U.S. patent application number 14/358483 was filed with the patent office on 2014-10-23 for cleaning tool and a method for treating an inner surface of a casing.
This patent application is currently assigned to WELLTEC A/S. The applicant listed for this patent is WELLTEC A/S. Invention is credited to Jorgen Hallundb.ae butted.k.
Application Number | 20140311528 14/358483 |
Document ID | / |
Family ID | 47227821 |
Filed Date | 2014-10-23 |
United States Patent
Application |
20140311528 |
Kind Code |
A1 |
Hallundb.ae butted.k;
Jorgen |
October 23, 2014 |
CLEANING TOOL AND A METHOD FOR TREATING AN INNER SURFACE OF A
CASING
Abstract
The present invention relates to a cleaning tool for cleaning
and treating an inner surface of a downhole casing. The cleaning
tool comprises a tool housing, a mechanical cleaning tool section
comprising mechanical cleaning elements for releasing elements of
the inner surface of the casing in order to clean the casing to
become substantially free from rigid debris and other precipitated
materials, and a jetting tool section for ejecting an
enzyme-containing fluid onto the cleaned inner surface. The jetting
tool section comprises a fluid chamber comprising the
enzyme-containing fluid, and a nozzle head comprising at least one
nozzle. The invention further relates to a method for treating an
inner surface of a casing by means of the cleaning tool.
Inventors: |
Hallundb.ae butted.k; Jorgen;
(Graested, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WELLTEC A/S |
Allerod |
|
DK |
|
|
Assignee: |
WELLTEC A/S
Allerod
DK
|
Family ID: |
47227821 |
Appl. No.: |
14/358483 |
Filed: |
November 29, 2012 |
PCT Filed: |
November 29, 2012 |
PCT NO: |
PCT/EP2012/073914 |
371 Date: |
May 15, 2014 |
Current U.S.
Class: |
134/22.12 ;
15/4 |
Current CPC
Class: |
E21B 37/00 20130101;
C09K 2208/22 20130101; C23F 11/173 20130101; E21B 37/06 20130101;
E21B 27/02 20130101; C09K 8/54 20130101 |
Class at
Publication: |
134/22.12 ;
15/4 |
International
Class: |
E21B 37/02 20060101
E21B037/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2011 |
EP |
11191284.6 |
Claims
1. A cleaning tool (1) for cleaning and treating an inner surface
(3) of a downhole casing (2), comprising: a tool housing (14), a
mechanical cleaning tool section (30) comprising mechanical
cleaning elements for releasing elements of the inner surface of
the casing in order to clean the casing to become substantially
free from rigid debris and other precipitated materials, and a
jetting tool section (17) for ejecting an enzyme-containing fluid
onto the cleaned inner surface, comprising: a fluid chamber (7)
comprising the enzyme-containing fluid, and a nozzle head (16)
comprising at least one nozzle (13).
2. A cleaning tool according to claim 1, wherein the jetting tool
comprises a pumping device (9) for pressurising the fluid before
the fluid is let out through the nozzle head.
3. A cleaning tool according to claim 1 or 2, further comprising a
flow-hindering element (8) arranged outside the housing (14),
expandable against the inner surface of the casing so as to divide
the casing (3) into a first casing part (20) and a second casing
part (21).
4. A cleaning tool according to claim 3, wherein the flow-hindering
element is a sweeper (10) sweeping the inner surface of the casing
after the mechanical cleaning tool section has released elements of
the inner surface.
5. A cleaning tool according to any of the preceding claims,
wherein the mechanical cleaning elements are brushes (23).
6. A cleaning tool according to any of the preceding claims,
further comprising an inlet (15) for letting well fluid into the
tool (1), which inlet is in fluid communication with the nozzle
through a valve (12) so as to clean the inner surface before the
inner surface is treated with enzyme-containing fluid.
7. A cleaning tool according to any of the preceding claims,
wherein the nozzle head is extendable radially from the tool
housing for contacting the inner surface of the casing with the
enzyme-containing fluid.
8. A cleaning tool according to any of the preceding claims,
wherein the jetting tool further comprises a hydraulic control unit
(18) for controlling rotation of the nozzle head.
9. A cleaning tool according to any of the preceding claims,
wherein the mechanical cleaning tool section comprises a pumping
device for pumping fluid containing elements released by the
brushes and ejecting the fluid through an outlet (22) of a first
end (24) or second end (25) of the cleaning tool.
