Note: Descriptions are shown in the official language in which they were submitted.
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DOWNHOLE PUMP WITH ANTI-GAS LOCK ORIFICE
FIELD OF THE INVENTION
[0001]
This application claims the benefit of priority to BR 10 2018 003152-
0, filed 19 February 2018, which is incorporated herein by reference in its
entirety.
[0002]
The present invention relates to downhole pumps (also known as
bottom-hole pumps). More specifically, the present invention relates to
downhole
pumps comprising means for preventing gas lock.
BACKGROUND OF THE INVENTION
[0003]
One of the most widely used methods of onshore oil extraction is
known as mechanical pumping. According to this method, as widely employed in
the prior art, a reciprocating pump is installed at the bottom of the well,
and this
pump is connected to a sucker-rod string with sufficient length so that the
other
end reaches the surface.
[0004]
At the surface, the sucker-rod string is connected to a device
known as a pumping unit, whose function is to convert the rotary motion of a
conventional motor into a reciprocating motion with slow rotation to the
sucker rod,
which in its turn transfers it to the pump installed at the bottom of the
well.
[0005] It is also known that each sample of oil consists of hundreds of
different molecules in different states, from gaseous to solid in varying
amounts. In
oils with a larger amount of gaseous fractions, the effect known as "gas lock"
occurs, which is the accumulation of gas in the space between the standing
valve
and the travelling valve. This accumulation of gas delays or even prevents
opening
of the travelling valve, limiting the flow of oil.
[0006]
In the state of the art, the problem of gas blocking of downhole
pumps is tackled with a manoeuvre known as "bottom checking", which consists
of
repositioning the travel of the pump so that at the end of the descending
cycle, the
piston collides with the barrel, causing maximum reduction of the dead space
between piston and standing valve, which reduces the possibility of
accumulation
of gas and helps to ensure that the maximum amount of gas is expelled.
[0007]
Another way of tackling this problem is the operation of reversed
circulation, where fluid is pumped from the surface through the annular space
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between the casing and production pipes via the downhole pump, so that the gas
is withdrawn.
[0008] The impacts caused by the bottom checking manoeuvre may
damage the pump to the point that its operation becomes impracticable, as
there
is constant direct impact between the standing valve and the travelling valve.
[0009] None of these problems is solved satisfactorily by the
prior art, as
is clear from the known examples described below.
[00010] Document W02008153698A1 discloses a downhole pump for
removing volumes of liquids, such as oil, gases and production water, from oil
wells. The pump described in that document comprises, among other elements: a
chamber for gas separation, with a standing valve; a piston with a travelling
valve;
and an actuator of the travelling valve. The actuator of the travelling valve
consists
of a pin that actuates the ball of the valve, opening the travelling valve, in
order to
equalize the pressure between the interior of the piston and the separating
chamber, preventing blocking by gas.
[0011] However, the downhole pump disclosed in document
W02008153698A1 makes use of a pin for actuating the ball valve of the
travelling
chamber, so that, owing to the repeated movements of the valve, the pin is
subjected to a high mechanical force, making it very susceptible to fractures.
[0012] Document US3215085A discloses a configuration of standing
valve for a downhole plunger pump. This document specifically envisages that,
fixed to the standing valve, a means is provided for actuating the ball of the
travelling valve fixed to the piston, when the piston is at the lowest point
of its
travel. In the configuration presented in this document, a pin is adopted for
actuating the ball of the travelling valve. Thus, it makes it possible for gas
trapped
in the stationary assembly (separating chamber) to be directed to the interior
of the
piston, preventing blocking of the pump by gas.
[0013] Similarly, the downhole pump disclosed in document
U53215085A
makes use of a pin for actuating the ball valve of the travelling chamber, so
that,
.. owing to the repeated movements of the valve, the pin is subjected to a
high
mechanical force, which makes it very susceptible to fractures.
[0014] Document U57909589B2 discloses a downhole pump that
comprises a separating chamber, with a standing valve, and a piston, with a
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travelling valve, in which the piston is divided into two parts. A chamber for
trapping sand is provided between the two parts of the piston, to prevent sand
present in the pumped fluid entering the piston.
