Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The present invention relates to a check valve for use ln a
fluid producing well. More particularl~y the ;.nvention relates to a
retrievable check valve which provi.des si`mple means for equalizati:on of
pressures above and below the valve. ;~
Check valves are commonly used wi:thin a string of tubing of
a fluid producing well wherein a submersible pump i`s being used to move
flu;d to the surface. The pump i:s usually located at the flui.d kearing
formation, adjacent the foot of the stri:ng of tubi:ng. Usually impe.llors
wi.thi:n the pump are electrically driven to Force the fluid upwardly. Thus,
wh;le the pump is in operati:on, a column af flui:d extends the length of
the tub.ing string above the pump. I:n the event of stopping the pump, this
suspended column~ i:f not res~tri.cted, would back flow through the pump.
This back flow would reverse the i.mpellors at hi:gh speed, thereby causi.ng ~:
damage to the thrust bearings. Therefore a check valve is placed ;:n the :~
tubing string above the pump to regulate the back flow of fluid th:rough the
pump.
Many such check valves arè i:n common use1 the simples.t of
wh~ich is a ball-in-a-cage valve. Here~ a tubular cage i:s provi.ded having
a seat at i.ts lower end. A b.a:ll withi.n the cage seats on the seat and is. ~:
dislodged in response to the upward flow of fluids. Back flow however i.s
restricted as the ball becomes reseated. Such valves suffer the di.s.-
advantage known as "s-qui:rrel cagi.ng", wherei:n the gaseous. nature of the ~ .
fluid flow causes the ball to bounce around i~n the cage, causing damage
: 25 to ~oth the ball and cage, and ulti:.mately resulting in a loss of e~fecti.ve
seal.
Flapper check valves. are also known ;n the art. Accord;.ng to .
this design, a hori.zonta.l f1ap in a tubular body~i:s h.lnged to open and closein response to flow pressures bearing ~rom a60ve and below the valve~ In
the past, both the flapper and the ball-in-a-cage type valves have had
the tubular body threaded into the tubi.ng string~ maki.ng the valves non-
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retrievable by design~ Thus to replace or repai.r the valve, i:t was nec-
essary to pull out the ent;re tuhi:ng s~ring, a time~consuming and costl~
process.
A further type of check valve us~ed in well stri`ngs. is. the
S dart-type valve. A dart i:s seated in the lower portion of a clos.ed tubular
body and is provided with an upper tuhular s:haft. A narrow upper neck
portion of the tubular body gui:des the dart shaft as. the dart i~ translated
upwardly to allow flow past the valve. Valves of this ~vpe are generally
subject to jamming problems, si:nce considerable sand tends ta lodge itself
in the upper tubular hody ab.ove the dart shaft, restricting th.e up~ard
movement of the dart.
These previously descri~bed check ~alves commonly suffer the
disadvantage of not provi.ding simple means to equalize pressures ab~ove
and below the valve. Once the valve has closed to restrict back Flow of
the flui:d therethrough, it i.s desirahle to allow the column of flui:d
sus.pended above the valve to drain slowly past the valve to thereb~ :
equali.ze pressures without damagi:ng the thrust bearings. Oth:erwi.se,~to
retnove the valve or pump~ the tubi:ng stri:ng, laden with the flu;.d col~umn,
must be pulled to the surface. In deep wells., the addïtional. weight of
20 the fluid column is considerable, maki.ng the pulling operati.on di~ficult. :
Heretofore, to provi:de:for equalization in check valves has been
a compl;cated matter of provïding by-pass ducts whi`ch open and close either
by surface control or i`n response to changing pressures bearing on th~e valve.
For i:nstance, i:n lJ.S. Patent No. 2,994,z8a to Daffin, there i.s. disclosed
a retri`evable check valve of a ball-i:n-a-cage deslgn whi:ch is provi:ded
with equalization means. Shear pi:ns. are used to hold an outer s.leeve of
the tubular body in place. An upward pull on the valve shears the p;n~,
al10~ing the sleeve to translate upwardly, thereby aligni:ng bypass ports
of the sleeve and i:nner tubular b.ody to allow. fluid to flo~ therethrough.
