Note: Descriptions are shown in the official language in which they were submitted.
~43~32
VIFFER~:NTIAL GP.S LI~T VI~LVE
BACKGROUND OF ~HE INVENT10
__ _
Field of the Invention
Thi6 invention relates to well tools and more particular~y
to gas lift valves used in operating oil well~ through practice
of gas lift technique~.
Description of the Prior Art
-
Gas lift valves have been used for many year~ to control
the injection of lift gas into a flow conductor from the
exterior thereof to aerate a column o liquid therein and aid
in lifting it to the surface. While fixed orifices have been
used ~uccessfully in lifting liquids from well conduits, they
waste lift gas. Gas lift valves, on the other hand, are more
efficient in that they need not remain open and passing lift
ga~ all the time, but mdy open only when conditions justify
their eficient oper~tion.
One type of valve u~ed in gas lift operations is the dif-
ferentially operated ga6 lift valve, commonly called "differ-
ential valve". Such valve~ are normally open but close upon
occurrence of a condition where the difference in pressures
between the ~a6 lift colu~n and the production column exceeds
predetermined value or which the ga& lift valve has been
adjusted t~ clo~e- Becau~e of thiB characteri6tic~ the
--1-- ~.
43~2
1 pressure of the lift ga6 is no- critical once the well has been
unloaded and placed on PIoduction. Generally, li~t yas jr~
injected into thc tubing-casing annu~us of a well throuyh a
choke which i~ sized to p~ss t~le quantity of lift gas which is
needed to produce the de6ired volu~e of li4uids from the well.
In ~ome cases, gas i6 injected into the tubing and well
products are lifted through the annulus.
Listed here are several U.S. patents which disclose a
variety of differential gas lift valves. They are:
10 2,144,144 2,236,864 2,256,70~ 2,288,6~5 2,305,250
2,314,~68 2,323,893 2,541,807 2,5~,715
~ 11 of the above listed patents, with the exception of U.S.
Patent 2,305,250, have a common basic structural design which
is, perhaps, more readily seen and understood when looking at
patent 2,144,144 which i~sued to C. S. Crick~er on January 17,
1939. In this patent, and in Figures 11 and 12 in particular,
the valve member has a piStOII 41 having its upper end exposed
to casing pressure transmitted into the valve housing through
lateral ports 46, and has its lower end exposed to tubing
pressure transmitted t?-ereto through tubing port 25. A coil
~pring 44 biases the valve oward open position (shown in
Figure 11). When the pre~sure in the casing exceeds the
pre6sure in the tubing by a ~ufficient margin, the difference
between these pressures actiny across the area of the piston 41
will create ~ufficient force to move the valve to closed
position (shown in Figure 12), as it overcomes the force of
8pring ~4, and engages seat 6urface 47 with the ~eat to 6top
the flow of lift gas from the casing into the tubing- When the
difference between the tubin'3 and casing pressure is reduced
6ufficiently, the sprinc3 44 will open the valve, i.e., return
the valve to it6 open po~ition (s?own in Figure 11). It is
readily seen that t?e pi~ton areas exposed to the tubing
pres~ure and the casing pre~sure are equal- Since the~e areas
--2--
lZ~43t~Z
are equal, the valve both opens and closes at substar,tially the
same pressure. ~nderstandably, the valve may quickly cycle
between open and closed po6itions several times before ass-lming
one position or the other. Thi6 i8 not desirable. It wastes
gas and causes unnecessary wear and tear on the mechallism.
The gas lift valve~ disclosed in the other paterlts in this
group also have valve mean~ with pistons having equal areas
exposed to tubing and casing pressures.
U.S. Patent 2,~56,704 which issued on September 23, 1941 to
C. S. Crickmer, et al., discloses a gas lift valve which is
similar to those just discussed. In operation, this valve is
in the position shown in Figure 2 of the pàtent. Lift gas from
the casing enters side purts 37, flows upwardly in flutes 36,
flows around the upper portion of valve 30 and past the tapered
upper end thereof, and from thence througll port 27. When the
pressure in the tubing decreases, the velocity of the gas
passing the upper end of the valve increases, and the valve
moves up toward the seat, pinching the flow therebetween. This
further increases the velocity. The upper portion 34 of the
valve acts as a piston and plunges into port 27 until it seats
as shown in Figure 3- When liquid rises sufficiently high in
the tubing to create sufficient back pressure acting against
the upper end of the valve (which acts liXe a piston), the
valve will move to open position.
Patents 2,288,605; 2,314,86~; and 2,323,B93 which issued to
A. Boynton on July 7, 19~2, March 30, 1943, and July 13, 1943,
respectively, each show a gas lift valve with a hollow-stemmed
valve, but these valves have their opposite ends formed with
equal seal ~urfaces ther~on and are addpted to enyage in equal
cup-shaped seats at eit~er end to stop flow through the hollow
stem when the differenLial pr~6sure across the mechani6m
create~ a force exceedin~ the force of centering spring means
associated with the tubular valve stem.
--3--
12~43~3z
U.S. Patent 2,305,25~ which issued on December 15, 1942 to
H. U. Garrett et al., discl(~ses a differeJltial 9a5 lift valve
which indeed is opera~e(~ by the differel-ce between tubin~ and
casing pres~ures, but i~ vdlve member does not always present
equzl areas to the tubirl~ al~d casin~ areas and, therefore, acts
differ~ntly from th~ device~ o the pat~ntB jUsL diBCU6Bed.
The device of patent 2,~05,250 has a valve member 21 (~ee
Figures 2 and 3) with a conical seat surface 23, 22 on its
upper and lower ends and a piston 28 just below the upper end.
