Note: Descriptions are shown in the official language in which they were submitted.
CA 02310198 2008-04-24
Hold Down Apparatus for Progressing Cavity Pump
Field of the Invention
This invention relates to progressing cavity pumps and, in particular, a
progressing cavity
pump moveable through production tubing in a well and a hold down apparatus
for holding
the pump in set position downhole.
Background of the Invention
A progressing cavity pump is a well known pump, frequently called a "Moineau"
pump, that
has an elastomeric outer element or stator with a helical inner surface. A
metal rotor having a
helical exterior inserts within the stator.
Progressing cavity pumps of this type are used for many purposes, particularly
for pumping
viscous liquids. These pumps are also used as oil well pumps. When used as an
oil well
pump, the stator is secured to the lower end of the well tubing, then lowered
into the casing of
the well. The rotor is secured to the lower end of the sucker rod and lowered
through the
tubing to position the rotor inside the stator. The sucker rod is rotated by
means of a rotary
power source at the surface. U.S. Pat. No 2,267,459 shows one type of
installation for an oil
pump.
One disadvantage is that if the stator needs to be serviced, the string of
tubing must be pulled.
This is time consuming and requires special equipment. U.S. Pat. No. 3,347,169
shows a
progressing cavity pump installation wherein the stator is lowered through the
tubing on a
flexible drive cable and secured by a seat.
U.S. Pat. No. 4,592,427 shows a progressing cavity pump installation that is
lowered through
the tubing on sucker rods and secured by a seating nipple and torque reactor
cup arrangement.
DM S Legal\044740\000 I 0\2859577v I
CA 02310198 2000-05-29
Summary of the Invention
The progressing cavity pump of the present invention is lowered through the
production tubing
on a rod string. The pump is releasably latched down hole and held against
rotation. A hold
down apparatus provides for correct positioning of the rotor within the stator
of the pump.
In accordance with a broad aspect of the present invention, there is provided
in a hold-down
apparatus for a progressing cavity pump of the type having a stator, a helical
rotor locatable in
the stator and rotated by a string of rods, the pump being insertable in a
bore of a tubing string by
carriage on a rod string, the hold-down apparatus comprising: a sub connected
to a lower end of
the tubing, the sub having a bore open to the bore of the tubing string and
including a pump-
engaging member; and a hold down member at the lower end of the stator for
insertion into the
sub. the hold down member having a bore therethrough with a tag bar extending
thereacross and
including a tubing-engaging member for engaging with the pump-engaging member
of the sub
and for abutting against the pump-engaging member to hold the stator against
rotation relative to
the sub.
The tubing-engaging member and the pump-engaging member are adapted to coact
to engage the
hold down member to the sub. In one embodiment, the pump-engaging member is
any member
that provides for positive engagement between the hold down member and the
sub. In one
embodiment, the pump-engaging member is an annular raised portion formed to
releasably
engage the tube-engaging member which is an annular recess on the hold down
member. To
facilitate engagement between the annular recess and the annular raised
portion, the tubing-
engaging member is preferably a collet including a plurality of spaced-apart
fingers, each finger
having a recess formed thereon adapted to engage over the annular raised
portion. The pump-
engaging member can further include a projection extending into the bore of
the bore of the sub.
The projection is adapted to fit between the fingers and act as a stop wall
against which the
fingers abut to prevent rotation of the tubing-engaging member within the pump-
engaging
member.
2
CA 02310198 2000-05-29
The hold down apparatus can further include a seal for sealing between the sub
and the hold
down member to prevent passage of fluid therebetween. In one embodiment, the
hold down
apparatus includes an upper seal positioned above the stator and adapted to
seal between the
stator, or an extension thereof, and the tubing. The upper seal seals against
passage of fluids and
also prevents material, such as formation solids, from becoming jammed between
the stator and
the tubing string inner wall.
Brief Description of the Drawings
A further, detailed, description of the invention, briefly described above,
will follow by reference
to the following drawings of specific embodiments of the invention. These
drawings depict only
typical embodiments of the invention and are therefore not to be considered
limiting of its scope.
In the drawings:
Figure 1 is a vertical section through a portion of production tubing
including in a set position
therein a progressing cavity pump according to the present invention and shown
in a partially cut
away configuration and with the rotor in pumping position within the stator;
Figure 2 is a view of the tubing and progressing cavity pump of Figure 1 with
the rotor removed
from the stator and in flush-by position for pulling uphole;
Figure 3 is a sectional view along line 3-3 of Figure 1;
Figure 4 is a sectional view along line 4-4 of Figure 1;
Figure 5 is a vertical section through a pump hold down inember useful in the
present invention;
and
Figure 6 is a vertical section through a tubing hold down sub useful in the
present invention.
