U.S. patent number 3,586,464 [Application Number 04/883,564] was granted by the patent office on 1971-06-22 for sucker rod compensator for subsurface well pumps.
This patent grant is currently assigned to Baker Oil Tools, Inc.. Invention is credited to Talmadge L. Crowe.
United States Patent |
3,586,464 |
Crowe |
June 22, 1971 |
SUCKER ROD COMPENSATOR FOR SUBSURFACE WELL PUMPS
Abstract
A compensator located in a sucker rod string adjacent to a deep
well pump and embodying upper and lower telescopically arranged
devices, one of said devices being a piston mechanism, the other of
the devices being a cylinder mechanism in which the piston
mechanism is telescopically arranged. A liquid supply trapped in
the cylinder mechanism and originating from the well bore fluid
transmits linear motion between the piston and cylinder mechanisms,
the liquid being forced in small increments past the piston
mechanism out of the cylinder mechanism of each upward stroke of
the sucker rod string and compensator, allowing the upper device to
shift in step-by-step fashion progressively relatively upwardly of
the lower device to increase the overall length of the compensator,
until the travelling valve of the pump taps against the standing
valve of the pump. When this occurs, the upper device overrides or
moves slightly downward of the lower device, causing fluid in the
well bore to flow into the cylinder mechanism through a check valve
in the piston mechanism to incrementally replenish the liquid
supply trapped in the cylinder mechanism.
Inventors: |
Crowe; Talmadge L. (Houston,
TX) |
Assignee: |
Baker Oil Tools, Inc. (City of
Commerce, CA)
|
Family
ID: |
25382847 |
Appl.
No.: |
04/883,564 |
Filed: |
December 9, 1969 |
Current U.S.
Class: |
417/434; 417/260;
417/448 |
Current CPC
Class: |
F04B
47/00 (20130101) |
Current International
Class: |
F04B
47/00 (20060101); F04b 003/00 (); F04b 047/08 ();
F04h 021/00 () |
Field of
Search: |
;417/554,448,432,396,260 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gerin; Leonard H.
Claims
I claim:
1. In a compensator for varying the effective length of a rod
string in a well bore: an outer cylinder device; an inner piston
device in said cylinder device and shiftable longitudinally with
respect thereto; said cylinder device and piston device providing a
chamber therebetween adapted to contain a liquid for transmitting
longitudinal motion between said devices; a portion of one of said
devices to one side of said chamber being communicable with the
well bore; and means for allowing escape of a portion of the liquid
from the chamber into the well bore to produce an increase in the
overall length of said devices.
2. In a compensator as defined in claim 1; and means for returning
liquid from the well bore to said chamber in response to
longitudinal movement of the compensator in the well bore.
3. In a compensator as defined in claim 1; and means for returning
liquid from the well bore to said chamber in response to
longitudinal movement of the compensator in the well bore
comprising a check valve in said piston device permitting liquid to
flow from the well bore to said chamber, but preventing flow of
liquid from said chamber to the well bore.
4. In a compensator as defined in claim 1; said means for allowing
escape of a portion of the liquid from the chamber comprising a
leakage path defined between the exterior of said piston device and
cylinder device.
5. In a compensator as defined in claim 1; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between the exterior of
said piston and cylinder sleeve.
6. In a compensator as defined in claim 1; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between the exterior of
said piston rod and cylinder head.
7. In a compensator as defined in claim 1; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between the exterior of
said piston and cylinder sleeve and a leakage path defined between
the exterior of said piston rod and cylinder head.
8. In a compensator as defined in claim 1; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between the exterior of
said piston and cylinder sleeve; and means for returning liquid
from the well bore to said chamber in response to the longitudinal
movement of the compensator in the well bore comprising a check
valve in said piston device permitting liquid to flow from the well
bore to said chamber, but preventing flow of liquid from said
chamber to the well bore.
