DOWNHOLE PUMP WITH A PRESSURE SEQUENCING VALVE

POMPE DE FOND DE TROU MUNIE D'UNE SOUPAPE DE SEQUENCE

English Abstract

A downhole pump has a master piston having a first side and a second side in a first piston chamber. The first piston chamber has a first inlet and a second inlet for alternatingly applying fluid pressure to the first side of the master piston to move the piston toward the top of a piston stroke, and to the second side of the master piston to move the piston toward the bottom of the piston stroke. A valve is carried by the master piston that relieves fluid pressure from the respective side of the master piston once the top or bottom of the stroke is reached. There is a sequencing valve with a first state that applies fluid pressure to the first inlet and a second state that applies fluid pressure to the second inlet. The sequencing valve switches between the first state and the second state once a drop in pressure occurs. A slave piston is driven by the master piston in a second piston chamber. The second piston chamber has at least one fluid inlet and at least one fluid outlet.

French Abstract

L'invention concerne une pompe de fond de trou présentant un piston principal qui comporte un premier côté et un second côté dans une première chambre de piston. La première chambre de piston présente une première admission et une seconde admission permettant d'appliquer alternativement une pression de fluide sur le premier côté du piston principal de manière à déplacer le piston vers l'extrémité supérieure d'une course du piston, et sur le second côté du piston principal de manière à déplacer le piston vers l'extrémité inférieure de la course du piston. Le piston principal présente une soupape qui limite la pression en évacuant du fluide depuis le côté respectif du piston principal une fois que le haut ou le bas de la course a été atteint. Une soupape de séquence applique, dans un premier état, une pression de fluide sur la première admission et, dans un second état, une pression de fluide sur la seconde admission, la soupape de séquence passant d'un état à l'autre en cas de chute de pression. Un piston secondaire est entraîné par le piston principal dans une seconde chambre de piston. La seconde chambre de piston présente au moins une admission de fluide et au moins une sortie de fluide.

Claims

6
What is Claimed is:
1. A downhole pump, comprising:
a master piston having a first side and a second side in a first piston
chamber, the first
piston chamber comprising a first inlet and a second inlet for alternatingly
applying fluid
pressure to the first side of the master piston to move the piston toward the
top of a piston
stroke, and to the second side of the master piston to move the piston toward
the bottom of the
piston stroke;
a valve carried by the master piston that relieves fluid pressure from the
respective
side of the master piston once the top or bottom of the stroke is reached;
a sequencing valve having a first state that applies fluid pressure to the
first inlet and a
second state that applies fluid pressure to the second inlet, the sequencing
valve switching
between the first state and the second state once a drop in pressure occurs;
and
a slave piston driven by the master piston in a second piston chamber, the
second
piston chamber having at least one fluid inlet and at least one fluid outlet.
2. The downhole pump of claim 1, wherein the valve is a poppet valve that
opens a flow
passage through the master piston.
3. The downhole pump of claim 1, wherein the slave piston is a double-acting
piston and the
second piston chamber has a fluid inlet and a fluid outlet on each side of the
slave piston.
4. The downhole pump of claim 1, wherein the master cylinder is driven by a
gas.
5. The downhole pump of claim 1, wherein the gas expelled from the master
cylinder is
expelled into at least one fluid outlet of the second piston chamber.
6. The downhole pump of claim 1, further comprising a travelling liquid seal
carried by the
slave piston that engages an inner surface of the second piston chamber, the
travelling liquid
creating a seal against fluid while permitting gas to pass.

7
7. The downhole pump of claim 6, wherein the second piston chamber comprises a
first
outlet on a first side of the slave piston and a second outlet on a second
side of the slave
piston, wherein the gas that passes the travelling liquid seal exits through
the second outlet.
8. A downhole pump, comprising:
a piston in a piston chamber;
a motive force for driving the piston;
a travelling liquid seal carried by the piston that engages an inner surface
of the
second piston chamber, the travelling liquid creating a seal against fluid
while permitting gas
to pass; and
the second piston chamber comprising a fluid inlet and a first outlet on a
first side of
the slave piston and a second outlet on a second side of the slave piston,
wherein the gas that
passes the travelling liquid seal exits through the second outlet.

