Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02800593 2013-01-07
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INSTRUMENTED ROD ROTATOR
BACKGROUND OF THE INVENTION
Field of the Invention
Embodiments of the present invention generally relate to monitoring the
rotation
of a member in a reciprocating rod lift system.
Description of the Related Art
The production of oil with a sucker-rod pump is common practice in the oil and
gas industry. An oil well generally comprises a casing, a string of smaller
steel pipe
inside the casing and generally known as the tubing, a pump at the bottom of
the well,
and a string of steel rods, commonly referred to as sucker rods, within the
tubing and
extending down into the pump for operating the pump. Various devices as are
well
known in the art are provided at the top of the well for reciprocating the
sucker rod to
operate the pump.
The crude oil generally contains paraffin and other substances which tend to
congeal and precipitate out of the oil and deposit upon the walls of the
tubing during the
passage of the oil through the tubing. Such deposits are quite objectionable
and tend to
restrict the flow of oil through the tubing. Moreover, operating the pump with
an
excessive amount of the deposits may lead to severe rod and tubing wear.
Various
means and methods have been proposed for preventing the formation of such
deposits
and for removing deposits so formed. Such means and methods generally include
the
use of chemicals, electrical heating and various mechanical scraping devices.
In
general, such means and methods may be expensive and have other objectionable
features.
A common mode of preventing the formation of deposits on the tubing and
removing such deposits as they are formed generally include attaching paraffin
scrapers
to the sucker rod. Such sucker rods may remove the deposits from the oil well
tubing
as it is formed so that it is flushed out of the well with the oil passing
therethrough. In
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many cases, the means for reciprocating the sucker rods include devices, such
as a rod
rotator, for rotating the rods through a predetermined angle during each
stroke of the
sucker rods. The rod rotator may be installed on the wellhead and connected to
a
walking beam. With each stroke of the pumping unit, the rotator may rotate the
rods a
fraction of one revolution. As the rods are rotated, paraffin may be scraped
off the walls
of the tubing in an effort to distribute wear.
SUMMARY OF THE INVENTION
One embodiment of the present invention is a method. The method generally
includes monitoring rotation of a member in a reciprocating rod lift system,
wherein the
member is to be rotated to distribute wear, and generating a signal indicative
of the
monitored rotation.
Another embodiment of the present invention provides an apparatus. The
apparatus generally includes a mechanism in a reciprocating rod lift system,
wherein
the mechanism is configured to monitor rotation of a member in the system,
wherein the
member is to be rotated to distribute wear, and generate a signal indicative
of the
monitored rotation.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above-recited features of the present
invention
can be understood in detail, a more particular description of the invention,
briefly
summarized above, may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however, that the
appended
drawings illustrate only typical embodiments of this invention and are
therefore not to be
considered limiting of its scope, for the invention may admit to other equally
effective
embodiments.
FIG. 1 is a schematic depiction of an illustrative sucker-rod pumping unit
with a
control unit for controlling the pump in an effort to extract fluid from a
well.
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FIG. 2 illustrates a reciprocating rod lift system with a rotator for rotating
a
member of the system, according to embodiments of the present invention.
FIG. 3 illustrates a rod rotator installed in a reciprocating rod lift system,
according to embodiments of the present invention.
FIG. 4 illustrates operations for monitoring the rotation of a member in a
reciprocating rod lift system, according to embodiments of the present
invention.
FIGs. 5A-B illustrate the inner rotating assembly of rotators, according to
embodiments of the present invention.
FIG. 6 illustrates an upgrade kit for a rod rotator, according to embodiments
of
the present invention.
FIG. 7 illustrates a cable connector design for monitoring the rotation of a
member in a reciprocating rod lift system, according to embodiments of the
present
invention.
DETAILED DESCRIPTION
The production of oil with a reciprocating rod lift system 100 (e.g., sucker-
rod
pump system), such as that depicted in FIG. 1, is common practice in the oil
and gas
industry. Although shown with a conventional pumping unit, any suitable
pumping unit
may be used. In the pump system 100, a rod pump 104 consists of a tubular
barrel 106
with a valve 114 (the "standing valve") located at the bottom that allows
fluid to enter
from the wellbore, but does not allow the fluid to leave. Inside the pump
barrel 106 is a
close-fitting hollow plunger 110 with another valve 112 (the "traveling
valve") located at
the top. This allows fluid to move from below the plunger 110 to the
production tubing
108 above and does not allow fluid to return from the tubing 108 to the pump
barrel 106
below the plunger 110. The plunger 110 may be moved up and down cyclically by
a
horsehead 101 at the surface via the rod string 102 (e.g., a string of steel
rods or a
continuous rod string), wherein the motion of the pump plunger 110 comprises
an
"upstroke" and a "downstroke," jointly referred to as a "stroke." The polished
rod 118,
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which is a portion of the rod string 102 passing through a stuffing box 103,
may enable
an efficient hydraulic seal to be made around the reciprocating rod string
102. A control
unit 116, which may be located at the surface, may control the system 100.
As mentioned above, the crude oil generally contains paraffin and other
substances which tend to congeal and precipitate out of the oil and deposit
upon the
walls of the tubing 108 during the passage of the oil through the tubing 108.
