Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02603138 2012-10-25
INTELLIGENT EFFICIENT SERVO-ACTUATOR FOR A DOWNHOLE PULSER
WITH NOVEL BRAKE AND LOCK
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a divisional of co-pending application Serial No.
2,463,354,
filed in Canada on April 6, 2004 with respect to subject matter herein that is
also
disclosed in the co-pending application. Any new subject matter in this
application will
have a claim date equivalent to the date of filing of this application.
FIELD OF TIIE INVENTION
The present invention relates generally to a telemetry system, and in
particular to a
measurement while drilling (MWD) system. More particularly, the present
invention
relates to a servo-actuator for a downhole mud pulser for sending information
from
downhole to surface.
BACKGROUND OF THE INVENTION
The desirability and effectiveness of well logging systems where information
is
sensed in the well hole and transmitted to the surface through mud pulse
telemetry has
long been recognized. Mud pulse telemetry systems provide the driller at the
surface with
means for quickly determining various kinds of downhole information, most
particularly
information about the location, orientation and direction of the drill string
at the bottom of
the well in a directional drilling operation. During normal drilling
operations, a continuous
column of mud is circulating within the drill string from the surface of the
well to the
drilling bit at the bottom of the well and then back to the surface. Mud pulse
telemetry
repeatedly restricts the flow of mud to propagate signals through the mud
upward to the
surface, thereby providing a very fast communication link between the drill
bit and the
surface. Depending on the type of drilling fluid used, the velocity may vary
between
approximately 3000 and 5000 feet per second.
A telemetry system may be lowered on a wireline located within the drill
string,
but is usually formed as an integral part of a special drill collar inserted
into the drill string
near the drilling bit. The basic operational concept of mud pulse telemetry is
to
intermittently restrict the flow of mud as it passes through a downhole
telemetry valve,
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thereby creating a pressure pulse in the mud stream that travels to the
surface of the well.
The information sensed by instrumentation in the vicinity of the drilling bit
is encoded
into a digital formatted signal and is transmitted by instructions to pulse
the mud by
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intermittently actuating the telemetry valve, which restricts the mud flow in
the drill string,
thereby transmitting pulses to the well surface where the pulses are detected
and
transformed into electrical signals which can be decoded and processed to
reveal
transmitted information.
Representative examples of previous mud pulse telemetry systems may be found
in
US Patents 3,949,354; 3,958,217; 4,216,536; 4,401,134; and 4,515,225.
Representative samples of mud pulse generators may be found in US Patents
4,386,422; 4,699,352; 5,103,420; and 5,787,052.
A telemetry system capable of performing the desired function with minimal
control energy is desirable, since the systems are typically powered by finite-
storage
batteries. One such example is found in US Patent 5,333,686, which describes a
mud
pulser having a main valve biased against a narrowed portion of the mud
flowpath to
restrict the flow of mud, with periodic actuation of the main valve to allow
mud to
temporarily flow freely within the flowpath. The main valve is actuated by a
pilot valve
that can be moved with minimal force. The pilot valve additionally provides
for pressure
equalization, thereby increasing the life of downhole batteries.
Another example of an energy efficient mud pulser is described in US Patent
6,016,288, the mud pulser having a rotary electric motor such as a DC motor
electrically
powered to drive a planetary gear which in turn powers a threaded drive shaft,
mounted in
a bearing assembly to rotate a ball nut lead screw. The rotating threaded
shaft lifts the lead
screw, which is attached to the pilot valve.
Solenoid-type pulser actuators have also been used to actuate the main pulser
valve, however, there are many problems with such a system. The use of a
spring to bias
the solenoid requires the actuator (servo) valve to overcome the force of the
spring (about
6 pounds) and of the mud prior to actuating the main valve. A typical solenoid
driven
actuator valve is capable of exerting only 11 pounds of pressure, leaving only
5 pounds of
pressure to actuate the pulser assembly. Under drilling conditions requiring
higher than
normal mud flow, the limited pressures exerted by the solenoid may be unable
to
overcome both the pressure of the return spring and the increased pressure of
the flowing
mud, resulting in a failure to open the servo-valve, resulting in the main
valve remaining
in a position in which mud flow is not restricted, and therefore failing to
communicate
useful information to the surface.