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SUMMARY OF T~!E ~5E~I INVENlION
The present invention provides a check valve whlch seats in
a se~ting nipple positioned above a submersible pump in the tubing striny
of a producing well.
The check valve is designed to be retrievable. It comprises
a hollow, generally tubular body having conventional latching means at its
upper end for engaging a wireline tool inserted in the string to remove it.
The tubular body further comprises conventional resilient holddown means
at its lower end, for anchoring the valve in the seating n;pple, and
conventional shoulder means between its ends, for preventing downward
displacement of the body through the seating nipple.
The tubular body is flow through in design, having a longi-
tud;nal bore extend;ng therethrough. The bore ;s preferably reduced in
cross section at its upper end and the body thus forms an inwardly pro-
ject;ng stop shoulder for a purpose to be explained. Spaced below this
stop shoulder, the tubular body wall projects inwardly to form an annular
valve seat. The portion of the body bore between the seat and the stop
shoulder ;s termed the valve chamber.
A valve element is positioned within the valve chamber. The
valve element is vertically moveable within the chamber. When seated
by downwardly d;rected pressure onto the annular valve seat, the valve ele-
ment prevents downward flu;d Flow through the bore. When unseated by
pressure from below, a clearance between the outer rim of the ualve body~
and the ;nner surface of the valve chamber wall perm;ts upward flow
around the valve element. The stop shoulder l;m;ts upward travel of the
valve element.
The valve element comprises a generally tubular body having a
transversely extend;ng p;erceable wall closing off or sealing its
10ngitudinal bore. The cross-sect;onal area of that segment of the
pierceable portion which is exposed or available to be pierced is
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substantially less than any cro~s-sectional area oF the longitudinal bore
of the tubular body~ Thus~ when the pi:erceable portion is pierced (as
by a wireline spear~9 the drain opening so formed is relatively small and
back Flow through it is restr;`cted, whereby the submers;ble pump is not
damaged by such back flow.
Broadly stated, the invention is a check valve for controlling
back flow in the tubing string of a fluid-producing well, said string
having a submersible pump positioned at its lower end, said tubing string ~-
further incorporating a seating nipple above the submersible pump, said
check valve compr~sing: a retrievable generally tubular body adapted
to seat in the seating nipple and having a first longitudinal bore ex-
tending therethrough, said body forming an annular valve seat and a stop
shoulder spaced above the valve seat, said valve seat and stop shoulder
defining the ends of a chamber which is part of the bore; a generally tubular :
valve element having a second longitudinal bore and being disposed in the
chamber~ said valve member having a transversely extending wall which is
pierceable by a wireline tool and which closes off the second bore against
fluid flow therethrough, said valve element being operative to prevent : :
fluid flow through the flrst bore when it seats on the valve seat9 said
valve element being operative to permit fluid flow through the first bore
when the valve element is unseated, the cross-sectional area of the
pierceable wall available to be pi:erced being substantially less than the
cross-sect;onal area of the first bore, whereby, when the wall is ;
pierced, only restricted flow is permitted therethrough so as to avoid ~:
damaging the submersible pump.
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Figure 1 is a sectional side view, illustrating the check valve
seated within the tubing string of a fluid producing well.
Figure 2 is a perspective view oF the check valve having a
cut-away portion to illustrate the valYe element in cross-section.
Figure 3 is a perspective view of the valve element having
a cut-away portion to ;llustrate the pierceable disc.
DESCRIPTION OF THE PREFERRE~ EMBODIMENT
With reference to the drawings, the check valve of the present
invention is comprised of hollow generally tubular body 1 having a
pierceable valve element 2 positioned therein. Valve element 2
is free to open and close in response to pressures bearing on it from
below and above.
The tubular body 1 is shown in Figure I removeably seated in a
conventional seating nipple 3 threaded into the tubing string 4. The
seating nipple 3 is located one or more lengths of tubing above an electri~
cal submersible pump 5. Leaving this amount of space between the check
valve and the pump is desirable to l;mit large gas pockets from Forming
therebetween when the pump is stopped. Large gas pockets cause con-
siderable problems in restarting the pumping operatlon.
Seating nipples are conventionally used in seating well tools `~
- within tubing strings by providing regions having smaller internal diameters
than that oF the tubing. Seating nipple 3 is threaded at its upper and~
lower ends 6 and 7 respectively, to be secured into the tubing string 4.