10. A cleaning tool according to any of the preceding claims,
further comprising a coating tool section (28) for coating the
inner surface of the casing.
11. A cleaning tool according to any of the preceding claims,
further comprising a driving unit (26) for propelling the tool
forward in the casing.
12. A method for treating an inner surface of a casing by means of
the cleaning tool according to any of the preceding claims, wherein
the contact of the inner surface of the downhole casing with an
enzyme comprises the steps of: providing an enzyme-containing fluid
in the fluid chamber of the jetting tool (17), cleaning the casing
to remove rigid debris and other precipitated materials, such as
scales, by applying a mechanical cleaning tool section comprising
brushes for brushing the inner surface of a casing downhole in
order to clean the casing to become substantially free from any
elements, such as rigid debris and other precipitated materials,
jetting the fluid through the nozzle head towards the inner surface
of the casing in a jet stream, and contacting the inner surface of
the casing with the enzyme-containing fluid in a jet stream.
13. A method according to claims 12, further comprising a final
step of arranging a wax layer on the inner surface of the casing,
comprising the steps of: providing a fluid containing wax particles
in a first casing part, activating a pumping device and
pressurising the first casing part, jetting the fluid containing
wax particles through the nozzle head towards the inner surface of
the casing in the second casing part in a jet stream, and arranging
the wax layer on the inner surface of the casing by the jet
stream.
14. A method according to claim 12 or 13, further comprising a
final step of arranging a layer of nanoparticles on the inner
surface of the casing, comprising the steps of: providing a liquid
containing nanoparticles in a first casing part, activating a
pumping device and pressurising the first casing part, jetting the
liquid through a nozzle head towards the inner surface of the
casing in the second casing part in a jet stream, and arranging the
layer of nanoparticles on the inner surface of the casing by the
jet stream.
15. A method according to any of claims 12-14, further comprising
an initial step of preparing surfaces of downhole casing parts,
such as casings, pipes, tubes, valves, plugs and collars, which may
come into contact with borehole fluids, comprising the steps of:
coating an inner surface of a casing part with a nanocover
material, and mounting the coated casing part to the casing.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a cleaning tool for
cleaning and treating an inner surface of a downhole casing and to
a method for treating an inner surface of a casing by means of the
cleaning tool.
BACKGROUND ART
[0002] Downhole borehole operations are becoming more and more
sophisticated with regard to tool operations, but also with regard
to the complexity of borehole casing parts, such as valves, sliding
sleeves, production zones, etc. This increased complexity results
in an increased demand for solutions as to how to avoid undesirable
effects, such as corrosion and fouling of the borehole casing
parts. Chemical incrustation is a major cause of decreased well
performance and eventual failure. Fouling can be described as
clogging and failure of mechanical downhole parts, e.g. due to
creation of scale, debris or similar elements. The effect of the
precipitating and depositing of minerals can plug and close valves
and sliding sleeves within a relatively short period of time.
Hence, a need exists for an effective method for avoiding
corrosion, depositing or fouling in downhole environments.
SUMMARY OF THE INVENTION
[0003] 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 tool for cleaning a
well and a method of preventing fouling which are cheaper and less
toxic than tools and methods associated with chemical cleaning.
[0004] The above objects, together with numerous other objects,
advantages, and features, which will become evident from the below
description, are accomplished by a solution in accordance with the
present invention by a cleaning tool for cleaning and treating an
inner surface of a downhole casing, comprising: [0005] a tool
housing, [0006] a mechanical cleaning tool section comprising
mechanical cleaning elements for releasing elements of the inner
surface of the casing in order to clean the casing to become
substantially free from rigid debris and other precipitated
materials, and [0007] a jetting tool section for ejecting an
enzyme-containing fluid onto the cleaned inner surface, comprising:
[0008] a fluid chamber comprising the enzyme-containing fluid, and
[0009] a nozzle head comprising at least one nozzle.
[0010] In an embodiment, the jetting tool may comprise a pumping
device for pressurising the fluid before the fluid is let out
through the nozzle head.
[0011] In another embodiment, the cleaning tool may further
comprise an inlet for letting well fluid into the tool.
[0012] In a third another embodiment, the cleaning tool may further
comprise a mixing chamber for mixing the well fluid with the
enzyme-containing fluid before the fluid is ejected out through the
nozzle head.
