Anti-gas lock valve for a reciprocating downhole pump

Abstract

Method and apparatus overcoming gas-lock in reciprocating downhole pumps. On the downstroke of a plunger in a barrel, gassy fluid is compressed in the pump chamber between standing and travelling valves. Downhole plunger movement drags a sleeve over a mandrel for opening a chamber valve to a staging chamber located at a downhole end of the travelling valve for receiving at least a portion of the compressed and gassy fluid therein. On the upstroke, the chamber valve is dragged closed for sealably retaining the compressed gassy fluid therein while drawing an additional increment of fluid through the standing valve into the pump chamber. Continued downstroke and upstroke cycles increases pressure of the compressed gassy fluid in the pump chamber until it exceeds the hydrostatic head above the travelling valve for resumption of normal fluid pumping.

Claims

1. An anti gas-locking apparatus in a pump positioned in a subterranean wellbore, the pump, having a barrel forming a pump chamber and a reciprocating plunger positioned therein, the plunger reciprocating uphole on an upstroke and downhole on a downstroke, and the pump having at least one standing valve in fluid communication with a downhole inlet end of the barrel, for receiving a charge of fluid from the subterranean wellbore into the pump chamber, and at least one traveling valve in fluid communication with a downhole inlet end of the plunger, the pump further comprising: a pre-valve forming a staging chamber, and having: a downhole inlet end having a chamber valve for receiving at least a portion of the charge of fluid from the pump chamber into the staging chamber; and an uphole outlet end fluidly connected at a downhole end of the at least one travelling valve, the pre-valve comprising: a reciprocating mandrel operatively connected to the plunger, the mandrel having a first uphole annular stop and a second downhole annular stop, and forming a space between the first and second annular stops; and a shifting sleeve, having a length, located concentrically about the mandrel and moveable therealong between the first and second annular stops; wherein, on the downstroke, the sleeve shifts uphole to open the chamber valve, and on the upstroke, the sleeve shifts downhole to close the chamber valve; and wherein the space between the first and second annular stops is greater than the length of the sleeve, and the chamber valve is formed in the clearance between the length of the shifting sleeve and the space between the first and second annular stops.

2. The apparatus of claim 1 wherein: the uphole end of the mandrel is mounted to a downhole end of the at least one travelling valve, wherein the staging chamber being in the mandrel is in fluid communication with the travelling valve.

3. The apparatus of claim 2 wherein: on the downstroke, the uphole shift of the sleeve opens the chamber valve by uncovering an inlet for fluid communication between the pump chamber and the staging chamber and, on the upstroke, the downhole shift of the sleeve closes the chamber valve to sealably cover the inlet.

4. The apparatus of claim 3 wherein: the mandrel forms a bore therealong forming the staging chamber; and the inlet further comprises ports through the mandrel to the bore.

5. The apparatus of claim 3 wherein: the staging chamber is formed in an chamber annulus between the mandrel and the shifting sleeve; the uphole end has passages therethrough between the annulus and the travelling valve; and the downhole valve end further comprises an annular downhole stop, wherein the downhole end of the shifting sleeve alternately engages the annular downhole stop for sealably blocking the chamber annulus to close the chamber valve on the upstroke, and being spaced therefrom for opening the chamber annulus adjacent the downhole valve end for fluid communication between the pump chamber and the chamber annulus upon the downstroke.