The upper edge of the seating nipple provides an upper landing seat 8,
on which is seated tubular body 1. The lower edge of the seat;ng nipple
provides a holddown shoulder 9 to restrict the upward displacement o-F the ;~
tubular body 1 under the normal upwardly directed pressures of fluids
being pumped to the surface.
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THE TUB.ULAR EQDY
The hollowt gen.erall~ tubular body l, as seen in Figure 2,
compri:ses. an upper body portion 1l and a lower body portion 12. A fi.rst
longitudi:nal bore 36 extends through the bocly 1. The lower body portion 12
is threadably received by the upper body portion 11. An outwardly pro-
truding lip 14 is provided at the upper end of the lower body portion 12.
In order to seal the body portions 11 and 12 together, a packing ring 13 is
carried by the lip 14 between the body portions 11 and 12.
The lower body portion 12 has an external diameter substantially
equal to the internal diameter of the seating nipple 3 for close fitting
relationship thereinto. The packing ring 13 has an external diameter
slightly larger than the external diameter of the lower body portion. In
this way, when the lower body portion 12 is fitted in seatiny nipple 3
the packing r;ng 13 bears on the inner wall of the seating n;pple 3 to ~
seal against leakage around the valve. -
In order to removeably seat the tubular body in the seating
n;pple 3, resilient holddown means 15 are provided at the lower end of :~
lower body portion 12. To form the resilient holddown means 15, the
lower body portion 12 is flared outwardly at 16 to form a holddown collar
17. This collar 17 thus has an external diameter greater than the internal
diameter of the seating nipple 3. The holddown collar 17 is tapered
inwardly at 18 to ~acilitate the installation of the tubular body 1 into
the seating nipple 3. The lower body portion 12 has at its lower end
circum~erentially spaced cut-out portions 19 extending a substantial
distance upwardly past the holddown collar 17, to for~ a plurality of
resilient flanges 20. The flanges 20 can he squeezed inwardly to allow
the holddown collar 17 to be passed through the narrow internal diameter .:
of the seating nipple. Once clear of the seating nipple however~ the
~langes 20 spring back to their original shape to restrict the upward
3Q displace~ent of the tubular body 1.
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Downward displacement of the tubular body 1 past the seating
nipple 3 is limited by the construction of the upper body portion 11. The
upper body portion 11 has a widened intermediate portion 21 of external
diameter greater than the internal diameter of the seating nipple 3 but
not greater ~han the internal diame~er of the tubing string 4. This
intermediate portion 21 is tapered inwardly at 22 to form an upper landing
shoulder 23~ When the tubular body 1 is positioned ;n the seating nipple 3, ~ -
this upper landing shoulder 23 seats on the upper landing seat 8 of the
seating nipple 3. It will now be noted that the distance between the upper
landing shoulder 23 and the holddown collar 17 o-F the tubular body 1 must
be substantially equal to the distance between the upper landing seat 8 ;~
and the holddown shoulder 6 of the seating nipple 3, to allow a fitting
relationship.
The upper end of the upper body portion 11 is tapered inwardly
at 24 to provide a narrow latching neck portion 25. This latching neck 25
can be engaged by a wireline tool (not shown) to remove the tubular body 1
from the seating nipple 3. For this purpose, the uppermost end of the
latching neck is beveled to form a latching head 26. ~ ~
The valve element 2 is positioned in the upper body portion ~- -
11 of the tubular body and is moveable between a closed seated position ~ -
and an open flow through position. In it~ seated position, the valve
element 2 is seated on an annular valve seat 34 which is carried by the
upper edge of the lower body portion 12. The intermediate portion 21 of
the tubular body 1 is provided with at least one transverse port 27 along ;
its length. In its open flow through position, the valve elemen~l 2, ~ ~
in its preferred embodiment, moves upwardly in the intermediate portion 21, ~ i
clearing transverse port 27 and allowing fluid to move upwardly through the
tubular body. A stop shoulder 37 is provided at the upper end of the ~ -
intermediate portion 21. The stop shoulder 37 prevents upward displacement ~` ;
3n of the valve element 2. The valve seat 34 and stop shoulder 37 thus define ~;
the ends of a chamber 35 in which the valve element 2 moves. ~ ~
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In order to guide the valve element, in its preferred form,
as it moves between the open and closed positions, the narrow latching
neck portion is formed having both an internal and external diameter
substantially smaller than the corresponding internall and external
diameter o~ the intermediate portion.
