Note: Descriptions are shown in the official language in which they were submitted.
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REPLACEABLE ELECTRICAL DEVICE FOR DRILLING TOOL
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates generally to a tool for use in an oilfield wellbore, and
more
specifically to an easily replaceable electrical device for use in such a
tool.
Description of the Related Art
Tools requiring electrical power are often used for conducting various
operations
in a wellbore. This creates a need for portable electrical power, preferably
power that
can be mounted directly onto a downhole tool. One way of providing electrical
power
downhole is through the use of a battery pack. Typically, the battery pack is
constructed of multiple cells mounted in rigid plastic, epoxy, fiberglass, or
aluminum
shells and is housed in a sonde or in an annular housing mounted in the bore
of a
downhole tool. One or more cells are typically contained within the battery
pack. The
cells can be electrically connected in various series or parallel
configurations to
provide the necessary voltage and current capacities required for the various
loads.
The cells generally are immobilized inside the battery pack by an epoxy. In
order to
change the battery pack in the downhole tool, the tool has to be disassembled.
Disassembly of the tool makes replacing a battery pack time consuming and, in
certain cases, is impossible at the job site. For quicker job turnaround, it
is desirable
that the battery be replaceable without requiring tool disassembly and without
the use
of specialized equipment typically not available at the job site.
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The methods and apparatus of the present invention overcome the foregoing
disadvantages of the prior art by providing an externally replaceable battery
pack that
does not require major tool disassembly.
SUMMARY OF THE INVENTION
In general, in one aspect of the present invention, a downhole tool for use in
a
wellbore, comprises a tubular member, such as a drill collar housing, in a
drill string.
The tubular member has at least one cavity formed on an external surface. A
housing
is adapted to insert in and extract from the cavity. The housing has at least
one
electrical device, such as a battery stack, disposed within the housing.
In another aspect of the present invention, sensors are disposed in the
housing for
measuring downhole parameters of interest including, but not limited to,
annulus
pressure and annulus temperature.
In another embodiment, a replaceable battery pack for a downhole tool in a
wellbore, comprises a housing adapted to be insertable in and extractable from
a
cavity on an external surface of the downhole tool, and has at least
oneelectrical
power cell disposed in the housing.
In one aspect, a method of replacing an electrical device in a downhole tool,
comprises removing a first housing containing the electrical device from a
cavity on
an external surface of the downhole tool, and installing a second housing
containing a
second electrical device in the cavity without disassembling the tool further.
In yet another embodiment, a method of replacing a battery pack in a downhole
tool, comprises removing a first housing containing a plurality of electrical
power
cells from a cavity on an external surface of the downhole tool, and
installing a
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second housing containing a second plurality of electrical power cells in the
cavity
without disassembling the tool further.
Accordingly, in one aspect of the present invention there is provided a
replaceable battery pack for a downhole tool in a wellbore comprising:
a) a housing adapted to be insertably extractable in a cavity on an external
surface of the downhole tool, said housing sized to fit substantially flush
with a
substantially uniform outer diameter of said downhole tool, said housing
adapted
to be extracted from said downhole tool without further disassembling said
downhole tool;
b) an electrical power cell disposed in the housing;
c) an electrical system disposed in said downhole tool disengageably
engaged to said replaceable battery pack for receiving power from said
replaceable battery pack; and
d) a seal disposed in a groove in said housing, said seal acting cooperatively
with said housing and a surface of said cavity to capture a volume at
atmospheric
pressure thereby forming a pressure lock when exposed to a downhole pressure,
said pressure lock acting to hold the housing in the cavity.
According to another aspect of the present invention there is provided a
method for providing a replaceable power source in a downhole tool comprising:
a) providing a downhole tool having a substantially uniform outer diameter
over at least a portion of the length of the downhole tool;
b) providing a replaceable battery pack including a housing having a battery
therein, said housing adapted to be insertably extractable in a cavity formed
into
an external surface of the downhole tool;
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c) extractably inserting said replaceable battery pack in said cavity while
disengagingly engaging an electrical system in said downhole tool to provide
electrical power thereto;
d) extracting said battery pack from said cavity while disengaging from said
at least one electrical system, without requiring any additional disassembly
of said
downhole tool; and
e) providing a seal disposed in a groove in said housing, said seal acting
cooperatively with said housing and a surface of said cavity to capture a
volume
at atmospheric pressure thereby forming a pressure lock when exposed to a
downhole pressure, said pressure lock acting to hold the housing in the
cavity.
