US3420183A

US3420183A - Subsurface pump

Info

Publication number: US3420183A
Application number: US609227A
Authority: US
Inventors: Merida L Hart
Original assignee: MERIDA L HART
Current assignee: MERIDA L HART
Priority date: 1967-01-13
Filing date: 1967-01-13
Publication date: 1969-01-07
Anticipated expiration: 1986-01-07

Description

M. L. HART Jan. 7, 1969 SUBSURFACE PUMP Sheet Filed Jan. 13, 1967 zzvvmvron. Mae/0,4 La H/wr M. L. HART SUBSURFACE PUMP Jan. 7, 1969 Filed Jan. 13. 1967 TLEE fizz-[i INVENTOR. A. HA/er ME- /bA M. L. HART SUBSURFACE PUMP Jan. 7, 1969 Filed Jan. 13, 1967 r1511 fits-i2 INVENTOR. L. HA r United States Patent 6 Claims ABSTRACT OF THE DISCLOSURE A hydraulically operated, rodless pump for use in subsurface pumping. The pump includes concentric power fluid and production fluid strings, and has a free, compound working piston mounted in the power fluid string and driven'downwardly therein by a hydraulic power fluid delivered from the surface. The upward stroke of the compound working piston is assisted by the hydrostatic head exerted by production fluid standing in the annulus between the strings, and by pneumatic pressure exerted by a gas entrapped above production fluid collected in a production fluid collection chamber at the top of the production tubing. Means is provided for automatically and continuously maintaining a constant volume of power fluid in the column of power fluid which extends between a power fluid piston located at the surface and the compound working piston located down hole.

This invention relates to a subsurface pump of the type used to produce liquids from a subterranean deposit. More specifically, but not by way of limitation, the present invention relates to a subsurface pump which concurrently uses hydraulic, hydrostatic, and pneumatic forces for efliciently producing petroleum from an underground formation.

Subsurface pumps utilizing a liquid piston in place of a metallic sucker rod string, and employing balanced columns of liquid to assist in the lifting of liquid from great depths and to reduce the power requirements of the pump have been heretofore proposed. This has been prompted by the recognition for some time, that due to the great depths to which wells for producing petroleum are now being drilled, the traditional sucker rod type pump is no longer satisfactory for producingoil from deep wells of this type. The rodless, subsurface pump system has the advantage of eliminating the long and heavy sucker rod string utilized in the older pumps, thus reducing the overall expense of pumping, and improving maintenance costs.

The present invention provides an improved, hydraulically driven' subsurface pump which provides assistance to the main-hydraulic power source in the form of a leg or column of liquid exerting hydrostatic pressure in a balancing action during an appropriate and pre-selected time during the pumping action, and also providing pneumatic assistance to reduce the total power required for pumping. The pump of the present invention is an improvement over subsurface, hydraulically operated pumps in several other respects. Thus, means are provided for automatically maintaining substantially constant the length of the power fluid rod which extends from a piston at the surface to a working piston which is located deep in the well so that losses of power fluid through leakage, and also thermal expansion of the power fluid, can be automatically compensated. The pump also provides means for removing a substantial part of the gas produced with the oil, as well as other features which assist in reducing or eliminating gas lock. Finally, the pump includes an improved sand trap feature which reduces the sand and sediment content of the produced oil, and facilitates easier and more convenient cleaning of the sand trap.

Broadly described, the subsurface pump of the inven- 3,420,183 Patented Jan. 7, 1969 tion comprises a power fluid tubing string and a production fluid tubing string which concentrically surrounds the power fluid tubing string and defines an annulus therewith. A free working piston is reciprocally and slidingly disposed in the power fluid tubing string, and a first check valve is disposed in the power fluid tubing string below the free piston for permitting flow of fluid upwardly in the power fluid tubing string while preventing the flow of fluid downwardly past the check valve. Passageway means extends through the power fluid tubing string at a location between the first check valve and the free piston, and places the annulus between the power fluid tubing string and the production fluid tubing string in communication with the interior of the power fluid tubing string. A second check valve is disposed in said pasageway means for preventing flow of production fluid from said annulus into said power fluid tubing string through the passageway means.

The free piston includes an upper piston element and a lower piston element with the upper and lower piston elements being interconnected by an elongated connecting rod. A second passageway means is formed through the power fluid tubing string to place the annulus between the two tubes in communication with the interior of the power fluid tubing string, such second passageway being formed at a point in the power fluid tubing string that is located between the upper and lower piston elements during the reciprocation of the free piston in the power fluid tubing string. The second passageway means permits a column of production liquid standing in the annulus between the production fluid tubing string and the power fluid tubing string to substantially balance or offset the weight of the power fluid above the piston in thepower fluid tubing string so that a minimum power requirement is involved in lifting this piston and the column of power fluid upwardly during the upstroke of the subsurface pump.

Secured to the upper end of the power fluid tubing string is a power fluid cylinder in which is mounted a reciprocating power fluid piston. Any suitable driving means is provided for driving the power fluid piston in reciprocation in the power fluid cylinder for directing the power fluid down into the power fluid tubing string during the down stroke of the free working piston in this tubing string. Means are provided adjacent to the power fluid cylinder for supplying makeup power fluid to this cylinder, and the power fluid piston mounted in the power fluid cylinder is equipped with suitable valving so that a substantially constant volume of power fluid can be maintained in the column of power fluid which extends between the power fluid piston and the free working piston disposed in the lower portion of the power fluid tubing string as hereinbefore described.