[0015] According to document US790958962, orifices are also
provided
between the two parts of the piston, which allow fluid communication between
the
interior of the piston and the separating chamber (balancing). Thus, these
orifices
allow the internal pressure of the piston and the pressure of the separating
chamber to be equalized, thus preventing blocking of the pump by gas.
[0016] To make it possible to equalize the internal pressure of
the piston
and the pressure of the separating chamber, a channel is maintained between
the
piston and the inside wall of the separating chamber, via which a fluid (such
as
gas) can drain away.
[0017] However, since the oil being pumped comprises a number of
impurities such as sand and mud, the channel maintained between the piston and
the inside wall of the separating chamber is liable to obstruction, which
could
cause blocking of the pump by gas.
[0018] Document US8858187B2 discloses a downhole pump that
comprises a filter provided in the piston adapted for separating the interior
of the
piston from the separating chamber. According to this document, the filter
comprises openings that allow passage of fluid with the aim of balancing the
pressure inside the piston and in the separating chamber, thus preventing
blocking
of the pump by gas.
[0019] In addition, it is described in US8858187B2 that to make it
possible to equalize the internal pressure of the piston and the pressure of
the
.. separating chamber, a space is maintained between the piston and the inside
wall
of the separating chamber, through which a fluid (such as gas) can drain away,
in
which the space maintained is preferably of the same thickness as the
openings.
[0020] However, since the oil being pumped comprises a number of
impurities such as sand and mud, the channel maintained between the piston and
the inside wall of the separating chamber is liable to obstruction, which
could
cause blocking of the pump by gas.
[0021] Document US6273690B1 discloses a downhole pump that
comprises a piston and a separating chamber, with standing and travelling
valves,
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in which a channel is provided between the piston and the separating chamber
so
as to provide communication around the piston. According to this document, the
channel is kept open when the piston is in the highest position of its travel,
and is
kept closed when the piston is in the lowest position of its travel. Thus,
when the
channel is open, the object described ensures that the internal pressure of
the
piston is equalized with the pressure of the separating chamber.
[0022] However, since the oil being pumped comprises a number of
impurities such as sand and mud, the channel maintained between the piston and
the separating chamber is liable to obstruction, which could cause blocking of
the
pump by gas.
[0023] Thus, it is clear that the prior art does not provide a
downhole
pumping system, preferably for onshore application, that is effective and free
from
the risk of blocking by gas.
[0024] As will be described in more detail hereunder, the present
disclosure aims to solve the problems of the prior art described above in a
practical and efficient manner.
SUMMARY OF THE INVENTION
[0025] The present disclosure aims to provide a downhole pump for
onshore oil production capable of substantially minimizing the gas lock
effect.
[0026] According to the present disclosure, there is provided a
downhole
pump, comprising at least one of an extension wall; a barrel that extends
vertically
to the interior of the extension wall; a gas separating chamber delimited by
the
barrel and the interior surface of the extension wall; and a piston comprising
a
travelling valve in its lower portion, wherein the piston is configured to
slide
vertically in the barrel to the interior of the separating chamber between an
upper
end of stroke position and a lower end of stroke position; wherein the piston
comprises at least one venting orifice, wherein the at least one venting
orifice is
configured to provide communication between the interior of the piston and the
gas separating chamber when the piston reaches the lower end of stroke
position,
wherein, in the lower end of stroke position, the venting orifice is
positioned below
the barrel.
[0027] Optionally, the piston comprises a plurality of venting
orifices.
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[0028] Optionally, the venting orifices are located at the same
horizontal
position on the piston.
[0029] Optionally, the venting orifices have different dimensions.
[0030] Optionally, the at least one venting orifice provides fluid
communication between the interior of the piston and the separating chamber in
the uppermost region of the separating chamber
[0031] Optionally, the pump further comprises a nipple configured
to be
connected to a lower end of a production pipe between the barrel and the
production pipe
[0032] Optionally, the pump further comprises an end-of-stroke sleeve
configured to be connected to the sucker rod, wherein the nipple is adapted to
interrupt the descending motion of the end-of-stroke sleeve when the piston
reaches the lower end of stroke position.