Examples of the more important features of the invention thus have been
summarized rather broadly in order that the detailed description thereof that
follows
may be better understood, and in order that the contributions to the art may
be
appreciated. There are, of course, additional features of the invention that
will be
described hereinafter and which will form the subject of the claims appended
hereto.
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BRIEF DESCRIPTION OF THE DRAWINGS
For detailed understanding of the present invention, references should be
made to the following detailed description of the preferred embodiment, taken
in
conjunction with the accompanying drawings, in which like elements have been
given
like numerals, wherein:
Figure 1 is a schematic of a downhole tool with a replaceable battery pack
according to one embodiment of the present invention;
Figure 2 is a schematic section of a downhole tool with a replaceable battery
pack installed therein; and
Figure 3 is an exploded schematic of a downhole battery pack according to
one embodiment of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 shows a schematic diagram of a drilling system 10 having a downhole
assembly containing a downhole sensor system and the surface devices according
to
one embodiment of present invention. As shown, the system 10 includes a
conventional derrick 11 erected on a derrick floor 12 which supports a rotary
table 14
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that is rotated by a prime mover (not shown) at a desired rotational speed. A
drill
string 20 that includes a drill pipe section 22 extends downward from the
rotary table
14 into a wellbore 26. A drill bit 50 attached to the drill string downhole
end
disintegrates the geological formations when it is rotated. The drill string
20 is
coupled to a drawworks 30 via a kelly joint 21, swivel 28 and line 29 through
a
system of pulleys (not shown). During the drilling operations, the drawworks
30 is
operated to control the weight on bit and the rate of penetration of the drill
string 20
into the wellbore 26. The operation of the drawworks is well known in the art
and is
thus not described in detail herein.
During drilling operations, a suitable drilling fluid (commonly referred to in
the
art as "mud") 31 from a mud pit 32 is circulated under pressure through the
drill string
20 by a mud pump 34. The drilling fluid 31 passes from the mud pump 34 into
the
drill string 20 via a desurger 36, fluid line 38 and the kelly joint 21. The
drilling fluid
is discharged at the wellbore bottom 51 through an opening in the drill bit
50. The
drilling fluid circulates uphole through the annular space 27 between the
drill string
20 and the wellbore 26 and is discharged into the mud pit 32 via a return line
35.
Preferably, a variety of sensors (not shown) are appropriately deployed on the
surface
according to known methods in the art to provide information about various
drilling-
related parameters, such as fluid flow rate, weight on bit, hook load, etc.
A surface control unit 40 receives signals from the downhole sensors and
devices
via a sensor 43 placed in the fluid line 38 and processes such signals
according to
programmed instructions provided to the surface control unit: The surface
control unit
displays desired drilling parameters and other information on a
display/monitor 42
which information is utilized by an operator to control the drilling
operations. The
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surface control unit 40 contains a computer, memory for storing data, data
recorder
and bther peripherals. The surface control unit 40 also includes models and
processes
data according to programmed instructions and responds to user commands
entered
through a suitable means, such as a keyboard. The control unit 40 is
preferably
adapted to activate alarms 44 when certain unsafe or undesirable operating
conditions
occur.
In the preferred embodiment of the system of present invention, the downhole
subassembly 59 (also referred to as the bottomhole assembly or "BHA"), which
contains the various sensors and MWD devices to provide information about the
formation and downhole drilling parameters, is coupled between the drill bit
50 and
the drill pipe 22. The downhole assembly 59 is modular in construction, in
that the
various devices are interconnected sections.
Referring to Figure 1, the BHA 59 also preferably contains downhole sensors
and
devices in addition to the above-described surface sensors to measure downhole
parameters of interest. Such devices include, but are not limited to, a device
for
measuring the formation resistivity near the drill bit, a gamma ray device for
measuring the formation gamma ray intensity and devices for determining the
inclination and azimuth of the drill string. The formation resistivity
measuring device
64 provides signals from which resistivity of the formation near the drill bit
50 is
determined.
The above-noted devices transmit data to the downhole telemetry system 72,
which in turn transmits the received data uphole to the surface control unit
40. The
present invention preferably utilizes a mud pulse telemetry technique to
communicate
data from downhole sensors and devices during drilling operations. A
transducer 43
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placed in the mud supply line 38 detects the mud puises responsive to the data
transmitted by the downhole telemetry 72. Transducei 43 generates electrical
signals
in response to the mud pressure variations and transmits such signals via a
conductor
45 to the surface control unit 40. Other telemetry techniques such
electromagnetic and
acoustic techniques or any other suitable technique may be utilized for the
purposes of
this invention.
