U.S. patent application number 14/420430 was filed with the patent office on 2015-08-06 for downhole turbine-driven system.
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, Lars Mangal, Ricardo Reves Vasques.
Application Number | 20150218900 14/420430 |
Document ID | / |
Family ID | 46750205 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150218900 |
Kind Code |
A1 |
Hallundb.ae butted.k; Jorgen ;
et al. |
August 6, 2015 |
DOWNHOLE TURBINE-DRIVEN SYSTEM
Abstract
The present invention relates to a downhole system for
performing an operation in a well downhole. The system comprises an
elongated tubing string (3) for conducting fluid in the well; a
turbine (7) driven by the fluid for driving a shaft (8); a
generator (9) driven by the turbine by means of the shaft, a
fluid-driven driving section (5) comprising a pump (6) driven by
the fluid supplied through the shaft for propelling the
fluid-driven driving section and the tubing string forward in the
well, and an electrically driven driving section (10) comprising an
electrical motor (11) powered by the generator (9) for propelling
the driving section and the tubing string forward in the well,
wherein the fluid-driven driving section (5) is arranged between
the generator (9) and the electrically driven driving section
(10).
Inventors: |
Hallundb.ae butted.k; Jorgen;
(Graested, DK) ; Mangal; Lars; (Hellerup, DK)
; Vasques; Ricardo Reves; (Holte, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WELLTEC A/S |
Allerod |
|
DK |
|
|
Assignee: |
WELLTEC A/S
Allerod
DK
|
Family ID: |
46750205 |
Appl. No.: |
14/420430 |
Filed: |
August 9, 2013 |
PCT Filed: |
August 9, 2013 |
PCT NO: |
PCT/EP2013/066724 |
371 Date: |
February 9, 2015 |
Current U.S.
Class: |
166/66.4 |
Current CPC
Class: |
E21B 43/25 20130101;
E21B 41/0085 20130101; E21B 23/14 20130101; E21B 23/001
20200501 |
International
Class: |
E21B 23/14 20060101
E21B023/14; E21B 43/25 20060101 E21B043/25; E21B 41/00 20060101
E21B041/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2012 |
EP |
12180078.3 |
Claims
1. A downhole system for performing an operation in a well
downhole, comprising: an elongated tubing string for conducting
fluid in the well, a turbine driven by the fluid for driving a
shaft, a generator driven by the turbine by means of the shaft, and
a fluid-driven driving section comprising a pump driven by the
fluid supplied through the shaft for propelling the fluid-driven
driving section and the tubing string forward in the well, wherein
the system further comprises an electrically driven driving section
comprising an electrical motor powered by the generator for
propelling the driving section and the tubing string forward in the
well, the fluid-driven driving section being arranged between the
generator and the electrically driven driving section.
2. A downhole system according to claim 1, wherein the generator
and the electrical motor are electrically connected through an
electrical connection extending through the fluid-driven driving
section.
3. A downhole system according to claim 1, wherein the fluid from
the tubing string is supplied to the pump of the fluid-driven
driving section through a fluid channel extending through the
turbine and the generator.
4. A downhole system according to claim 1, wherein the driving
section comprises propelling units contacting an inner surface of
the well for propelling the driving sections forward in the
well.
5. A downhole system according to claim 4, wherein the propelling
units are non-hydraulically driven units and driven by the
electrical motor.
6. A downhole system according to claim 4, wherein the propelling
units are wheels contacting an inner surface of the well.
7. A downhole system according to claim 6, wherein each wheel is
arranged on a projectable wheel arm.
8. A downhole system according to any of claim 4, wherein each
propelling unit of the electrically driven driving section
comprises an electrical motor powered by the generator.
9. A downhole system according to claim 1, wherein the electrically
driven driving section comprises a pump driven by the electrical
motor for driving the electrically driven driving section forward
in the well.
10. A downhole system according to claim 1, wherein the
electrically driven driving section comprises a rechargeable
battery.
11. A downhole system according to claim 1, further comprising a
flow diverter for diverting at least part of the fluid from the
tubing string into the well.
12. A downhole system according to claim 11, wherein the flow
diverter is arranged in a dispersion unit for dispersion of fluids,
such as chemical reactants in the well.