9. In a compensator as defined in claim 1; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between the exterior of
said piston rod and cylinder head; and means for returning liquid
from the well bore to said chamber in response to the longitudinal
movement of the compensator in the well bore comprising a check
valve in said piston device permitting liquid to flow from the well
bore to said chamber, but preventing flow of liquid from said
chamber to the well bore.
10. In a compensator as defined in claim 1; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between the exterior of
said piston and cylinder sleeve and a leakage path defined between
the exterior of said piston rod and cylinder head; and means for
returning liquid from the well bore to said chamber in response to
the longitudinal movement of the compensator in the well bore
comprising a check valve in said piston device permitting liquid to
flow from the well bore to said chamber, but preventing flow of
liquid from said chamber to the well bore.
11. In apparatus wherein a pump is disposed in a well bore, said
pump including a standing valve mechanism and a travelling valve
mechanism thereabove reciprocable by a string of sucker rods for
elevating the well production to the top of the well bore, the
combination therewith of a compensator in the sucker rod string
comprising an upper device connected to an adjacent sucker rod
member and a lower device connected to the travelling valve
mechanism; one of said devices being an outer cylinder device; the
other of said devices being a piston device in said cylinder device
and shiftable longitudinally with respect to said cylinder device;
said cylinder device and piston device providing a chamber
therebetween adapted to contain a liquid for transmitting
longitudinal motion between said piston device and cylinder device
to effect reciprocation of said travelling valve mechanism toward
and from said standing valve mechanism; a portion of one of said
cylinder device and piston device to one side of said chamber being
communicable with the well bore; and means for allowing escape of a
portion of the liquid from the chamber into the well bore to effect
relative shifting of said upper device upwardly along said lower
device to increase the overall length of said upper and lower
devices and bring the travelling valve mechanism to a bottom
position closer to said standing valve mechanism.
12. In apparatus as defined in claim 11; and means for returning
liquid from the well bore to said chamber in response to
longitudinal movement of the compensator in the well bore.
13. In apparatus as defined in claim 11; and means for returning
liquid from the well bore to said chamber in response to
longitudinal movement of the compensator in the well bore
comprising a check valve in said piston device permitting liquid to
flow from the well bore to said chamber, but preventing flow of
liquid from said chamber to the well bore.
14. In apparatus as defined in claim 11; said means for allowing
escape of a portion of the liquid from the chamber comprising a
leakage path defined between said piston device and cylinder
device.
15. In apparatus as defined in claim 11; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between said piston and
cylinder sleeve.
16. In apparatus as defined in claim 11; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable along said sleeve and a
piston rod connected to said piston and slidable in and along said
head; said means for allowing escape of a portion of the liquid
from the chamber comprising a leakage path defined between said
piston rod and cylinder head.
17. In apparatus as defined in claim 11; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between said piston and
cylinder sleeve and a leakage path defined between said piston rod
and cylinder head.
18. In apparatus as defined in claim 11; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between said piston and
cylinder sleeve; and means for returning liquid from the well bore
to said chamber in response to the longitudinal movement of the
compensator in the well bore comprising a check valve in said
piston device permitting liquid to flow from the well bore to said
chamber, but preventing flow of liquid from said chamber to the
well bore.
19. In apparatus as defined in claim 11; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable along said sleeve and a
piston rod connected to said piston and slidable in and along said
head; said means for allowing escape of a portion of the liquid
from the chamber comprising a leakage path defined between said
piston rod and cylinder head; and means for returning liquid from
the well bore to said chamber in response to the longitudinal
movement of the compensator in the well bore comprising a check
valve in said piston device permitting liquid to flow from the well
bore to said chamber, but preventing flow of liquid from said
chamber to the well bore.
