Note: Descriptions are shown in the official language in which they were submitted.
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DOWNHOLE CLEANING SYSTEM
Field of the invention
The present invention relates to a downhole cleaning system for cleaning an
ele-
ment inside a casing in a wellbore comprising well fluid having a wellbore
pres-
sure, comprising the casing, a cleaning tool having a longitudinal direction
and
comprising a rotatable nozzle head having a plurality of nozzles, a tool
housing
having an inlet being in fluid communication with the nozzles for letting well
fluid
into the tool, a flow hindering element arranged on an outside of the housing
di-
viding the tool in a first and a second tool part and dividing the casing in a
first
and a second casing part and a rotatable shaft connecting the nozzle head with
the housing. Furthermore, the invention relates to a wireline cleaning tool
and to
a cleaning method.
Background art
During oil production, the completion needs to be optimised in order to
produce
as much oil as possible. Therefore, it is necessary that some valves are open
and
others closed. However, such valves may get stuck due to precipitation of
scales
and other particles accumulated on the valve so that the valve is blocked.
Thus,
it is sometimes necessary to clean the valves before they can be operated.
Known cleaning tools require the presence of coiled tubing on the rig or
vessel in
order to clean a valve in a casing within a wellbore. However, such coiled
tubing
is not always situated on the rig or vessel and therefore needs to be
transported
to the rig or vessel.
Summary of the invention
It is an object of the present invention to wholly or partly overcome the
above
disadvantages and drawbacks of the prior art. More specifically, it is an
object to
provide a downhole cleaning system which is more simple and easier to sub-
merge into a wellbore without using drill pipes or coiled tubing.
The above objects, together with numerous other objects, advantages, and fea-
3 5 tures, which will become evident from the below description, are
accomplished by
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a solution in accordance with the present invention by a downhole cleaning sys-
tem for cleaning an element inside a casing in a wellbore comprising well
fluid
having a wellbore pressure, comprising:
- the casing,
- a wireline cleaning tool having a longitudinal direction and comprising:
- a rotatable nozzle head having a plurality of nozzles,
- a tool housing having an inlet being in fluid communication with the
nozzles for letting well fluid into the tool,
- a flow hindering element arranged on an outside of the housing divid-
ing the tool in a first and a second tool part and dividing the casing in a
first and
a second casing part, and
- a rotatable shaft connecting the nozzle head with the housing,
wherein the system further comprises a pumping device for pressurising the
well
fluid in the first part of the casing to a pressure substantially above the
wellbore
pressure and above a pressure in the second part of the casing so that well
fluid
is pumped in through the inlet and out through the nozzles.
In an embodiment, the nozzle head may have a side face facing an inner face of
the casing, and the nozzles of the nozzle head may be arranged along the side
face.
By having the nozzles in the side face, the nozzles are arranged closer to the
ob-
ject to be cleaned e.g. a gas lift valve (GLV) arranged in a side pocket of
the cas-
ing than if arranged in front of the tool.
Also, part of the nozzles may form part of the side face.
Moreover, the nozzle head may have a circumference and the nozzles may be ar-
ranged along the circumference facing the inner face of the casing.
Further, the nozzles may be arranged in rows along the side face.
Arranging the nozzles in rows expands the range of the ejecting area in the
longi-
tudinal direction of the tool. In order to clean an object e.g. a GLV, the
nozzle
head has to be moved in the longitudinal direction, and by having rows of
nozzles
the nozzle head does not have to be moved for a distance as long as when hay-
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ing only one row of nozzles or only one nozzle nor as many times as a head hav-
ing only one row.
Additionally, each nozzle may eject the fluid in one beam being a focused
beam.
Ejecting fluid through the nozzle in a beam is more efficient for removing
scales
and other solid elements fastened to the wall of the casing or a GLV than more
diffused droplets which is to a greater extent used for just washing or
flushing
the object to be cleaned.
Each nozzle may be arranged in an angle in relation to a longitudinal
extension of
the tool.
In an embodiment, the nozzles may be arranged in a predetermined pattern
along the side face of the nozzle head.
The pattern is determined by the pressure in the well at the location of the
object
or area of the casing to be cleaned and the pressure available in the fluid to
be
ejected through the nozzles, so that the power of the pump is used in the most
optimal manner. Hereby, it is ensured that the nozzles are not arranged too
close
to each other and hence that the beam of fluid ejected through one nozzle does
not merge with a beam of an adjacent nozzle, thereby reducing its cleaning ef-
fect.