6. A method of overcoming gas-lock in a pump positioned in a subterranean wellbore, the pump having a barrel forming a pump chamber and a reciprocating plunger positioned therein, the plunger reciprocating uphole on an upstroke and downhole on a downstroke, and the pump having at least one standing valve in fluid communication with a downhole inlet end of the barrel, for receiving a charge of fluid from the subterranean wellbore into the pump chamber, and at least one traveling valve in fluid communication with a downhole inlet end of the plunger, the method comprising: providing a pre-valve having a downhole inlet end forming a chamber valve in fluid communication with the pump chamber, for receiving the charge of fluid from the pump chamber into a staging chamber formed therein, and having an uphole outlet end in fluid communication with the at least one traveling valve for discharging fluid from the pre-valve staging chamber through the at least one traveling valve, the pre-valve comprising: a mandrel operatively reciprocated with the plunger, the mandrel having a first uphole annular stop and a second downhole annular stop, and forming a space between the first and second annular stops, and a sleeve, having a length, located concentrically about the mandrel and movable therealong between the first and second annular stops, wherein the chamber valve is formed by the clearance between the length of the sleeve and the space between the first and second annular stops; reciprocating the plunger uphole, shifting the sleeve downhole along the mandrel, closing the chamber valve and opening the at least one standing valve to receive the charge of fluid from the subterranean wellbore into the pump chamber; reciprocating the plunger downhole, compressing the charge of fluid in the pump chamber, shifting the sleeve uphole along the mandrel, opening the chamber valve and receiving at least a portion of the charge of fluid from the pump chamber into the staging chamber; reciprocating the plunger uphole, shifting the sleeve downhole along the mandrel, closing the chamber valve and sealably retaining the at least a portion of the charge of fluid within the staging chamber while re-opening the at least one standing valve and drawing a further charge of fluid from the subterranean wellbore into the pump chamber; reciprocating the plunger downhole, compressing the further charge of fluid in the pump chamber, shifting the sleeve uphole along the mandrel, opening the chamber valve and receiving at least a portion of the further charge of fluid from the pump chamber into the staging chamber; and repeatedly reciprocating the plunger uphole and downhole wherein on each downstroke, a pressure of the charge of fluid received in the pump chamber increases until it exceeds the hydrostatic head uphole of the at least one travelling valve, opening the at least one traveling valve for normal fluid pumping.

7. The method of overcoming gas-lock of claim 6, wherein, on the downstroke, the sleeve shifts uphole along the mandrel to open inlets into the chamber valve; and on the upstroke, the sleeve shifts downhole along the mandrel to close the inlets into the chamber valve.

8. The method of overcoming gas-lock of claim 6, wherein, on the downstroke, the sleeve shifts uphole along the mandrel by dragging along the barrel; and on the upstroke, the sleeve shifts downhole along the mandrel by dragging along the barrel.

9. The method of overcoming gas-lock of claim 8 wherein the staging chamber is formed in a bore of the mandrel, further comprising on the downstroke, opening the chamber valve for fluid communication between the pump chamber and the mandrel's bore, the bore being in fluid communication with at least one the travelling valve.

10. The method of overcoming gas-lock of claim 8 wherein the staging chamber is formed in a chamber annulus between the mandrel and the sleeve, further comprising on the downstroke, opening the chamber valve for fluid communication between the annulus, the annulus being in fluid communication with the travelling valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a cross-sectional view of a downhole reciprocating insert rod pump having an anti-gas lock pre-valve installed therein;

(2) FIGS. 1B and 1C are a side-by-side disassembled view of the pump according to FIG. 1A having the plunger, travelling valve and pre-valve of FIG. 1C shown separated from the barrel and standing valve of FIG. 1B;

(3) FIG. 2A is a cross-sectional view of an embodiment of the pre-valve in the downstroke position with the staging chamber inlet open in the flow-through position;

(4) FIG. 2B is a cross-sectional view of the pre-valve of FIG. 2A in the upstroke position with the staging chamber inlet closed in the lift position;

(5) FIG. 3A is a cross-sectional view of the pre-valve of FIG. 2A installed in the pump barrel and actuated in the downstroke position with the staging chamber inlet and travelling valve open in the flow-through position;

(6) FIG. 3B is a cross-sectional view of the pre-valve of FIG. 2A installed in the pump barrel and actuated in the upstroke position with the staging chamber inlet and travelling valve closed in the lift position;

(7) FIG. 4A is a cross-sectional view of another embodiment of the pre-valve in the downstroke position with the annular staging chamber inlet open in the flow-through position;

(8) FIG. 4B is a cross-sectional view of the pre-valve of FIG. 4A in the upstroke position with the annular staging chamber inlet closed in the lift position; and

(9) FIG. 5 is an exploded, disassembled cross-sectional view of three components of an embodiment of the pre-valve according to FIG. 2A having an uphole end for post-sleeve installation, threaded assembly with the mandrel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) With reference to FIGS. 1A, 1B and 1C, a typical reciprocating plunger pump 10 comprises a barrel 12, typically about 20 feet in length, fluidly connected to the bore of a tubing string (not shown) extending from a hydrocarbon formation and uphole to surface, the barrel 12 having a standing valve 14 at a bottom or downhole end. A plunger 16, in the order of about four or five feet in length, has a travelling valve 18 at a downhole end thereof. As is conventional, the pump 10 is secured in the tubing string with either or both a top or bottom hold-down 19 between the pump 10 and a seating nipple in the tubing string. Further, the hold-down 19 seals the pump 10 within the tubing string.