[0033] Optionally, the end-of stroke sleeve is configured to be
connected
at an end of the sucker rod, wherein the pump further comprises a connecting
rod
which connects the end-of-stroke sleeve to the piston
[0034] Optionally, the end-of-stroke sleeve is configured to be
adjustably
connected to the sucker rod.
[0035] Optionally, the extension wall is an extension of the
barrel, the
interior of the extension wall having a larger diameter than the interior of
the barrel.
[0036] Optionally, the gas separating chamber comprises a standing
valve.
[0037] Optionally, the piston is configured to be driven by a
sucker rod.
[0038] Optionally, the venting orifice is configured not to
provide
communication between the interior of the piston and the gas separating
chamber
when the piston is away from the lower end of stroke position.
[0039] There is also disclosed a bottom-hole pump with gas
separator
and anti-gas lock orifice, comprising: a nipple (5) connected to a lower end
of a
production pipe (2), and comprising a barrel (6) that extends vertically to
the
interior of an extension wall (10) of the pump; a gas separating chamber (11)
comprising a standing valve (9), wherein the gas separating chamber (11) is
delimited by the barrel (6) and the extension wall (10) of the pump; and a
piston
(7) comprising a travelling valve (8) in its lower portion, wherein the piston
(7) is
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driven by the sucker rod (3), and adapted to slide vertically in the barrel
(6) to the
interior of the separating chamber, the bottom-hole pump being characterized
in
that the piston (7) comprises at least one venting orifice (12), wherein the
at least
one venting orifice (12) is adapted for providing communication between the
interior of the piston (7) and the gas separating chamber (11) when the piston
(7)
reaches an end of stroke position, wherein, in the end of stroke position, the
venting orifice (12) is positioned below the barrel (6).
[0040] Optionally, the piston (7) comprises a plurality of venting
orifices,
wherein the venting orifices are positioned in one and the same horizontal
line.
[0041] Optionally, the venting orifices comprise different dimensions.
[0042] Optionally, the at least one venting orifice (12) provides
fluid
communication between the interior of the piston (7) and the separating
chamber
(11) in the uppermost region (110) of the separating chamber (11).
[0043] Optionally, the pump comprises an end-of-stroke sleeve (4)
fixed
to the sucker rod (3), wherein the nipple (5) is adapted to interrupt the
descending
motion of the end-of-stroke sleeve (4) when the piston (7) reaches a lowest
position of travel.
[0044] Optionally, the end-of-stroke sleeve (4) is fixed in a
final position of
the sucker rod (3), wherein a connecting rod (13) is adopted, connecting the
end-
of-stroke sleeve (4) to the piston (7).
[0045] Optionally, that the end-of-stroke sleeve (4) is connected
adjustably to the sucker rod (3).
BRIEF DESCRIPTION OF THE FIGURES
[0046] The detailed description presented hereunder refers to the
appended figures and their respective reference numbers.
[0047] Fig. 1 illustrates a schematic view of the downhole pump
with gas
separator and anti-gas lock orifice according to an optional configuration of
the
present disclosure.
[0048] Fig. 2 illustrates a schematic view of the detail of the
operation of
the venting orifice of the piston illustrated in Fig. 1.
[0049] Fig. 3a illustrates a schematic view of the downhole pump
with
gas separator and anti-gas lock orifice from Fig. 1 in the initial position of
the cycle.
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[0050] Fig. 3b illustrates a schematic view of the downhole pump
with gas
separator and anti-gas lock orifice from Fig. 1 in an initial position of the
ascending
cycle.
[0051] Fig. 3c illustrates a schematic view of the downhole pump
with gas
separator and anti-gas lock orifice from Fig. 1 in an initial position of the
descending cycle.
[0052] Fig. 3d illustrates a schematic view of the downhole pump
with gas
separator and anti-gas lock orifice from Fig. 1 in the final position of the
cycle.