20. In apparatus as defined in claim 11; said cylinder device
including a cylinder head and a cylinder sleeve; said piston device
including a piston slidable along said sleeve and a piston rod
connected to said piston and slidable in and along said head; said
means for allowing escape of a portion of the liquid from the
chamber comprising a leakage path defined between said piston and
cylinder sleeve and a leakage path defined between said piston rod
and cylinder head; and means for returning liquid from the well
bore to said chamber in response to the longitudinal movement of
the compensator in the well bore comprising a check valve in said
piston device permitting liquid to flow from the well bore to said
chamber, but preventing flow of liquid from said chamber to the
well bore.
Description
The present invention relates to subsurface well pumps, and more
particularly to devices for insuring the proper length of stroke or
travel of a pump plunger in its companion barrel.
In a deep well pump operated by a string of reciprocating sucker
rods, the efficiency of the pump is oftentimes comparatively low
because of the inability of the travelling valve of the pump to
shift downwardly toward the standing valve of the pump to a
sufficient extent. Preferably, the travelling valve should move on
its downstroke to an extent in which it is disposed closely
adjacent to the standing valve of the pump. Such close spacing in
not obtained in many cases for a variety of reasons, including
improper initial spacing between the travelling and standing valves
upon assembly of a pumping apparatus, or variations in the spacing
between the travelling valve and standing valve caused by changes
in fluid levels in the well, the temperature of the fluid in the
well, and in the density of the fluid being pumped. The incomplete
or insufficient lowering of the travel valve on the downstroke
results in reduction in efficiency, ranging from complete inability
to pump the fluid caused by trapping of gas between the travelling
and standing valves (a gas lock condition) to no loss of efficiency
whatsoever, which would occur where the pump barrel fills
completely with an incompressible fluid of consistent density, a
condition occurring rarely in oil and gas well operations.
When pumping a compressible fluid, a portion of the downstroke is
consumed in compressing a fluid below the travelling valve to a
pressure somewhat greater than the hydrostatic pressure of the
column of fluid in the tubing above the travelling valve. At this
point, the travelling valve will open and fluid previously trapped
or contained between the travelling valve and standing valve will
be transferred relatively upwardly through the travelling valve for
the remainder of the downstroke. It is evident that the amount of
downstroke consumed before the travelling valve opens can vary
considerably, since it depends on the hydrostatic pressure, the
pump intake pressure, flow restriction, and the compressibility of
the fluids entering the pump. It is only after the travelling valve
opens that effective work can be performed. Accordingly, to obtain
maximum possible pump volumetric efficiently, it is necessary that
the unswept volume of the pump be held to a minimum; that is, at
the bottom of the stroke, the travelling valve should be as close
to contacting or bottoming out on the standing valve cage as is
practical.
To avoid the above-noted difficulties, the sucker rod string can be
adjusted in length to cause the travelling valve or pump plunger to
actually pound against the barrel at the bottom of each stroke.
This procedure may produce a high volumetric efficiency, but it
normally occasions premature fatigue failure of the pumping system
in general and of the rod string in particular, producing high and
somewhat prohibitive operating expenses.
The aforenoted difficulties are overcome in a sucker rod
compensator as illustrated in U.S. Pat. No. 3,376,826. In that
compensator, the length of the sucker rod string is automatically
changed to the extent required to insure positioning of the
travelling valve of the pump plunger closely adjacent to the
standing valve of the pump at the bottom of the travelling valve
stroke. That particular compensator transmits the reciprocation of
the sucker rod string to the pump through a trapped body of a clean
fluid, such as a body of oil, which is maintained separate from the
well bore fluid. The clean fluid is trapped, despite the fact that
parts of the compensator must move linearly with respect to each
other, by the use of elastomer seals. Such seals have a short life,
and also allow gas in the formation fluid to enter the chamber
containing the clean fluid and commingle with the trapped clean
fluid, resulting in the trapped fluid becoming partially
compressible, and thereby reducing the efficiency of the sucker rod
compensator. In addition, the structure of the tool is such tat it
is relatively long and comparatively costly to manufacture.