Description

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TITLE
[0001] Downhole pump with a pressure sequencing valve
FIELD
[0002] This relates to a downhole pump that uses a pressure sequencing valve
BACKGROUND
[0003] Downhole pumps may be hydraulically driven, such as the pump described
in
Canadian patent application no. 2,576,693 (Hoffarth) entitled "Hydraulic
submersible pump
with electric motor drive".
SUMMARY
[0004] There is provided a downhole pump, comprising a master piston having a
first
side and a second side in a first piston chamber and a slave piston driven by
the master piston
in a second piston chamber. The first piston chamber comprises a first inlet
and a second inlet
for alternatingly applying fluid pressure to the first side of the master
piston to move the
piston toward the top of a piston stroke, and to the second side of the master
piston to move
the piston toward the bottom of the piston stroke. A valve is carried by the
master piston that
relieves fluid pressure from the respective side of the master piston once the
top or bottom of
the stroke is reached. There is a sequencing valve that has a first state that
applies fluid
pressure to the first inlet and a second state that applies fluid pressure to
the second inlet. The
sequencing valve switches between the first state and the second state once a
drop in pressure
occurs. The second piston chamber has at least one fluid inlet and at least
one fluid outlet.
The valve may be a poppet valve that opens a flow passage through the master
piston. The
slave piston may be a double-acting piston and the second piston chamber may
have a fluid
inlet and a fluid outlet on each side of the slave piston
[0005] According to another aspect, there is provided a downhole pump,
comprising a
master piston in a first piston chamber, a slave piston in a second piston
chamber, and a
travelling liquid seal carried by the slave piston that engages an inner
surface of the second
piston chamber. The travelling liquid creates a seal against fluid while
permitting gas to pass.
The second piston chamber comprises a fluid inlet and a first outlet on a
first side of the slave
piston and a second outlet on a second side of the slave piston, wherein the
gas that passes the

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travelling liquid seal exits through the second outlet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] These and other features will become more apparent from the following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to be in any way limiting,
wherein:
FIG. 1 is a side elevation view in section of a downhole pump at the bottom of
a
stroke.
FIG. 2 is a side elevation view in section of the downhole pump at the top of
the
stroke.
FIG. 3 is a side elevation view in section of an alternative downhole pump.
FIG. 4 is a detailed side elevation view in section of a poppet valve system.
FIG. 5 is a detailed side elevation view in section of the liquid seals.
DETAILED DESCRIPTION
[0007] Referring to FIG. 1, a downhole pump, generally identified by reference
numeral
10 has a master piston 12 with a first side 14 and a second side 16 in a first
piston chamber 18.
There is also a slave piston 20 driven by master piston 12 by a shaft 22 that
is positioned in a
second piston chamber 24. First piston chamber 18 has a first inlet 26 and a
second inlet 28
on either side of master piston 12. As fluid pressure is alternatingly applied
to either side 14
and 16, master piston 12 moves between the bottom of a piston stroke, as shown
in FIG. 1,
toward the top of a piston stroke as shown in FIG. 2. As master piston 12
reciprocates, it
drives slave piston 20, which pumps fluid through second piston chamber 24
using fluid inlets
21 and fluid outlets 23. While slave piston 20 and second piston chamber 24
are configured
as a double-acting piston, it may also be configured as a single acting
piston. Furthermore,
while second piston chamber 24 is shown above first piston chamber 18, it will
be understood
that the actual orientation may be changed, depending on the preferences of
the user, and the
conditions of the well being pumped. Referring to FIG. 4, master piston 12 is
sealed against
first piston chamber 18 by travelling seals 25. Referring to FIG. 5, slave
piston 12 will also
have seals 42, although the seals may be different as slave piston 12
encounters "dirty" fluid,
whereas master piston 12 will generally only encounter clean hydraulic fluid.