Moreover, the nozzles may be fixedly arranged in the nozzle head.
Furthermore, the nozzles may be arranged spaced apart along the circumference.
Also, the downhole cleaning system according to the invention may comprise a
control device to control the rotation of the shaft and the nozzle head.
In an embodiment, the downhole cleaning system may comprise a control device
for controlling a rotational speed of the nozzle head or which nozzle/nozzles
is/are allowed to eject fluid.
By having a control device, the nozzle/nozzles is/are hindered from free
rotation
as known from prior art tools where some nozzles are designed to rotate as the
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pressurised fluid is forced through them. Hereby, substantially all energy of
the
pressurised fluid is used only for rotation of the nozzle and not for
providing a
beam of pressurised fluid ejected through the nozzles.
Moreover, the control device may be a hydraulic control unit arranged in the
tool
for controlling which nozzles are open and which nozzles are closed.
In one embodiment, the control device may be an electrical motor for rotating
the shaft.
In another embodiment, the control device may comprise a gear, a motor brake
or a centrifugal brake.
Also, the control device may be a hydraulic control unit arranged in the tool
for
controlling which nozzles are open and which nozzles are closed.
Furthermore, the nozzle head may comprise a hydraulic control unit for control-
ling which nozzles are open and which nozzles are closed.
By having a hydraulic control unit for controlling which nozzles are ejecting
fluid,
the nozzles not facing the object to be cleaned are not ejecting fluid and all
pres-
sure in the fluid is used for ejecting fluid through the nozzle or nozzles
facing the
object to be cleaned. Thus, no energy of the pressurised fluid is lost in
nozzles
not facing the object to be cleaned and/or no energy is used for rotating the
noz-
zle head. Furthermore, by controlling which nozzle/nozzles is/are allowed to
eject
fluid, only one or a few of the nozzles is/are ejecting fluid and the pressure
of the
fluid ejected from that or these nozzles is significantly larger than if
ejected
through all the nozzles at the same time even if the object is extending along
the
whole circumference of the casing. In this way, each nozzle is able to clean
hard-
er materials such as scales than what is possible in prior art tools in which
most
energy in the pressure fluid is used for rotating the nozzles.
In addition, the nozzle head may comprise a hydraulic control unit for
controlling
a supply of fluid to each nozzle.
In one embodiment, the shaft may be hollow for supplying the well fluid to the
nozzle head.
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In another embodiment, the flow hindering element may be a packer, an inflata-
ble unit, a rubber element or an elastomeric element
The downhole cleaning system according to the invention may further comprise a
5 stroker being a device providing a stroking reciprocating movement of the
nozzle
head in relation to the longitudinal direction of the tool, or a piston
interacting
with a piston housing in which a spring device is arranged for providing a
recipro-
cating movement of the nozzle head in relation to the longitudinal direction
of the
tool.
In one embodiment, the tool may comprise anchoring units.
In another embodiment, a filter may be arranged upstream of the inlet or
inside
the inlet.
Furthermore, the downhole cleaning system may comprise a downhole driving
unit driving the tool and itself in the casing.
Also, the downhole cleaning system may comprise a measuring device measuring
a rotational speed of the nozzle head.
Additionally, the downhole cleaning system may comprise a control unit to con-
trol the measuring device from surface.
In one embodiment, the nozzle head may comprise a check valve.
Moreover, the well fluid being pressurised may be the fluid being in the first
part.
Further, the well fluid may be pressurised when being in the first part of the
cas-
ing.
The well fluid may be taken from the first part for being pressurised.
Furthermore, the pumping device may pump the fluid out through the nozzles.
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The present invention also relates to a wireline cleaning tool arranged in a
casing
downhole and having a longitudinal direction, comprising:
- a rotatable nozzle head having a plurality of nozzles,
- a tool housing having an inlet being in fluid communication with the
nozzles for letting well fluid into the tool and out through the nozzles,
- a flow hindering element arranged on an outside of the housing divid-
ing the tool in a first and a second tool part and dividing the casing in a
first and
a second casing part, and
- a rotatable shaft connecting the nozzle head with the housing,
wherein the shaft may be a hollow shaft for supplying the nozzles with well
fluid.