By virtue of the present invention, a sucker rod compensator is
provided that uses the well bore fluid itself as a medium for
transferring the linear motion of the sucker rod to the pump.
Elastomer seals, slidably sealing against relatively movable parts,
are eliminated completely, and any gases that might leak into the
well bore fluid trapped in the compensator are automatically
purged. The automatic increase in length of the compensator is
accomplished by permitting a slight leakage of the trapped fluid
therein past a control piston disposed in a cylinder portion of the
compensator receiving the piston, and such fluid may also be
permitted to leak slightly past a sleeve constituting a portion of
a head end of the cylinder in which the piston portion of the
mechanism is telescopically received. When the compensator has
achieved its maximum overall length as a result of its automatic
elongation, such length is retained by an automatic replenishing of
the well bore fluid that has previously leaked from the cylinder
mechanism, the well fluid being caused to automatically flow back
thereinto.
By virtue of the present invention, an improved compensator is
provided that overcomes the disadvantages of the prior device
illustrated in U.S. Pat. No. 3,376,826, it has a significantly
shorter overall length, a substantially lower manufacturing cost,
and a longer useful life.
This invention possesses many other advantages, and has other
purposes which may be made more clearly apparent from a
consideration of a form in which it may be embodied. This form is
shown in the drawings accompanying and forming part of the present
specification. It will now be described in detail, for the purpose
of illustrating the general principles of the invention; but is is
to be understood that such detailed description is not to be taken
in a limiting sense.
Referring to the drawings:
FIG. 1 is a diagrammatic view of a sucker rod operated pumping
system for pumping fluid from the well bore;
FIGS. 2a and 2b together constitute a longitudinal section and side
elevational view through a sucker rod compensator embodied in the
system shown in FIG. 1, FIG. 2b being a lower continuation of FIG.
2a;
FIGS. 3a and 3b are a diagrammatic section through the rod
compensator of FIGS. 2a and 2b in combination with a pump, FIG. 3b
being a lower continuation of FIG. 3a.
As disclosed in the drawings, a string of tubing A is disposed in a
well bore B and has a known type of deep well pump C therewithin
that includes a barrel 10 suitably secured or anchored in the
tubing string, and a plunger 11 reciprocable in the barrel through
upward and downward movement of a sucker rod string 12 connected
thereto. As is well known, the sucker rod string may be connected
to a suitable mechanism for effecting its reciprocation, such as a
walking beam mechanism D, hydraulic pumping mechanism, or the
like.
The outer barrel 10 of the pump C has a standing valve (FIG. 3b),
including a valve seat 13 through which well bore fluid can flow
upwardly into the barrel, downward flow of the fluid from the
barrel being prevented by a standing valve element 14 adapted to
move downwardly into engagement with the seat. The pump plunger 11
is movable upwardly and downwardly in the barrel, containing a
travelling valve device in the form of a ball valve element 15
adapted to shift downwardly into engagement with its companion seat
16 surrounding the inlet 17 of the plunger. During the downstroke
of the plunger 11, its travelling valve 15, 16 moves downwardly
toward the standing valve 13, 14, the latter closing and the fluid
thereabove passing through the seat 16 of the travelling valve,
unseating its valve element 15 in an upward direction and then
passing upwardly through the openings 20 in a plunger partition 21
to a position thereabove.
When the plunger 11 is moved upwardly, its valve element 15 engages
its seat 16, causing the plunger to lift the entire fluid column in
the tubing string A and discharge a portion of it at the top of the
well bore. The fluid in the plunger itself can pass through its
upper ports 22 into the barrel 10 thereabove and through the upper
ports 23 in the guide portion 24 of the barrel through which the
plunger rod 25 is reciprocable. During the upward movement of the
plunger 11, its travelling valve 15, 16 moves upwardly away from
the standing valve 13, 14, the valve element 14 of the latter
moving off its seat 13 and allowing well bore fluid to flow
upwardly through the seat 13 and through openings 18 in a barrel
partition 19 into the barrel.