_HE VALVE ELEMENT
In its preferred form, the ~alve element 2 as seen in Figures 2
and 3, is a hollow plunger 28 having a second longitudinal bore 38. The
plunger is sized for fitting relationship into the chamber 35 of the
upper body portion 11. The plunger 28 has a lower plunger head 29 and an
upper tubular guide shaft 30. The plunger head 29 is sized to fit loosely
within the intermed;ate portion 21 while the guide shaft 30 is sized to
fit loosely within the latching neck portion 25. The guide shaft 30
has at least one equalization window 32 formed along its length.
A transverse pierceable disc or wall 31 is formed across the lower
end of the plunger 28, preferably intermediate the guide shaft 30 and the
plunger head 29. In this manner, a fluid pocket 33 is formed beneath the
pierceable disc 31 within the confines of the plunger head 29. As fluid
is moving upwardly through the tubular body 1~ the fluid in this fluid
pocket 33 remains dead~ thereby decreasing the wear on the pierceable disc.
The cross-sectional area of the pierceable disc 31 1s substantially
less than the cross-sectional area of the first bore 36. By this pro-
vision, the disc 31, when pierced, permits a slow rate of flow therethrough
to prevent damage to the submersible pump.
The plunger 28 is preferably machined as a single unit. In
this way, the pierceable disc, being integral with the plunger, provides the
increased strength necessary to support a column of fluid in the tubing
string when the va~ve element 2 is in the seated posit;on.
By providing a loose fit between the plunger 28 and the
chamber 35 of the upper body portion 11, a clearance is provided therebetween.
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This clearance is sized to allow sand and shale particles to pass through the
tubular bady 1 without lodging therein or causing abrasive damage to
either the tubular body 1 or the plunger 28.
Conce~vably, the valve element could take the form of a
S hinged flap having a pierceable portion located therein.
OPERATION `~
The two piece tubular body 1, loaded with the valve element 2,
the packing r;ng 13 and the ring seat 34, is threaded together. The body 1 ,
thus assembled, is lowered into well tubing string 4 on a conventional
wireline ~ool (not shown) which engages latching head 26. Upon reaching
the restrictive diameter of the seating nipple 3, the resilient flanges
20 are forced to bend inwardly to clear the seating nipple 3, springing
outwardly again once the restriction is cleared. Once seated, the tubular
body 1 cannot be displaced under the normal pressures of fluid flow.
To retrieve the tubular body 1, a conventional pulling tool
(not shown) is latched onto latching head 26. An upward force from the
surface is applied to dislodge the device.
As the submersible pump forces the Fluids upwardly, fluid
pressure bearing from below against the pierceable d;sc 31 force the hollow
plunger 28 to move upwardly. This movement clears transverse port 27
to permit the fluid to communicate upwardly past the tubular body 1 to
the surface. In this open flow through position, the plunger head 29
bears against the stop shoulder 37, thereby restricting the upward dis-
placement of the plunger 28.
In the event that the pump is stopped~ the downward pressure
exerted on the pierceable disc by the column of fluids suspended above the
device forces the plunger 28 to move to a closed seated position. The
plunger is thereby seated on ring seat 34 to prevent an uncontrolled back
flow through the device. ~;
To equalize the pressures above and below the device, a spear
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(not shown) is run clown the tubing string 4 on a wireline (not shown)
to rupture the pierceable disc 31. The orifice thus Formed in the disc 31
is sufficiently small so as to allow the column of fluid above the device
to drain at speeds which do not damage the pump.
Once the pressures have been equalized the device may be
retrieved with a pulling tool ~not shown). The plunger 28 and packing ring
13 may be replaced and the de~ice may be rerun back down the well.
The thickness of the disc 31 together with the number of
packing rings 13 and ring seats 34 needed to seal the device against the
pressures of operation are adjusted with the depth of the well.
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