(11) Simply, a fluid pump has barrel 12 and the plunger 16 within that reciprocates uphole on an upstroke to draw a charge of fluid from the formation into a pump chamber 17, to charge the pump barrel 12 with fluid, and downhole on a downstroke to transfer the fluid into the hollow plunger 16 for lifting to surface in subsequent pump cycles. The pump chamber 17 of the barrel 12 receives the charge of fluid through the standing valve 14 at a downhole end thereof, and the plunger 16 receives fluid from the pump chamber 17 through the travelling valve 18 at a downhole end thereof.

(12) With reference to FIG. 1C, the plunger 16 is connected through a top plunger adapter 20 to a valve rod 22 and a valve rod bushing 23, which is in turn connected to a rod string (not shown) extending to surface for imparting reciprocating motion of the plunger 16 within the barrel 12. The top plunger adapter 20 mechanically connects the plunger 16 to and valve rod 22. As shown in FIG. 1A, the valve rod 22 extends through a valve rod guide 25 attached to a top of the pump barrel 16, and directs fluid from a bore of the plunger 16 to an annulus between the valve rod 22 and pump barrel 12. Fluid passes up and out through the valve rod guide 25 and into the tubing string. Reciprocation of the plunger 16 alternatively draws a charge or increment of fluid, through the standing valve 14, into the pump chamber 17 of barrel 12, on an upstroke, and out of the pump chamber 17 on a downstroke. On the downstroke, the fluid increment transfers through the travelling valve 18 into the plunger, out through the top plunger adapter and into the annular area between the valve rod 22 and the barrel 12, and out through the valve rod guide 25 into the tubing string above the pump 10, ready for lift to surface on the upstroke of the next pumping cycle.

(13) Herein, embodiments of an anti-gas lock apparatus or pre-valve are provided, supplemental to the travelling valve 18, for mitigating the effects of free gas and foaming. The pre-valve manages gassy fluids in the pump chamber 17 downhole of the travelling valve 18.

(14) With reference to FIGS. 1A, 1C and FIGS. 2A and 2B, a pre-valve 30 is installed to a travelling valve 18 of an otherwise usual configuration of a standard pump 10 for overcoming gas lock. As shown in FIG. 3A, the pre-valve 30 is connected to, and below, the standard traveling valve 18 such as through threaded connection or other arrangement.

(15) In a first pre-valve embodiment, best shown in FIGS. 2A and 2B, the pre-valve 30 has a staging chamber 32 open at an uphole end 50 for fluid communication to the travelling valve 18 and is alternately openable and closeable at a downhole valve end 56 at chamber valve 34. The staging chamber 32 has an open or flow-through mode (FIG. 2A) and a closed, or lift mode (FIG. 2B). In this embodiment, the chamber valve 34 is the primary element affecting alternating flow-through and lift modes and is located a downhole valve end 56. As discussed, the uphole end 50 is adapted for connection to a downhole end of the travelling valve 18. The staging chamber 32 is in fluid communication with the travelling valve 18 through passage 52.

(16) The staging chamber 32 extends between the uphole end 50 and the downhole chamber valve 34.

(17) With reference to FIGS. 2B and 3B, during an upstroke, in the lift mode, the downhole chamber valve 34 closes, isolating a downhole port or inlet 44 of the staging chamber 32 from fluid in the pump chamber 17 therebelow while an uphole discharge 46 of the staging chamber 32 remains in fluid communication with the travelling valve 18 thereabove. During a downstroke, in a flow-through mode, the downhole chamber valve 34 opens the downhole inlet 44 of the staging chamber to the pump chamber 17 therebelow, while the uphole discharge 46 of the chamber 32 remains in fluid communication with the travelling valve 18 thereabove.