Said wireline cleaning tool may further comprise a wireline connector
connected
with the tool housing for connecting the tool with a wireline.
The tool may further comprise a pumping device for pressurising the well fluid
in
the first part of casing to a pressure substantially above the wellbore
pressure
and above a pressure in the second part of the casing so that well fluid is
pumped in through the inlet and out through the nozzles.
Also, the wireline cleaning tool as described above may comprise a control
device
for controlling a rotational speed of the nozzle head or which nozzle/nozzles
is/are allowed to eject fluid.
Moreover, the control device may be a hydraulic control unit arranged in the
tool
for controlling which nozzles are open and which nozzles are closed.
The tool may further comprise a control device to control the rotation of the
shaft
and the nozzle head.
Also, the tool may further comprise a control device for controlling a
rotational
speed of the nozzle head.
Said control device may be an electrical motor for rotating the shaft.
Further, the control device may comprise a gear, a motor brake or a
centrifugal
brake.
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Additionally, the tool may further comprise a stroker being a device providing
a
stroking reciprocating movement of the nozzle head in relation to the
longitudinal
direction of the tool, or a piston interacting with a piston housing in which
a
spring device is arranged for providing a reciprocating movement of the nozzle
head along the longitudinal direction of the tool housing.
The tool may further comprise a measuring device measuring a rotational speed
of the nozzle head.
Finally, the invention relates to a cleaning method comprising the steps of
enter-
ing a cleaning tool of the system according to the invention into a casing,
activat-
ing the pumping device and pressurising the first casing part, turning the
nozzle
head and cleaning a casing element by letting well fluid in through the inlet
in the
pressurised first casing part and out through nozzles in the second casing
part.
Brief description of the drawings
The invention and its many advantages will be described in further detail
below
with reference to the accompanying schematic drawings, which for the purpose
of
illustration show some non-limiting embodiments and in which
Fig. 1 shows a downhole cleaning system in a casing,
Fig. 2 shows a partly cross-sectional view along the longitudinal direction of
the
downhole cleaning system seen from the side,
Fig. 3 shows a partly cross-sectional view of another embodiment of the
system,
and
Fig. 4 shows another embodiment of the downhole cleaning system in a casing.
All the figures are highly schematic and not necessarily to scale, and they
show
only those parts which are necessary in order to elucidate the invention,
other
parts being omitted or merely suggested.
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Detailed description of the invention
Fig. 1 shows a downhole cleaning system 1 for cleaning an element 2, such as a
gas lift valve (GLV), a sleeve or a side pocket mandrel, in a casing 3 in a
wellbore
4 comprising well fluid 5 having a well fluid pressure Pw. The downhole
cleaning
system 1 comprises the casing 3 and a wireline cleaning tool 10. The wireline
cleaning tool 10 has a longitudinal direction 11, and comprises in the end
furthest
away from the surface a rotatable nozzle head 12 having a plurality of nozzles
13
for cleaning the gas lift valve by jetting high pressurised well fluid out
through
the nozzles towards the valve.
By having a cleaning tool or a wireline cleaning tool 10, the cleaning
operation
can be performed anywhere in the well, also in the more horizontal parts of
the
well. No landing nipple is required in order to perform a cleaning operation.
The
system is easy to use and the cleaning tool easily retrieved from the well by
pull-
ing in the wireline.
The wireline cleaning tool 10 has a tool housing 14 having an inlet 15 for
letting
well fluid into the tool 10 and the inlet 15 is inside the tool in fluid
communication
with the nozzles 13. The well fluid travels in through the inlet and out
through
the nozzle head, illustrated with arrows. The wireline cleaning tool 10 is sub-
merged into the casing 3 in the well and a flow hindering element 16 arranged
on
an outside 17 of the housing 14 is set or inflated so that it divides the
casing 3 in
a first 20 and a second casing part 21. This enables that the well fluid in
the first
casing part 21 can be pressurised from the top of the well by a pumping device
23 and the fluid is forced into the inlets 15 and out through the nozzles in
order
to clean the casing or elements therein. Thus, the second part of the casing
21
has a substantially lower well fluid pressure so that the high pressurised
well fluid
in the first part 20 can be ejected as jets or beams in the well fluid in the
second
part of the casing. In this way, the casing is used as the coiled tubing or
drill pipe
in order to provide the nozzles with high pressurised fluid; however, the
fluid jet-
ted from the nozzles is not a special cleaning fluid but merely the well fluid
sur-
rounding the tool. Thus, the environment surrounding the gas lift valve to be
cleaned is not interfered.