[0013] In a fourth embodiment, the cleaning tool may further
comprise a flow-hindering element arranged outside the housing,
expandable against the inner surface of the casing so as to divide
the casing into a first casing part and a second casing part.
[0014] The flow-hindering element may be a sweeper sweeping the
inner surface of the casing after the mechanical cleaning tool
section has released elements of the inner surface.
[0015] Furthermore, the cleaning tool may further comprise a
sweeper sweeping the inner surface of the casing after the
mechanical cleaning tool section has released elements of the inner
surface.
[0016] Moreover, the mechanical cleaning elements may be
brushes.
[0017] In an embodiment, the cleaning tool as described above may
further comprise an inlet for letting well fluid into the tool,
which inlet is in fluid communication with the nozzle through a
valve so as to clean the inner surface before the inner surface is
treated with enzyme-containing fluid.
[0018] Furthermore, the nozzle head may be extendable radially from
the tool housing for contacting the inner surface of the casing
with the enzyme-containing fluid.
[0019] Additionally, the jetting tool may further comprise a
hydraulic control unit for controlling rotation of the nozzle
head.
[0020] Having a hydraulic control unit for controlling which
nozzles are ejecting fluid ensures that the nozzles not facing the
object to be cleaned are not ejecting fluid and that all the
pressure in the fluid is used for ejecting fluid through the
nozzle/nozzles facing the object to be cleaned. Thus, no energy of
the pressurised fluid is wasted on nozzles not facing the object to
be cleaned, and/or no energy is wasted on rotating the nozzle head.
Furthermore, by controlling which nozzle/nozzles is/are allowed to
eject fluid, it is possible to ensure that only one or few of the
nozzles is/are in fact ejecting fluid, and the pressure of the
fluid ejected from that or those nozzles is thus significantly
higher than if the fluid was ejected through all the nozzles at the
same time, even if the object to be cleaned is extending along the
entire circumference of the casing. In this way, each nozzle is
able to clean harder materials, such as scales, than nozzles of
prior art tools where most of the energy of the pressurised fluid
is used for rotating the nozzles.
[0021] In one embodiment, the hydraulic control unit may comprise a
motor for breaking the free rotation of the nozzle head.
[0022] Moreover, the mechanical cleaning tool section may comprise
a pumping device for pumping fluid containing elements released by
the brushes and ejecting the fluid through an outlet of a first end
or second end of the cleaning tool.
[0023] The cleaning tool as described above may further comprise a
coating tool section for coating the inner surface of the
casing.
[0024] Furthermore, the coating tool section may comprise a brush
arranged on a projectable brush arm and wherein coating is ejected
through openings in the brush and the brush arm is rotated around a
tool axis for contacting an inner surface of the casing with the
coating.
[0025] Also, the cleaning tool as described above may further
comprise a driving unit for propelling the tool forward in the
casing.
[0026] Additionally, the tool may further comprise a wax fluid
chamber comprising fluid containing wax particles.
[0027] In an embodiment, the wax particles may comprise ceramic
particles having a significantly higher density than the wax.
[0028] Furthermore, the wax particles may comprise magnetic
particles, and the wax particles comprising magnetic particles may
be retained near the casing wall due to magnetic attraction between
the casing and the magnetic particles.
[0029] Said inner surface may be comprised in an oil and gas well
drilling system.
[0030] The present invention furthermore relates to a method for
treating an inner surface of a casing by means of the cleaning tool
according to any of the preceding claims, wherein the contact of
the inner surface of the downhole casing with an enzyme comprises
the steps of: [0031] providing an enzyme-containing fluid in the
fluid chamber of the jetting tool, [0032] cleaning the casing to
remove rigid debris and other precipitated materials, such as
scales, by applying a mechanical cleaning tool section comprising
brushes for brushing the inner surface of a casing downhole in
order to clean the casing to become substantially free from any
elements, such as rigid debris and other precipitated materials,
[0033] jetting the fluid through the nozzle head towards the inner
surface of the casing in a jet stream, and [0034] contacting the
inner surface of the casing with the enzyme-containing fluid in a
jet stream.
[0035] Moreover, the contact of the inner surface of the downhole
casing with an enzyme may comprise the steps of providing a fluid
containing enzymes in a fluid chamber of a jetting tool, activating
a pumping device in the jetting tool and pressurising the fluid
chamber of the jetting tool, jetting the fluid through a nozzle
head towards the inner surface of the casing in a jet stream, and
contacting the inner surface of the casing with an enzyme in a jet
stream.