DETAILED DESCRIPTION OF THE INVENTION
[0053] Firstly, it is emphasized that the description given
hereunder is
based on a preferred embodiment of the disclosure. As will be obvious to a
person
skilled in the art, however, the invention is not limited to this particular
embodiment.
[0054] The present disclosure relates to a downhole pump preferably for
onshore use. As already described in earlier sections, a pump of this type is
usually installed at the bottom of a production well. Such a pump can be
connected to a sucker-rod string of sufficient length so that the other end
reaches
the surface. At the surface, the sucker-rod string can be connected to a
device
known as a pumping unit. The function of the pumping unit is to convert the
rotary
motion of a conventional motor into a reciprocating motion and slow rotation
for
the sucker rod. The sucker rod can in turn transfer the motion to the pump
installed at the bottom of the well.
[0055] However, a very common phenomenon in this type of pump is
the
so-called gas lock effect, caused by the accumulation of gas in the separating
chamber of the downhole pump (the space between the standing valve and the
travelling valve). This accumulation of gas delays or even prevents opening of
the
travelling valve, literally obstructing the flow of oil, causing loss of
production.
[0056] Being well known in the field of oil extraction, this
phenomenon
occurs through the presence of light hydrocarbon fractions, that change phase
during the suction cycle of the downhole pump, so that the pressure in the
separating chamber is not high enough to cause opening of the travelling valve
of
the piston, which prevents entry of liquid produced therein, interrupting
pumping.
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In the case of conventional pumps, there is no separating chamber, but the
effect
occurs in the same way as the space between piston and barrel expands.
[0057] In one arrangement, there is provided a downhole pump as
illustrated schematically in Fig. 1, which illustrates an optional
configuration of the
bottom-hole pump with gas separator and anti-gas lock orifice, comprising:
a sucker rod 3 connected to a pumping unit;
a nipple 5 connected to a lower end of a production pipe 2, and
comprising a barrel 6 that extends vertically to the interior of an extension
wall 10
of the pump;
a chamber for gas separation comprising a standing valve 9,
wherein the separating chamber is delimited by the barrel 6 and the extension
wall
10 of the pump; and
a piston 7 (also known as a plunger) comprising a travelling valve
8 in its lower portion, wherein the piston 7 is driven by the sucker rod 3,
and
adapted for sliding vertically in the barrel 6 to the interior of the
separating
chamber.
[0058] According to the present disclosure, there is also provided
a
downhole pump comprising one or more of an extension wall 10; a barrel 6 that
extends vertically to the interior of the extension wall 10; a gas separating
chamber 11 comprising a standing valve 9, wherein the gas separating chamber 9
is delimited by the barrel 6 and the interior surface of the extension wall
10; and a
piston 7 comprising a travelling valve 8 in its lower portion, wherein the
piston is
configured to slide vertically in the barrel 6 to the interior of the
separating
chamber between an upper end of stroke position and a lower end of stroke
position; wherein the piston 7 comprises at least one venting orifice 12,
wherein
the at least one venting orifice 12 is configured to provide communication
(i.e. fluid
communication) between the interior of the piston and the gas separating
chamber
11 when the piston reaches the lower end of stroke position, wherein, in the
lower
end of stroke position, the venting orifice 12 is positioned below the barrel.
It will
be appreciated that "upper" and "lower" are in the sense of the pump when
installed at the bottom of a well. The piston 7 may be configured to be driven
by a
sucker rod 7.
[0059] The extension wall 10 may take the form of a cylindrical
wall. The
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cylindrical wall may have a side portion and a bottom portion. The standing
valve 9
may be disposed in the bottom portion.
[0060] As set out above, and as shown in Figure 1, the interior of
the
pump defines a volume formed by the interior of the barrel 6 and the extension
wall 10. The barrel 6 has a smaller interior diameter than the extension wall
10.
The extension wall 10 may be thought of as an extension of the barrel, with a
larger interior diameter. The exterior diameters of the barrel 6 and the
extension
wall 10 may be substantially the same, as shown in Figure 1.
