flow passage through said stop and create a differential pressure across said stop when said free piston is lifted by said fluid pressure and contacts said stop, and means actuated by said differential pressure to contract said packer so that fluid in said tubing will pass said packer and said free piston will fall on a return cycle in said tubing.

5. A free piston for automatic reciprocation in a well tubing having an outlet at the top, an upper free piston stop below said outlet and a flow passage through said stop which includes an elongated cylindrical body, a packer on the periphery of said body to form a fluid seal with said tubing, bypass means to permit fluid to flow past said free piston so that said free piston will fall in said tubing, closure means to close said bypass means when said free piston is at the lower end of its travel and prevent fluid from passing said free piston so that said free piston can be lifted through said tubing by fluid pressure beneath said free piston, means on said free piston to close said flow passage through said stop and create a differential pressure across said stop when said free piston is lifted by said fluid pressure and contacts said stop, and means actuated by said differential pressure to open said bypass means so that said free piston will fall on a return cycle in said tubing.

6. A free piston for automatic reciprocation in a well tubing having an outlet at the top an upper free piston stop below said outlet and a flow passage through said stop, which free piston includes an elongated cylindrical body, a packer on the periphery of said body to form a fluid seal with said tubing, means to expand said packer within said tubing so that it forms a fluid seal with said tubing and said free piston can be lifted through said tubing by fluid pressure beneath said free piston, valve means on said body to close said flow passage through said stop and create a differential pressure across said stop when said free piston reaches the surface, and means actuated by said ditferential pressure to contract said packer.

7. A free piston for automatic reciprocation in a well tubing, said well tubing having an outlet at the top an upper free piston stop below said outlet and an axial flow passage through said stop, said free piston including an elongated cylindrical tubular body, an expansible packer on the periphery of said body to form a fluid seal with said tubing, means connecting one end of said packer to said body, a control rod within said body, means connecting the other end of said packer to said control rod, means forming a variable volume pressure chamber in said control rod, a piston forming a movable wall in said pressure chamber, means connecting said piston and said body, said piston being forced into said pressure chamber to decrease the volume of said pressure chamber and expand said packer when said free piston is exposed to a high pressure, a peripheral valve member on the upper end of said tubular body adapted to close said flow passage through said stop when said free piston is at the surface, and a plunger on the upper end of said control rod disposed within said tubular body and adapted to prevent flow through said tubular body when said flow passage is closed by said valve member, whereby said plunger and said control rod are moved in said body by a pressure on the bottom of said plunger greater than the pressure in said outlet to contract said packer when said flow passage through said stop is closed.

8. A free piston for automatic reciprocation in a well tubing, said Well tubing having an outlet at the top an upper free piston stop below said outlet and an axial fiow passage through said stop, said free piston including an elongated cylindrical tubular body, an expansible packer on the periphery of said body to form a fluid seal with said tubing, means connecting one end of said packer to said body, a control rod within said body, means connecting the other end of said packer to said control rod, means forming a variable volume pressure chamber in said control rod, a piston forming a moveable wall in said pressure chamber, means connecting said piston and said body, said piston being forced into said pressure chamber to decrease the volume of said pressure chamber and said control rod being lowered in said body to expand said packer when said free piston is exposed to a high pressure, a peripheral valve member on the upper end of said tubular body adapted to close said flow passage through said stop when said free piston is at the surface, and a plunger on the upper end of said control rod disposed within said tubular body and adapted to prevent flow through said tubular body when said flow passage is closed by said valve member, whereby said plunger and said control rod are lifted in said body by a pressure on the bottom of said plunger greater than the pressure in said outlet to contract said packer when said flow passage through said stop is closed.

9. A free piston according to claim 8 including snapacting means between said body and said control rod to cause the movement of said control rod to be delayed during contraction and expansion of said packer and then to cause said control rod to move rapidly respectively to contract and to expand said packer.