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[0008] Referring to FIG. 1, fluid is supplied to first inlet 26 and second
inlet 28 by a
supply of fluid 30. As is common in the art, this may be hydraulic oil from a
hydraulic pump
on surface. Other fluids and pumps may also be used, as is known in the art. A
sequencing
valve 32 controls where the fluid flows. In particular, sequencing valve 32
has a first state
that applies fluid pressure to first inlet 26 and a second state that applies
fluid pressure to
second inlet 28. Sequencing valve 32 switches between the two states once a
drop in pressure
occurs. The drop in pressure is induced by a valve 34 that is carried by
master piston 12.
Sequencing valve 32 also preferably has a pressure relief valve (not shown) to
protect it.
Valve 34 relieves fluid pressure from the respective side of master piston 12
once the top or
bottom of the stroke is reached. Referring to FIG. 4, as shown, valve 34 is
made up of two
poppet valves 36 carried by the master piston. Poppet valves 36 are biased
closed by a spring
38, and each has a corresponding flow channel 40. As master piston 12 reaches
the bottom of
the stroke, one of the poppets 36 is depressed, which opens flow channel 40.
This causes the
fluid pressure on first side 14 to reduce the pressure toward the pressure on
second side 16 of
master valve 12. This pressure drop triggers sequencing valve 32 to switch to
the other state,
and causes pressure to be applied in the opposite direction, thus causing
master valve 12 to
reciprocate. It will be understood that valve 34 may take other forms other
than the depicted
poppet valves that are activated to release pressure when the piston reaches
the end of its
stroke. While not shown, it will be understood that, as master piston 12
moves, fluid on the
opposite side is vented, either back to the source of hydraulic fluid, or
directly into the
wellbore.
[0009] In some wells, gas may be present in the downhole fluids, which can
cause
problems in a pump if not addressed properly. Referring to FIG. 3 and 5, an
option of dealing
with this is to replace seals 25 with deliberately leaky seals 42. Leaky seals
42 would be
sufficient to seal against liquid, but would permit gas to pass by piston 20.
In the depicted
embodiment, slave piston 20 and second piston chamber 24 are configured as a
single-acting
piston. Second piston chamber 24 has inlet 21 and outlet 23, and an additional
gas outlet 44
on the opposite side from inlet 21 and outlet 23. As fluid enters inlet 21,
gas would be
permitted to migrate past slave piston 20. The remaining fluid would be
ejected through

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outlet 23 on the downstroke, with the gas being ejected through outlet 44 on
the upstroke.
This design may be also used with other types of pumps aside from those
described herein,
such as a pump with another type of drive mechanisms. Seals 42 may be made
"leaky" in the
way that they are cut. This design also has the added advantage of reducing
the wear on seals
42, or being able to make them more robust, such that their service life is
extended.
[0010] The motive fluid used to drive master piston 12 may vary, as will the
means for
exhausting the motive fluid. Referring to FIG. 1, motive fluid is exhausted
back through
sequencing valve, where it may be returned to surface, or it may be expelled
into the
wellbore. Alternatively, referring to FIG. 3, motive fluid may be expelled
directly from first
piston chamber 18 through a fluid line 46 by check valves 48. As shown, fluid
line 46 is
connected downstream from check valve 23 off chamber 24, such that the motive
fluid travels
to surface with the produced fluids.
[0011] While a liquid, such as hydraulic fluid or water, may be used to drive
master
piston 12, gas may also be used to drive piston 12. This may be particularly
useful if the
embodiment in FIG. 3 is used, as the gas may be used to help lift the produced
fluids and any
formation fines to surface. For example, say the pressure in the tubing is 5
psi. If the gas in
first chamber 18 is at 500 psi and the volume of first chamber 18 is 1.9 gal,
then there will be
an equivalent volume of 190 gal in the outlet tubular, which would be more
than enough to
clear an outlet tubular with a volume of between 40 and 50 gal. Other volumes
and pressures
may be encountered and used. Another benefit is that, as there will be less
pressure required
to pump the fluids to surface, this may result in a smaller pressure
differential across seals 25
in first chamber 18, which reduces the wear on seals 25.
[0012] In this patent document, the word "comprising" is used in its non-
limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
there be one and only one of the elements.

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[0013] The following claims are to be understood to include what is
specifically
illustrated and described above, what is conceptually equivalent, and what can
be obviously
substituted. Those skilled in the art will appreciate that various adaptations
and modifications
of the described embodiments can be configured without departing from the
scope of the
5 claims. The illustrated embodiments have been set forth only as examples and
should not be
taken as limiting the invention. It is to be understood that, within the scope
of the following
claims, the invention may be practiced other than as specifically illustrated
and described.

Representative Drawing