13. A downhole system according to claim 1, further comprising an
inflation unit for shielding the driving section while a
stimulation operation is performed or the well is treated with an
acid or base containing fluid.
14. A downhole system according to claim 1, further comprising a
detachment unit for detaching the driving section from the tubing
string.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a downhole system for
performing an operation in a well downhole, comprising an elongated
tubing string for conducting fluid in the well.
BACKGROUND ART
[0002] Hydrocarbon wells often have more than one branch or lateral
radiating from the main borehole. The laterals may again have
laterals and be of various lengths. When a borehole having a long
lateral have been completed, the borehole is treated with acid to
make the hydrocarbon-containing fluid flow and the production is
initiated. In order to perform an acid treatment in a lateral, the
coiled tubing is pushed down through the borehole or cased hole
into the lateral. However, when the coiled tubing is pushed down
from surface, it tends to curl as its moves into the lateral which
is more horizontal than the main borehole, and at some point the
coiled tubing gets stuck in the lateral. The laterals are therefore
not made as long as it is actually possible to drill them, as the
later acid and service equipment is not able to enter the last part
of such long laterals, as the known equipment cannot enter laterals
with such a small diameter.
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 an improved downhole
system capable of servicing a long lateral with a tubing
string.
[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 downhole system for performing an operation
in a well downhole, comprising: [0005] an elongated tubing string
for conducting fluid in the well, [0006] a turbine driven by the
fluid for driving a shaft, [0007] a generator driven by the turbine
by means of the shaft, and [0008] a fluid-driven driving section
comprising a pump driven by the fluid supplied through the shaft
for propelling the fluid-driven driving section and the tubing
string forward in the well, wherein the system further comprises an
electrically driven driving section comprising an electrical motor
powered by the generator for propelling the driving section and the
tubing string forward in the well, the fluid-driven driving section
being arranged between the generator and the electrically driven
driving section.
[0009] In an embodiment, the pump may be driven by the shaft of the
turbine.
[0010] Furthermore, the elongated tubing string may be coiled
tubing.
[0011] Furthermore, the driving sections may have outer diameters
of less than 7 inches, preferably less than 6 inches, and more
preferably less than 5 inches.
[0012] Moreover, the tubing string may have a length of at least 5
km, preferably a length of at least 7 km, more preferably a length
of at least 9 km, and even more preferably a length of at least 10
km.
[0013] Additionally, the generator and the electrical motor may be
electrically connected through an electrical connection extending
through the fluid-driven driving section.
[0014] Also, the fluid from the tubing string may be supplied to
the pump of the fluid-driven driving section through a fluid
channel extending through the turbine and the generator.
[0015] In addition, a pressure control valve may be arranged in the
fluid channel for reducing the passage of fluid to the pump of the
fluid-driven driving section.
[0016] Further, a flow diverter valve may be arranged in the fluid
channel for diverting the fluid supplied to the channel to the
turbine.
[0017] Moreover, the driving section may comprise propelling units
contacting an inner surface of the well for propelling the driving
sections forward in the well.
[0018] Also, the propelling units may be non-hydraulically driven
units and driven by the electrical motor.
[0019] Furthermore, the propelling units may be wheels contacting
an inner surface of the well.
[0020] In an embodiment, each wheel may be arranged on a
projectable wheel arm.
[0021] In addition, the wheel arms of the fluid-driven driving
section may project in a first direction from a section housing,
and the wheel arms of the electrically driven driving section may
project in a second direction substantially perpendicular to the
first direction.
[0022] Furthermore, the electrical motor may drive the wheels of
the electrically driven driving section.
[0023] Moreover, each propelling unit of the electrically driven
driving section may comprise an electrical motor powered by the
generator.
[0024] Additionally, the electrically driven driving section may
comprise a pump driven by the electrical motor for driving the
electrically driven driving section forward in the well.
[0025] The downhole system may further comprise a second
electrically driven driving section driven by the generator through
an electrical connection in the other electrically driven driving
section arranged closest to the tubing string.
[0026] In one embodiment, the electrically driven driving section
arranged closest to the tubing string may comprise a pump for
driving hydraulically driven propelling units.