3
CA 02310198 2008-04-24
Description of the Preferred Embodiments of the Invention
Referring to Figures 1 and 2, a portion of a string of production tubing is
generally indicated
at 11. Tubing 11 extends in a well usually through casing (not shown). A PCP
pump hold
down section of tubing, generally indicated at 13, is secured at the lower end
of the tubing.
Section 13 includes a tubing seal sub 15 and a tubing-engaging hold down sub
16 connected
by a string of tubing l la. Section 13 is formed to releasably engage and form
a seal about a
progressing cavity pump 17 (shown in the set position in Figures 1 and 2). The
subs 15 and
16 and tubing strings 11 and 11 a are connected in any durable way such as,
for example, by
standard threaded connections.
Tubing seal sub 15 and tubing hold down sub 16 are each formed with a diameter
that is less
than the diameter dl of tubing 11 and about the same size or slightly larger
than the outer
diameter of pump 17. Referring for greater detail to Figures 3 and 6, tubing
hold down sub
16 includes an annular raised portion 18 having an upper ramped shoulder 18a
and a lower
stop shoulder 18b. Raised portion 18 acts to hold the pump down in position in
tubing
section 13, as will be described hereinafter. Anti-rotation projections 19a,
19b are mounted,
as by welding, in the bore of tubing hold down sub 16. Anti-rotation
projection 19a is
formed as a bar that extends across the bore of tubing hold down sub 16.
Projections 19b
extend out a short distance into the bore of sub 16. The projections must
withstand
significant shearing forces and therefore are preferably welded in ports 16a
formed through
the wall of tubing sub 16. Anti-rotation projections 19a, 19b act to prevent
rotation of the
pump when it is engaged in the tubing section 13 and assist in the positioning
and support of
the pump, as will be described hereinafter.
Pump 17 includes a stator 20, which is elastomeric and has a helical inner
bore 21. A hold-
down member 25 is secured to the lower end of stator 20, while the upper end
of stator 20 is
secured to a flush-by housing 27.
Flush-by housing 27 is a tubular member with an outer diameter approximately
equal to that
of stator 20. Flush-by housing 27 includes a collar 28 at the upper end
thereof. Collar 28 is
mounted in flush-by housing, for example, by threaded engagement, welds or by
being formed
DMSLega1\044740\00010\2859577v1 4
CA 02310198 2000-05-29
integral therewith. Referring also to Figure 4, collar 28 defines a central
aperture 28a
therethrough.
The pump's helical rotor 29 and stator 20 are of conventional design. Rotor 29
is adapted to be
located in the stator and has a length greater than that of the stator. Rotor
29 is connected to a
rod string 31 by a pick-up coupling 33. Rod string 31 is of a conventional
design such as, for
example, including a plurality of rigid sucker rods extending to surface or a
continuous rod. Rod
string 31 extends loosely through aperture 28a providing clearance for well
fluids to be pumped
through the aperture. Coupling 33 is larger in diameter than the minimum
diameter across
aperture 28a and, therefore, cannot pass therethrough. Rotor 29 can be moved
by rod string 31
between a position within the stator and a position within the flush-by
housing 27 but is
prevented from being removed from the flush-by housing 27 by abutment of
coupling 33 against
collar 28. Flush-by housing 27 is of a length to permit rotor 29 to be fully
withdrawn from stator
bore 21.
Seals 36, such as 0-rings, are mounted about outer surface of flush-by housing
27 and are sized
such that they will seal against inner surface of tubing seal sub 15. Seals 36
prevent formation
solids from migrating down and becoming jammed between the pump and tubing 13.
The upper
end of flush-by housing 27 has formed thereon a fishing profile 38 for
engagement by a fishing
tool (not shown), should that be required.
Hold down member 25 is attached at the lower end of stator 20 and has a bore
40 therethrough
for passage of well fluids. A tag bar 41, which can be formed as a bar or
plate, extends across
bore 40, while permitting passage of fluids therepast through the bore. Tag
bar 41 is a known
distance from stator 20 and permits proper positioning of rotor 29 within
stator.
Referring also to Figure 5, hold down member 25 includes a collet having four
fingers 42. Each
finger has a recess 44 formed on its outer surface. Together the recesses 44
form an annular
recess on the collet adapted to engage over annular raised portion 18. Fingers
42 each have
tapered leading edges 42a that facilitate passing over the raised portion.
However, recesses 44
each have an angular shoulder 44a that engages against the lower shoulder 18b
of raised portion
5
CA 02310198 2000-05-29
18, creating resistance to fingers 42 being pulled upwardly out of engagement
with the raised
portion.
Fingers 42 are spaced apart and therebetween define slits 46. Slits 46 are
sized to accommodate
anti-rotation projections 19a, 19b. Sides 42b of the fingers are inclined to
facilitate movement of
fingers 42 past the projections.
Seals 48, such as 0-rings, are mounted about the outer surface of hold down
member 25. The
seals are sized such that they will seal against inner surface of tubing hold
down sub 16.