Spring 30 biases the valve toward open position (shown in
Figure 2). ~he upper end of the valve member can close upper
seat 20 which opens to the casing, or its lower end can close
lower seat 14 which opens to the tubing. Lateral ports 31 in
the valve housing conduct lift gas fro~l the casing into the
housing and to lower seat 1~ when the valve is open. The ports
31 have a combined area ~uch smaller than the area of either
port }4 or port 20.
When the valve is open and is seated on upper port ~0,
ca6ing pressure cannot act upon the upper side of piston 28,
but acts upon the upper end of the valve through port 20. Port
20 is smaller than port 14, and the piston is larger than port
14. Thus, when the difference between the casing and tubing
pres6ures be~omes 6ufficiently great to unseat the valve from
upper 6eat 20, ca6ing pres~ure immediately acts upon the
greater area of piston 28, causing the valve to move to fully
clo6ed po6ition with a "snap action". This imparts positive
operation to the ga~ lift valve and prevent6 the unwanted
cycling mentioned above- It also save6 gas and avoids unnece~-
6ary wear and tear on the valve mechanism.
It i6 obvious that when the valve is open, the differential
pres6ure acts upon the area of upper seat 20, and when it is
clo~ed~ the differ~ntial pres6ur~ act6 upon the larger area of
lower seat 14- Thi6 difference in port sizefi cau~es the gas
--4--
lZ~43~2
lift valve to close at a first differential pre6sure valuc and
to reopen at a 6ec~r)d diff~rential value whicll is lesser than
the first.
~ e present invention ifi an improvement over the differ-
ential gas lift valves mentioned hereinabove. It i6 formed
with unequal areas acros~ w~lich the differential pressure ~ay
act to actuate the valve to open or closed po8i tion so that the
valve will close at a first differential pressure value and
close at a lesser value without cycling and without need of a
special piston to provide snap action because the openiny and
closing differentials are 80 ~ifferent. Also, the present
invention provides a gas lift valve having a less tortuous flow
passa~e through it in that the flow passage passes straight
through the valve. The valve stem is hollow and conducts lift
ga.s to the ball valve closure member attached thereto, tl-e lift
gas exiting the stem througl) lateral ports at the ball and
passing aro~nd the ball and through the seat. A choke or flow
bean is advantageously provided in the hollow valve stem.
Further, the present invention provides a gas lift valve having
novel mean~ for preventing backflow thro~gh it.
There is not found in the known prior art a gas lift valve
having a valve stem hollow from end to end which closes at one
differential pressure and reopens at a le~ser differential
pressure and having a s-raicJht flow pas6age therethrough with
only a ~mall but streamlined detour around it~ ball closure.
Neither was there foun~ a gas lift valve in the known prior art
having a floating valve seat which also actS-as a check valve
and at the same time provides a straight unobstructed flow
passage therethrough when in open position- In addition, there
was n~t found a ga~ lift valve having a hollow valve stem in
which a flow re~trictor i~ provided.
~ le present invention ovcrcomes many of the problems as-
sociated with differential ga~ lift valve~ by providing gas
lZ~43~32
lift valves haviny a ~Lr~i(3ht-t}lrouc3h flc-w passage, a hollow
stem constituting a portion of that strait3ht passage, a flow
re6trictor in the h~llow steln, a floating valve seat which also
serves to check again~t backflow, a closing differ~nt;al which
i8 higher than its operling differential, and simple con-
~truction which i~ less coutly to manuf~cture.
SUMMA RY OF' THE I NVENT I ON
~ . .
The present invention is directed to a ~as lift valve for
attachment to a well flow c~nductor and having a body with a
flow passage therethrough for conducting lift gas between the
exterior of the conductor and the interior thereof, a valve
~eat in the body s~rrounding the flow passage, a valve closure
in the body engageable with the seat to control fluid flow
through the flow passage, a hollow valve ~tem having one end
expo~ed to up~tream pre~ure and its other end attached tQ the
clo~ure ~ember, lateral port ~ean6 in the stem adjacent the
closure membex and means for ~iasing the closure member toward
open position to permit fluid flow through the hollow stem,
around the valve closure and throu9h the valve 6eat. This
invention i8 al80 directed to such gas lift valves having flow
restrictor mearls in the hollow ~tem, a floating seat for pre-
venting backflow through Lhe valve, and having means whereby
~he valves close in responRe to a first differential pressure
and open at a second differential pre~sure which is le~er than
the first.
It i~ therefore one object of this invention to provide an
improved gas lift valve for controllin9 fluid flow between the
interior and the exterior of a flow conductor and which i~
re~ponr,ive to the diff~rerlce between the upstream and the
downstream pre6sure~ to which it i~ ~ubjected.
Anothcr object i6 to ~rovide a ga~ lift valve of the
i~43~32
character descri~ed whicll will cl~se w~lell Lhe dif~erential
pressure incre~ses to a prl!(3eLer~illed val~e but will reope
when tl-e diff~r~ntidl prLs~ur-~ d~cre~ses to a ~redetermined
value which iB 8Ubstalltially lc~s than the valuo at which the
valve closes.
Another o~ject is ~o provid~ a gas liC- valve of the
character described ~aving a ~ubstarltially straight, relatively
non-tortuous ~low passage therethrough.
Another object is to provi~e a gas lift valve of the
character described having a valve closure with a hollow stem
providing a portion of a non-tortuous flow passage therethrough.
A further object iu to provide sllch a gas lift valve having
flow restrictiny means in the valve stem thereof.
Another object is to provide a gas lift valve of the
character descri~ed ~lavillg im~rov~d m~arlR therein ~or pre-
venting backflow therethrough.