[0061] A nipple 5 (also known as a seating nipple) may be provided
.. above the barrel 6. The nipple 5 may be positioned at the top of the pump
to allow
a connection to a production pipe 2. The barrel 6 may be considered as part of
the nipple 5, or alternatively, the barrel 6 can be considered as a separate
part,
with the nipple being positioned between the production pipe 2 and the barrel
6.
The extension wall 10, barrel 6, and, where present, the nipple 5 may be
considered to form a main body of the pump.
[0062] The gas separating chamber 11 is defined by the space
between
the side and bottom walls of the extension wall 10, and the boundary between
the
extension wall and the barrel 6. The gas separating chamber 11 may comprise a
standing valve 9. The standing valve 9 may be located at the bottom of the gas
separating chamber 11 (i.e. in the bottom wall of the extension wall 10).
[0063] As explained above, the oil extracted from the well
consists of a
mixture of molecules, some of which are in a gas phase and some of which are
in
a liquid phase. The separating chamber 11 promotes phase separation of the
mixture extracted from the well, wherein the gas phase tends to be displaced
and
to accumulate in the upper portion 110 of the separating chamber 11, and the
liquid phases are displaced and accumulate in the lower portion 111 of the
separating chamber 11.
[0064] In order to prevent loss of production due to the gas lock
effect,
the piston 7 of the downhole pump of the present disclosure comprises at least
one venting orifice 12. The venting orifice 12 is adapted for providing fluid
communication between the interior of the piston 7 and the gas separating
chamber 11 when the piston 7 reaches the lower end of stroke position. At the
lower end of stroke position the venting orifice 12 is positioned below the
barrel 6.
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In other words, the venting orifice 12 is an opening in the wall of the piston
which
allows gas to pass from the gas separating chamber 11 to the interior of the
piston
7 when the piston 7 is at its lowest position.
[0065] It will be appreciated that, when the piston 7 is away from
the
lower end of stroke position, the venting orifice 12 is configured not to
provide
communication between the interior of the piston 7 and the gas separating
chamber 11. This may be because the orifice 12 can be blocked by the inner
wall
of the barrel 6. This may occur because the inner diameter of the barrel 6 may
be
smaller than the inner diameter of the extension wall 10. The state in which
the
piston 7 is considered to be away from the lower end of stroke position may
be, for
example, when the piston 7 is in the upper 90% of its travel. Any other
suitable
proportion of the stroke may also be chosen.
[0066] The functioning of the feature described in the preceding
paragraphs may be visualized in Fig. 2, which illustrates a schematic view of
the
detail of the operation of the venting orifice 12 of the piston 7 illustrated
in Fig. 1. In
a situation of gas lock, due to accumulation of gas in the separating chamber
11,
this chamber is expected to have a pressure greater than that of the interior
of the
piston 7, but the pressure difference between the separating chamber 11 and
the
piston 7 is not sufficient to actuate (i.e. open) the travelling valve 8.
[0067] This is due to the fact, in a gas lock condition, there is a large
amount of gas 18 accumulated in the upper portion 110 of this chamber., Since
the compressibility of gases is very high compared to liquids, the piston 7
does not
exert sufficient pressure on the separating chamber 11 to actuate the
travelling
valve 8, which would allow the liquid phase 111 to be directed to the interior
of the
piston 7 through the travelling valve 8.
[0068] However, due to the presence of the venting orifice 12,
when the
piston 7 reaches the lower end of stroke position, in which the venting
orifice 12 is
positioned below the barrel 6, the venting orifice 12 now allows fluid
communication between the interior of the piston 7 and the separating chamber
11. In this situation, since the pressure in the separating chamber 11 is
greater
than the pressure in the piston 7, the gas accumulated in the upper portion
110 of
the separating chamber 11 is impelled to the interior of the piston 7.
[0069] With the expulsion of the gas from this region (i.e. the
separating
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chamber 11), the pressure difference between the separating chamber 11 and the
piston 7 is sufficient to actuate (i.e. open) the travelling valve 8. Thus,
the pump
operates normally again in the next pumping cycle, without any interruption of
production.