As will be appreciated, hold down member 25 and seals 36 of the flush-by
housing are spaced
apart a distance selected to correspond with the distance between tubing seal
sub 15 and tubing
hold down sub 16.
In use, section 13 is secured to the lower end of a tubing string 11 and the
entire string is lowered
into a well. After the tubing 11 is positioned, pump 17 is lowered into the
tubing. Pump 17 is
assembled with hold down member 25 mounted below the stator and flush-by
housing 27
mounted above the stator. Rotor 29 is positioned in flush-by housing 27 and
connected by pick-
up coupling 33 to rod string 31. Pump 17 is supported on rod string 31 with
collar 28 and pick-
up coupling 33 contacting each other. Pump 17 is then lowered on the rod
string through tubing
string 11 into the well. While being lowered into the well, rotor 29 is
positioned within flush-by
housing and does not extend into bore 21 of the stator. Thus, as pump 17 moves
through the
tubing, well fluids can pass up through bore 40 of the hold down member, bore
21, the bore of
flush by housing 27 and out through aperture 28a.
When the pump 17 reaches section 13, seals 48 will pass through the restricted
diameter of
tubing seal sub 15. Relatively little force is required to do this and
generally the weight of the
stator 20, flush-by housing 27 and member 25 will move seals 48 past sub 15.
However, if
necessary, the rotor 29 can be pushed against tag bar 41 to force the pump
through the tubing.
Once seals 48 are past sub 15, fingers 42 will eventually contact projections
19a, 19b. Inclined
edges 42b will cause member 25 and the pump 17 and housing 27 connected
thereto to rotate
6
CA 02310198 2000-05-29
such that fingers pass through the open space between the projections. Member
25 will continue
to move down until leading ends 42a of finger pass over raised portion 18 and
recesses 44
become engaged over the raised portion. In this position, shoulders 44a are
engaged under the
lower shoulder of raised portion 18. When this occurs, the pump is in the set
position wherein
force is required to pull the member 25 out of engagement with the hold down
sub 16 and pump
is prevented from rotating by abutment of fingers 42 against projections 19a,
19b. Seals 36 and
48 are sealed against the inner surfaces of subs 15 and 16, respectively,
sealing against passage
of fluids and preventing materials from becoming jammed between housing 27 and
sub 15. It
will be appreciated that the hold down apparatus is best supported if
projections 19a, 19b are
spaced from raised portion 18 such that when recesses 44 are engaged over
raised portion 18,
member 25 is supported on bar 19a. This arrangement is further preferred as it
permits positive
placement of recesses 44 over raised portion 18 without reliance on sensing
small changes in
string weight at surface.
It will be appreciated that other engaging arrangements between the fingers
and the sub can be
used. For example, instead of raised portion 18 an annular recess can be used
which is engaged
by projections on the fingers.
Once pump 17 is seated within section 13, rod string 31 is lowered to move
rotor 29 into bore 21
of the stator. Rotor 29 is lowered until it abuts against tag bar 41 at which
point the exact
position of the rotor with respect to the stator is known. The rotor is then
raised a selected
distance above tag bar 41 as required to move coupling 33 sufficiently above
stator 20, with
consideration as to rod stretch, to prevent the coupling from abutting
against, and thereby
damaging, the stator. Rod string 31 is then connected to a rotary power source
(not shown) for
rotation.
When the string 31 rotates, it rotates rotor 29 to cause fluid to flow through
hold down member
25, bore 21, housing 27 and aperture 28a. Undesirable rotation of pump 17
during rod string
rotation is avoided by abutment of collet fingers 42 against projections 19a,
19b.
7
CA 02310198 2000-05-29
When it becomes necessary to pull the pump for maintenance, the string 31 is
uncoupled from
the motor at the surface. Then string 31 is raised to cause pick-up coupling
33 to go up and abut
against collar 28. Continued upward force then dislodges collet fingers 42
from engagement
with annular raised portion 18. As an example, in one embodiment of the
invention useful for
3'/2" tubing, a string weight of 1501bs. is useful to set the pump in the
tubing string, while a force
of 20,000 lbs. is needed to unseat the pump.
Seals 36, 40 will also release from their seating position against subs 15 and
16. Once dislodged,
the pump 17 is pulled to surface on rod string 31. Tubing 11 and section 13
remain in the well.
Since it is desired to leave the tubing string downhole for long periods, the
tubing string
components are preferably formed of durable materials. Preferably the raised
portion 18 is
treated as by boronizing to increase its hardness and durability over the
steel used in the
remainder of the tubing string and subs and over the steel used for hold down
member 25. To
reduce scaling and damage to the sub surfaces against which the seals are
positioned, preferably,
these surfaces are polished and hardened as by chroming.
It will be apparent that many other changes may be made to the illustrative
embodiments, while
falling within the scope of the invention and it is intended that all such
changes be covered by the
claims appended hereto.
8