For maximum volumetric efficiency, it is desirable for the plunger
11 to move on its downstroke to a position in which its travelling
valve 15, 16 is closely adjacent to the standing valve 13, 14 of
the barrel. Accordingly, on the upstroke, the plunger 11 will
partake of a maximum effective travel in the barrel 10 and will
lift the maximum quantity of fluid that may have passed through the
travelling valve seat 16 into the plunger and outer barrel
thereabove. If the fluid contains a substantial quality of gas,
assurance is had that the gas between the travelling and standing
valves will be compressed sufficiently on the downstroke of the
plunger to overcome the hydrostatic head of fluid in the tubing
string A, for the purpose of unseating the travelling valve element
15 and causing the fluid above the standing valve 13, 14, including
the gas therein, to travel upwardly into and through the plunger
11. If the travelling valve 15, 16 does not move downwardly to its
maximum extent, then gas locking might occur under some conditions
in which the travelling valve does not open on its downstroke, the
plunger 11 on its upstroke merely allowing the trapped gas to
expand, the standing valve element 14 also remaining in its closed
condition, with no additional fluid from the well bore flowing past
it and into the pump barrel 10.
To offer assurance that the plunger 11 and the travelling valve 15,
16 will shift downwardly to the desired maximum extent, an
automatically adjustable compensator 27 is included in the sucker
rod string 12, as between the plunger rod 25 and a sucker rod
section 28. As disclosed, the plunger rod 25 is preferably secured
to a suitable length of polished rod 29, which, for example, may be
30 feet long, and this polished rod is attached directly or through
a short pony rod (not shown) to the threaded pin 30 of a bottom sub
or head 50 constituting a portion of the compensator apparatus. The
threaded pin 32 of a top sub 51 of the compensator apparatus is
secured to the sucker rod section 28 of the string 12, the sucker
rod string 12 extending to the top of the hole. The top sub 51 is
threadedly secured to a piston rod 52 depending therefrom and
having a lower threaded pin 53 threadedly securing it to a piston
54, the rod and piston being relatively reciprocable in a cylinder
55 composed of several sections. Thus, the cylinder includes the
bottom sub section 50, the upper end of which is threadedly secured
to a lower sleeve section 56, which is, in turn, threadedly secured
to an upper sleeve section 57 providing an annular cylinder head
portion 58 including an inwardly directed flange or seat 59 against
which is held a sleeve 60, which is retained in the upper sleeve
section and against the flange by a sleeve retainer 61 threaded
into the upper end of the upper sleeve section 57. The sleeve 60
makes a sliding, sealing fit with the piston rod 52, allowing the
latter to shift longitudinally relative to the sleeve, and also
permitting a very slight fluid leakage past the piston rod 52.
Leakage of fluid past the exterior of the metal sleeve 60 is
prevented by a suitable side seal ring 62 disposed in an internal
circumferential groove 63 in the upper sleeve section 57 and
sealingly engaging the periphery of the sleeve 60. In the event
that rotary motion or torque is to be transmitted through the
compensator to the pump, a clutch 64 is provided of the dog type.
As disclosed, axial lugs or clutch teeth 65 are integral with and
depend from the top sub 51, meshing with upwardly directed teeth or
dogs 66 integral with and extending upwardly from the sleeve
retainer 61.