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A further problem with the use of a solenoid to actuate the pulser assembly is
the
limited speed of response and recovery that is typical of solenoid systems.
Following
application of a current to a solenoid, there is a recovery period during
which the magnetic
field decays to a point at which it can be overcome by the force of the
solenoid's own
return spring to close the servo-valve. This delay results in a maximum data
rate (pulse
width) of approximately 0.8 seconds/pulse, limiting the application of the
technology.
Moreover, the linear alignment of the solenoid must be exactly tuned (i.e. the
magnetic shaft must be precisely positioned within the coil) in order to keep
the actuator's
power characteristics within a reliable operating range. Therefore, inclusion
of a solenoid
within the tool adds complexity to the process of assembling and repairing the
pulser
actuator, and impairs the overall operability and reliability of the system.
Existing tools are also prone to jamming due to accumulation of debris,
reducing
the range of motion of the pilot valve. Particularly when combined with
conditions of high
mud flow, the power of the solenoid is unable to clear the jam, and the tool
is rendered
non-functional. The tool must then be brought to the surface for service.
Reversible rotary electric motors such as stepper motors have been used in mud
pulsing systems, specifically, in negative pulse systems (see for example US
5,115,415).
The use of a reversible rotary electric motor such as a stepper motor to
directly control the
main pulse valve, however, requires a large amount of electrical power,
possibly requiring
a turbine generator to supply adequate power to operate the system for any
length of time
downho le.
Repair of previous pulsers has been an as yet unresolved difficulty.
Typically, the
entire tool has been contained within one housing, making access and
replacement of
small parts difficult and time-consuming. Furthermore, a bellows seal within
the servo-
poppet has typically been the only barrier between the mud flowing past the
pilot valve's
poppet and the pressurized oil contained within the servo-valve actuating
tool, which is
required to equalize the hydrostatic pressure of the downhole mud with the
tool's internal
spaces. Therefore, in order to dissemble the tool for repair, the bellows seal
had to be
removed, causing the integrity of the pressurized oil chamber to be lost at
each repair.
Furthermore, a key area of failure of MWD pulser drivers has been the failure
of
the bellows seal around the servo-valve activating shaft, which separates the
drilling mud
from the internal oil. In existing systems, the addition of a second seal is
not feasible,
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particularly in servo-drivers in which the servo-valve is closed by a spring
due to the
limited force which may be exerted by the spring, which is in turn limited by
the available
force of the solenoid, and cannot overcome the friction or drag of an
additional
static/dynamic linear seal.
It remains desirable within the art to provide a pulse generator that has an
energy
efficiency sufficient to operate reliably and to adapt to a variety of hostile
downhole
conditions, has reduced susceptibility to jamming by debris, and is simpler to
repair than
previous systems.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate or mitigate at least one
disadvantage of previous mud pulsers and pulse generators.
In a first aspect, the present invention provides a downhole measurement-while-
drilling pulser actuator comprising a servo valve movable between an open
position which
permits mud flow through a servo-orifice and a restricted position which
restricts mud
flow through the servo-orifice, the servo-valve powered to the open position
and powered
to the closed position by a reversible rotary electric motor.
In one embodiment, the servo valve includes a servo-poppet powered by the
reversible rotary electric motor in reciprocating linear movement towards and
away from
the servo-orifice.
In a further embodiment, the actuator may include a rotary to linear
conversion
system for converting rotary motion of the reversible electric motor into
linear
reciprocating movement of the poppet. The rotary to linear conversion system
may include
a threaded lead screw held stationary and driven in rotation by a reversible
rotary electric
motor. In this embodiment, the lead screw may be threadably attached to a ball
nut from
which the poppet depends, whereby the rotary motion of the reversible rotary
electric
motor causes rotation of the screw to result in driven linear movement of the
ball nut and
the poppet in either direction.