As shown in Fig. 1, the wireline cleaning tool 10 is connected with a wireline
41.
The tool comprises an electronic section 30, a motor 31, a pump 32 and an an-
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choring device 33 in a first tool part 18 above the flow hindering element 16.
In a
second tool part 19 below the flow hindering element 16, the nozzle head 12 is
arranged. In another embodiment, the cleaning tool could have a battery pack,
and thus the wireline can be dispensed with if needed, and the tool could flow
upwards with the flow when the hindering element was somewhat deflated or re-
leased from the casing and thus the hindering element serves as a parachute.
In Fig. 2, the tool 10 is shown having a rotatable shaft 22 connecting the
nozzle
head 12 with the housing 14. The rotation of the shaft is controlled by a
control
device 24 in the form of an electrical motor having a gear, a motor brake or a
centrifugal brake 25. The shaft 22 is hollow and in fluid communication with
the
inlet 15 for supplying well fluid to the nozzles 13 of the nozzle head 12. The
shaft
22 is connected with the motor control device 24 which controls the rotation
of
the nozzle head 12 while fluid is jetted out through the nozzles 13. If the
nozzle
head was not controlled, the well fluid jet stream or beam 43 ejected from the
nozzles would lose its effect as fluid ejected through the nozzles would then
force
the nozzle head to rotate too fast resulting in the jet stream being spread
along
an inner circumference of the casing and not ejected as a straight line in the
ra-
dial direction of the casing. Hereby, substantially all energy of the
pressurised
fluid is used for rotation of the nozzle and not for providing a beam of
pressurised
fluid ejected through the nozzles.
The flow hindering element 16 is shown as a rubber element being squeezed in
the longitudinal direction 11 of the tool between two rings 42 forcing the
rubber
element radially outwards to seal against the casing at a pressure of 3000-
5000
PSI. The flow hindering element could also be a packer, an inflatable unit or
an
elastomeric element. The flow hindering element does not necessarily have to
seal against the inner wall of the casing in order to be able to create a
pressure
difference between the first and upper part of the casing and the second and
lower part of the casing.
The tool 10 is anchored up inside the casing 3 by means of anchoring units 35
so
that the nozzle head 12 is arranged outside a target area to be cleaned. The
flow
hindering element 16 is then inflated or set, and the pumping device 23
pressur-
ising the well fluid in the first and top part of the casing 20 is activated.
High
pressurised fluid is subsequently jetted as a jet stream out through the
nozzles
13 of the nozzle head 12 as the nozzle head turns in a controlled manner so
that
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the jet streams do not loose too much jetting power. In some embodiments, the
tool has only a hindering element which is sufficient to hold the tool in the
in-
tended position opposite the object or the area of the casing to be cleaned.
5 The nozzle head comprises a hydraulic control unit 34 for controlling
which of the
nozzles is allowed to emit or jet fluid to clean a valve or similar element.
The hy-
draulic control unit 34 controls the openings and closings of the nozzles
and/or
the supply of fluid to each nozzle. As can be seen in Fig. 1, only two of the
noz-
zles jet fluid into the casing in order to clean an element, such as a valve.
In Fig.
10 2, only one nozzle jets fluid. If a high fluid velocity is needed in
order to clean an
object free of e.g. hard scales, the hydraulic control unit only lets one
nozzle jet
at a time. However, if a high volume of fluid is needed, the hydraulic control
unit
lets several nozzles jet. Furthermore, the hydraulic control unit has means to
control in which angles along the circumference of the nozzle head the nozzles
are to jet so that their jets hit the element which is to be cleaned.
The nozzle head has an end face 51 and a side face 50, and the nozzles are ar-
ranged in a predetermined pattern 52 along the side face of the nozzle head.