~ nother object is to provide a gas lift valve of the
character described having a f loating seat which upon
occurrence of backflow will ~ove into engagement with the
valve's closure member to ~reclude further backflow through the
device.
Another object of this invention is to provide a gas lift
valve of the character described having its inlet provided in
the form of narrow slits for precludin9 entrance of larger
particles such as sand or debris into the valve ~echanism.
A further object is to provide a gas lift valve of the
character described which is attcchable to a lock or latch
device to be rè~ovably installed in a seating receptacle, such
as, for instance, a side pocket receptacle or a landing nipple
formirlg a part of a well Ilow conductor.
Other objects and advanta~es may become apparent from
reading the descriptioll which follows and from studying the
accompanying drawing w}lereir-,:
1~43~Z
l Brief Descr~t:ion o~ t},c l)rawiu~
_ _ _ _ . _ _ _
Figure l i8 a diagram~ tical view of a gas lift. well having
- a 6ingle ~tring of tUbill-J with a plurality of gas lift valves
attached thereto;
Figure 2 is a diagrammatical view of a gas lift well having
~ultiple tubing strings therein with a plurality of gas lift
valves in each tubing string;
Pig~re 3 is a longitudinal view, partly in section and
partly in elevation, 6howing a gas lift valve constructed in
accordance with thi~ invention showing the valve in open
position;
Figure 4 is a cross-sectiorlal view taken along line 4--4 of
Figure 3;
Figure 5 i5 a view ~imilar to ~igure 3 showing the device
of Figure 3 with the valve in closed position;
Figure 6 i6 a fragmentary view similar to Figure 3 showing
the valve of Figure 3 in po~ition preventing backflow;
Figure 7 is a fragmentary view similar to Figure 6 showing
a ~odified form of ga~ lift valve having a spring for biasing
the floating 6eat toward backflow preventing position;
Figure 8 i6 a diagrammatical view similar to Figure l but
~howing a well with a single string of tubing which includes
side pocket mandrel6 with g2l~ lift valves installed therein; and
~ igure 9 i6 a view si~ilar to Figure 3 ~howing a gas lift
valve embodying this invention and adapted for attachment to an
anchoring device for retrievable in6tallation in a landing
receptacle in a well flow conductor.
Description of the Preferred Embodi~ent~
The device of thi~ invention i 8 u~eful in sas lift wells
such a6 the well lO illustrated diagrammatically in ~igure l.
~his well has a casing ll perforated a~ at l2 to provide inlet~
for well product~- A well tubing 13 ~a~ it~ ~ower open end in
--8--
i2~b43~32
fluid communic~ion with t~e ca~ing near ~he p~rforations. A
well packer 14 closes the tubing-casing arlnulus 15 just above
the perforations while a wellhead 16 closes the annulus 15 at
the upper end of the casing. The ~pper end of the tubing
~onnects to the wellhead 1~ and a conventional Christmas tree
represented by the valve 17. A flow line 18 containing a wing
valve 19 ie connected to the Christma~ tree to conduct well
product~ to conventional surface equipment (not shown).
The well tubing is equipped with a plurality of gas lift
valves only two of whic}l are shown. These are identified by
the reference numerals 20 and 22. These gas lift valves are
constructed in accordance with this invention and may be
identical to the ga~ lift valve ~hown in Figures 2-6.
Lift gas i~ supplied through yas line 23 connected to the
casing 11 as shown and includes a valve 24 for controlling flow
therethrough. A flow choke (not shown) may be included in line
23 near valve 24, if desired.
All of the gas lift valves described herein and embodying
this invention are of tl-e differential type. They are actuated
by the difference in pres~ures of the lift gas and the
production fluids which act upon them- These valves are
~tructured such that they close at a predetermined differential
pres6ure and open at a predetermined differential pressure
which i~ con~iderably lower than the closing differential
preEisure .
Referring now to Figur~6 3-6 it will be seen tha~ the gas
lit valve of this invention is indicated generally by the
numeral 25. This valve 25 may be identical to valve~ 20 and 22
6een in Figure~ 2 and function in exactly the same manner and
used for the ~ame purpo~e.
Valve 25 include6 a hou~ing or body 28 having a flow
pasfiage 29 extending it~ full length, flow normally taking
place therethrough in the direction 8hown by the arrow 29. The
_g_
3~3Z
1 body 28 comprises a main housing member 30 which is internally
threaded at its lower end (upstream end) as at 32 for attach-
ment of the pluy member 33 while its upper or downstream end
is internally threaded as at 34 for attachment of sub 36. This
connec-tion is preferably sealed by suitable means such as
resilient seal ring 35. Sub 3G is externally threaded at its
upper end as at 36a for attachment to the lug 37a of a con-
ventional lug-type mandrel 37 (shown in dotted lines) rnade up
in the tubing string and providing a passageway (not shown)
between the tubing bore and the annulus. When the gas lift
valve 25 is attached to the tubing via the lug-type mandrel 37,
gas may be conducted from the annulus to the interior of the
tubing when the gas lift valve is open.
Plug member 33 is bored as at 38 from its upper end, but
this bore terminates short of its lower end. An inlet for
lift gas is preferably provided by narrow cross slots or slits
39 for excluding sizeable particles of debris, et cetera,
which may otherwise enter the valve mechanism and cause damage
thereto. These slots 39 can be made as wide or as narrow as
desired, but they should provide an inlet of adequate flow
capacity (at least as great as bore 38).
The main body member 30 has a main bore 40 having a lower
portion thereof much enlarged as at 41 providing a downwardly
facing shoulder 42. The upper portion of bore 40 is enlarged
as at 43 and further enlarged as at 44 providing an inclined
shoulder 45, all for purposes to be made clear later.