[0036] Further, the fluid chamber may be cooled. Since the activity
of the enzymes may be deteriorated by elevated temperatures, the
fluid chamber containing enzymes may be cooled to below a critical
temperature, such that all enzymes are viable when applied downhole
in the borehole. Temperature fluctuations downhole may be caused by
various different effects, such as high temperature fluids flowing
past the tool, high temperature regions of the formation, e.g. due
to proximity of magma layers, explosions during perforations and so
on. Therefore, temperature control of the fluid chamber may help
avoid damages to the enzymes downhole.
[0037] Moreover, the method as described above may further comprise
a final step of arranging a wax layer on the inner surface of the
casing, the method comprising the steps of providing a fluid
containing wax particles in a first casing part, activating a
pumping device and pressurising the first casing part, jetting the
fluid containing wax particles through the nozzle head towards the
inner surface of the casing in the second casing part in a jet
stream, and arranging the wax layer on the inner surface of the
casing by the jet stream.
[0038] In one embodiment, the particles may be made of metal.
[0039] The method as described above may further comprise a final
step of arranging a layer of nanoparticles on the inner surface of
the casing, comprising the steps of providing a liquid containing
nanoparticles in a first casing part, activating a pumping device
and pressurising the first casing part, jetting the liquid through
a nozzle head towards the inner surface of the casing in the second
casing part in a jet stream, and arranging the layer of
nanoparticles on the inner surface of the casing by the jet
stream.
[0040] In addition, the method as described above may further
comprise an initial step of preparing surfaces of downhole casing
parts, such as casings, pipes, tubes, valves, plugs and collars,
which may come into contact with borehole fluids, comprising the
steps of coating an inner surface of a casing part with a nanocover
material, and mounting the coated casing part to the casing.
[0041] Finally, the method as described above may further comprise
a step of preparing surfaces of downhole casing parts, such as
casings, pipes, tubes, valves, plugs and collars, which may come
into contact with borehole fluids, comprising the steps of lowering
a coating tool into the borehole, and coating at least a surface of
a casing part with a nanocover material.
[0042] In one embodiment, the nanocover material may be
graphene.
[0043] Moreover, the nanocover may be below 500 nanometers in
thickness, such as below 100 nm, such as below 50 nm, such as below
20 nm, such as below 10 nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] The invention and its many advantages will be described in
more detail below with reference to the accompanying schematic
drawings, which for the purpose of illustration show some
non-limiting embodiments and in which
[0045] FIG. 1 shows a partly cross-sectional view of a tool
according to the invention,
[0046] FIG. 2 shows another embodiment of the tool having brushes
for cleaning an inner surface of a borehole casing,
[0047] FIG. 3 shows another embodiment of the tool having a jetting
tool section for cleaning the inner surface of the borehole
casing,
[0048] FIG. 4 shows yet another embodiment of the tool for cleaning
the inner surface of the borehole casing,
[0049] FIG. 5 shows an embodiment of the tool arranged in a section
of the borehole casing comprising a mechanical sliding sleeve,
[0050] FIG. 6 shows yet another embodiment of the tool,
[0051] FIG. 7 shows yet another embodiment of the tool, and
[0052] FIG. 8 shows yet another embodiment of the tool for cleaning
and coating the inner surface of the borehole casing.
[0053] 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.
DETAILED DESCRIPTION OF THE INVENTION
[0054] The present invention relates to a cleaning tool 1 for
inhibiting corrosion or degrading of a downhole casing 2 by
hindering scale 5 being deposited on an inner surface of the
casing. FIG. 1 shows how an enzyme-containing fluid 4 is ejected
from an ejecting member 6 or nozzles 13 comprised in a nozzle head
16 of the cleaning tool 1. By ejecting the enzyme-containing fluid
4 towards the inner surface 3 of the borehole casing 2, the enzymes
come into contact with the inner surface 3. To hinder any future
deposits of scale 5 or similar layers on the inner surface, the
enzyme-containing fluid 4 needs to contact a clean surface, and to
this effect, an initial cleaning step of releasing the rigid scale
or debris and other deposit materials may be carried out. This
cleaning step may be performed by a mechanical cleaning tool
section 30 comprising mechanical cleaning elements 23 for releasing
elements, such as scales, of the inner surface of the casing 2. The
mechanical cleaning tool section 30 is connected with the nozzle
head 16 so that when the cleaning tool 1 moves forwards or
backwards in the well, the mechanical cleaning tool section 30
releases the scale or debris of the inner surface 3, and
subsequently, the enzyme-containing fluid 4 is ejected from the
nozzle head 16 to contact the cleaned surface. Thus, if the
cleaning tool 1 is retracted while cleaning and treating the
casing, the mechanical cleaning tool section 30 is arranged closest
to the top of the well, as shown in FIG. 2, and if the cleaning
tool is moving forward while cleaning and treating the casing, the
nozzle head 16 is arranged closest to the top of the well, as shown
in FIG. 1.