The
nozzles are arranged in rows 53 along the circumference 54 of the nozzle head
having a mutual distance along the circumference. The pattern is determined by
the pressure available in the fluid to be ejected through the nozzles and the
pres-
sure in the second part of the well at the location of the object or area of
the cas-
ing to be cleaned and so that the power of the pump is used in the most
optimal
manner. The predetermined pattern is to ensure that the nozzles are not ar-
ranged too close to each other hence ensuring that the beam of fluid ejected
through one nozzle does not merge with a beam or jet of an adjacent nozzle,
thereby reducing the cleaning effect of each beam or jet. The nozzles may be
fix-
edly arranged in the nozzle head ensuring that energy of the pressurised fluid
is
used for providing a jet or beam out through the nozzles at the most optimal
an-
gle of attack in relation to the scales type or the type of the undesired
element to
be removed from the object to be cleaned. The nozzles are designed to eject a
focused beam at a predetermined angle to provide needle punching effect or a
wedging effect to crack the material to be removed.
In order to reach a larger target area, the tool may have means for moving the
nozzle head in a reciprocating movement. In Fig. 2, a piston 26 interacting
with a
piston housing 27 in which a spring device 28 is arranged provides a
reciprocat-
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ing movement of the nozzle head 12 in relation to the longitudinal direction
11 of
the tool 10. In Fig. 3, the tool 10 comprises a stroker 29 being a device
providing
a stroking reciprocating movement of the nozzle head 12 in relation to the
longi-
tudinal direction 11 of the tool 10. The reciprocating movement of the nozzle
head 12 is illustrated by a double arrow in Fig. 3.
In another embodiment, the control device is a hydraulic control unit
comprising
the shaft having grooves in the form of channels extending in the longitudinal
di-
rection and the outer surface of the shaft and the fluid supplied to the
nozzles
flows in the channels. The shaft is rotated so that some channels are opposite
some nozzles which in this way is allowed to eject fluid, and when the shaft
is ro-
tated again, the channels are arranged opposite other nozzles which will then
be
the next to be allowed to eject a beam of pressurised fluid. In this way, the
shaft
is rotated to control which nozzle is allowed to eject fluid.
The wireline cleaning tool comprises a filter 36 arranged upstream of the
inlet 15
or in the inlet. In Fig. 2, the filter 36 or screen surrounds the part of the
tool 10
having the inlet 15. The tool 10 comprises several inlets, all in fluid
communica-
tion with the hollow shaft. The hollow shaft may be internally sectionised
having
an internal frame structure to strengthen the shaft.
As shown in Fig. 4, the downhole cleaning system 1 may further comprise a
downhole driving unit 37 driving the tool 10 and itself forward in the casing
3.
The driving unit 37 has wheels on arms and can be used as the anchoring device
in order to set the packer. The downhole cleaning system 1 may also comprise a
measuring device 38 measuring a rotational speed of the nozzle head 12. As
shown in Fig. 4, the measuring device 38 may be arranged in the motor control
device 24 around the shaft 22 so that the nozzle head is controlled to rotate
at a
speed lower than 30 RPM, preferably lower than 25 RPM and more preferably
lower than 20 RPM. The control device 24 may be controlled from above surface
by means of a control unit 39 shown in Fig. 4.
Before and after the cleaning operation, a logging unit of the cleaning tool
can in-
vestigate the casing to see which part or element of the casing needs to be
cleaned and if the element to be cleaned is properly cleaned.
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The nozzle head 12 may further comprise a check valve 40 in an end opposite
the end connected with the shaft 22.
The tool 10 may comprise a chamber with a cleaning fluid which is mixed with
the well fluid before being jetted out through the nozzles 13.
By fluid or well fluid is meant any kind of fluid which may be present in oil
or gas
wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By
gas is
meant any kind of gas composition present in a well, completion, or open hole,
and by oil is meant any kind of oil composition, such as crude oil, an oil-
containing fluid, etc. Gas, oil, and water fluids may thus all comprise other
ele-
ments or substances than gas, oil, and/or water, respectively.
By high pressurised fluid is meant fluid flowing at a volume flow rate of at
least
250 L/min, preferably at least 300 L/min and even more preferably 350 L/min.
By a casing is meant any kind of pipe, tubing, tubular, liner, string etc.
used
downhole in relation to oil or natural gas production.
In the event that the system is not submerged all the way into the casing, a
downhole tractor can be used to push the system all the way into position in
the
well. A downhole tractor is any kind of driving tool capable of pushing or
pulling
tools in a well downhole, such as a Well Tractor .
Although the invention has been described in the above in connection with pre-
ferred embodiments of the invention, it will be evident for a person skilled
in the
art that several modifications are conceivable without departing from the
inven-
tion as defined by the following claims.