[0070] Figs. 3a, 3b, 3c, and 3d illustrate, respectively, the pump from
Fig.
1 in the initial position, in the ascending cycle of the piston 7, in the
descending
cycle of the piston 7, and in the final position. Note that the initial and
final
positions represent the same position of the pump, or of the piston 7, since
at the
end of a cycle, the pump begins a new cycle immediately. It is also emphasized
that the initial position of the piston 7 represents the point where the
piston 7
reaches the lower end of stroke position, i.e. the lowest position of its
travel. The
upper end of stroke position is the position of the piston 7 at which the
piston stops
ascending (as shown in in Figure 3b) and starts descending again. It will be
understood that in each cycle, the piston 7 travels from the lower end of
stroke
position, to the upper end of stroke position, and back down to the lower end
of
stroke position.
[0071] Although the figures show that the piston 7 comprises only
one
venting orifice 12, a plurality of venting orifices may optionally be provided
in the
piston 7. Preferably, these orifices are positioned on one and the same
horizontal
line. The orifices may comprise different sizes (i.e. be of different
dimensions).
Thus, if there is obstruction of one of the venting orifices 12, others can
provide
fluid communication between the interior of the piston 7 and the separating
chamber 11. The varying sizes of orifices 12 may allow at least one orifice to
remain clear of obstructions if the obstruction is made up of particles of a
particular
size, because those particles may block an orifice of a certain size, but pass
through an orifice of a different size.
[0072] In general, it can be seen that during the ascending and
descending motion of the piston 7, the venting orifice 12 remains obstructed
by the
barrel 6 of the pump, so that the venting orifice 12 is only in communication
with
the separating chamber 11 when the piston 7 is closer to its lower end of
stroke.
[0073] Thus, in a situation of normal operation the venting
orifice 12 only
provides communication between the interior of the piston 7 and the separating
chamber 11 in the uppermost region 110 of the separating chamber 11, which
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normally is only filled with the gas phase.
[0074]
So as to ensure that the lower travel of the piston 7 does not
exceed a tolerable limit, there is optionally provided an end-of-stroke sleeve
4
connected (or fixed) to the sucker rod 3. The nipple 5 may be adapted to
interrupt
the descending motion of the end-of-stroke sleeve 4 when the piston 7 reaches
a
lowest position of travel. In this configuration, the lowest position of
travel is such
that the venting orifice 12 is positioned below the barrel 6. This can allow
fluid
communication between the interior of the piston 7 and the separating chamber
11. It will be understood that "fixed" need not mean "permanently fixed" and
that
any suitable attachment or connection may be used.
[0075]
Optionally the end-of-stroke sleeve 4 may be fixed at the end of
the sucker rod 3, wherein a connecting rod 13 is adopted, connecting the end-
of-
stroke sleeve 4 to the piston 7. In other words, the pump may comprise a
connecting rod 13 between the end-of-stroke sleeve 4 and the piston 7 to
provide
a connection between the sucker rod 3, end-of stroke sleeve 4 and piston 7.
However, a connecting rod 13 need not be provided, and the end-of-stroke
sleeve
4 may be directly connected to the piston or connected to the piston using an
arrangement other than a connecting rod 13.
[0076]
In particular configurations the end-of-stroke sleeve 4 may be
.. connected adjustably to the sucker rod 3. In this configuration, the limit
position of
end of stroke defined by the position of the sleeve 4 may be adjustable.
[0077]
As is known by a person skilled in the art, the standing and
travelling valves 8,9 may be any that are known from the prior art, so that
this
feature does not limit the scope of protection of the invention.
[0078] Thus, it will be clear that the invention now described solves, in a
hitherto unpublished manner, the problems of the prior art for which it is
proposed,
namely to provide a downhole pump for onshore oil production that overcomes
problems through blocking by gas.
[0079]
Modifications of the above-described apparatuses and methods,
.. combinations between different variations as practicable, and variations of
aspects
of the invention that are obvious to those of skill in the art are intended to
be within
the spirit and scope of the claims.