(18) In other words, the pre-valve 30 has a staging chamber 32 having an outlet in fluid communication to the travelling valve 18 and an inlet for fluid communication with the pump chamber when open. The chamber valve at the inlet is actuated between open and closed positions by dragging against the barrel for alternately opening and closing the inlets. On the downstroke, the chamber valve 34 opens the inlet 44 to the staging chamber 32 for receiving fluid from the pump chamber 17; and on the upstroke, to close the chamber valve 34 to close the inlet 44 to the staging chamber and retain fluid therein.

(19) In the flow-through mode, the pre-valve 30 encroaches on the volume or charge of fluid in the pump chamber 17 between the pre-valve 30 and the standing valve 14. As discussed below the downhole chamber valve 34 opens to enable staging chamber 32 to receive at least a portion of the fluid charge from the pump chamber 17. If the fluid is primarily liquid then the incompressible liquid passes through staging chamber 32 and, as is the case in conventional operation, opens the travelling valve against the hydrostatic head thereabove for pumping an increment of liquid uphole next pump cycle. However, if the fluid is gassy and somewhat compressible, then the staging chamber receives at least some fluid in a compressed state between the standing valve 14 and the closed travelling valve 18.

(20) The gassy nature of the fluid compromises the normal compression and increase in pressure in the chamber 32, and accordingly, pressure changes may be insufficient to overcome the hydrostatic head above the closed travelling valve 18, the travelling valve therefore remaining closed. Regardless, there is a staged or localized compression of the fluid charge in the staging chamber 32.

(21) On the next upstroke, in lift mode, with the downhole chamber valve 34 closed, at least a measure of the compressed fluid charge remains retained in the staging chamber 32 in a compressed state, now staged between the travelling valve 18 and the downhole chamber valve 34 and therefore increasing the opportunity for drawing additional fluid into the pump chamber 17.

(22) Each cycle of the flow-through and lift mode cycles results in an incremental increase in the competency and pressure of the fluid charge in the pump chamber 17, and staging chamber 32, until such time as the pressure in the pump chamber 17 is sufficient to open the travelling valve 18 on a subsequent downstroke. In practice, this occurs in several pump downstroke and upstroke cycles. Accordingly, the travelling valve 18 is then enabled to actuated to open and operate as intended, receiving its increment of fluid for subsequent lifting to surface, without need for tapping or other gas-lock mitigation techniques.

(23) The downhole chamber valve 34 is positively actuated to open and close through reciprocation the plunger 16 and pre-valve 30 attached thereto.

(24) In FIGS. 2A and 2B, the pre-valve 30 comprises a mandrel 54 extending between the uphole end 50 and the downhole valve end 56. The mandrel 54 further comprises the staging chamber 32, in fluid communication with the travelling valve at the uphole valve end 50, and having the downhole chamber valve 34 at the downhole valve end 56 for alternately opening and closing fluid communication between the staging chamber 32 and the barrel 12 between the pre-valve 30 and the standing valve 14.

(25) In this embodiment, the mandrel 54 has a bore 58 extending axially therethrough for forming the staging chamber 32. The downhole inlet 44 to the staging chamber 32 is formed through one or more ports though the mandrel 54 to access the bore 58. The inlet 44 extends between the bore 58 and the pump chamber 17. The inlet 44 is located adjacent, and uphole, of the downhole valve end 56.

(26) In this embodiment, the positive actuation of the downhole chamber valve 34 is enabled using a drag sleeve 60 fit concentrically about the mandrel 54 and axially movable therealong. The chamber valve 34 is actuable through shifting the sleeve 60 to uncover the inlet on the downstroke for fluid communication between the pump chamber 17 and the bore 58 upon the downstroke, and shifting the sleeve 60 to sealably cover the inlet 44 on the upstroke.

(27) The sleeve 60 has a downhole end 64 and an uphole end 66. The sleeve 60 is sized to be movable along in the barrel 12 yet to frictionally or viscously drag therein for alternating displacement along the mandrel 54 between and an annular shoulder or uphole stop 36s and an annular downhole stop 34s. The sleeve 60 is movably fit to the barrel 12 however is sized to viscously drag therealong, lagging movement of the pre-valve as it is reciprocated uphole and downhole, the shifting of the sleeve acting to open and close the downhole chamber valve 34. The downhole chamber valve 34 is formed of the corresponding angled, hardened, and polished or lapped surfaces at the downhole stop 34s and downhole end 64 of the sleeve 60.