A preferred embodiment of the pump also includes in addition to the described structure, a production fluid collection chamber which is disposed at the surface and is connected to the upper end of the production tubing string to receive production fluid therefrom. The production fluid collecting chamber has connected thereto a discharge line in which is interposed a balanced hydrostatic fluid level control valve which is responsive to the accumulation of a predetermined amount of production fluid in the production fluid collection chamber to permit this fluid to be periodically discharged through the discharge line. A gas supply system is connected to the upper portion of the production fluid collection chamber and functions to supply a gas under pressure to the collection chamber for pneumatically assisting the discharge of production fluid from this collection chamber, as well as to assist the hydrostatic balancing effect of the column of production fluid as it acts in opposition to, or balances, the

column of power fluid extending above the free working piston in the power fluid tubing string.

From the foregoing description of the invention, it will have become apparent that it is an important object of the present invention to provide an improved subsurface pump which employs hydraulic, hydrostatic and pneumatic forces to more efficiently produce subterranean liquids with a power input requirement which is lower than has been characteristic of the subsurface pump systems heretofore utilized.

Another object of the invention is to provide a subsurface pump which, in operation, displaces substantially 100 per cent of the effective bore capacity of the pump barrels with power fluid and production fluid on each stroke of the pump, thereby substantially reducing or eliminating the problem of gas locking.

Another object of the present invention is to provide a subsurface, hydraulically operated pump which employs a hydraulic power fluid and is constructed so that the power fluid utilized in operating the pump is not permitted to contact, or mix with, the pumped or produced fluid at any time during the use of the pump.

An additional object of the present invention is to provide a subsurface hydraulic pump which provides a gas accumulator at the surface which functions to collect gas entrained in the production fluid and to usefully employ such collected gas for directing the produced fluid through a discharge line to a storage facility, and also for maintaining a preselected pressure differential across a downhole free working piston so that the piston may be operated with maximum efliciency, and lowest power input, using such pneumatic pressure in combination with the hydrostatic head exerted by the column of production fluid standing in an annulus between a production fluid string and power fluid tubing string of the pump.

Another object of the invention is to provide a rodless type subsurface pump which may be manufactured relatively economically and operated with small power costs as compared to sucker rod type subsurface pumps, and also as compared to present hydraulic and pneumatic pumps now in use.

An additional object of the invention is to provide an improved subsurface, hydraulically operated rodless pump in which a substantial portion of any sand or other solid contaminant or foreign material present in the fluid produced by the pump is removed prior to the time such fluid is moved to the surface by the pump.

An additional object of the present invention is to provide an improved subsurface, hydraulic, rodless pump which effectively extracts or removes a substantial portion of the entrained gas from the production fluid prior to the time the production fluid reaches the surface.

In addition to the foregoing described objects and advantages, additional objects and advantages will become apparent as the following detailed description of the invention is read in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic, vertical sectional view showing the subsurface hydraulic pump of the present invention installed in a conventional oil well casing.

FIGURE 2 is an enlarged sectional view of wellhead apparatus forming a portion of the subsurface pump of the present invention.

FIGURE 3 is a vertical sectional view taken through an upper portion of the concentric tubing strings of the subsurface pump of the invention, and through the well casing which surrounds the pump.

FIGURE 4 is a vertical sectional view taken through the concentric tubing strings of the subsurface pump of the invention at a point immediately below that portion of the pump illustrated in section in FIGURE 3.

FIGURE 5 is a transverse sectional view taken along line 5-5 of FIGURE 4.

FIGURE 6 is a transverse sectional view taken along line 6-6 of FIGURE 4.

FIGURE 7 is a transverse sectional view taken along line 77 of FIGURE 4.

FIGURE 8 is a vertical sectional view of the concentric tubing strings of the subsurface pump of the invention with such sectional view being taken through that portion of the pump which is disposed immediately below the portion of the pump depicted in FIGURE 4.

FIGURE 9 is a transverse sectional view taken along line 99 of FIGURE 8.

FIGURE 10 is a transverse sectional view taken along line-10-10 of FIGURE 8.

FIGURE 11 is a vertical sectional view taken through the concentric tubing strings of the pump at a point in the pump which is immediately below that portion of the pump depicted in FIGURE 8.

FIGURE 12 is a vertical sectional view taken through the lower end of the subsurface pump of the present invention.

Referring now to the drawings in detail, and particularly to FIGURE 1, the subsurface pump of the invention is shown extended into a well casing 10 which extends downwardly into the earth to an oil bearing formation. An outer or production fluid tubing string of the pump is designated by reference numeral 12. At the lower end of the production fluid tubing string 12 a perforated gas anchor 14 is connected by a special connector sub 16 to a sand trap sleeve 18. The sand trap sleeve 18 is con nected at its upper end to a seating collar 20. The seating collar 20 is connected through

subs

21, 22 and 24 to the lower end of the production fluid tubing string 12.

Secured to the upper end of the subsurface pump and located above the ground thereover is a wellhead assembly designated generally by reference numeral 28. The wellhead assembly includes (as depicted in FIGURES 1 and 2) a production fluid collecting chamber 30 and a production fluid discharge conduit 32 in which is interposed a balanced hydrostatic fluid level control valve 34. A power fluid cylinder 36 extends downwardly into the collecting chamber 30 and is sealed with respect thereto by a suitable flange and sealing ring connection 38. A gas pressure gauge 40 is mounted on the top of the production fluid collection chamber 30 for registering the pressure of a gas 41 occupying the upper portion of this chamber.

For the purpose of supplying makeup power fluid to the power fluid cylinder 36, a makeup tank 42 is supported on, or secured to, a suitable flange 44 formed on the collecting chamber 30 and supplies make up power fluid via a conduit 46 to the upper end of the power fluid cylinder 36. A suitable vented filling cap 48 is provided on the makeup tank 42 for venting gas from the upper portion of this tank in the event an excessive pressure is built up therein, and also to permit the supply of makeup power fluid in the tank to be replenished if necessary. A gas reservoir or accumulator 50 is supported by a suitable bracket 52 on the upper end of the power fluid cylinder 36 and is connected through a conduit 53 to the upper end of the production fluid collection chamber 30. A pressure regulator valve 54 is interposed'in the conduit 53 for regulating the pressure differential between the collecting chamber 30 and the accumulator 50. In a preferred embodiment of the invention, air may be supplied to the accumulator 50 by a suitable air compressor 56 which is connected to the accumulator 50 through a suitable conduit 58. A pop valve 60 is provided in association with the compressor 56 and accumulator 50 for relieving excessive pressure in the system.