In a further embodiment, there is provided a servo-controller for controlling
the
powering of the servo-valve by the reversible rotary electric motor. The servo-
controller
may further be capable of sensing the position of the poppet with respect to
the servo-
orifice, such that the poppet position is sensed when mud flow through the
servo-orifice is
restricted or unrestricted, and wherein the amount and direction of rotation
of the
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reversible rotary electric motor from the sensed poppet position is counted
and stored by
the controller.
In another embodiment, the sensed position of the orifice restriction is
calibrated as
the fully closed position of the poppet. The poppet's travel is thereby
monitored and
controlled during operation to avoid unneeded collision or frictional wear
between the
poppet and the servo-orifice. The servo controller may sense the position of
the poppet by
sensing whether movement of the poppet is impeded, and the servo-controller
counts the
number of rotations of the reversible rotary electric motor until the poppet
is impeded and
compares the number of rotations to an expected number of rotations to
determine the
position of the poppet with respect to the servo-orifice. The expected number
of rotations
can be preset to allow a predetermined rate of mud flow past the servo-orifice
when the
poppet is moved away from the servo-orifice by the preset expected number of
rotations.
In a still further embodiment, the servo-controller may include a debris
clearing
command that is initiated when the number of rotations counted is not equal to
the
expected number of rotations. The debris clearing command may cause the
reversible
rotary electric motor to rapidly reciprocate the poppet to dislodge any debris
present
between the poppet and the servo-orifice.
In another embodiment, the attachment between the poppet and the reversible
rotary electric motor comprises a dynamic seal to isolate the reversible
rotary electric
motor, rotary to linear conversion system and related drive components from
the drilling
mud in which the poppet and orifice are immersed when in operation.
In a further aspect, the present invention provides a method for causing the
generation of a mud pulse by a controlled pulser's main pulse valve comprising
the steps
of: powering a pulser servo-valve in a first direction using a reversible
rotary electric
motor such that mud is permitted to flow past a servo-orifice to activate a
main mud pulse
valve; and powering the servo-valve in a second direction using the reversible
rotary
electric motor such that mud flow past the servo-orifice is restricted to
deactivate the main
mud pulse valve.
In one embodiment, the method further comprises the step of cutting power to
the
reversible rotary electric motor to hold the servo-valve in a particular
position within its
range of motion to tailor the actuator's effect on the main pulse valve and
thereby tailor
the pressure and duration characteristics of a mud pulse. By shorting or
connecting its
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coils together in a tailored way, the effect is to provide a braking and
holding function by
the motor on the servo-valve's linear motion.
In another aspect, the invention provides a servo-controller for use with a
downhole measurement-while-drilling pulser actuator, the servo-controller
comprising a
sensor, memory, control circuitry, and an operator interface.
In one embodiment, the sensor is a mud flow sensor, pressure sensor,
temperature
sensor, rotation-step counter, position sensor, velocity sensor, current level
sensor, battery
voltage sensor, timer, or an error monitor.
In another embodiment, the memory stores time-stamped or counted sensed events
together with an event-type indication. The servo-controller may be
programmable to
cause an action within the actuator responsive to a sensed event, a time, an
elapsed time, a
series of sensed events, or any combination thereof.
In a further embodiment, the user interface provides information from memory
to
the operator, and may allow an operator to alter the programming of the
control circuitry.
Other aspects and features of the present invention will become apparent to
those
ordinarily skilled in the art upon review of the following description of
specific
embodiments of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of example
only, with reference to the attached Figures, wherein:
Figs. IA and B are a longitudinal cross sectional view of the upper and lower
portions of an embodiment of the mud pulser during mud flow through the
servo orifice; and
Fig. 2A and 2B are a longitudinal cross sectional view of the upper and lower
portions of an embodiment of the mud pulser during mud flow restriction by the
poppet.
DETAILED DESCRIPTION
The present invention relates to an apparatus and method for actuating a mud
pulser telemetry system used during well-drilling operations. The present
apparatus allows
a servo-valve to be powered both in opening and closing to activate a main mud
pulser
valve, and does not rely on a solenoid system. The powered opening and closing
of the
servo-valve results in various functional and economic advantages, including
the ability to
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clear debris from the restricted portion of the mud flowpath, and faster data
rates due to
elimination of inherent operating delays in the solenoid systems of previous
tools, with the
end result of providing a pulser driver which consumes a minimal amount of DC
power
while providing more force with which to drive the servo-valve's poppet in
each direction.