[0027] Moreover, the second electrically driven driving section may
comprise propelling units which are non-hydraulically driven
units.
[0028] In another embodiment, each propelling unit of the second
electrically driven driving section may comprise an electrical
motor powered by the generator.
[0029] Furthermore, the electrically driven driving section may
comprise a rechargeable battery.
[0030] The downhole system may further comprise a flow diverter for
diverting at least part of the fluid from the tubing string into
the well.
[0031] It is hereby possible to perform acid treatment of the well
after the tubing string has been pulled all the way into the very
long lateral by starting to pump an acid composition into the
tubing string from surface.
[0032] In an embodiment, the flow diverter may be arranged in a
dispersion unit for dispersion of fluids, such as chemical
reactants in the well.
[0033] The chemical reactants may be acid or base containing
fluid.
[0034] The downhole system may further comprise an inflation unit
for shielding the driving section while a stimulation operation is
performed or the well is treated with an acid or base containing
fluid.
[0035] Furthermore, the downhole system may comprise a detachment
unit for detaching the driving section from the tubing string.
[0036] In an embodiment, the detachment unit may be comprised in
the dispersion unit.
[0037] Furthermore, the downhole system may comprise several
electrically driven driving sections, all powered by the
generator.
[0038] Moreover, the downhole system may comprise several
generators driven by the shaft.
[0039] Finally, the present invention relates to a stimulation
method for performing acid treatment of a long lateral by the
downhole system described above, comprising the steps of: [0040]
connecting the turbine with the tubing string, [0041] connecting
the generator with the turbine, [0042] connecting the fluid-driven
driving section with the turbine, [0043] connecting the
electrically driven driving section with the fluid-driven driving
section so that electricity is conducted from the generator to the
electrically driven driving section, [0044] supplying pressurised
fluid into the tubing string, [0045] pulling the tubing string into
the lateral by means of the driving sections, and [0046] supplying
fluid having an acid concentration down the tubing string to an
outlet in the downhole system for treating the lateral with
acid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] 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
[0048] FIG. 1 shows a downhole system according to the present
invention,
[0049] FIG. 2 shows a side view of a downhole system according to
the invention,
[0050] FIG. 3 shows a side view of another downhole system
according to the invention,
[0051] FIG. 4 shows a side view of the downhole system according to
FIG. 1,
[0052] FIG. 5 shows a side view of another embodiment of the
downhole system,
[0053] FIG. 6 shows a cross-sectional view of the fluid-driven
driving section shown in FIG. 4,
[0054] FIG. 7 shows a side view of another downhole system,
[0055] FIG. 8 shows a side view of yet another downhole system,
[0056] FIG. 9 shows a side view of yet another downhole system in
its deflated position, and
[0057] FIG. 10 shows the downhole system in its inflated and
detached position.
[0058] 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
[0059] FIG. 1 shows a hydrocarbon well 2 having laterals radiating
from a main borehole 12. In one of the long laterals 13, a tubing
string 3, also called coiled tubing, is being pulled into the more
horizontal part of the lateral 13 by two driving sections 5, 10,
being a fluid-driven driving section 5 and an electrically driven
driving section 10. The driving sections 5, 10 propel themselves
and the tubing string within a casing 15 in the lateral. The
driving sections 5, 10 are connected with the end 14 of the tubing
string which is the furthest away from a well head 30 at the top of
the well at the surface or seabed. When entering long laterals by
forcing a tubing string down the well, the tubing string will curl
at some point--also called the "coiled tubing hang-up point"--which
causes the string to get stuck. By arranging the driving sections
in front of the tubing string, the end of the tubing string is
forced forward, preventing the string from curling and getting
stuck, and the tubing string is thereby pulled further into the
lateral beyond the hang-up point.
[0060] Today, laterals are made as long as operation and service
equipment are able to operate and service along the entire length
of the lateral. Once the operation equipment is able to enter
further into the ground, the borehole and the laterals can be made
longer. Laterals are made with a substantially smaller diameter
than the main borehole, which limits the diameter of the equipment
and service tools and thus the types of equipment and tools capable
of entering even the final and smallest part of a long lateral.