The sub 36 has a bore 48 which is enlarged as at 49. The
outer end of enlarged bore 49 is flared as at 50 to provide a
frusto-conical shoulder whose purpose is soon to be explained.
The device 25 is provided with a valve seat having a seat
surface which surrounds the flow passage 29 passing through the
body 28. This seat may be formed integrally with the sub 36 or
could possibly be formed in the main member 3~. However, in
--10--
4382
the form illustrated in t~e drawing, and particular~y ~igures 3
and 5, such seat surface i~ provided in a floating valve seat
member 60 having a bore 61 therethrough whic}) is enlarged at 62
to provide frusto-conical ~eat surface 63 adapted to be engaged
by a valve member, to ~e described later, for controlling flow
through the bore 61 of the ~eat member. Enlarged bore 62 of
the seat member is flared at its lower end a~ at 64 to
streamline the flow passage and to provide a guide surface for
the valve member.
The lower portion of the valve seat member 60 is slidable
in bGre 45 and has a fairly close fit therewith yet will ~lide
freely therein. Its outer ~urface 66 is provided with an
external annular rece~6 in wl~ich i~ carried a resilient seal
ring 67. The upper portion of seat member 60 i5 reduced in
outside diameter a~ at 65 ~nd is telescoped into enlarged borc
49 of ~ub 36 as shown where it is ~reely slidable. The tran-
sition between the enlarged and reduced outer surfaces of the
seat member 60 provides an external frusto-conical surface 68
in which is formed an external annular reces~ fitted with a
resilient seal ring 69.
~ he valve ~eat member 60 is slidable between an upper
position, shown in Figures 3 and 5, and a lower pnsition, shown
in Figure 6. When the seat member is in its upper position,
it~ upwardly facing external frusto-conical surface 68 engages
downwardly facing fru~to-conical surface 50 of ~ub 36 and seal
ring 69 ~eal~ therebetween to prevent leakage between the sub
36 and seat member 60.
~ he seat me~ber 60 i~ very freely movable to an inter-
mediate position wherein its ~eal ring 67 reaches upwardly
facing inclined ~houlder 45 in the main hou~ing member, and is
further filidable to it~ lower po~ition ~een in Figure 6 wherein
its seal ring 67 ~ealingly e~lgages bore 43 in the main housing
12~43~3Z
member, a position w~,ich will be In~l-e ~llly ~xplairled ll~reill-
below.
7~
A valve closure mem~r\i~i disl~osed in the main flow passage
29 of -the body c~nd is movable longitudinally relative to tlle
seat member 60 between ';~lt~ dnd un~ated positions. T~lis
valve closure member m~ly lle c~f any suitdbl~ shape, but th~t
illustrated in the drawil~y i~ in the ~nl~C of a ball or sp21ere
72. This ball is eng~lyeable with seat surface 63 to preclude
flow through the seat meml~er, and when the ball is thus seated,
there is but ~ small clearance between it and the inner wall of
- bore 62 of the seat member. The lower portion of the seat
member which surrounds bore 62 may be termed a lip and is
indicated by the referel~ce numeral 60a.
The ball or valve closure 72 has attached thereto a hollow
valve stem 74 which is secured to the ball as by silver
soldering or other suitable means. The hollow valve stem 74
has a passage 75 extending the full length thereof. Slot6 76
are formed in the wall of the valve stem adjacent the ball 72
to enable gas flowing upwardly through the hollow stem to exit
just below the ball and bypass it before passing through the
valve seat. The flow area through slots 76 should be at least
as large and preferably larger than the area of flow passage 75
through the stem.
It is preferable to provide flow restrictor means in the
passage of the valve stem 74. If the valve stem is formed in
one piece, a restriction may be provided in it~ bore. For
instance, the sten can be bored from its upper end to within a
fraction of an inch, say 3/8 to 1/2 inch, of it~ lower end.
Then this portion can be drilled through with a ~maller drill
to provide a bore of de~ired orifice- Alternatively, a screw
having an orifice therethrougll could be threaded into the ~tem
bore.
-12-
12~P43t32
1 In the device illu6~r~ed in Figures ~ and S, the valve
stem 7~ is for~led in ~wo pieces: a stem 77 and an adapter 78.
The adapter 7a is tubular, ~laving a bore 7~a, and is internally
threaded as at 79. At ur ne~r its upper end it is provided
with lateral slots 76 as ~own. The upper end face 78~ is
shaped to fit the valve closure or ball 72 which is attached
thereto as by suitable means such as silvcr soldering. The
stem 77 is threadedly attac~cd as at thread 79 to the lower end
of the adapter 78 as shown. 'rhe stem 77 is provided with an
external flange B0 near its lower end and below flange B0, the
stem is reduced in outside di~meter as shown at ~1 to provide a
piston of suitable diameter. If desired, the bore 77a of the
stem may be restricted ~y reducil-lg the diameter of the bore,
say at one or the other of its ends as previously described, or
a screw orifice could be threaded into one of it~ ends.
However, it may be desirable to provide a flow restrictor in
the form of replaceable flow bean ~4. Bean B4 is captured in
sealing engagement between the upper end of stem 77 and down-
wardly facing shoulder 85 formed in adapter 78 below 610ts 76.
The flow bean is provided with a bore 86 therethrough of
suitable orifice. The flow l~ean may be readily replaced by
another bean when such becomes necessary.
A spring 90, preferably a straig21t helical coil compression
spring. is disposed within enlarged bore 41 of the main body
member 30 and surrounds the stem 77 with its lower end engaged
with the upper side of stem flange 80 and its upper end engaged
with downwardly facing shoulder 42 of main body member 30.