Therefore, the actuator remains functional at a comprehensive range of
downhole drilling
conditions.
Furthermore, in the embodiment shown in the Figures, the present device is
designed to have several independent, interconnected housings, and employs a
double seal
between the oil compartment and the drilling mud, which simplifies assembly
and repair
of the tool.
Additionally, the use of a reversible rotary electric motor such as a stepper
motor,
electric load sensors, and control circuitry in a powered-both-directions
servo-valve
system will allow for self-calibration of the tool and self-diagnosis and
error correction
unavailable in other systems. In an embodiment of the invention, as shown in
Figures 1A
and 1B, a reversible rotary electric motor such as a three-phase stepper
rotary motor 1 is
monitored and controlled by a servo-controller 10, the rotary movement of the
reversible
rotary electric motor 1 being converted into linear movement of a poppet 21,
thereby
opening and closing a servo-valve assembly 20 to actuate a mud pulser main
valve (not
shown). Communication of information to the well surface is accomplished by
encoded
signals, which are translated to produce pressure surges in the downward flow
of the
pressurized mud. It is recognized that although the drilling fluid is
generally referred to as
mud, other drilling fluids are also suitable for use with the present
invention, as is well
known in the art.
With reference to the Figures, the mud pulser actuator is lowered downhole
and, in
the embodiment shown, generally includes a plurality of serially
interconnected housings
2, 3, 4, 5, 6, 7, and 8, an electrical connector 9, a servo-controller 10 for
controlling the
operation of a reversible rotary electric motor 1, and a servo-valve assembly
20 that is
driven in linear motion by the reversible rotary electric motor 1. The servo-
valve assembly
includes a poppet 21 capable of linear reciprocating movement to and from a
servo valve
seat 22 of a servo orifice 23, thereby opening and closing the servo orifice
23 to allow or
prevent the passage of pressurized mud and thereby actuate a pulser (not
shown,
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connected to the lower end 2a of the lowermost housing 2) to generate a
pressure pulse for
telemetric purposes.
MECHANICAL SYSTEM
A rotary-to-linear coupling system 30a, 30b (hereinafter referred to as
coupling
system 30) is used to translate the torque from the reversible rotary electric
motor 1 into
linear movement of the servo-valve shaft 24a, which is preferably a series of
connected
shafts for transferring linear movement from the coupling system 30 to the
servo poppet
21. Preferably, the servo shaft includes a spline shaft 24a, which passes
through a spline
coupling 24b that can be used to prevent rotation of the servo-valve shaft 24a
when
necessary. The coupling system 30 also includes seals which serve to isolate
the rotating
mechanism from the downhole mud.
In the embodiment pictured in Figure 1 A and 1B, the reversible rotary
electric
motor 1, is electrically powered through an electrical connection 9, by a
power source (not
shown). When activated, the reversible rotary electric motor 1 rotates a lead
screw 31 that
is mounted within a bearing support 32, causing a ball nut 33 to move
threadably along the
lead screw 31. Linear movement of the ball nut 33 results in dependent linear
movement
of the servo-valve shaft 24a, and servo poppet 21. When driven in the forward
direction,
the reversible rotary electric motor 1 will cause linear movement of the
poppet 21 away
from the servo-valve seat 22, to allow passage of pressurized mud through the
servo-
orifice 23 to activate the main mud pulser valve to close. When the reversible
rotary
electric motor 1 drives the lead screw 31 in the reverse direction, poppet 21
is urged
towards the servo-valve seat 22 to cover the servo orifice 23, as shown in
Figure 2B, and
mud is therefore prevented from passing through the servo orifice 23 to
actuate the mud
pulser main valve to open.
The servo-valve shaft 24a is surrounded by lubricating fluid, which must be
pressurized against the downhole hydrostatic pressure. In addition to a
bellows seal 40, an
additional seal 41 may be added to hold oil inside the chamber of the tool,
with the
bellows seal 40 preventing mud from reaching the additional seal 41. The dual
seal 40, 41
maintains the integrity of the lubrication chamber during operation and during
replacement
of the bellows seal 40 during maintenance. The addition of this seal 41 does
not negatively
impact performance of the actuator due to the improved power characteristics
of the
system, as will be discussed below.