[0055] As shown in FIG. 1, the tool further comprises a jetting
tool section 17 for contacting the inner surface of the downhole
casing with an enzyme. The fluid containing enzymes 4 is contained
in a fluid chamber 7 of the jetting tool 17, and after pressurising
the chamber 7, either by a pumping device 9 downhole pressurising
locally in the jetting tool chamber 7 or by a pumping device uphole
(not shown), e.g. pressurising the entire borehole casing above the
jetting tool 17, the fluid 4 containing enzymes may be jetted
through the nozzle head 16 towards the inner surface 3 of the
casing in a jet stream, thereby contacting the inner surface of the
casing with an enzyme in the jet stream.
[0056] A mechanical cleaning tool section 30 for carrying out the
above-mentioned mechanical cleaning using brushes 23 is shown in
FIG. 1. The mechanical cleaning tool section 30 may comprise
brushes 23 for brushing the interior of the casing downhole in
order to clean the casing to become substantially free from rigid
debris and other precipitated materials. In another embodiment, the
initial step of cleaning the casing to remove rigid debris and
other deposit materials, such as scales, may alternatively be
carried out by another mechanical cleaning tool section 30 in the
form of the jetting tool section 17, as shown in FIG. 3. The
jetting tool 17 may be very powerful in removing even rigid debris
and other precipitated materials strongly attached to the inner
surface of the borehole.
[0057] Scale is formed downhole by constituents from the formation
and/or from fluid injected into the well. Scale tends to deposit on
the inner surface of the casing in a heterogeneous reaction, but by
applying enzymes onto the clean inner surface 3, the enzymes react
with the scale constituents, causing the scale to form as a
homogeneous reaction rather than a heterogeneous reaction. The
enzymes thus promote a homogeneous reaction where the scale
precipitates in the fluid and does not deposit on the inner surface
of the casing. The enzymes for promoting a homogeneous reaction may
be ligases.
[0058] FIG. 2 shows the cleaning tool 1 comprising a tool housing
14 and an inlet 15 for letting well fluid into the tool 1, and the
inlet 15 is arranged inside the tool in fluid communication with
the nozzles 13, as illustrated by the dotted lines. The well fluid
travels in through the inlet and out through the nozzle head 16, as
illustrated by arrows. The well fluid is mixed with the
enzyme-containing fluid 4 inside the cleaning tool before being
ejected onto the nozzle head 16. The cleaning tool is submerged
into the casing 2 in the well, and a flow-hindering element 8
arranged outside the housing 14 is set or inflated so that it
divides the casing 3 into a first 20 and a second casing part 21.
Thereby, the well fluid in the first casing part 20 can be
pressurised, and the fluid is forced into the inlets 15 and out
through the nozzles 13. 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 in the well fluid in the second part of the casing. The
flow-hindering element 8 also has the function of sweeping the
inner surface 3 of the casing 2 after the mechanical cleaning tool
section 30 has released the scales 5 as the tool 1 is moved forward
in the well, forward being downwards in FIG. 2. The flow-hindering
element is thus also functioning as a sweeper.