The aid compressor 56 is driven by a suitable transmission linkage (not visible) from a motor 62 or other suitable prime mover. The motor 62 also functions to drive through a suitable linkage, a crank or connecting arm 64 which is pivotally connected to the upper end of a piston rod 66 which is coaxially disposed in the power fluid cylinder 36. At its end opposite the end connected to the connecting arm 64, the piston rod 66 carries a fluid piston 68 formed by a series of stacked or super-imposed flexible resilient cups. The piston 68 is provided with a first passageway therethrough in which is interposed a check valve 70. The check valve 70 is constructed to prevent flow of liquid from the lower side of the piston 68 through the piston to the upper side thereof, but to permit flow of liquid in a downward direction across the piston and through the check valve. A second passageway is also provided through the piston 68, and the entrance to the second passageway is provided with a pre-set pressure responsive valve 72 which will permit fluid to pass therethrough from the lower side of the piston when the pressure differential across the piston exceeds a preselected value.

Secured through a suitable sub 76 to the lower end of the collection chamber 30 is the production tubing string designated generally by reference numeral 12. The production tubing string 12 concentrically surrounds a power fluid tubing string designated generally by reference numeral 80 which is secured to the lower end of the power fluid cylinder 36 and communicates with the interior thereof. The upper sections of the power fluid tubing string 80 are connected to an upper working barrel portion of the string designated by reference numeral 82 and depicted in FIGURES 3 and 4. The lower end of the production tubing string 12 is connected to a sub 24 as hereinbefore explained.

Disposed within the working barrel 82 of the power fluid string 80 is a compound power fluid working piston designated generally by reference numeral 84, and shown in its entirety when FIGURES 3 and 4 are considered conjunctively. The compound power fluid working piston is a free piston and includes an upper piston element designated generally by reference numeral 86, a lower piston element designated generally by reference numeral 88, and an elongated connecting rod 90. A fishing neck 92 may be conveniently threadedly secured to the upper end of the upper piston element 86, and this piston element is preferably constructed as a hollow or cylindrical mandrel 94 which carries a plurality of sealing cups 96 which are mounted on the mandrel with a plurality of annular metallic spacers 98 in a manner well understood in the art. It will be noted that a number of the sealing cups 96 face upwardly and thus function to prevent by-pass of the piston by a power fluid acting on the piston from above, whereas others of the sealing cups face downwardly and prevent leakage of fluid past the piston from a position therebelow.

The hollow mandrel 94 is connected at its lower end to the elongated connecting rod 90, and also threadedly engages an annular guide collar 100 which is slightly smaller in outside diameter than the inside diameter of the working barrel 80. The guide collar 100 functions to L guide the compound working fluid piston 84 during its reciprocating movement, but does not absolutely prevent fluid by-pass between the guide collar 100 and the internal wall of the Working barrel 82.

Similarly to the upper piston element 86 of the compound power fluid piston 84, the lower piston element 88 includes a generally cylindrical mandrel 102 which has mounted thereon a plurality of annular metallic spacers 104 which position and support a plurality of downwardly facing sealing cups 105. The sealing cups 105 bear against the internal wall of a lower working barrel 106 of the power fluid tubing string 80, and provide a fluid tight seal therewith. At its upper end, the mandrel 102 is internally threaded and receives the lower end of the elongated connecting rod 90. It will be noted that the lower end of the elongated connecting rod 90 is of reduced diameter and is externally threaded for engagement with the mandrel 102. It will further be noted that the lower end of the elongated connecting rod 90 is provided with an axially extending bore 108 which communicates with the hollow interior of the mandrel 102, and which has extending thereinto a plurality of radial ports 110 formed through the connecting rod 90. The function of the ports 110 and the axial bore 108 will be hereinafter explained.

Adjacent its lower end, the upper working barrel 82 of the power fluid tubing string 80 is connected through a special lubricating sub 112 to the lower Working barrel 106 of the power fluid tubing string. The special lubricating sub 112 is machined to relatively closely surround the elongated connecting rod 90 and is provided with annular grooves which accommodate sealing rings 114. The sealing rings 114 provide a fluid tight seal between the elongated connecting rod 90 and the special lubricating sub 112. In its central portion, the special lubricating sub 112 has a lubricant chamber 115 which extends around the elongated connecting rod 90 and provides a space into which a lubricant may be injected through a suitable grease or lubricant fitting 116. It will be noted that the grease fitting 116 is located in a recess 118 which renders the fitting accessible without requiring its protrusion beyond the circumference of the working

barrels

82 and 106 of the power fluid tubing string 80. The lower end 120 of the special lubricating sub 112 is of reduced diameter to permit a decelerating collar 122 which is threadedly secured to the upper end of the mandrel 102 to be loosely received thereover. Stated differently, the decelerating collar 122 has a large bore formed in the end thereof which is diametrically sized to assure the presence of an annulus between this collar and the reduced diameter lower end 120 of the special lubricating sub 112. At a point immediately above the upper end of the special lubricating sub 112, a plurality of ports or passageways 124 are formed through the upper working barrel 82 of the power fluid tubing string 80 and it will be noted that an annular bumper member 125 of resilient material loosely surrounds the elongated connecting rod 90 and rests upon the upper end of the lubricating sub 112 at this point.