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In a preferred embodiment, the construction of the device allows most downhole
clogs, where debris in the mud may stop the poppet 21 from sealing with the
servo-valve
seat 22, to be easily cleared as will be described below, and the serially
interconnected
housing design allows simple and rapid repair of the tool when necessary.
The servo-valve assembly 20 is preferably composed of a wear resistant
material
such as tungsten carbide or ceramic to maximize the efficiency of the tool and
to minimize
maintenance of the tool, and is preferably replaceable.
OPERATION
When restriction of mud flow by the main valve is desired, the reversible
rotary
electric motor 1 will be activated by the servo-controller 10 in the forward
direction. As
shown in Figure 1B, forward powering of the reversible rotary electric motor 1
will cause
the lead screw 31 to turn in the forward (for example, clockwise) direction,
thereby raising
the ball nut 33 and lifting the servo poppet 21 from the servo-valve seat 22.
This will
allow mud flow to pass unrestricted through the servo-orifice 23 to actuate
the main mud
pulse valve, restricting mud flow to generate a pulse that is transmitted to
the surface. The
current-consuming portion of the circuit is then shut down until a further
signal is received
from the servo-controller 10. The lack of current to the reversible rotary
electric motor 1
results in the reversible rotary electric motor 1 being immovable and
therefore acting as a
brake to prevent further movement of the poppet 21 until further activation of
the
reversible rotary electric motor 1.
Subsequently, when the servo-controller 10 initiates reverse motion by the
reversible rotary electric motor 1, the lead screw 31 is rotated in the
reverse direction (in
the example, counterclockwise) by the reversible rotary electric motor 1,
causing the ball
nut 33 and servo-valve shaft 24a to move towards the servo-valve seat 22 as
shown in
Figure 2B. Closure of the servo-valve assembly 20 causes opening of the main
mud pulser
valve to allow mud to flow unrestricted to the surface. The current-consuming
portion of
the circuit is then shut down until a further signal is received from the
servo-controller 10.
The reversible rotary electric motor again acts as a brake until further power
is applied (by
shorting or connecting its coils together).
The lead screw 31 and ball nut 33 may be replaced by an alternate system of
rotary
to linear conversion, however a lead screw 31 and ball nut 33 are advantageous
as they are
relatively small in size and may be provided with bearings to provide a low-
friction
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mechanism with high load capacity, durability, and low backlash tolerance. The
lead
screw 31 may be held in contact with the reversible rotary electric motor 1 by
a bearing
support 32 or any other suitable means.
The presently described system of using a reversible rotary electric motor
such as a
stepper motor 1 to drive a servo-valve has several advantages. The powering of
the servo-
valve assembly 20 in both directions allows greater direct control of the
servo-valve
assembly 20, avoids the previous necessity of using a return spring in the
servo assembly,
and therefore the energy required is similar to that of the force of the
downhole mud flow.
This results in an energy efficient system, and results to date indicate that
the presently
described system can supply a force of 100 pounds of pressure for less energy
than
previous systems, particularly than those which employ a solenoid activator.
Thus, the
present system can overcome higher pressures on the poppet valve 21, allowing
the system
to clear itself of debris, and permitting use in a wide range of downhole
conditions,
including conditions of higher pressure and higher volume mud flow, and in
conditions
when the mud is contaminated or is very dense.
Use of a reversible rotary electric motor powering the servo-valve in both
directions also allows the system to be more responsive than solenoid systems,
resulting in
a faster data rate with more accurate or precise pulse-edge timing.
Experimental results
indicate that data rates of 0.25 seconds/pulse are possible with this system,
as compared to
0.8 to 1.5 seconds/pulse in solenoid systems.