Before a well is able to produce, it is subjected to acid
treatment. In order to treat even the final part of the lateral,
i.e. the part which is the furthest away from the main borehole,
with acid, the tubing string supplying the acid needs to be pulled
almost all the way to the end of the lateral. If this is not done,
the tubing string will curl, which will render acid treatment of
the entire lateral impossible and thereby prevent it from producing
hydrocarbons. Pulling tools which are able to pull the tubing in
the narrow and long laterals therefore need to be self-powered as
they cannot be powered sufficiently through wireline from
surface.
[0061] Therefore, between the driving sections 5, 10 and the tubing
string 3, a turbine 7 is connected with the tubing string and is
driven by high pressure fluid supplied through the tubing string
from the top of the well. The turbine 7 drives a generator 9
supplying power through the fluid-driven driving section 5 to the
electrically driven driving section 10. When the driving sections
enter the end or final part of the lateral, the lateral diameter is
highly reduced, meaning that the diameter of the driving sections
needs to be equally smaller. Therefore, there is no room in the
first fluid-driven driving section for supplying fluid to a second
driving section, and the second driving section therefore needs to
be electrically driven, as electricity can be conducted through the
fluid-driven driving section to the next electrically driven
driving section 10.
[0062] The electrically driven driving section 10 comprises
propelling units 18 in the form of wheels, and each wheel comprises
an electrical motor for rotating the wheel and propelling the
driving unit and the tubing string forward in the well. Thus, the
electrically driven driving section comprises non-hydraulically
driven propelling units which are directly driven by the generator
9 through a control package 25. The downhole system may comprise
several electrically driven driving sections arranged successively
and all driven by the generator, as shown in FIGS. 9 and 10.
[0063] The propelling units 18 of the electrically driven driving
section 10 may also be rotating units 36 around which a track 37 is
arranged as shown in FIG. 3. One rotating unit 18 per track
comprises an electrical motor 11 driving the track 37 or belt and
thus propelling the driving section forward in the well.
[0064] As shown in FIG. 4, the fluid-driven driving section 5
comprises a pump 6. The pump 6 is either driven by the rotational
shaft of the turbine or by the fluid which is supplied to the pump
through a fluid channel 16 penetrating the turbine 7 and the
generator 9. The electrically driven driving section 10 comprises
the electrical motor 11 powered by the generator for providing a
propelling motion of the electrically driven driving section 10.
The propelling units of the second driving section are driven by
the motor 11 arranged between the driving sections, said motor
driving a pump which drives an internal separate hydraulic system
driving hydraulic motors in each wheel of the second driving
section 10.
[0065] In FIG. 4, part of the high pressure fluid drives the
turbine 7 and thus the generator 9, and the generator powers the
motor of the electrically driven driving section 10, and part of
the fluid drives the pump 6 of the fluid-driven driving section 5.
The fluid in the tubing string 3 thus powers the driving section or
sections as the tubing string is pulled into the long lateral 13
(as shown in FIG. 1) by the self-propelling driving sections.
Hereby, the fluid from the tubing string is used to drive the
tubing string forward in the lateral, and the fluid in the tubing
string is simultaneously and/or subsequently used to perform an
operation. The tubing string is thus able to enter even long and
narrow laterals, such as laterals longer than 2 km and having an
inner diameter of the casing or borehole smaller than 7 inches.
[0066] In order to propel the driving sections and the tubing
string forward or backward in the well, the driving sections
comprise propelling units 18, such as wheels 39, for contacting an
inner surface of the casing or borehole in the well, as shown in
FIGS. 2, 4-5, and 7-10. The wheels 39 are arranged on projectable
wheel arms 19 projecting from a housing 20 of the driving sections
5, 10.
[0067] In FIG. 5, the wheel arms of the fluid-driven driving
section project in a first direction 21 from a section housing, and
the wheel arms of the electrically driven driving section project
in a second direction 22 substantially perpendicular to the first
direction. The wheels are pressed into contact with the inner face
of the casing or borehole by the projectable wheel arms for
propelling the driving sections forward in the well.
[0068] The wheels of the fluid-driven driving section are rotated
as each wheel comprises a hydraulic motor 23. All the hydraulic
motors 23 of the fluid-driven driving section 5 are driven by the
pump 6.