At its lower end, the cylindrical mandrel 102 is provided with a large threaded counterbore 126, and an externally threaded pressure relief valve assembly designated generally by reference numeral 128 is threaded into the counterbore 126. The pressure relief valve assembly 128 includes a generally cylindrical member 130 having an elongated bore formed in the lower end thereof, and a counterbore 142 communicating with the bore 140 at the upper end thereof. A spring 144 is seated in the counterbore 142 and biases a ball check member 146 against a valve seat 148 which is threaded into the counterbore 142 from the upper end of the pressure relief valve assembly 128.

The lower end of the lower working barrel 106 of the power fluid tubing string 80 is threadedly connected to a generally cylindrical valve body 154. The cylindrical valve body 154 is circumferentially recessed or undercut at its central portion, as indicated by reference numeral 156, for the accommodation of a pivoted valve assembly designated generally by reference numeral 158. The construction of the pivoted valve assembly 158 can be best understood by reference to FIGURES 8 and 9, and includes a supporting ring 160 which surrounds the recessed portion 156 of the cylindrical valve body 154 and carries a plurality of cars (not seen) which pivotally support three valve arms 162. The valve arms 162 are thus each free to pivot about a horizontal axis. Adjacent their upper ends, each of the valve arms carries a recess 164 which accommodates a small ball valve 166. The ball valves 166 seat in and close radial ports 170 provided around the periphery of the cylindrical valve body 154 in the recessed portion 156 thereof. The pivoted valve arms 162 are retained in their seated positions as depicted in FIGURES 8 and 9 by a circumferential or annular coil spring 172 which extends around all of the valve arms and biases them inwardly. From the described construction of the pivoted valve assembly 158, it will now be understood that the assembly functions to provide a plurality of check valves acting to close the ports 170 against the flow of fluid from the annulus between the production fluid tubing string 12 and the power fluid tubing string 80.

The lower end of the cylindrical valve body 154 is provided with a large, threaded counterbore 176 into which is threaded a valve cage 178. The lower end of the cylindrical valve body 154 is also externally threaded for threaded engagement with a tapered seating nipple 180. The valve cage 178 is an elongated, generally cylindrical member having a ball limiting restriction 182 formed at the upper end thereof, and having a plurality of elongated ports 184 formed below the restriction 182 to permit production fluid to pass from the inside of the valve cage 178 into the counterbore 176 formed in the lower end of the cylindrical valve body 154. The lower end of the valve cage 178 is provided with a downwardly facing shoulder 186 and a valve seat 188 abuts against the shoulder and supports a spherical or ball-shaped standing valve 190. The valve seat 188 is retained against the shoulder 186 by a retaining tube 192.

The retaining tube 192 is pressed through a seating nipple plug 194, and this plug is threaded into the lower end of the seating nipple 180. The seating nipple plug 194 is peripherally grooved for the accommodation of an O-ring seal 196. The O-ring seal 196 sealingly engages the internal wall of a seating collar 198 which is provided with a tapering bore at its upper end for receiving and seating the seating nipple 180. The seating collar 198, which is connected at its upper end to the sub 21, is a generally cylindrical member having a plurality of axially extending, circumferentially spaced passageways 200 formed through the wall thereof as best illustrated in FIGURES 8 and 9. The passageways 200 communicate with the annulus which is defined between the cylindrical valve body 154 and the sub 21 interposed in the production tubing string 12. The passageways 200* also communicate at their lower ends with an annulus 204 formed between an elongated sand trap sleeve 206 and a production fluid pipe 208. The production fluid pipe 208 is threaded at its upper end into a connector fitting 210- by which it is threadedly connected to the inside of the lower end portion of the seating collar 198. The sand trap sleeve 206 is externally threaded and is threadedly engaged with threads formed in a large counterbore 212 positioned at the lowermost end of the seating collar 198.

The production fluid pipe 208, as shown in FIGURE 12, extends through a packing 211 which is retained against a shoulder 213 in a special connector sub 214 by a threaded retaining ring 216. The special connector sub 214 has a large, internally threaded counterbore at its upper end which threadedly receives the lower end of the sand trap sleeve 206. The special connector sub 214 also has a large, internally threaded counterbore at its lower end which threadedly receives the upper end of a perforated, generally cylindrical gas anchor 218.

Intermediate its length, the gas anchor 218 is provided 1 with a plurality of perforations or apertures 220. The gas anchor surrounds a production fluid pick up tubing 222 which is threadedly connected at its upper end through a connecting sleeve 224 to the lower end of the production fluid pipe 208.

Operation In the operation of the subsurface pump of the invention, the power fluid tubing string 80 is initially filled with power fluid so that the space in this tubing string between the compound working piston 84 and the power fluid piston 68 located at the top of the well in the power fluid cylinder 36 is completely filled with a power fluid. The power fluid is preferably a relatively inert, low volatility non-corrosive vegetable oil. A special heat resisting oil which contains and develops practically no gas at high bottom hole temperatures is preferably employed. At the time of filling the power fluid tubing string 80 in the space between the working piston assembly 84 and the power fluid piston 68, it is preferred that both the power fluid piston and the working piston assembly 84 be in their lowermost positions. This arrangement assures that the length of the column of power fluid between these two elements of the subsurface pump will correspond to the volumetric displacement which will be required to characterize the power fluid column during all portions of the pump stroke. An additional amount of the power fluid is placed in the power fluid cylinder 36 above the power fluid piston 68, and the power fluid makup tank 42 is filled with makeup power fluid and is connected to the power fluid cylinder 36 through the conduit 46. In some instances, in order to provide for the most expeditious full stroke, complete cycle operation of the subsurface pump, it may be desirable to fill the production fluid collection chamber 30 and the production fluid tubing string .12 with oil or other suitable, low cost fluid at the outset of the pumping operation to prime or assist the initial stroking of the pump as hereinafter described. This expedient is not a requirement, however, in the operation of the pump.