The fluid in the well bore is permitted to enter the annular
cylinder space 67 between the piston 54 and piston rod 52, on the
one hand, and the cylinder 55 and its cylinder head 58, on the
other hand, through side ports 68 in the bottom sub or head 50
extending from the exterior thereof to a central passage 69 in the
latter, such passage communicating with the interior of the lower
sleeve section 56 below the piston 54, and with a passageway 70
extending from the annular cylinder space 67 above the piston to
the cylinder sleeve 56 below the piston 54. Such passageway
includes a valve seat 71 held against a downwardly facing shoulder
72 in the piston by a seat retainer 73 threaded into the piston,
this valve seat being engaged by a ball valve element 74 therewith,
which bears against a spring seat 75 receiving the lower end of a
helical compression spring 76, the upper end of which bears against
a downwardly facing piston shoulder 77. When the valve ball 74 is
elevated from its seat, fluid can flow upwardly through the seat
retainer 73, valve seat 71, and around the ball valve element 74
into the passage through the piston thereabove, flowing through the
spring 76 and into a lateral passage branch 78 that opens into the
annular space 67 between the piston and piston rod 54, 52 and the
cylinder 55. Fluid is prevented from passing downwardly through the
passageway 70 by the downward engagement of the ball valve 74 with
its companion valve seat 71.
During the upstroke of the sucker rod string 12, the piston rod 52
and piston 54 tend to move relatively upwardly in the cylinder 55.
However, the annular cylinder space 67 is filled with a liquid,
which initially may be oil or the well bore liquid, such liquid
being trapped in the annular cylinder space between the piston 54
and the upper cylinder head portion 58 of the compensator, and
transmitting the linear motion through the piston and piston rod
mechanism 54, 52 to the cylinder 55. Fluid in substantial quantity
is prevented from leaking from the annular cylinder space 67 on
each upward stroke of the rods 12 by a plurality of piston rings 79
mounted in ring grooves 80 in the piston and sealingly engaging the
inner wall of the lower sleeve section 56 of the cylinder. These
piston rings may be of any suitable type. As an example, they each
may be of the split type, being deflectable laterally in the
grooves 80 to conform to any irregularities that may be present in
the wall of the cylinder sleeve section. Although they seal
effectively against the wall of the cylinder sleeve section, they
still permit a slight leakage or bypassing of fluid past the
multiplicity of piston rings 79 from the cylinder space 67
downwardly past the piston 54 into the cylinder below the piston.
The metal sleeve 60, which has working clearance only with the
piston rod 52, may also permit a slight passage of fluid from the
annular cylinder space 67 in an upward direction past the sleeve 60
during the upstroke of the sucker rods 12 and rod compensator 27
forming a part thereof. The extent of fluid displacement form the
annular cylinder space 67, however, is relatively small during each
upward stroke of the string of sucker rods, compensator and
travelling portion 11 of the pump.
In the use of the apparatus illustrated, the pump assembly C is
connected to the polished rod 29, the latter being connected to the
lower sub 50 of the compensator apparatus 27, the upper sub 51
being connected to the sucker rods 12 thereabove. A sufficient
length of polished rod 29 is provided to maintain tension on the
rod compensator 27 and to overcome friction of the pump plunger 11
on its downstroke. This assembly is run in the well bore on the
sucker rod string 12, the pump being forced into its seat 90 in the
tubing string A upon reaching bottom. After the pump has been
seated, the rod string 12 is spaced out and the usual polish rod 91
at the top of the hole is appropriately hung on the power mechanism
D at the top of the hole, so that when pumping is started, the pump
will be tapping bottom very lightly; that is to say, the plunger 11
will be tapping the barrel 10 lightly, or a coupling 92 on the
plunger rod 25 will be tapping the barrel guide 24 lightly. At this
time, it may be assumed that the compensator is fully telescoped,
such as disclosed in FIGS. 2a and 2b, the clutch elements 65, 66
being engaged and permitting torque to be transmitted through the
compensator 27, if required.