Thus the spring applies a bias to the valve ~tem 74 tending t~
maintain it in its lower position as shown in Figure 3 with the
lower side of its flange engaged with the upper end of plug
33. Thus, the valve stem's longitudinal movel~ent is limited in
one direction by its flan~e B0 engaging the plug and in the
-13-
lZ~43~3Z
other direction by its bclll closure 72 engaying the seat 60 as
clearly sh~wn in Figure 5.
The 6pring 90 can be made of suitable ~trength to provide
the characteristics desir~d in the valve. The required load of
the spring will be dictated ~rincipally by the size of pi~ton
81 and the differential pres6ure at which the valve will be
desired to respond. It is preferably for~ed with a strength
~omewhat less than ~laximum with one or more spacer6 added later
if more spring load is needed- Thus, a single spring together
with suitable spacers may suffice for many differing instal-
lation~. Such 6pacer~ are shown in the drawing and are indi-
cated by the numeral B8. The~e ~pacers, like the flow bean 84,
are readily replaced by disassembling at least a portion of the
device 25 and reasse~bling with the desired bean and/or spacer
6i zes.
It is readily ~een that lift gas may enter the device 25
through the inlet 610ts 39 in the plug, flow upwardly through
bore 38, passageway 75 of the valve ~tem 74 and exit through
~lots 76, flow around the ball 72 tbetween the ball 72 and the
wall 43 of the body), flow through the bore 61 of valve seat
60, through bore 49, and exit the device through the bore 4~ o~
sub 36. Since the flow pa~ge 29 throu~h the valve conduct~
lift ga6 therethrough. such ga~ is conducted fro~l the tubing-
ca~ing annulus into the well tubing through the lug-type
mandrel 39.
The flow path through the device is almost perfectly
straight, rather than being tortuous a6 i6 t-he case with most
BUCh devices. The lift gas only make~ but a 6ingle jog as it
veer6 momentarily to bypa~3 the b~ll 72.
The spring 90, a~ previously 6tated, tend~ to maintain the
valve in open position ~6~0wn in Figure 3)- Back pressure from
the tubing act6 in conjunction with the load of spring gO
t~nding to move the v~lve to open position. The pre6Lure of
-14-
:12~43~2
1 lift gas in the casing and up~tream of tlle flow restrictor in
the valve ste~ applie~ a bia~ to the piston tending to close
the valve. Thi~ force is equal to the casing pressure (at the
valve depth) times the area of the piston.
The piston is a rather close fit in bore 3~ of the plu~ 33,
it~ exterior surface as well as the cylinder, or the wall of
plug bore -~, being carefully formed and finished to provide a
very close but free sliding fit. At the same time the valve
~tem has a loose fit in body bore 40 above the spring 90.
Thus, the pressure in the spring chamber and exterior of the
valve stem will be the same as the pressure existing ~etween
the flow restrictor (bean ~4) and the valve seat 60, that is,
in body bore 43 below the valve seat 60.
Thus, when the valve is open as ~een in ~igure 3, the
difference ~etween tubing and casing pressures acts across the
cross-sectional area of piston 81. When the tubing pressure
decreases sufficiently, this differential pressure becomes
sufficiently high to overcome the bias of spring 90 and the
valve will begin to move toward its closed position, seen in
Figure 5.
When the valve is clo~ed as seen in Figure 5, the ball 72
i~ sealingly engaged with seat surface 63 of seat 60 and ~eals
an area the 6ize of or very ~lightly larger than the cross-
eectional area of seat bore 61- Seat bore 61 i5 somewhat
larger than cylinder bore 38 of plug 33- Thus, when the valve
i8 in closed position, the differential pressure act~ across an
area larger than that across which it acts when the valve is in
open positi~n.
In a valve manufactur~d according to this invention, the
area of the pisto~ was 5/16 inch diameter with a cross-
sectional area approximately 0-0767 square inch. The ~eat
member 60 had a bore 61 of 3/~" diameter- The valve clo~ure
contacted the ~harp corner of thi~ bore to seal the pa~sage
--15--
%
1 through the s~at. l'he area ~ealed by this contact equaling a
cross-sectional area approximately 0.1104 square inch.
When such valve i~ open, the differential pressure acts
across the area of pi~torl 81 or the cylinder bore 38 of the
plug 33, or 0.0767 square inch. And, when such valve i5
closed, the differential pressure acts across the area of
sealing contact between valve and seat, or an area of 0.1104
square inch, an area about 1.44 times as large as the piston.
~ or this reason, the valve, after it has been closed by the
differential pressure acting across piston 81, will remain
closed without cycling until the tubing pressure rises suf-
ficientl~ to reduce the differential pressure between tubing
and casing sufficiently, to enable the tubing pressure and
the sprin~ load together to move the valve closure to open
position. All of this, of course, is assuming that the casing
pressure remains constant, as well it might. And, of course,
the above figures hold true regardless of the annulus p~essure.
In the example just given, if the casing pressure remains
at 600 psi and the spring load is lg pounds, the tubing
pressure at the time the valve begins to move toward closed
position will be: 600 ~ o Q9767 = 352 psi.
Thus, the tubing pressure is 352 psi, the casing pressure
i6 600 psi, and the differential pressure is 600-352 or 248
psi. So, the valve in this example will close when the dif-
ferential pressure rises to 248 psi.
Since both the tùbing and the casing pre6sures act across a
common area lthe area of the piston ~1), the spring governs the
differential at which the valve closes. Note that the ~pring
load of 19 pounds acting against the piston area offsets a
pressure of o 1967 or 248 psi.
In a similar manner, both tubing and casing pressures act
across the sealed area of Lhe seat when the valve is closed.
