Note: Descriptions are shown in the official language in which they were submitted.
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A TOOL STRING
Field of the invention
The present invention relates to a tool string for being suspended in a well,
the
tool string extending in a longitudinal direction and comprising a first
string part
and a second string part, each having a centre axis and comprising; an
electrical
connection in a first end, and a fluid channel extending at least partly
through the
string part. Furthermore, the present invention relates to a method for
assembling two string parts of a tool string.
Background art
The extraction rate from hydrocarbon-producing wells and the surrounding
formations is becoming increasingly important due to decreasing oil reserves.
Therefore, increasingly advanced tools are being developed and deployed in the
search for and extraction of oil and gas. Tools deployed downhole in a well
are
often assembled or joined in a tool string comprising multiple tools, such as
driving tools for driving the tool string forward in inclining sections of the
well
and/or operational tools for performing various operations downhole.
Various principles for joining pipe sections for use in a drill string of a
casing are
known from the prior art. Such pipe couplings may provide a fluid-tight
coupling
between pipe sections and may also comprise an electrical coupling for
transferring electrical power. However, known couplings do not provide the
necessary connection between advanced tools and tool parts. Present downhole
tools, such as a downhole tractor, require a supply of both electrical power
and
hydraulic fluid in order to operate. A need has therefore arisen for a
coupling
between different tool string parts, wherein both fluid and electrical power
can be
transferred. Some downhole tools may require several separate fluid channels
running between different parts of the tool string. The coupling has to be
robust
and capable of withstanding considerable tensile forces and twisting during
deployment downhole. At the same time, the coupling has to be relatively easy
and fast to assemble.
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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 an improved tool string, wherein electrical power and fluid(s) can be
transferred from one part of the tool string to another. Further, it is an
object to
provide a connection between two string parts, wherein fluid channels in each
of
the string parts are brought into fluid communication and wiring in each of
the
string parts are connected.
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 tool string for
being
suspended in a well, the tool string extending in a longitudinal direction and
comprising:
- a first string part and a second string part, each having a centre axis and
comprising;
- an electrical connection in a first end, and
- a fluid channel extending at least partly through the string part, and
- a connecting element rotatably connected to one string part and adapted to
be
threadably connected to a threaded portion of the other string part, to join
the
electrical connections of the first and second string parts;
wherein one of the string parts comprises a pipe connection extending in the
longitudinal direction from the first end and into the fluid channel of the
other
string part when the string parts are mutually connected by the connecting
element, the pipe connection being arranged eccentrically in relation to the
centre axis for preventing mutual rotation of the string parts.
Hereby, a connection for transferring both electrical power and fluid between
two
string parts of a tool string may be provided. The connection has the
necessary
rigidity to provide and maintain a fluid-tight seal between the fluid channels
of
the first and second string parts. Furthermore, the electrical wires are not
twisted
or bent.
In one embodiment, one of the string parts may comprise at least two pipe
connections.
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In another embodiment, one of the string parts may comprise a guide pin and
the other string part may comprise a hole for receiving the guide pin when the
string parts are mutually connected by the connecting element.
Further, the connecting element may comprise two connectable collar elements
adapted to be mutually connected around a section of one of the string parts.
Moreover, the connecting element may comprise an outer threaded portion.
Also, the connecting element may be arranged around a protrusion of one of the
string parts, having a reduced diameter compared to a maximum diameter of the
string part.
Additionally, the connecting element may be arranged in a recess of one of the
string parts, whereby the connecting element is prevented from substantially
moving in the longitudinal direction.
Furthermore, the connecting element may be prevented from substantially
moving in the longitudinal direction towards the first end by a protruding
part of
the string part having an increased outer diameter.
Said connecting element may have an outer diameter being equal to or less than
an outer diameter of the tool string.
Also, the connecting element may have an outer diameter being equal to or less
than a minimum outer diameter of the tool string.
In one embodiment, the pipe connection may comprise a circumferential sealing
element adapted to provide a fluid-tight seal between the pipe connection and
the corresponding fluid channel into which it extends.
In addition, one of the string parts may comprise a circumferential sealing
element adapted to provide a fluid-tight seal between the first and second
string
parts.
In one embodiment, one of the string parts may be a driving unit for
propelling
the tool string in the well.
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The present invention furthermore relates to a method for assembling two
string
parts of a tool string, the method comprising the steps of:
- moving a first end of a first string part towards a first end of a second
string
part,
- arranging a guide pin of one of the string parts in a hole in another string
part,
- connecting a threaded portion of a connecting element rotatably connected
to
one of the string parts with a threaded portion of the other string part, and
- rotating the connecting element to join electrical connections of the
first and
second string parts and to force a pipe connection of one string part into a
hole in
fluid communication with a fluid channel of the other string part.