The power mechanism D at the top of the hole is then caused to
reciprocate, effecting reciprocation of the sucker rods 12, to
shift the plunger 11 in the barrel 10. When the pumping operation
starts, the tubing string A will elongate as a result of increased
hydrostatic pressure therewithin, due to the rising column of
liquid and also due to a decreased hydrostatic pressure or head in
the well bore annulus 100 surrounding the tubing string, reducing
the buoyant effect of the liquid in the well casing on the tubing
string. In addition, the initiation of the pumping operation will
increase the average temperature of the tubing string A, causing it
to elongate, and such increased temperature will also tend to cause
the sucker rod string 12 to elongate. However, the rod string 12
may also shorten as a result of the buoyancy of the liquid within
the tubing string A. The overall net result is that the initial
relative spacing of the travelling valve 15, 16 and standing valve
13, 14 of the pump will start changing with the first stroke of the
pump, and will continue changing throughout the life of the well,
the changes also being due to changes of density of the fluid in
the well bore passing through the pump. In a typical case, the
travelling valve may be spaced above the standing valve at the
bottom of each plunger stroke.
The rod compensator 27, within he limits of the relative movement
that can take place between the cylinder and piston structure 55,
54, 52, automatically compensates for the changing well conditions.
On the upstroke of the sucker rods 12, the upward force required to
lift the fluid in the tubing string A is being transmitted from the
piston 54 through the load transmitting liquid in the annular
chamber or cylinder 67 to the upper cylinder head 58, the piston
and piston rod structure and the cylinder moving essentially
upwardly as a unit to elevate the travelling valve 15, 16 with
respect to the standing valve 13, 14. The pressure developed in the
trapped liquid within the annular cylinder space 67 will cause some
of the liquid to bleed past the multiplicity of piston rings 79 and
also through the small working clearance space between the metal
sleeve 60 and piston rod 52 completely out of the compensator 27
and into the well bore. Only a very small amount of liquid will
actually be displaced from the annular cylinder 67, since the
clearance space between the piston rod 52 and metal sleeve 60
amounts to a relatively small choke orifice in area, which is also
true of the amount of liquid that can leak past the multiplicity of
piston rings and into the bottom sub or head 50, and then out
through its ports 68 into the well bore. As a result, the upward
shifting of the piston rod 52 and piston 54 relative to the
cylinder 55 is very small during each upward stroke of the
mechanism. As an example, only sufficient liquid or other fluid
will be able to transfer through the sleeve 60 and past the piston
54 and piston rings 79 during each complete upward stroke of the
piston rod and piston as to result in an elevation of the piston
and piston rod within the cylinder by approximately 0.05 inches. In
other words, the rod compensator 27 will extend or elongate a
comparatively short distance on each upward stroke of the sucker
rods 12, the rod compensator 27, and pump C connected thereto. On
the downstroke of the sucker rods 12, rod compensator 27 and pump
C, essentially no transfer of liquid will take place, the trapped
liquid in the cylinder space retaining the cylinder 55 in its
relative position along the piston rod 52 and piston 54.
The elongation of the rod compensator 27 will continue on each
upstroke, fluid transfer from the cylinder space 67 taking place to
a small degree, allowing the overall length of the rod compensator
to increase by small increments, which, in the example given above,
may be 0.05 inches per upstroke. The progressive incremental
elongation of the rod compensator will actually result in the
plunger 11 and the travelling valve 15, 16 occupying a lower
position in the barrel 10 on each subsequent downstroke of the pump
mechanism, until the pump valve rod coupling 92 engages or taps the
guide 24, or the plunger 11 taps a shoulder 95 in the pump
barrel.
When the tapping commences at the bottom of each stroke of the pump
mechanism, the piston rod 52 and piston 54 will shift downwardly
relative to the cylinder 55 by a short distance, because of the
fact that the string of sucker rods 12 thereabove can still move
downwardly by a short distance, which, in the example given above,
will be 0.05 inches. This will result in the piston 54 moving
downwardly within the cylinder 55 by an incremental distance (0.05
inches), forcing the fluid in the cylinder below the piston 54
upwardly through the return passage 70, after unseating the check
valve 74, and flowing into the annular cylinder space 67 above the
piston, thereby effecting a resupply of liquid to such cylinder
space. As a result of the downward shifting of the piston 54 along
and within the cylinder 55 by the short distance, the overall
length of the rod compensator 27 is decreased, and this decrease is
equivalent to the amount of its elongation on each upstroke.