Thus, if the spring (now mor~ compre6sed) exerts a force of 22
-16-
~4;~
1 pounds against the ~eat ar~a of 0.1104 square inches, the valve
will open at a differenti~l pres~ure of ~ = 199 psi.
Thus, the tubing pres~ure nt valve opening will be 600 - 199
or 401 p~i.
Thus, the valve in this example will close at a dif-
ferential pressure o~ about 248 psi. It will not cycle, but
will remain firmly closed until the differential pressure is
reduced to about 199 psi, ~t which differential pressure it
will open.
The valve i6 normally open and will pass lift gas from the
casing into the tubing to aerate the column of fluids therein
to aid in lifting them to the ~urface until the load of such
column lightens to the point where the pressure thereof at the
valve is so low that it i~ le~s than the casing pressure by the
differential required to close the valve, or about 248 psi.
Subsequently, the well fluids must rise in the tubing to
~ufficient height to exert a tubing pressure on the valve of
about 401 psi to provide a differential of 199 psi and open the
valve again.
lt should be understood that when the differential pressure
reaches sufficient value to cau~e the valve to begin its
movement toward closed position, it must rise even higher to
cause the valve to move farther in that direction. This i8
because 6uch movement increases the co~pression of the spring,
thus increasing the resistance to such valve movement. When
the valve has moved about half way to closed positisn, however,
the annular clearance between the ball 72 and the seat lip 60a
which now surround~ it becomes ~o reduced that the flow stream
is pinched or throttled, thereby causing a drop in pressure
therebeyond while pressure begins to build up upstream
thereof. With very little delay, the valve then is moved the
other half of its travel to fully clossd po~ition, further
compres6ing the spring.
-17
lZ~43~2
1 Now, please refer again to Figure 1 of the drawing.
Gas lift valves 20 an~ 22 are valves of the type described
herein, and are considered, for the moment, to be identical to
the gas lift valve 25 of E`igures 2-6. ~lso, let us suppose
that well 10 has just been completed and that both the tubing
13 and the annulus 15 are full of salt water having a pressure
gradient of 0.5 psi per foot of depth. For the sake of
simplicity, let us further assu~e hat the well will produce
nothing but ~alt water with a gradient of 0.5 pound per foot.
If valves 20 and 22 are each adjusted to close when the
differential pressure acting across them is 250 pounds per
square inch, then, at closing, the spring load acting against
the 5/16" piston (area = 0.0767 square inch) will be: 250 x
0.0767 = 19.175 pounds.
The valve will move an additional 0.21 inch (approximately)
before engaging the valve ~eat surface 63, and this additional
movement increaqes the co~pression in the spring. lf the rate
~f spring 90 is 12.5 pounds per inch, its load when the valve
is fully closed will be: 19-175 + (12-5 x 0.21) = 21.8 pounds.
Accordingly, the differential pressure required to open the
valve when the spring i~ ap~lying a load of 21.8 pounds against
the valve closure now engaged with the valve seat sealing an
area of 0.1104 square inches, will be: o21io84 = 197 psi
~approximately).
It is readily 6een then that the valves 20 and 22 will each
close at a differential pressure of 250 psi and will open at a
differential pressure of about lg7 psi.
In placing the gas lift valves in well 10, the top valve,
valve 20, would be placed at a depth of about (6000 55) =
1100 feet. This allows 50 psi for tubing surface pressure.
The second valve, valve 22, wou~d be placea below valve 20
by a distance equal to the closing differential of the valve
divided by the pre~sure gradient of 0- 5, or 0 5 = 500 feet.
1~43~Z
1 Thus the valve 22 would be placed 500 feet below valve 20 or at
a depth o-f 3100 + 500 = 1600 feet. Other like valves would
also be placed at 500-foot in~ervals below one another.
Lift gas in injected into the well's annulus 15 at the
surface throuc3h a small choke. Gas lift valves 20 and 22 are
both open becau~e the differential acros~ th~m i~ less thall the
closing differential of the valves. Valves 17 and 19 are open
and salt water issues from the tubing because as lift gas is
slowly and carefully applied to the annulus, thè salt water
U-tubes through the open valves. As the salt water U-tubes
from casing to tubing and is produced from the well, the fluid
level in the annulu~ is d~prcssed and casing pressure is
gradually increased to 600 psi. When the fluid level in the
casing is depressed to 1100 fect, gas enters valve 20 and
aerates the fluid column in the tubing and decreases its
density. The gradient in the upper 1100 feet of tubing becomes
considerably less than 0.5. Salt water continues to U-tube
through valve 22 and any other like valves therebelow. The gas
in the annulus reaches valve 22, enters it and aerates the
fluid in the tubing thereabove. Now, both valves 20 and 22 are
injecting gas into the tubin~- This so decreases the tubing
pressure at valve 20 that it exceeds the valve's set dif-
ferential pressure, thus it closes. Now, valve 20 continues to
inject gas into the tubing to produce more salt water~ If
there are other ga~ lift valves below valve 22, they will come
into play and will be operated automatically until the working
fluid level is reached ~nd the well stabilizes.
After the well has been "kic~ed off" or "unloaded" and
placed on production, thc casiny pressure can be reduced if
desired, and the 250 psi differential of the valves will
continue to enable the valves to operate with their 500-foot
spacing.
For more detailed in~tructions in gas lift operation ana
--19--
12~43~
] the spacing of various g~u lift valves for th~ n~any types of
in~tallations, et cetera, a cJo~d gas lift manual should be
consulted. A good ~ook on ga~ lift is that entitled "GAS LIFT
THEORY AND PRACTICE," by Dr. ~ermit E. Brown, Head of the
Petroleum Engineering Department at the University of Tulsa,
Tulsa, Oklahomat
~ hould bac~flow occur through the ga& lift valve, the
floating seat member 60 will move toward the valve closure 72
and seat thereon to stop such backflow. This i 6 shown in
Pigure 6, which see.