The sensors and telemetry devices can be powered by batteries, downhole
alternators, or a combination of such devices. In conventional systems, the
power
sources are typically contained in the bore of the BHA 59 and require .some
time-
consuming and difficult disassembly to change out batteries. In many
instances, such
a change-out is impractical at the rig site.
Figures 2-4 shows downhole tool 125 suitable for placement in a portion of a
drill
string such as BHA 59. In a preferred embodiment, tool 125 comprises a tubular
member 101 such as a drill collar. Tool 125 has a replaceable battery module
120,
also called a battery pack, inserted in a cavity 121 formed in. an external
surface of
tubular member 101. Downhole sensors and circuits as discussed above may be
disposed in the tubular member 101. The battery module 120 may provide power
for
such devices.
The battery module 120 comprises a housing 102 having a bore 115 adapted to
receive a battery stack 108. Battery stack 108 may be a combination of
multiple cells
(not shown) or a single cell. If multiple cells are used for battery stack
108, they are
typically encased in a plastic or metal cylinder. Such techniques are known in
the art
and are not discussed here further. Battery stack 108 is suitably wired to
provide the
required voltage and current properties for the particular application and has
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connection contacts 117 for engaging mating contacts 118 on connector 107.
Elec'trical connector 107 is fitted into the end of bore 115 and is connected
to
connector 112 by wires 116. Battery stack 108 is inserted in bore 115 and is
aligned
by key 119 in stack 108 that aligns with a suitable groove (not shown) in
housing 102.
The key 119 provides alignment to ensure proper mating of contact pins 117 in
stack
108 with mating contacts 118 in connector 107. Key 119 also prevents rotation
of
stack 108 during downhole drilling that might damage the connection between
stack
108 and connector 107. Stack 108 is held in place by spring 109 that is
captured in a
compressed state between stack 108 and cap 110. The spring preload minimizes
axial
movement of the stack 108 during downhole drilling. Elastomeric seals 111 and
112
are used to sea] out borehole fluids. Seal 112 resides in groove 105 and acts
as a face
type seal with surface 123 when module 120 is fastened to member 101 by
mechanical fasteners 122 inserted though holes 103 and screwed into mating
threaded
holes (not shown) suitably arranged in cavity 121 in member 101. As module 120
is
inserted into cavity 121, electrical connection is made between connector 106
in
module 120 and connector 113 in member 101. Wires (not shown) are connected
between the connector 113 and sensors and circuits (not shown) disposed in
member
101. Such wiring techniques are known in the art and are not discussed here
further.
Any suitable mating connectors may be used for connectors 106 and 113
including
but not limited to individual pin-to-socket connectors and coaxial connectors.
In another preferred embodiment, suitable circuitry (not shown) is included in
module 120 to facilitate the use of inductive coupling techniques for
transferring
power between module 120 and circuits and sensors (not shown) in member 101.
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Grooves 104, see Figure 3, are adapted to receive an elastomeric seal 130 for
use
in providing a pressure lock to assist in holding the niodule 120 in cavity
121. When
the module 120 is installed in the cavity 121, the seals 130 mate with the
surface (not
shown) in cavity 121. The volume enclosed by the seal 130 is at atmospheric
pressure. Effectively, the downhole pressure times the area enclosed by the
seal
generates a force holding the housing 102 against the surface of cavity 121.
At
downhole pressures of several thousand pounds per square inch, even a small
enclosed area results in a substantial holding force.
While the module 120 is described above as containing power cells, it is
anticipated that such a module may contain other devices including but not
limited to
electronic circuits and .sensors for measuring downhole parameters of
interest. Such
parameters include but are not limited to, annulus fluid pressure and annulus
fluid
temperature.
While only one module 120 is described as being attached to the tubular member
101, several such modules can be disposed on the tubular member. Such modules
can
be disposed at multiple angular positions around the tubular member at the
same axial
location; at multiple axial locations; or a combination of these.
The foregoing description is directed to particular embodiments of the present
invention for the purpose of illustration and explanation. It will be
apparent, however,
to one skilled in the art that many modifications and changes to the
embodiment set
forth above are possible without departing from the scope and the spirit of
the
invention. It is intended that the following claims be interpreted to embrace
all such
modifications and changes.