On the next upstroke of the sucker rod string 12, including the
compensator 27 and the travelling valve 15, 16 of the pump, the rod
compensator will again elongate by virtue of the transfer of a
small amount of liquid from the annular cylinder space 67 past the
piston 54 and its piston rings 79 into the cylinder below the
piston, and also upwardly through the clearance space between the
sleeve 60 and piston rod 52 into the well bore thereabove. However,
on the downstroke, a light tapping of the coupling 92 against the
valve rod guide 24, or of the plunger 11 against the barrel 10,
will again occur, the compensator 27 shortening again by the fact
of the downward movement of the piston within the cylinder, causing
unseating of the check valve 74 and flow of a slight amount of well
bore liquid through the passageway 70 back into the annular
cylinder space 67.
As a result, the rod compensator 27 elongates and contracts,
depending on the variable conditions in the well bore, Any excess
stroke that will bring the valve rod coupling 92 into contact with
the valve rod guide 24 will arrest further downward movement of the
cylinder structure 55, resulting in a slight downward movement of
the piston structure 52, 54 and transfer of fluid from below the
piston 54 upwardly through the check valve 74, 71 into the annular
cylinder space 67, to automatically shorten the compensator 27 and
the effective length of the entire sucker rod string 12. Assurance
is had that the plunger 11 will be lowered within its companion
barrel 10 to the maximum desired extent on each downstroke of the
sucker rods 12, insuring a complete upward sweep of the pump barrel
10 by the plunger on its upstroke.
Not only is assurance had that a maximum upstroke of the plunger 11
and the barrel 10 is secured, but the fact that the plunger is
shifted downwardly to its lowermost position on each downstroke
insures against gas locking, since the bringing of the travelling
valve 15, 16 closely adjacent to the standing valve 13, 14 will
insure sufficient compression of the gas between the two valves as
to overcome the hydrostatic head of the fluid in the tubing string
A above the travelling valve, effecting opening of the latter and
upward passage of gas into the plunger 11. Accordingly, upon the
upstroke of the plunger 11 and the upward shifting of the
travelling valve 15, 16 away from the standing valve 13, 14, the
latter will be opened, and additional fluid, including gas, if
present, will unseat the travelling valve element 14 and pass into
the plunger 11 and the barrel 10 thereabove.
The compensator 27 automatically adjusts the plunger 11, so that it
will merely lightly tap the barrel 10. In the example given above,
it is only necessary to effect a downward travel of the piston rod
and piston within the cylinder structure of about 0.05 inches to
relieve the engaging force of the plunger on the barrel, and such
light tapping is insufficient to effect any fatiguing of the
pumping system and of the rod string. This light tapping is to be
distinguished from the pounding action that has occurred heretofore
when sucker rod lengths were used as to cause striking of the
plunger mechanism 11 against the barrel 10.
The compensator 27 avoids the necessity for trapping a body of
clean fluid in the annular cylinder space 67, using the fluid in
the well bore as makeup fluid when the compensator has
automatically elongated to its maximum length. The avoidance of a
trapped and self-contained body of clean fluid permits the
compensator to be made of a shorter overall length and manufactured
at a lower cost than the prior device disclosed in the above
patent. Moreover, there are no elastomer seals between the
relatively movable parts of the compensator apparatus. Instead,
metal-to-metal seals are employed, which have a long life. Such
seals may permit gas to leak thereby and into the confined cylinder
space or chamber 67, but such gas leakage does not adversely affect
the operation of the apparatus since the gas is constantly being
purged from the cylinder space 67 by being permitted to leak past
the piston rings 79, and also through the slight orificelike
clearance space between the piston rod 52 and metal sleeve 10.
* * * * *