Brief description of the drawings
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
Fig. 1 shows a tool string being suspended in a well,
Fig. 2 shows the ends of two string parts in an assembled state being
connected
by a connecting element,
Figs. 3a and 3b show layouts of the end faces of two string parts adapted to
be
assembled,
Fig. 4 shows a connecting element comprising two connectable collar elements,
and
Fig. 5 shows a tool string comprising a downhole tractor having wheel
sections.
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 tool string 1 being suspended in a well 4 from a wireline 5.
The
tool string 1 may also be suspended using coiled tubing or by being part of a
drill
5 string. The shown well comprises a casing 14, but the tool string 1 may
also be
used in an uncased well.
The tool string 1 extends in a longitudinal direction and comprises at least a
first
tool string part 2 and a second tool string part 3. A first end 200 of the
first string
part 2 and a first end 400 of the second string part 3 are connected via a
connecting element 6 arranged between the two string parts 2, 3 in the
longitudinal direction. The dotted lines in Fig. 1 illustrate how part of the
first end
200 of the first string part extends through the connecting element 6 and into
the
first end 400 of the second string part.
Referring to Fig. 2, the connection shown in Fig. 1 between the first string
part 2
and the second string part 3 will be described in further detail below. For
the
purpose of clarity, the connecting element 6 and part of the second string
part 3
have been cut through and are shown in a cross-sectional view.
The string parts 2, 3 and the connecting element 6 each have a circular cross-
section. In the first end 200, the first string part 2 comprises a protrusion
27
having a reduced diameter 37b. The protrusion 27 extends between a face 39 of
the first string part and an end face 201. Towards the end face 201, the
protrusion 27 comprises a circumferential projecting flange 29. Together with
the
face 39, the projecting flange 29 defines a recess 28 encircling the
protrusion 27.
At the end face 201, a plurality of pipe connections 22, 23, 24 and a guide
pin 26
extend. Further, an electrical connection, such as a plug 21, is provided in
the
end face 201, and a circumferential seal 33 is arranged around the protrusion
27
adjacent the end face 201. Each of the pipe connections extends in the
longitudinal direction 10 from the end face 201 towards a tapered free end. At
a
distance from the tapered end, a circumferential seal 30, 31 is arranged
around
each of the pipe connections. The guide pin 26 also extends in the
longitudinal
direction from the end face 201 towards a tapered free end. The connecting
element 6 is provided around the protrusion 27 in a recess 28 of the reduced
diameter. . The connecting element 6 is comprised by two connectable collar
elements 601, 602, as shown in Fig. 4. During assembly, the two collar
elements
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601, 602 are arranged in the recess 28 around the protrusion 27 and are
connected by bolts 62. The connecting element 6 is thereby rotatably connected
to the first string part 2 and restricted from moving in the longitudinal
direction
by the face 39 and the projecting flange 29. The connecting element 6
comprises
an outer threaded portion 61 adapted to be connected to a threaded portion 48
of the second string part 3, as shown in Fig. 2. It is obvious to the person
skilled
in the art that the connecting element may be designed in a number of other
ways without departing from the essence of the invention. Providing a
rotatably
connected connecting element 6 may be achieved in a number of different ways
known to the skilled person, such as by applying a swivel connection, a ball
and
socket joint or other types of connections connecting two separate objects
while
allowing mutual rotation.
In the first end 400, the second string part 3 comprises a bore 47 adapted to
receive the protrusion 27 of the first string part 2 and the connecting
element 6.
The bore is encircled by a threaded portion 48 of the second string part 3
adapted to be connected to the threaded portion 61 of the connecting element
6.
At one end, the bore 47 is delimited by a face 401 comprising a plurality of
holes
42, 43, 44 adapted to receive the pipe connections 22, 23, 24, as shown in
Figs.
3a and 3b. The face 401 further comprises a hole 46 adapted to receive the
guide
pin 26 and an electrical connection, such as a socket 41, adapted to be
connected
to the plug 21, as shown in Fig. 3a and Fig. 3b.
An approximated layout of the protruding pipe connections 22, 23, 24, guide
pin
26 and plug 21 is shown in Fig. 3a, and a layout of the matching holes 42, 43,
44
and socket 41 is shown in Fig. 3b. The pipe connections 22, 23, 24 are fluidly
connected to respective fluid channels 220, 240 in the first string part, and
the
holes 42, 43, 44 are in fluid communication with respective fluid channels
420,
440 in the second string part 3. By arranging the pipe connections 22, 23, 24
in
the respective holes 42, 43, 44, the fluid channels 220, 240 of the first
string
part are brought into fluid communication with the fluid channels of the
second
string part. In a similar manner, the plug 21 and the socket 41 provide an
electrical connection between the first and second string parts.