Prior to starting the operation of the motor of prime mover 62, the accumulator or reservoir of compressed gas is connected through the conduit 53 to the upper portion of the collection chamber 30, but it is preferred that no gas is passed into the upper portion of the collection chamber. As the motor 62 is started up, the piston rod 66 drives the power fluid piston 68 in reciprocation. As a result of this motion of the power fluid piston 68, the column of power fluid which is positioned between this piston and the compound working piston 84 is also reciprocated and drives the compound working piston 84 in reciprocation. During the upstroke of the power fluid piston 68, the vacuum created by this upstroke, coupled with the hydrostatic force exerted by the column of production fluid standing in the annulus between the production fluid tubing string 12 and the power fluid tubing string will simultaneously pull and push the compound working piston 84 upwardly in the power fluid tubing string 80. It will be noted that the production fluid collection chamber 30 is of relatively large diameter as compared to the diameter of the production fluid tubing string 12 and the power fluid tubing string 80, so that a relatively large movement of the compound working piston 84 in the power fluid tubing string will not result in a large subsidence in the level of the production fluid contained within the production fluid collection chamber 30 as production fluid follows the compound working piston 84 upwardly in the power fluid tubing string.

It is to be noted that the working area of the power fluid piston 68 is many times greater than the crosssectional area of the upper piston element 86 of the compound working piston 84. Thus, a relatively short stroke of the power fluid piston 68 is multiplied to produce a long stroke by the working piston 84.

On the upstroke of the compound working piston 84, oil, water or other fluid to be produced by the subsurface pump is drawn inwardly through the perforations or apertures 220 in the gas anchor 218 located at the lower end of the subsurface pump. This gas anchor is, of course, disposed opposite the fluid producing formation so that the production fluid can flow freely through the perforations 220. In the case of oil which has a high gas content, as such oil is drawn through the perforations 220 in the gas anchor 218, a substantial portion of any gas which is entrained therein tends to weather off, or to move upwa-rdly into the upper portion of the gas anchor 218 and is there entrapped. The liquid hydrocarbon, on the other hand, moves downwardly in the annulus between the production fluid pickup tubing 222 and the gas anchor 220.

In the lower end of the gas anchor 218, the production fluid turns upwardly in the subsurface ump and enters the open lower end of the production fluid pickup tubing 222. Continued upward movement of the compound working piston 84 draws the production fluid through the connecting sleeve 224 and into the production fluid pipe 208. The

production fluid pipe 208 conveys the production fluid into the interior of the seating collar 198 and, from this point, the production fluid moves upwardly through the retaining tube 192, past the standing valve 190, which is opened during the upstroke of the pump, and through the elongated ports 184 in the upper end of the valve cage 178. Since the upstroke of the compound working piston 84 coupled with the action of spring 172 draws the valve elements of the pivoted valve assembly 158 to their closed position where they are held on their seat by the hydrostatic pressure in the production string, the production fluid continues upwardly and enters the lower working barrel 106 of the power fluid tubing string 12. At the top of the stroke of the power fluid piston 68, the lower piston element 88 of the compound working piston 84 occupies the position depicted in FIGURE 4 in which the decelerating collar 122 loosely surrounds the lower end 120 of the special lubricating sub 112. The importance of this relationship of these elements which occurs at the upper end of the stroke will be hereinafter described in greater detail.

During the downstroke of the pump, the compound working piston 84 is driven downwardly in the upper Working barrel 82 of the power fluid tubing string 12 by the impress of the power fluid directed downwardly in the power fluid tubing string by the downward reciprocation of the power fluid piston 68. The length of the column of power fluid between the power fluid piston 68 and the compound working piston 84 is such that the lower limit of the stroke will occur at a time when the lower piston element 88 of the compound working piston 84 is adjacent the generally cylindrical valve body 154. At this time, the generally cylindrical member 130 will project downwardly into the bore through the generally cylindrical valve body 154 so as to provide a loose fit therewith and to result in a dash pot or decelerating effect as hereinafter described.

During the downstroke of the compound working piston 84, production fluid standing in the lower working barrel 106 below the lower piston element 88 is forced downwardly by the lower piston element. This action results in seating the ball-shaped standing valve 190, and opening of the ball valves 166 forming a part of the pivoted valve assembly 158. This opens the ports 170 and permits the production fluid to move through these ports into the annulus between the production tubing string 12 and the power fluid tubing string 80. As production fluid moves through the ports 170 into the annulus, a tendency exists to throw out of the production fluid by centrifugal force, a substantial amount of any sand which may be entrained in the production fluid, such sand settling into the annulus between the lower end of the cylindrical valve body 154 and the surrounding sub 21. This gravitating sand then moves on downwardly through quiescent production fluid which stands in this space, through the axially extending passageways 200 formed in the seating collar 198 and into the sand trap sleeve 206. The sand thus ultimately accumulates at the bottom of the sand trap sleeve 206 and on top of the closure which is formed or constituted by the special connector sub 214. It may be noted at this point that after extended periods of operation of the subsurface pump, the sand trap sleeve 206 may become substantially filled with sand, and it will be desirable to pull the pump and clean the sand trap sleeve 206 to remove all the accumulated sand therefrom. This may be easily accomplished by simply disconnecting the sand trap sleeve 206 from the special connector sub 214, and from the lower end of the seating collar 198.