[0069] The wheels of the electrically driven driving section shown
in FIG. 5 are also driven by a pump 24 comprised in the
electrically driven driving section, which pump is driven by the
electrical motor and drives the hydraulic motors 23 in each wheel
39.
[0070] In FIGS. 2 and 7, the wheels 39 of the electrically driven
driving section 10 each comprises an electrical motor 11 powered by
the generator 9. As shown in FIG. 7, the electrically driven
driving section 10 may comprise a control package 25 and a
rechargeable battery 26. The rechargeable battery 26 may be charged
as the tubing string is pushed down into the first part of the well
where there is no risk of the tubing string curling and getting
stuck, and when the tubing string enters the last part of the well,
the electrically driven driving section 10 is activated to pull the
end of the tubing string into the lateral.
[0071] The generator 9 generates electricity for powering the
electrical motor arranged in the electrically driven driving
section. The generator and the electrical motor are electrically
connected through an electrical connection 17 extending through the
fluid-driven driving section 5, as shown in FIG. 6.
[0072] In FIG. 4, a pressure control valve 28 is arranged in the
fluid channel 16 for reducing the passage of fluid to the pump of
the fluid-driven driving section. In this way, the pressure of the
pressurised fluid does not need to be controlled as accurately from
surface to avoid harming the components of the pump. If the
pressure of the fluid is too high and in order to prevent damage of
the components of the turbine and the generator, a flow diverter 29
is arranged in connection with the turbine for diverting at least
part of the fluid supplied to the turbine out through an outlet 33
and into the well surrounding the downhole system, as shown in FIG.
5.
[0073] As shown in FIG. 7, a flow diverter valve 31 is arranged in
the fluid channel for diverting the fluid supplied to the channel
to the turbine, and thus, if the pressure of the fluid in the
channel is too high, more fluid is allowed to pass through the
turbine.
[0074] When the tubing string 3 has been pulled all the way into
the long lateral and the acid operation is to be performed, the
fluid having a high acid concentration is supplied down through the
tubing string. When performing this type of operation, the downhole
system may comprise a flow diverter 29, as shown in
[0075] FIG. 5, for diverting at least part of the fluid from the
tubing string into the well to eliminate the need for detaching the
driving sections to let the fluid out of the tubing to perform the
acid treatment or acid stimulation of the well. The flow diverter
29 is arranged in a dispersion unit 32 for dispersion of a chemical
reactant, such as acid, in the well which is supplied to the
chemical dispersion unit through the tubing string 3.
[0076] In FIG. 2, the dispersion unit 32 comprises a ball seat 40
which is activated by dropping a ball 41 down the tubing string to
move the seat and enable passage of the fluid to the outlets 33.
The ball in the ball seat closes the passage of fluid to the
turbine.
[0077] A downhole system comprising both a fluid-driven driving
section and an electrically driven driving section is shown in FIG.
7. This downhole system further comprises an operational tool
arranged in front of the driving section and the furthest away from
the tubing string. When the tubing string has been pulled to a
certain position in the well, the enormous amount of power in the
pressurised fluid in the tubing string can be used to generate
power through the turbine and the generator to drive the
operational tool.
[0078] The operational tool 38 shown in FIGS. 2 and 7 may be any
kind of tool, such as a setting tool, a release tool, a stroker
tool, a key tool, a logging tool, etc. Due to the enormous amount
of power in the pressurised fluid in the tubing string, the logging
tool may operate when the tubing string is pulled down into the
well without diminishing the propelling speed of the driving
sections.
[0079] The downhole system shown in FIG. 9 comprises an inflation
unit 35. The inflation unit 35 is inflated to shield the driving
section while performing a stimulation operation, such as treating
the well with acid or base containing fluid. The inflation unit 35
can be any kind of packer inflatable by high pressure fluid. The
inflation unit 35 is inflated e.g. by dropping a ball of one size
into the fluid to move the ball seat from a position where the
fluid is allowed to pass into the turbine to a second position
where the fluid is let into the inflation unit. After inflation of
the inflation unit, a second and larger ball is dropped, moving the
ball seat to a third position where the fluid is let into the
well.