(28) A spacing S between the downhole and uphole stops 34s, 36s is greater than a length L of the sleeve, the difference or clearance V enabling alternate covering, or closing, and uncovering, or opening, of the downhole inlet 44. The downhole end 64 of the sleeve 60 downhole alternately engages and disengages from the downhole stop 34s for closing and opens the downhole chamber valve 34 respectively. The downhole chamber valve 34 opens and closes the staging chamber 32 for receiving at least a compressed portion of the charge of fluid from the barrel 12 on the downstroke, and closing the staging chamber 32 to the barrel on the upstroke.

(29) As shown also in FIG. 3A, in the flow-through mode, a downhole movement of the plunger 16, and attached travelling valve 18, lowers the pre-valve's mandrel 54. The sleeve 60 drags in the barrel, lagging behind the downhole movement of the mandrel 54, shifting relative to the mandrel, the uphole end 66 of the sleeve 60 engaging the uphole stop 36s. The uphole end 66 and uphole stop 36s can form an uphole valve 36, increasing the effective length of the plunger 16 by the length S of the sleeve 60. Shifted, the downhole end 64 of the sleeve is spaced sufficiently, a clearance V, from the downhole stop 34s to open the chamber downhole inlet 44, enabling flow-through of the fluid from pump chamber 17 into the staging chamber 32. As shown in FIG. 3A, if the fluids therein are sufficiently gas-free, the travelling valve 18 opens as well for flow-through to the plunger 16.

(30) As shown in FIG. 3B, during the lift mode on the upstroke, the mandrel 54, being connected to the plunger 16, also moves uphole. The sleeve 60 drags on the barrel 12 and lags moving uphole, shifting relative to the mandrel 54, the downhole end 64 engaging the downhole stop 34s and sealing thereto for capturing or retaining the compressed fluid in the staging chamber 32. In this embodiment, the downhole chamber valve 34 is operable through alternating sealing and unsealing of the sleeve's downhole end 64 and the downhole stop 34s. The uphole end 66 of the sleeve 60 is spaced clearance V from the uphole stop 36s. Due to plunger-like the clearances of the sleeve 60 to the barrel 12 any impetus to flow from the chamber 32 and along between sleeve and mandrel, is restricted by the sleeve/barrel interface and therefor minimized.

(31) Turning to an alternate embodiment of the pre-valve 30, best shown in FIGS. 4A and 4B, the staging chamber 32 is formed in an annulus 72 between the sleeve 60 and the mandrel 54. The passage 52 is now includes or is in fluid communication with one or more cross-over ports 74 through uphole end 50 and extending between the annulus 72 and the travelling valve 18. The uphole stop 36s and the uphole end 66 of the sleeve 60 now form the uphole chamber valve 36. As both an uphole end 50 and a downhole valve end 56 of the annulus alternately opens and closes as the sleeve 60 moves axially, the uphole chamber valve 36 ensures the flow-through mode fluidly connects the pump chamber 17, below the pre-valve 30, to the travelling valve 18.

(32) With reference to FIGS. 2A, 2B and 5 the pre-valve 30 comprises: the ported mandrel 54 having a uphole end 50 and a downhole valve end 56. Sleeve 60 is fit slidably along a middle section 84 of the mandrel 56. The mandrel's uphole and downhole valve end 50, 56 are spaced sufficiently to enable the sliding sleeve 60 to move back and forth thereon. To facilitate installation of the sleeve 60, one of the uphole end 50 or downhole valve end 56 is removably secured to the mandrel 54. As shown, in one embodiment of FIG. 5, the downhole valve end 56 is integrated with the mandrel's middle section 84 and the uphole end 50 is comprises a cap 86 removably and threadably connected to the mandrel 54 and is further fit for connection, such as by threaded connection, to mate with the downhole end of the plunger's traveling valve 18.