[0059] In FIG. 3, the cleaning tool 1 is also submerged into the
casing 3 in the well, and the flow-hindering element 8 is arranged
outside the housing 14, dividing the casing 3 into the first 20 and
the second casing part 21. The well fluid in the first casing part
20 is pressurised, and the fluid is forced into the inlets 15 and
out through the nozzles 13 in the jetting tool section 17 for
cleaning the surface 3. The well fluid jetted through the jetting
tool section 17 is not mixed with the fluid for cleaning the inner
surface, as a valve directs part of the fluid into the jetting tool
section and not through the chamber. In some embodiments, the
cleaning fluid may therefore be fluid from the casing jetted
through the nozzles, and not a special cleaning fluid contained in
a fluid chamber in the jetting tool section 17. The other part of
the fluid is directed into the mixing chamber to be mixed with the
enzyme-containing fluid 4 and ejected through the nozzle head 16 to
contact the clean inner surface with enzymes. The sweeper 10
arranged between the jetting tool section 17 and the nozzle head 16
sweeps the inner surface from released scale 5 before the surface
is contacted by enzymes.
[0060] The cleaning tool of FIG. 3 further comprises a hydraulic
control unit 18 for controlling rotation of the nozzle head. The
jetting tool section may in a similar manner comprise a hydraulic
control unit 18 for controlling the nozzle head of the jetting tool
section 17. The hydraulic control unit may comprise an electric
motor for breaking the free rotation of the nozzle head. Having a
hydraulic control unit for controlling which nozzles are ejecting
fluid ensures that the nozzles not facing the object to be cleaned
are not ejecting fluid and that all the pressure 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
wasted on nozzles not facing the object to be cleaned, and/or no
energy is wasted on rotating the nozzle head. Furthermore, by
controlling which nozzle/nozzles is/are allowed to eject fluid, it
is possible to ensure that only one or few of the nozzles is/are in
fact ejecting fluid, and the pressure of the fluid ejected from
that or these nozzles is thus significantly higher than if the
fluid was ejected through all the nozzles at the same time, even if
the object is extending along the entire circumference of the
casing. In this way, each nozzle is able to clean harder materials,
such as scales, than nozzles of prior art tools where most of the
energy of the pressurised fluid is used for rotating the
nozzles.
[0061] In FIG. 4, the pumping device 9 pumps fluid into the tool 1,
which fluid is subsequently mixed with enzymes from the chamber 7
in the mixing chamber 11 before being ejected through the nozzle
head 16.
[0062] Scale may cause clogging or malfunction of a mechanical
device, such as a sliding sleeve downhole. Scale depositing on
mechanical devices may be inhibited by contacting the mechanical
device with an enzyme-containing fluid by means of the tool 1, as
shown in FIG. 5. The sliding sleeve 19 and the inner surface 3 of
the casing are cleaned by brushes which are made of cut plates but
may in another embodiment be made of wires extending radially
outwards, as shown in FIG. 6. The mechanical cleaning tool section
of FIG. 5 comprises a pumping device 9 for pumping fluid containing
elements released by the brushes and ejecting the fluid through an
outlet 22 of a first end 24 or second end 25 of the cleaning
tool.
[0063] As shown in FIG. 7, the nozzle head 16 is extendable
radially from the tool housing for contacting the inner surface of
the casing with the enzyme-containing fluid. In FIG. 6, the nozzle
head 16 is in its retracted position, and in FIG. 7, the nozzle
head 16 is in its projected position, extending radially outwards
from the tool axis. The cleaning tool 1 of FIGS. 6 and 7 comprises
two driving units 26 powered by wireline 27 for propelling the tool
forward in the casing.
[0064] In FIG. 7, the cleaning tool further comprises a coating
tool section 28 for coating the inner surface of the casing. In
FIG. 8, the coating tool section 28 comprises a brush 31 arranged
on a projectable brush arm 32, and coating is ejected through
openings in the brush while the brush arm is rotated around a tool
axis 40 for contacting the inner surface 3 of the casing 2 with the
coating. The brush thus coats the cleaned inner surface of the
casing before the enzyme-containing fluid 4 is ejected to contact
the inner surface.
[0065] The tool may further comprise a wax fluid chamber comprising
fluid containing wax particles which, like the coating, is applied
to the surface of the casing before the casing is treated with
enzymes. The wax particles may comprise ceramic particles having a
significantly higher density than the wax so that the wax particles
may be ejected through nozzles or ejecting members 6 to contact the
inner surface of the casing. The wax particles may also comprise
magnetic particles, and the ejected wax particles comprising
magnetic particles are thus retained near the casing wall due to
magnetic attraction between the casing and the magnetic
particles.
[0066] The enzyme-containing fluid may also contain wax, adhesive
or similar constituents to be able to adhere to the inner surface.