When backflow develops, the valve closure i8 already in its
fully open or lowermost position. Gravity tends to move the
valve seat 60 downwards, and this moveMent is aided by the
backflow. When the seal ring 67 on the seat reaches 'he lower
extremity of bore 44 of the main body member 30, it may lodge
momentarily at the upper extremity of bore 43, that i 5, at
upwardly facing 6houlder 45. ~owever, at thi~ ti~e, the lip
60a of the seat will be so close to the ball 72 that the flow
therebetween is pinched and the differential pressure acting
across the seat quickly increa~es and promptly ~oves the seat
to its seated position ayainst the ball as seen in Figure 6.
When flow occurs again in the n~rmal direction, the seat
will be returned to its normal po5ition shown in Figures 3 and
5.
There is a distinct advantage in having the valve seat 60
slidable in the body 80 that it will serve not only as a seat
but also as a check valve- Most check valves have a tortuous
flow passage through or hround them- Seat 60 provides a
straight-through, non-tortuous, unobstructed flow passage in
the form of bore 61.
When the valve 25 i6 installed with its up~tream end
looking downward as i6 6hown in the drawing~, gravity applies a
constant bia8 to the valve seat member 60 tending to ~ove it to
~20-
~Z~43'~2
i backflow checking po~ition. If it i~ desire-l to increase such
bia~ or to operate the v~lve in another position, such as an
inverted position with it~ upstream end looking upward, a valve
~odified as seen in Figure 7 is to be preferred. In Figure 7,
the modified gas lift valv~ i8 indicated generally by the
reference numeral 125. lt~ ~ub 13~ is provided with a bore 149
which may be considerably deeper and a little larger than bore
49 of valve 25, and this bore provides a downwardly facing
shoulder 150 which is preferably abrupt. The valve seat member
160 is ~ormed with itB upr~er end face 170 perhaps a little
broader than that of iti counterpart, the upper end face of
seat 60. A seat spriny 171 is placed between downwardly facing
~houlder 150 and the upper end 170 of the seat member 160 to
apply a constant bias to the seat member tending to move it
toward the valve closure 72 regardless of which way gravity
happens to act thereon.
Gas lift valves of the type described hereinabove will
operate automatically after the well has been unloaded and will
continue to do so even though the pressure of the lift gas in
the annulus may vary over a wide range because these valves
operate on the difference between the tubing and annulus
pre~ures rather than bein9 operated by ~res6ure only.
Such valves as described hereinabove will not only operate
automatically as just ~entioned s~ch as well 1~ having valves
in a single tubing string, but they are well suited for u6e in
multiple wells where they may be used in a plurality of tubing
~trings simultaneously- Thu6, a well ~ay be equipped with any
xea60nable n~mber of tubing trings having 6uch ga~ lift valves
therein. The valves will be ~paced according to the conditions
attendant with each ~tring of tubing, and al~o5t as6uredly
their ~pacing will ~e different in each tubing, causing the
valves to be located at ~cattered level6 in the well- Al60,
the operation of the variou5 valves in the various tubing6 will
iZ~3~3Z
1 surely cause the annulu~ pres~ure to vary con~iderably. Even
80, the valves will continue to operate auto~atically.
Whether unloading a ~ingle or a multiple well, it should ~e
done unhurriedly with t~e lift ga~ injected into the annulu~
slowly and preferably throu~h a choke to limit ~uch injection,
le6t the lift gas be injected too fast, causiny the differ-
ential pressures to rise s~lddenly across the valves and close
all of them. Should thi B happen, it may be necessary to bleed
gas fro~ the annulus to reduce the annulu~ pressure, or com-
municate the annulus with the tubing at the surface to equalize
pressures across the valves, or to pre6surize the tubing, in
order to reduce the differential to where the valves will open
before 6tarting the ~nloading process over again.
Referring to Figure 2, it is 6een that a dual well 200 is
diagram~atically illustrated. This well iB provided with a
casing 201 perforated opposite a lower ~one as at 202 ~nd
opposite an upper zone as at 203. A first tubing string 204
communicates with the lower perforations 202 and the second
tubing string 205 communicates with the upper perforations. A
single packer 206 seals between the tubing 204 and casing at a
location between the two ~et~ of perforations. A dual pacXer
207 ~eals between the tubinys ~204 and 205) and the casing
i~mediately above the upper perforations. The annulus 20B
extends to the surface where a wellhead 209 seals the casing
around both tubing~. A Christ~as tree represente~d by master
valves 210 and 211 connectL the tubing6 204 and 205 to flow
lines 212 and 213 having wing valves 214 and 215, respectively.
Tubing string 204 i~ provided with a plurality of gas lift
valves such a~ valve6 220 and 221 a~ shown and tubing 205 i~
provided with a plurality of ga6 lift valves 6uch a6 valves 222
and 223. TheBe valve6 are 6paced according to g~od gas lift
practices for efficient operation a6 before explained.
A lift ga6 line 224 having a valve 225 i6 connected ~o
-22-
~2~438Z
1 the annulus at the ~urface to ~pply gas for this gas lift
operation.
Well 200 may be unloaded in the sa~e manner as was well 10
of Figure 1 and either or both tubing ~trings may be used in
doing 60, preferably only one. After the well has been un-
loaded, the valves will operate as they are needed and will do
80 ~ndependently of each other Rince each valve i5 operated by
the differential pressure across it and each is opened by fluid
rising in the tubing. T~us, each valve will pass gas only when
such gas is needed. And, these valves will continue to operate
automatically in spite of excur6ions in annulus presfiure as
before explained.