As shown in Figs. 3a and 3b, the pipe connections 22, 23, 24 of the first
string
part 2 and the respective holes 42, 43, 44 in the second string part 3 are
arranged eccentrically in relation to a centre axis 10. By at least one of the
pipe
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connections 22, 23, 24 being arranged eccentrically at a distance from the
centre
axis, the first and second string parts 2, 3 are prevented from mutually
rotating
around the centre axis 10. The one or more pipe connections thus have the
additional functionality of fixating the string parts in relation to one
another, both
during assembly of the string parts and use of the tool string downhole.
The guide pin 26 extends further away from the end face 201 than the pipe
connections. During assembly of the first and second string parts, the guide
pin
26 is thus inserted into the hole 46 to control the assembly process and
prevent
damage caused by the string parts being rotated or angled in relation to one
another. The plug and socket and the pipe connections may be bent or destroyed
if the string parts are not properly aligned during assembly and disassembly.
When the guide pin 26 is at least partially arranged in the hole 46, the two
string
parts are kept substantially parallel relative to each other. By having a
guide pin,
the first and second string parts are prevented from tilting slightly in the
connection therebetween. Such slight tilting in the connection itself may
result in
the pipe connections leaking, either because the pipe connection being an
integral part of the one end of the string parts has been bent and thus
slightly
separated, forming a fracture, or because the pipe connection as a separate
part
has tilted in the holes.
The pipe connections may be integral parts of one of the string parts or they
may
be separate pipes. One pipe connection may be arranged in one string part and
another pipe connection in the other so that, when joining the string parts,
the
pipe connections function as guides during the assembly process.
The connecting element 6 is arranged in the recess 28 of the first string
part, and
in Fig. 2, the first string part 2 also comprises the pipe connection and the
pin.
However, the connecting element 6 may be arranged in the recess of the first
string part, and the pipe connection and the pin may be arranged in the second
string part 3.
Fig. 5 shows a downhole tractor 81 being part of a tool string 1, wherein two
string parts 2, 3 are assembled using the connecting element 6 described
above.
The downhole tractor is suspended from and powered through a wireline 5
connected with the downhole tractor through a top connector 71. The downhole
tractor 81 comprises an electronics section 72, an electrical motor 73, a
hydraulic
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pump 74 and two wheel sections 80 driven by hydraulics. The wheel sections are
in fluid communication with the hydraulic pump 74 and may also be denoted as
driving units 80 for propelling the downhole tractor and the tool string in
the well.
The downhole tractor may be connected to one or more operational downhole
tools 75 also being part of the tool string 1. Such operational tools could be
a
stroker tool providing an axial force in one or more strokes, a key tool
opening or
closing valves in the well, positioning tools such as a casing collar locator
(CCL),
a milling tool, a drilling tool, etc.
The connection between two string parts 2, 3, e.g. two wheel sections 80 of a
downhole tractor, may be used for transferring fluid(s) and/or electrical
power.
Electrical power may be transferred from the wireline 5 to the first string
part and
via the plug 21 and socket 41 to the subsequent string part. The pipe
connection
22 may be used for connecting fluid channels providing a pressurised fluid
from
the hydraulic pump 74 to the wheel sections for projecting pivotally mounted
wheel arms 76. The pipe connection 24 may be used for connecting fluid
channels providing a pressurised fluid from the hydraulic pump 74 to the wheel
sections for rotating wheels 77 mounted at the wheel arms 76 in a clockwise
direction. The pipe connection 23 may be used for connecting fluid channels
providing a pressurised fluid from the hydraulic pump 74 to the wheel sections
for rotating wheels 77 mounted at the wheel arms 76 in a counterclockwise
direction. The pipe connection 25 and the hole 45 may be used for connecting
fluid channels providing a return channel for fluid supplied to the wheel
sections.
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, 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.
By rotatably connected is meant that a first rotatable object is connected to
a
second object so that the first object may rotate while being connected to the
second object and the connection between the first and the second object is
maintained during rotation of the first object in relation to the second
object.By a
casing is meant any kind of pipe, tubing, tubular, liner, string etc. used
downhole
in relation to oil or natural gas production.
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In the event that the tools are not submergible all the way into the casing, a
downhole tractor can be used to push the tools 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
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.