The enzymes are then slowly "washed off" or "abraded" and mixed
with the well fluid to promote a homogeneous reaction, and scales
are thus formed in the well fluid and drops to the bottom of the
well in a vertical well.
[0067] The nozzles of the nozzle head may be angled in relation to
a radial direction of the nozzle head being perpendicular to the
tool axis. The nozzles are arranged in rows and along a
circumference of the nozzle head with a mutual circumferential
distance. By angling the nozzles, the rotation of the nozzle head
is provided by the pressurised fluid.
[0068] Due to elevated downhole temperatures, enzymes are
preferably thermophile or hyperthermophile in order to withstand
temperatures above 50 degrees Celsius, such as above 60 degrees
Celsius, such as above 70 degrees Celsius, such as above 80 degrees
Celsius, such as above 90 degrees Celsius, such as above 100
degrees Celsius, such as above 110 degrees Celsius, such as above
120 degrees Celsius, such as above 130 degrees Celsius, such as
above 140 degrees Celsius, such as above 150 degrees Celsius, such
as even above 200 degrees Celsius.
[0069] As known from examples such as an ordinary carwash, a wax
layer may be arranged on a cleaned surface to extend the period of
maintaining a clean surface and to inhibit corrosion effects.
Applying wax to a surface in a downhole environment is, however, a
much more difficult task due to the nature of the downhole
environment being a casing filled with various fluids, e.g.
drilling muds, oil, water, acid, etc. Therefore, application of a
light and relatively volatile substance, such as a wax, is quite
difficult. However, by injecting wax particles into a pressurised
fluid chamber of the jetting tool section 17 and subsequently
ejecting them towards the inner surface of the borehole casing in a
jet stream may enable the user to arrange a layer of wax on the
inner surface.
[0070] Furthermore, experiments have shown that in very troublesome
conditions, such as during high fluid flow rates in the borehole
casing, very good results have been obtained by encapsulating
relatively heavy ceramic particles, such as aluminium oxide
particles encapsulated in wax, thereby constituting a ceramic
carrier material and ejecting these wax-encapsulated ceramic
particles towards the inner surface of the borehole casing. These
wax-encapsulated ceramic particles are much more easily directed
through a flowing fluid, such as by the jetting stream, in order to
reach the inner surface of the borehole casing or other mechanical
parts, preferably to be covered by a wax layer after cleaning and
application of enzyme since the density of the wax may be
significantly increased by the ceramic carrier material. The
particles may also be made of another suitable material, such as
metals, alloys, etc.
[0071] Furthermore, experiments have also shown that extension of
the period wherein the surface is clean by applying a wax layer may
be prolonged by adding magnetic particles also encapsulated by wax
to increase adherence to the inner surface of the borehole casing
by magnetic attraction between particles and casing, when the
casing is magnetic.
[0072] Other materials such as nano-scaled materials, e.g.
self-assembling nanotube layers, graphene layers, nano-crystalline
thin films, etc., may be used to cover the inner surface of the
borehole casing or mechanical casing parts, such as sliding
sleeves, in order to avoid or inhibit rigid debris, precipitated
materials and scale. The nano-scaled materials may be applied to
the casing components before mounting the casing parts in the
borehole or before the nano-scaled materials are applied downhole
by a downhole tool, such as a jetting tool section. The nano-scaled
materials may comprise enzymes diffusing slowly to the surface
facing the well fluid in the casing and thus mixing with the well
fluid.
[0073] The preparation of casing part surfaces may include
application of nano-scaled materials on pipes, tubes, valves,
plugs, collars which may come into contact with borehole
fluids.
[0074] By well fluid is meant any kind of fluid that 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
elements or substances than gas, oil, and/or water,
respectively.
[0075] By a casing is meant any kind of pipe, tubing, tubular,
liner, string etc. used downhole in relation to oil or natural gas
production.
[0076] In the event that the tool is not submergible all the way
into the casing, a downhole tractor can be used to push the tool
all the way into position in the well. The downhole tractor may
have projectable arms having wheels, wherein the wheels contact the
inner surface of the casing for propelling the tractor and the tool
forward in the casing. A downhole tractor is any kind of driving
tool capable of pushing or pulling tools in a well downhole, such
as a Well Tractor.RTM..
[0077] Although the invention has been described in the above in
connection with preferred embodiments of the invention, it will be
evident for a person skilled in the art that several modifications
are conceivable without departing from the invention as defined by
the following claims.
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