Continued downward movement of the compound working piston 84 continues to drive the production fluid accumuated in the lower working barrel out through the ports 170 and up into the annulus between the production fluid tubing string 12 and the power fluid tubing string 78. This will result in an increase or elevation of the level of production fluid standing in the production fluid collection chamber 30 at the surface. Any residual 10 gas entrained in the production fluid will be vented into the upper portion of the collection chamber 30. The balanced hydrostatic fluid level control valve 34 which is interposed in the production fluid discharge line 32 can be preset to respond periodically to the hydrostatic and pneumatic pressures ac.ing from inside the production fluid collection chamber 30 so that the valve 34 opens and closes periodically to automatically retain the level of the production fluid in the colle.-tion chamber 30 between certain predetermined limits. The purpose of this arrangement is to provide maximum assistance to the pumping action of the power fluid piston 68 as a result of the presence in the annulus between the tubing strings of a standing column of production fluid, and the presence in the upper portion of the production fluid collection chamber 30 of a gas under pressure. Thus, by continuously maintaining the production fluid in the collection chamber 30 at a substantial depth, and retaining gas pressure in the upper portion of this chamber at a certain preselected value, hydrostatic and pneumatic forces may be brought to bear to assist the power fluid piston 68 during its upstroke in the retraction or upward movement of the compound working piston 84.

The precise manner in which the hydrostatic force exerted by the column of production fluid standing in the annulus between the tubing strings is brought to bear may be better understood by reference to FIGURE 4 of the drawings. In referring to this figure, it will be noted that the ports or passageways 124 remain open constantly and thus permit continuous communication be.ween the interior of the working barrel 82 and the annulus between this working barrel and the production fluid tubing string 12. The production fluid retained in this annulus is therefore, at all times, in communication with the interior of the working barrel 82, and fills the space above the special lubricating sub 112 and the lower side of the upper piston element 86 of the compound Working piston 84. Thus, the hydrostatic force developed by the column of production fluid in the annulus between the tubing strings exerts a constantly ac.ing, upwardly directed force against the lower side of the upper piston element 86, and tends toforce the compound working piston assembly 84 upwardly during the upstroke of the pump. This upward force is further augmented by the downwardly acting pressure of gas retained under compression in the upper portion of the collection chamber 30. The combined hydrostatic and pneumatic forces can be adjusted so that very little power must be applied by the prime mover 62 through the piston rod 66 to the power fluid piston 68 in order to retract this piston in an upward direction, and to have the piston followed by the column of power fluid which is positioned between the power fluid piston and the upper piston element 86 of the compound working piston 84.

A more selective and "versatile control of the pneumatic assistance provided to the pumping action is attained in the illustrated preferred embodiment of the invention by the inclusion in the system of the pressure gauge 40 and the gas reservoir or accumulator 50 and associated controls. By means of these elements, air or other gas under pressure may be introduced to the upper end of the production fluid collection chamber 30 at a desired pressure so as to retain the gas pressure in this chamber at a desired value. The compressor 56 may be operated from the prime mover 62 to constantly regenerate pressure in the accumulator 50 so that a constant supply of gas under pressure is available in the eventthe system should develop leaks, or the pumping of a relatively high viscosity material should require a higher pressure in the collection chamber 30.

An important feature of the present invention is the characteristic of the subsurface pump of maintaining a relatively constant volume of power fluid between the power fluid piston 68 and the compound working piston 84. In many rodless pumps of general similarity to the present invention in which a column of power fluid has been provided to extend between a reciprocating piston located at the surface and a working piston located within a power fluid string in the well, some difficulty has been experienced in maintaining a constant volume characteristic of this column of power fluid. This difficulty has been in part due to leakage or loss of power fluid from this zone through evaporation and the like. When such loss occurs, the length of stroke of the working piston may be shortened, or the working piston may be made to move through a path which is substantially less than optimum. As contrasted with such power fluid losses, a disruption in smooth and eflicient pumping operations may occur in the rodless pumps of the prior art as a result of the power fluid between the power fluid piston and the working piston becoming hot and expanding so as to occupy a greater volume. When this occurs, the effect is to cause the freely mounted working piston to be displaced further down into the power fluid tubing string with the result that its full stroke may bring it into contact with stops or other elements in a forcible manner so as to damage the pump.

In order to accommodate or make provision for the described loss of power fluid, or the expansion of the body of power fluid between the power fluid piston and the working piston, the present invention incorporates a novel arrangement for adding makeup power fluid to this column of power fluid when losses occur, or for bypassing and removing power fluid where the volume of power fluid is undesirably increased as result of thermal expansion. The structure for accomplishing these functions is best illustrated in FIGURE 2 of the drawings. It will there be noted that a downwardly opening check valve 70 is provided in a passageway which extends through the power fluid piston 68, and that a second passageway extended through this piston is provided with a preset pressure responsive valve 72. Where fluid is lost from the column of power fluid between the power fluid piston 68 and the compound working piston 84, the result is the creation of a pressure differential across the power fluid piston 68 during the upstroke which causes power fluid above this piston to move through the open check valve 70 and to fill the void resulting from loss of power fluid below the piston. In other words, when power fluid is lost from the column, a partial vacuum is created on the lower side of the power fluid piston 68.

during its upstroke, and this partial vacuum causes the check valve 70 to open, and draws power fluid standing in the power fluid cylinder 36 above the power fluid piston 68 downwardly through the passageway. This makeup power fluid is added to the column of power fluid below the piston 68. Thus, the constant volume of power fluid required in this space is maintained despite small losses of such fluid over a period of extended operation.

In those instances where the power fluid between the power fluid piston 68 and the compound working piston 84 has been expanded due to heating, such expansion will tend to increase the volume of power fluid in the column, and the result will be that on the downstroke of the power fluid piston 68, the lower end of the upper piston element 86 will be driven against the bumper 125 positioned on the upper end of the special lubricating sub 112. Once the downward movement of the compound working piston 84 is positively arrested in this manner, continued downward movement of the power fluid piston 68 will result in a tendency to compress the power fluid column standing in the power fluid tubing string 80. Such compression overcomes the clgsing bias of the pressure responsive valve 72, and permits the excessive power fluid disposed in the column to be vented or bled through the passageway in the power fluid piston 68 in which the pressure responsive valve 72 is located. Then on the next upstroke of the pump, the precise and desired amount of power fluid will be located between the compound working piston 84 and the power fluid piston 68. In order to assure that a readily available supply of makeup power fluid is constantly available above the power fluid piston 68, the makeup power fluid tank 42 is provided, and feeds makeup power fluid through the conduit 46 to the upper end of the power fluid cylinder 36.