FLOW DETECTION & DIAGNOSTIC SOFTWARE
The servo controller detects the position of the poppet 21 against the servo-
valve
seat 22 by counting the number of rotations made by the reversible rotary
electric motor
until further movement of the poppet is impeded. For example, if the poppet 21
is
generally programmed to attain an unseated position that is three forward
motor rotations
away from the seated position, upon seating activation by the servo-controller
10, the
reversible rotary electric motor will turn three reverse rotations, at which
point further
rotation will be impeded due to seating of the poppet 21 on the servo-valve
seat 22. On
unseating activation by the servo controller 10, the reversible rotary
electric motor will
turn three complete forward rotations to return the poppet to its pre-
programmed unseated
position. Seating can be sensed by an increase in current drawn by the
reversible rotary
electric motor, from which a large opposing force (like stopped motion due to
valve
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seating) is inferred. The control circuitry also senses rotation of the
reversible rotary
electric motor and can count rotations and direction of rotation.
Debris may enter the device with the mud, potentially causing jamming of the
poppet. The servo controller 10 can be programmed to detect and clear jams
from the
servo-valve assembly 20. For example, debris may become lodged at the servo-
valve seat
22, preventing the poppet from fully sealing against the servo-valve seat 22.
In such a
situation, the reversible rotary electric motor would be prevented from
completing its three
reverse rotations. This is sensed by the servo-controller 10, which will then
attempt to
dislodge the debris. The dislodging sequence may include rapid reciprocation
of the
poppet 21 towards and away from the servo-valve seat 22, or may include
further reverse
rotations on the subsequent reverse rotation. For example, if the reversible
rotary electric
motor was able to turn only two reverse rotations, the servo-controller 10
will recognize
that the valve did not properly close, and will adjust one or more subsequent
forward
and/or reverse rotations to ensure that the poppet 21 is able to seat against
the servo-valve
seat 22. Similarly, debris may cause the poppet to not fully open, resulting
in appropriate
corrective action by the servo-controller on the next activation of the
reversible rotary
electric motor 1 activation. In either case, a processor provides a report of
measurements
recorded and controls the following cycle of the brushless reversible rotary
electric
motor's rotation accordingly.
The ability to detect and clear most jams within the tool allows a more robust
design of the tool in other respects. For example, as the tool can easily
clear particulate
matter from the servo-valve assembly, the tool can be provided with larger and
fewer mud
ports, and may include reduced amounts of screening. Screening is susceptible
to
clogging, and so reducing screening leads to longer mean time between
operation failure
of the device in-hole; and will reduce the velocity of any mud flow through
the tool,
reducing wear on the bladder and other parts. Further, the removal of several
previously
necessary components (such as the return spring, transformer, and solenoid and
related
electronics) contributes to a tool of smaller size (in both length and
diameter) that is more
versatile in a variety of situations. For example, embodiments with outside
diameter less
than 1-3/8" or length less than four feet have been achieved, although these
dimensions
are not by way of limitation, but by example only.
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Custom software also has the ability to track downhole conditions, and also
uses a
sensor to detect mud flow. When mud flow is detected, a signal is sent to the
Directional
Module Unit (not shown), to activate the overall system. The system also has
the ability to
time stamp events such as start or end of mud flow, incomplete cycles or
system errors,
low voltages, current, and the like, as well as accumulated run-time, number
of pulses,
number of errors, running totals of rotations or reversible rotary electric
motor pulses.
Wires or conductors may also be easily passed by the pulser section to service
additional
near-bit sensors or other debris. The software that detects the mud flow can
be configured
for different time delays to enable it to operate under a larger variety of
downhole drilling
conditions than its predecessors. The mud flow detection capability can also
be used to
calibrate or confirm the closed position of the poppet.
In addition, a user may monitor such data as well as any downhole sensors
using a
user interface attachable to the tool. Such sensors may include pressure or
temperature
sensors, rotation step-counters, travel or depth sensors, current levels,
battery voltage, or
timers. The user could monitor each component of the actuator to determine
when the tool
must be removed from downhole for repair. A user may, in turn, program an
activity to
cause an action or correction in response to a sensed event.
The above-described embodiments of the present invention are intended to be
examples only. Alterations, modifications and variations may be effected to
the particular
embodiments by those of skill in the art without departing from the scope of
the invention,
which is defined solely by the claims appended hereto.
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