(33) Further, like the sleeve 60, the uphole end 50 has an outside diameter (OD) similar to that of the standard plunger that is sized to fit the barrel 12. The OD of the middle section 84 of the mandrel 54 is sized to allow for a clearance between mandrel and an inside diameter of the sliding sleeve 60. The chamber's inlet 44 comprises one or more ports 88 adjacent the downhole valve end 56. In an embodiment, the inlet 44 comprises four ports 88 are shown are machined through middle section 84 adjacent downhole valve end 56. The downhole stop 34s is hardened with Stellite or other hard material and subsequently lapped or polished. The downhole end 64 of the shiftable sleeve for sealing against the downhole stop 34s and can be similarly hardened with Stellite or other hard material lapped or polished.

(34) Normal Pump OperationNo GasLock

(35) As with prior art systems, substantially gas-free fluids such as liquid oil is pumped from a wellbore through a series of downstrokes and upstrokes of the pump 10, which motion is imparted by an above-ground pumping unit.

(36) During the upstroke, the travelling valve 18 and pre-valve 30 are lifted with the plunger 16 while friction or drag, created as a result of the close tolerances between inside of the pump barrel 12 and the outside of the sliding drag sleeve 60, causes the sleeve 60 to shift and close the downhole chamber valve 34. The standing valve 14 opens, and plunger suction and formation pressure permits liquid to flow into pump chamber 17 below the pre-valve 30. This liquid is temporarily held in place between the standing valve 14 and the traveling valve 18. The hydrostatic weight of the liquid to surface keeps the traveling valve 18 closed.

(37) During the normal downstroke, as the plunger 16 and pre-valve 30 travel downwards, the standing valve 14 closes, and as liquids cannot be compressed, the oil is forced up through the pre-valve 18 and through the traveling valve 18 into the hollow plunger 16 for lifting towards surface next pump cycle. Again, frictional force or viscous drag causes the sleeve to shift up to engage the uphole stop 36s, a 45 degree angular portion of the uphole end 50 of the mandrel 54. The clearance between the downhole stop 34s and the sleeve 60 opens the multi-ported fluid inlet 44. The decreasing volume of the pump chamber forces liquid through into the ports 44 and up the staging chamber 32, and through the open traveling valve 18 to joining previously displaced fluid in the plunger 16 to flow through the plunger 16, out of the top plunger adapter 20, and through the valve rod guide 25 into the tubing string.

(38) In the case of gassy fluids, the travelling valve 18 does not open reliably, previously resulting in gas lock, with the prior art arrangements applying repeated cycles struggling to build sufficient pressure to open the travelling valve 18.

(39) Gas Interference

(40) The pre-valve 30 overcomes the limitations of the conventional travelling valve. As before, during the upstroke, and due substantially to the hydrostatic head, the standard traveling valve 30 closes, and due to the drag on the shifting sleeve 60, the downhole pre-valve 30 closes. As the pre-valve 30 continues to be dragged upwardly, a pressure drop in the pump chamber 17 causes the standing valve 14 to open and formation fluid, such as gassy oil, is drawn into pump chamber 17.

(41) During the downstroke, when gas-locking often presents, as the plunger 16 and attached pre-valve 30 travel downhole, the standing valve 14 closes. However with gassy liquids, unlike normal operation with non-compressible liquids, the traveling valve 18 may not open, but could stay closed as a result of the minimal rise in pressure of the compressible gas or gassy liquids being insufficient to overcome the hydrostatic head of the liquid above the traveling valve 18. In the prior art pump, the charge of gassy liquid in pump chamber 17 merely recompresses. However, using pre-valve 30, the gas-lock recompression cycle is broken. As a result of drag, the sleeve 60 shifts, the downhole chamber valve 34 opens and gassy liquid in the pump chamber is at least somewhat compressed. The inlets 44 open for actuating the entirely of the staging chamber and pump chamber 17 to receive compressed or recompressed fluids within the diminishing volume between standing valve 14 and the travelling valve 18. While compressed, the resulting pressure is not yet high enough to open the travelling valve 18.

(42) During the next or subsequent upstroke, the pre-valve 30 changes the behavior of the pump chamber refilling cycle. The sleeve 60 shifts to close the downhole chamber valve 34, trapping a portion of the compressed fluids therein and thereby reducing the effective volume of the pump chamber 17 therebelow. A like pump stroke, having a smaller effective volume results in a more vigorous suction and filling impetus. Substantially only the volume between the pre-valve's downhole valve end 56 and the standing valve 14 is effective or active. The standing valve 14 opens and at least an additional increment of gassy fluid or liquid is drawn into pump chamber 17 below the pre-valve 30. Compressed gassy liquid is retained in the pre-valve while suction is enhanced therebelow. Minimal fluid bleeds out the uphole end of the staging chamber between the sleeve 60 and the barrel 12.