The subsurface pump of the invention is smooth in its operation and little or no chattering or bumping occurs. Smoothness of operation is achieved by the provision of dash pot effects at each end of the stroke of the compound working piston 84. Thus, during the upstroke of the compound working piston 84, the decelerating collar 122 moves upwardly to a position at the end of the stroke in which it surrounds the reduced diameter lower end of the special lubricating sub 112. As these elements move into this relationship, any fluid which may be entrapped therebetween, whether it be gas, or production fluid which has bypassed the sealing cups 105, is entrapped in the restricted annular zone between the reduced diameter lower end 120 of the special lubricating sub 112 and the decelerating collar 122. This fluid will be passed through the small radial ports 110 and into the axial bore 108 formed in the lower end of the connecting rod 90. The fluid displaced through the radial ports 110 at the end of the upstroke of the compound working piston 84 will move into the hollow interior of the cylindrical mandrel 102 and will there accumulate until such time as the pressure of the fluid in this zone becomes great enough to open the ball check member 146 against the bias of its spring 144 and permit venting of the interior of the mandrel 102. The fluid accumulated within the mandrel 102 is, of course, vented through the ball check member 146 into the open interior of the lower working barrel 106 below the lower piston element 88.

On the downstroke of the pump, the dash pot decelerating effect is obtained by the entry of the lower end of the generally cylindrical member into the interior of the generally cylindrical valve body 154.

From the foregoing description of the invention, it will be perceived that the subsurface pump described provides a hydraulichydrostatic-pneumatic pump actuation which results in a low external power requirement for the pump, and which, because of the use of a simple power piston at the surface, involves a low initial installation cost. A substantial portion of any entrained gas or sand is removed during the operation of the pump so that the produced fluid is relatively clean, and requires a minimum of processing prior to pipelining or ultimate use. No mixing of the power fluid with the production fluid occurs during the operation of the pump, and the provision of structure for maintaining a constant volume of power fluid in the power fluid column extending between the working piston in the well and the power fluid piston at the surface assures an extended and trouble-free operating life. The pumping stroke pressure of the downhole pump is in a downward direction, and therefore no unseating of the pump barrel occurs. Additional hydrostatic and pneumatic pressure constantly act downwardly in the pump through the annulus of the production string. These downwardly acting forces all prevent pumping off or lifting of the downhole pump from its seating nipple, a common, undesirable occurrence in many types of downhole pumps heretofore in use.

Although certain preferred embodiments of the present in vention have been hereinbefore described and depicted in the accompanying drawings, it will be understood that various modifications and changes may be effected in the illustrated structure without departure from the basic principles. which underlie the invention. Insofar as such changes and modifications do not entail a departure from the basic principles of the invention, such changes and modifications are deemed to be circumscribed by the appended claims or reasonable equivalents thereof.

What is claimed is:

1. A subsurface pump comprising:

a power fluid tubing string;

a production fluid tubing string concentrically surrounding the power fluid tubing string and defining an annulus therewith;

a power fluid cylinder connected to the upper end of said power fluid tubing string;

a power fluid piston reciprocably disposed in said power fluid cylinder, said power fluid piston having a pair of power fluid passageways extending therethrough;

valve means in said power fluid passageways for selectively passing power fluid across said power fluid piston whereby a substantially constant volume of power fluid may be maintained below said power fluid piston;

prime mover means drivingly connected to said power fluid piston for driving said power fluid piston in reciprocation in said power fluid cylinder;

a free, working piston reciprocally and slidingly dis- A posed in said power fluid tubing string, said free, working piston including an upper piston element and a lower piston element and an elongated connecting rod interconnecting the upper and lower piston elements;

first check valve means disposed in the power fluid tubing String below the free piston for permitting flow of production fluid upwardly in the power fluid tubing string while preventing the flow of fluid downwardly past the check valve;

first passageway means extending through the power fluid tubing string at a location between said first check valve means and the free, working piston and placing the annulus between the tubing strings in communication with the interior of the power fluid tubing string;

second check valve means disposed in said first passageway means for preventing the flow of production fluid from said annulus into said power fluid tubing string through said first passageway means;

second passageway means extending through the power fluid tubing string at a location which is always disposed between said upper and lower piston elements during reciprocation of said free, working piston, said second passageway means placing the interior of said power fluid tubing string in communication with the annulus between said tubing strings;

a tank for making power fluid positioned adjacent said power fluid cylinder;

a conduit connected between said tank and power fluid cylinder for introducing'makeup power fluid from said tank to said cylinder on the opposite side of said power fluid piston from its side nearest adjacent said power fluid tubing string;

upper end of said production fluid tubing string for receivi g production fluid therefrom;

means for periodically discharging production fluid from said collection chamber to maintain the level of production fluid in said collection chamber within predetermined limits;

an air compressor drivingly connected to said prime mover; and

conduit means connected between said air compressor and said collection chamber for introducing air under pressure to said collection chamber.