10. A free piston pumping system for pumping a well equipped with a tubing including a flow line connection for well fluids at the upper end of said tubing, an upper tubing outlet above said flow line connection, an upper free piston stop disposed in said tubing between said flow line connection and said upper tubing outlet, valve means in said upper tubing outlet to control the flow of the fluid therethrough, shock absorber means connected to said upper free piston stop to decelerate a free piston arriving at the surface, a flow passage through said upper free piston stop, a valve seat in said stop at the lower end of said flow passage, :1 free piston in said tubing below said upper free piston stop, said free piston having a cylindrical tubular body, an annular valve member on the upper end of said tubular body adapted to seat in said valve seat and close said flow passage, a control rod disposed axially in said body, at least one packer on said body, means connecting the lower end of said packer to said body, means connecting the upper end of said packer to said control rod, a cylinder in said control rod, said cylinder being open at the lower end, a piston connected to said body and sealing the lower end of said cylinder, and a plunger on said control rod closing the opening through said body at said valve member, the opening in the upper end of said body extending above said valve member, whereby said con trol rod is driven with respect to said body in a direction to contract said packer when said valve member is in said valve seat and the pressure in said tubing is greater than the pressure in said upper tubing outlet.

11. A free piston pumping system according to claim 10 including means to equalize the pressure across said valve member periodically so that said free piston will be released and will fall through said tubing.

[2. A free piston pumping system according to claim 11 including means to inject gas into the lower end of said tubing after said pressure has been equalized and said free piston has fallen in said tubing.

13. A free piston pumping system according to claim 10 including a snap-acting means between said tubular body and said control rod to cause said control rod to first delay movement and then to move rapidly to expand and to contract said packer when said free piston is at the lower and the upper ends of its travel, respectively.

14. A free piston pumping system according to claim 10 including resilient means urging said control rod axially of said body in a direction to counteract the movement of said piston into said chamber produced by pressure on said free piston, where by the expansion of said packer is retarded as said free piston is submerged in liquid in said tubing.

15. A free piston pumping system according to claim 14 including means to adjust the 'force produced by said resilient means whereby said free piston may be submerged to difierent predetermined liquid depths before said packer is expanded.

16. A free piston pump for a well including a casing in said well, "a tubing head connected to the upper end of said casing, a tubing in said casing, an enlarged tubing section at the upper end of said tubing extending through said tubing head, a fluid outlet in the upper end of said enlarged tubing section, an upper free piston stop at the lower end of said enlarged tubing section, a flow passage through said stop, a free piston in said tubing, bypass means to permit fluid to flow past said free piston so that said free piston will fall in said tubing, closure means to close said bypass means when said free piston is at the lower end of its travel and prevent fluid from passing said free piston so that said free piston can be lifted through said tubing by fluid pressure beneath said free piston, means on said free piston to close said flow passage through said stop and create a differential pressure across said stop when said free piston is lifted by said fluid pressure and contacts said stop, and means actuated by said differential pressure to open said bypass means so that fluid will pass said free piston in said tubing and said free piston will fall on a return cycle in said tubing.

17. A free piston pump according to claim 16 in which said upper free piston stop is resiliently mounted in said enlarged tubing section to absorb the shock produced by said free piston when it arrives at the upper end of said tubing.

18. A free piston including an tubular body, a control rod movable axially within said body, an annular valve member on the upper end of said body for cooperation with a valve seat in an upper tree piston stop in a vertical tubing to close a flow passage through said stop, a multiplicity of packers disposed on said body and adapted to seal the annular space between said body and the wall of said tubing, means resiliently connecting the lower ends of said packers to said body,

elongated cylindrical means connecting the upper ends of said packers to said control rod so that said packers are expanded when said control rod is moved downward relative to said body to compress said packer axially, 'a plunger on said control rod forming a fluid seal with said body in the area of said valve member, means to admit the fluid pressure outside said body to the bottom side of said plunger, a cylinder in said control rod forming a pressure chamber open at the bottom, a piston connected to said 'body and sealing the lower end of said cylinder whereby said fluid pressures outside said body urges said piston into said chamber to expand said packers when the pressure on both sides of said plunger 'are equal and whereby said fluid pressure outside said body contracts said packers when said fluid pressure outside said body is substantially greater than the pressure on the top side of said plunger.

19. A free piston according to claim 18 including a 14 snap-acting means between said tubular body and said control rod to cause said control rod to first delay movement and then to move rapidly to expand and to contract said packer when said rfree piston is at the lower and the upper ends of its travel, respectively.

20. A free piston according to claim 18 including an upper cylinder in the upper end of said body below said valve member and an opening from said upper cylinder axially through said valve member, said plunger forming 10 a seal with the inner wall of said upper cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 2,714,855 Brown Aug. 9, 1955