[0080] The downhole system may further comprise a detachment unit
43 arranged inside the dispersion unit 32 for detaching the driving
sections from the tubing string, as shown in FIG. 9. Each driving
section comprises a battery 26 and a control package 25 so that
when the driving sections are detached from the tubing string and
when e.g. the acid treatment has been performed, the driving
sections are able to propel themselves out of the well.
[0081] The detachment of the tubing string may take place when the
second ball is dropped and the ball seat is moved into a second
position where the tubing string is detached from the driving
section, thus allowing the fluid to enter into the well.
[0082] When the inflation unit has been inflated and the driving
sections have been detached from the tubing string, as shown in
FIG. 10, the tubing string may be pulled backwards, and the
stimulation operation, such as the acid treatment, may be
initiated.
[0083] Instead of having an inflation unit 35, the detached tubing
string may be pulled further backwards to prevent damage of the
driving sections while e.g. the acid treatment is performed.
[0084] Timers may be used for deflating the inflation unit and
activating the driving section to propel themselves out of the
well.
[0085] The electrical motor of the electrically driven driving
section may also drive a gearing system driving the propelling
units 18 or belts, and one electrical motor is thus able to drive
several propelling units or even all propelling units.
[0086] When the downhole system comprises a second electrically
driven driving section, this electrically driven driving section is
driven by the generator through an electrical connection 17 in the
other electrically driven driving section arranged closest to the
tubing string. Hereby, a large number of electrically driven
driving sections can be mounted onto the tubing string for pulling
the tubing string forward in the well.
[0087] In another embodiment, the electrically driven driving
section arranged closest to the tubing string may comprise a pump
for driving the hydraulically driven propelling units each
comprising a hydraulic motor 23.
[0088] Thus, an electrically driven driving section powered by the
generator may comprise electrical motors in each wheel or hydraulic
motors in each wheel, the hydraulic motors being driven by a pump
driven by the electricity from the generator.
[0089] In the event that two driving sections, such as one
fluid-driven driving section and one electrically driven driving
section, are not able to pull the tubing string all the way into
the lateral, the downhole system may comprise several electrically
driven driving sections all powered by the generator, as shown in
FIG. 8. The downhole system may also comprise several generators
driven by the output shaft 8 of the turbine in order to gain more
power for pulling the tubing string.
[0090] In order to perform acid treatment or other fluid
stimulations, such as scale removing operations, of the lateral of
the well, the downhole system is mounted by connecting the turbine
with the tubing string and connecting the generator with the
turbine so that the generator is driven by the output shaft 8.
Then, the fluid-driven driving section is connected with the
turbine so that the fluid channel 16 is connected with the pump 6
of the fluid-driven driving section, and the electrically driven
driving section is then connected with the fluid-driven driving
section so that electricity is conducted from the generator through
the fluid-driven driving section to the electrically driven driving
section. The pressurised fluid is supplied down the tubing string
to the turbine and the fluid channel. In this way, the tubing
string is pulled directly into the lateral by the fluid-driven
driving section by means of the pressurised fluid and by the
electrically driven driving section by means of the turbine, the
generator and the electrical motor. When the tubing string is in
place for performing the acid treatment or another stimulation
operation, fluid having a particular composition, e.g. an acid or
base concentration, or fluid comprising enzymes, is supplied down
through the tubing string to an outlet 33 in the downhole system
for treating the lateral with acid.
[0091] The downhole system may comprise a dispersion unit 32 for
dispersion of the fluid, such as acid or base, into the lateral.
The dispersion unit may also comprise valves angled so that the
unit is rotated as the pressurised acid containing fluid enters
through the valves.
[0092] Driving sections capable of containing long laterals may
have an outer diameter of less than 5 inches and more preferably
less than 4 inches. By long laterals is meant laterals, branches or
side tracks having a length of at least 4 km, more preferably a
length of at least 5 km, and more preferably a length of at least 7
km.
[0093] By fluid or 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, or a chemical composition, such as an
acid composition. 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.
[0094] By a casing is meant any kind of pipe, tubing, tubular,
liner, string etc. used downhole in relation to oil or natural gas
production.
[0095] The driving sections may be a downhole tractor or any kind
of driving tool capable of pushing or pulling tools in a well
downhole, such as a Well Tractor.RTM..
[0096] 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.
* * * * *