Gas lift valves embodying the present invention are also
u~eful in wells equipped with side pocket mandrels. Figure R
diagrammatically illustrates such a well. Well 300 is a single
well completed in a conventional manner, having a casing 301,
perforations 302, packer 303, tubing 304, wellhead 305, tree
306, flowline 30~, wing valve 308, lift gas supply line 309,
and valve 310. The tubing i6 equipped with a plurality of side
20 pocket mandrels 312 and 313 having offset receptacles 314 and
315, communicating with the annulus 316 through lateral port6
317 and 318 and having 9a6 lift valves 319 and 320, respec-
tively, in6talled therein to control admi~sion of lift gas into
the tubing to aid in liftin9 well product6 to the surface, for
thu6 producing the well. The~e ga~ lift valves are spaced in
the manner before explained, and the well i~ u~loaded and
placed on production in the manner before explained.
Gas lift valves 319 and 320 may contain the 6ame mechanism
a6 in the valves previou~ly described, but they must be adapted
for use in 6ide pocket mandrels.
Figure 9 illustrate6 a valve such as valve 319 or 320. The
valve in Figure 9 i6 indicated generally by the reference
numersl 325- ~he innQr workings of the valve 325 are identical
-23-
1~43~2
1 to those of valve 25 ~een in Yiyures 2 and 3, but could be like
those of valve 125 seen in ~igure 7.
Valve 325 differs from valves 25 and 125 in that its upper
and lower end~ are different, being adapted to carry packing
rings for sealing above and below the lateral port means of
~ide pocket mandrel receptacles such as tho6e ~een in well 300
illustrated in Figure 8.
The plug 333 at the lower end of gas lift valve 325 i~
threadedly attached as at 332 to the lower end of the main body
member 30 and has a blind central bore or cylinder 338 in which
the pi~ton 81 at the lower end of valve 74 i6 61idably re
ceived. Inlet openings for the upstream end of valve 325 are
provided by the narrow filter 610ts or slits 339, as 6hown,
through which lift gas enter~ the valve. The plug is reduced
in outside diameter in the region of the slits as at 340 to
provide for free passage of lift gas therearound flowing
between the mandrel ports (317, 318 of Figure 8).
Plug 333 has its lower portion reduced in diameter as at
334 to fit the bore of packing rings 335 and providing a
downwardly facing ~houlder 360 shaped to conform to the packing
as 6hown to serve as a female packing adapter and save 6pace.
A double male adapter ring 361 i6 disposed between the upper
and lower groups of packing rings 335 facing in opposite
directions a5 shown to 60al in both directions. A female
packing adapter ring 362 i~ placed beneath the lowermost
packing ring 335. The lower end of the lug is threaded as at
363 and cap 364 is attached as 6hown to reLain the packing in
place and to guide the valve as it i6 lowered into the well as
by wireline to be removably installed in a 6uitable landing
receptacle.
At the upper end of valve 325, it6 adapter 336 ha6 it~
upper portion reduced in dianleter a6 at 3~0 to fit the upper
packing ~et which may be exactly like the packing 6et on the
lZ~43~3Z
1 lower portion o~ the valve as just describ~d. This upper
packing set i6 indic.,te~ by the reference nullleral 371. Reduced
diameter 370 of the aaa~ter provides an upwardly facing
shoulder 372 which corlform6 to the ~pper packing as shoulder
335 conforms to the lower packing set.
The upper end of adapter 336 is threaded as at 374 for
attachment to device 373 (~hown in dotted lines) by which the
valve 325 is anchored in place in the side pock~t mandr0l
receptacle or in another ~uitable receptacle, such as a bypass
landing receptacle. When the device is in place in the
mandrel, its upper and lower packing sets will be disposed
above and below the lateral port (317 or 318) of the mandrel to
direct lift gas to irllet openings 363. Lift gas entering the
mandrel through its lateral ports may flow around the valve at
its external annular recess 340 in the region of the inlet
openings 339 and enter therein to pass through the valve
mechanism in the manner before explained on its way to the well
tubing.
It should be understood that tlle valves illustrated and
described herein could be readily modified for use in gas lift
wells where well products are lifted through the tubing-casing
annulus. For such use, the plug 33 at the lower end of valve
device 25 would be replaced with a plug in which its central
bore ran end to end and the lower end of the plug as seen in
Figure 3 would be provided with an external thread not unlike
thread 36a seen on the upper end of adapter 36. This modifiea
valve could then be inverted and attached ~o the lug 37.
Since, in the inverted valve, gravity would no longer bias the
valve seat 60 toward valve closure 72, it would be desirable,
even necessary, to spring load the seat as taught with respect
to gas lift valve 125 illustrated in Yigure 7. Al~o, since the
thread 32 (connecting the modified plug to the housing ~ember
30) in the inverted valve would now be subjected to a greater
-25-
3t~2
.~ differential pressure (t?,e s~lme difIerentidl which exists
acros6 the flow bean B4), it would be desirable to seal this
threaded connectiorl with a resilient seal ring in the manner
taught with respect to thread 34 at the opposite end of the
housing member 30. Alternatively, the gas lift mandrel 39
could be inverted in the tubing 6tring, in which case the gas
lift valve would remain upright. In either case, the valve
would control the flow of lift gas from the well tubing into
the casing for lifting well products through the annulus to the
surface.
Thus, it has been shown that the devices ill.ustrated ana
described herein which embody the present invention fulfill all
of the objects set forth at the beginning of thîs specification,
and changes in the sizes, shape~, and arrangement of its parts
may be had without departing from the true ~pirit of the in-
vention.
-26-