(43) Thus, on each subsequent downstroke, the additional fluid drawn into the pump chamber 17 is incrementally increases the pressure in the pump chamber 17 until the travelling valve 18 opens and normal pump resumes. The cycle of upstroke and downstroke is repeated, and at each cycle the staging chamber withholds a portion of the compressible gassy liquids from the pump chamber permitting another increment of fluid to be drawn into the pumping chamber 17 through the standing valve 14. While the traveling valve 18 may stay closed for a number of cycles, the fluid eventually compresses to a pressure on the travelling valve that exceeds the hydrostatic weight of the column of liquid thereabove.

(44) Ideally close spacing is desirable between the downhole chamber valve 34 and the standing valve 14, as shown in FIG. 3A, arranged to approach as close as possible together without contact.

(45) Accordingly, within a few cycles the pre-valve 30 corrects the gas-locked condition and normal pumping resumes. This may happen a few or many times in the course of a day but only does so when required to overcome gas-locking, the balance of the operation continuing to pump as a conventional does The operation is automatic in that pumping operation continues whether there are gassy liquids or not. When gassy liquids are encountered, the pump continues stroking while the pre-valve commences clearing the gassy liquid from the pump. This may take several cycles.

(46) An example pump having a 1.5 inch ID barrel 12 might have a plunger 16 fit with a one foot long pre-valve 30 installed at a downhole end thereof. Thus, a typical five foot long plunger might be swapped out for a four foot long plunger, plus one foot of pre-valve, for retaining an effective 5 foot long plunger length. The pre-valve's drag sleeve 60 can be about 8 inches long having about a 1 inch travel or clearance V between uphole and downhole stops 36s, 34s for opening and closing the downhole chamber valve 34. The sleeve 12 can have an OD of about 1.495 having about a 0.003 inch clearance to the barrel 12.

(47) For the pre-valve embodiment of FIGS. 2A, 2B and 5, four 0.25 wide by 0.875 inch long ports form the inlet 44 alternately exposed and blocked as the sleeve 60 opens and closes. Sleeve 60 can have an ID of 1.035 inches being slidably movable over a mandrel OD of 1 inch, the mandrel 54 having a bore ID of 0.75 inches.

(48) The mandrel 54 and sleeve 60 can be manufactured of 316 stainless steel (SS) or the like. In one embodiment, the sleeve is 304 SS while the mandrel is 316 SS. The sleeve 60 can also be conveniently manufactured from otherwise conventional pump plunger stock, having the same dimensions as a plunger 16 employed in a like-sized pump 10. As stated, the sleeve 60 can be an otherwise conventional, spray metal oil pump plunger stock modified to be bored out and machined to length and to accommodate the mandrel. The specifications and types of spray metal coatings can adhere to API Specification 11AX, for plunger outside surface condition and base core hardness. In the case of the hollow mandrel of FIGS. 2A and 2B, the bore 58 can be formed using gun-drilling techniques.

(49) The uphole and downhole stops 36s and 34s respectively, can be hardened with vanadium carbide or made of a tool steel such as a high air hardening, high-carbon, high-chromium steel ANSI D-2 material possessing high wear resisting properties for maximum wear resistance. In another embodiment, the downhole stop 34s is modified for severe metal-to-metal service. Stellite is suitable for high impact and wear resistance and is applied to the downhole stop 34s such as by plasma or electric-arc welding and machined to form the sealing surface.

(50) Turing to FIG. 5, to facilitate assembly and in particular, installation of the drag sleeve 60 to mandrel 54, either end of the mandrel is assembled with a removable upset such as a cap 86 to form one of either the uphole or downhole stop 36s, 34s and retain the sleeve 60 for slidable movement over the middle section 84. In an embodiment, the downhole valve end 56 of the mandrel 54 is integral with the mandrel and the cap 86 at the uphole end 50, is threadably connected the mandrel once the sleeve has been fit concentrically thereto. The cap 86 is also threadably connected to a downhole end of the travelling valve.