2. A subsurface pump comprising:

a power fluid tubing string;

a production fluid tubing string concentrically surroundthe power fluid tubing string and defining an annulus therewith;

means for periodically delivering power fluid under pressure to said power fluid tubing string;

a free, working piston reciprocally and slidingly disposed in said power fluid tubing string, said free,

production fluid collection chamber connected to the r working piston including an upper piston element and a lower piston element and an elongated connecting rod interconnecting the upper and lower piston elements;

first check valve means disposed in the power fluid tubing string below the free piston for permitting flow of production fluid upwardly in the power fluid tubing string while preventing the flow of fluid downwardly past said first check valve means;

first passageway means extending through the power fluid tubing string at a location between said first check valve means and the free piston and placing the annulus between the tubing strings in communication with the interior of the power fluid tubing string;

a generally cylindrical valve body connected in the lower end of the power fluid tubing string and having said first passageway means extending radially therethrough;

at least one valve arm pivotally mounted on the outside of said cylindrical valve body for pivotation about a horizontal axis;

a valve closure member carried by each of said valve arms and positioned thereon for closing said first passageway means in one position of the respective pivotally mounted valve arms;

annular spring means surrounding said generally cylindrical valve body and said valve arms, and biasing said valve arms to a position in which said valve closure members bear against said cylindrical valve body and close said first passageway means;

second passageway means extending through the power fluid tubing string at a location which is always disposed between said upper and lower piston elements during reciprocation of said free, working piston, said second passageway means placing the interior of said power fluid tubing string in communication with the annulus between said tubing strings; and

power fluid makeup means connected to said means for periodically delivering said power fluid for supplying makeup power fluid thereto.

3. A subsurface pump comprising:

a power fluid tubing string;

a power fluid piston reciprocably disposed in said power fluid cylinder, said piston having first and second power fluid passageways therethrough;

a preset pressure responsive valve connected to said first power fluid passageway through said power fluid piston for selectively controlling the passage of a power fluid from said power fluid tubing string to the opposite side of said power fluid piston from said power fluid tubing string;

a check valve in said second passageway through said power fluid piston for permitting flow of power fluid from above said power fluid piston through said power fluid piston toward said power fluid tubing string, and preventing power fluid flow in the opposite direction through said second passageway;

a tank for makeup power fluid positioned adjacent said power fluid cylinder;

a conduit connected between said tank and said power fluid cylinder for introducing makeup power fluid from said tank to said power fluid cylinder on the opposite side of said power fluid piston from said power fluid tubing string;

a free, working piston reciprocably and slidingly disposed in said power fluid tubing string, said free,

working piston including an upper piston element, and a lower piston element, and an elongated connecting rod interconnecting the upper and lower piston elements;

a column of power fluid of constant volume disposed between said free, working piston and said power fluid piston;

means secured in said power fluid tubing string and slidingly and sealingly surrounding said elongated connecting rod at a location between said upper and lower piston elements;

first check valve means disposed in the power fluid tubing string below the free, working piston for permitting flow of production fluid upwardly in the power fluid tubing string While preventing the flow of fluid downwardly past the check valve means;

second check valve means disposed in said first passageway means for preventing the flow of production fluid from said annulus into said power fluid tubing string through said first passageway means; and

second passageway means extending through the power fluid tubing string at a location which is always disposed between said upper and lower piston elements and above said means slidingly and sealingly surrounding said elongated connecting rod during reciprocation of said free, working piston, said second passageway means placing the interior of said power fluid tubing string in communication with the annulus between said tubing strings.

4. A subsurface pump as defined in claim 3 and further characterized to include a production fluid collection chamber connected to the upper end of said production fluid tubing string for receiving production fluid therefrom; and

means for periodically discharging production fluid from said collection chamber to maintain the level of production fluid in said collection chamber within predetermined limits.

5. A subsurface pump comprising:

a power fluid tubing string;

a production fluid tubing string concentrically surrounding the power fluid string and defining an annulus therewith;

a free, working piston reciprocally and slidingly disposed in said power fluid tubing string, said free, working piston including an upper piston element and a lower piston element and an elongated connecting rod interconnecting the upper and lower piston elements;

first check valve means disposed in the power fluid tubing string below the free piston for permitting flow of production fluid upwardly in the power fluid tubing string while preventing the flow of fluid downwardly past the first check valve means; I

first passageway means extending through the power fluid tubing string at a location between said first check valve means and the free piston and placing the annulus between the tubing string in communication with the interior of the power fluid tubing string; second check valve means disposed in" said first passageway means for preventing the flow of production fluid from said annulus into said power fluid tubing string through said first passageway means;

second passageway means extending through the power fluid tubing string at a location which is always disposed between said upper and lower piston elements during reciprocation of said free, working piston, said second passageway means placing the interior of said power fluid tubing string in communication with the annulus between said tubing string;

power fluid makeup means connected to said means for periodically delivering power fluid for supplying makeup power fluid thereto;

a production fluid collection chamber connected to the upper end of said production fluid tubing string for receiving production fluid therefrom;

a prime mover connected to said means for periodically delivering power fluid under pressure to said power fluid tubing string;

an air compressor drivingly connected to said prime mover; and

6. A subsurface pump defined in claim 3 and further characterized to include:

a seating collar connected in said production fluid string below said first passageway means and having a downwardly extending passageway therethrough communicating at its upper end with the annulus between said production fluid tubing string and said power fluid string for receiving sand gravitating downwardly in said annulus from the level of said first passageway means;

a tubular sand trap sleeve connected to the lower end of said seating collar and having its hollow interior in communication with the passageway through said seating collar for receiving sand therefrom; and

means closing the lower end of the sand trap sleeve.

References Cited UNITED STATES PATENTS 1,643,616 9/1927 Zinn et al. 103 44 1,922,264 8/1933 Shimer 103--46 2,277,306 3/1942 Coffey 103 44 2,386,564 10/1945 Mumk 103-203 3,304,870 2/1967 Growell et al. 103-44 FOREIGN PATENTS 673,850 1/1930 France.

ROBERT M. WALKER, Primary Examiner.

U.S. Cl. X.R. 10346, 220