As a result,
as the rod string 102 is moved up and down cyclically, the rod string 102 may
cause
excessive and uneven wear inside the tubing 108, and cause wear on the rod
string
102. For some embodiments, the means for reciprocating the sucker rods may
include
devices, such as a rod rotator or a tubular rotator, for rotating members,
such as the rod
string 102 or the tubing 108, respectively, through a predetermined angle
during each
stroke of the rod string 102. By rotating the rod string 102 or the tubing 108
while the
reciprocating rod lift system 100 is operating, the inside surface of the
tubing 108 may
be worn evenly, which may extend the life of the tubing 108 and the rod string
102. The
rotator may be installed on the wellhead and connected to a walking beam, as
illustrated in FIG. 2.
FIG. 2 illustrates a reciprocating rod lift system 200 with a rotator 202 for
rotating
a member of the system 200, according to embodiments of the present invention.
The
rotator 202 may be installed above the wellhead. As the horsehead 101
operates, an
interconnecting chain 204 may pull a lever 206 of a ratchet or similar
mechanism
coupled to the rotator 202. With the cyclical motion of the horsehead 101, the
rotator
202 may then rotate a member, such as the rod string 102 or the tubing 108 by
at least
a fraction of one revolution (e.g., several degrees). In this way, wear inside
the tubing
108 caused by the rod string 102 may be more evenly distributed around an
internal
circumference of the tubing 108. Although FIG. 2 illustrates activation of the
rotator 202
by way of the horsehead 101, the rotator 202 may be activated by other means,
such
as, but not limited to, a flexible drive cable, an electronically controlled
drive, or
hydraulic pressure.
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FIG. 3 illustrates a rod rotator 302 installed in a reciprocating rod lift
system,
according to embodiments of the present invention. The rod rotator 302 may be
disposed below a rod clamp 304 that is clamped around a rod string 102. As the
rod
rotator 302 rotates, the weight of the rod clamp 304 on the rod rotator 302
causes the
rod clamp 304 (and rod string 102) to rotate also. The rod rotator 302 may be
disposed
above a load cell 306 that detects the tensional or compressional forces being
imparted
to the rod string 102at surface.
In certain situations, a rotator may not function as desired. For example, the
rod
string or the rotator may not always rotate with each stroke of the pumping
unit.
Referring back to FIG. 2, there may be issues with the connection between the
rotator
202 and the walking beam (e.g., due to interconnecting chain 204) that may not
actuate
the lever 206 of the rotator 202. A lack of knowledge whether the rotator 202
is
functioning properly may lead to increased expenditures and a decrease in well
production.
Certain embodiments of the present invention provide methods and apparatus for
monitoring rotation of a rod string in a reciprocating rod lift system. In
addition to
monitoring the rod string, any member in the reciprocating rod lift system may
be
monitored for rotation. Examples of other members include the tubing that
surrounds
the rod string (e.g., by a tubular rotator), or any other member attached to
one of these
that rotates at the same time.
FIG. 4 illustrates operations 400 for monitoring the rotation of a member in a
reciprocating rod lift system, according to embodiments of the present
invention. The
operations may begin at 410 by monitoring the rotation of the member (e.g.,
rod string
102 or tubing 108) in the reciprocating rod lift system, wherein the member is
rotated to
distribute wear, as described above. Examples of the member generally include
a
sucker rod string, a continuous rod string, tubing that surrounds the sucker
rod string or
the continuous rod string, or any other member attached to one of these that
rotates at
the same time. As an example, the monitoring may be performed by a mechanism
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incorporated in at least one of a load cell, a rod rotator, or a tubing
rotator. At 420, a
signal indicative of the monitored rotation may be generated.
For some embodiments, monitoring may include detecting one or more magnets.
For some embodiments, the magnets may be installed in one or more locations
around
the member. For some embodiments, the magnets may be installed in one or more
locations within the mechanism. The signal indicative of the monitored
rotation may be
generated by a switch when the magnets pass a fixed location. Examples of the
switch
generally include at least one of a Hall Effect sensor, a reed switch, or a
position/proximity sensor. With one magnet, the signal generated by the switch
may
indicate a complete revolution of the member. However, with multiple magnets,
signals
generated by the switch may indicate partial revolutions of the member.
For some embodiments, monitoring may include detecting one or more radio-
frequency identification (RFID) tags. Use of RFID tags may be desirable due to
its light
weight & low power requirements. The signal indicative of the monitored
rotation may
be generated by a receiver when the RFID tags pass a fixed location. As an
example, if
an RFID tag is affixed to a rod rotator, the receiver may monitor every time
the RFID tag
passes the fixed location. Therefore, it may be known how often the member
makes a
complete revolution.
With regards to a load cell, a mechanism incorporated in the load cell may
generally include a Hall Effect sensor, a reed switch, or other sensor, as
described
above. It may be possible to monitor the rotation of a rod string disposed
within the load
cell. For some embodiments, the rod string may have one or more magnetic
strips or
RFID tags disposed along a length of rod string, wherein a signal indicative
of the
monitored rotation may be generated by the sensor when the magnetic strips or
RFID
tags pass a fixed location.
With regards to a rotator, such as a rod rotator or a tubular rotator, the
member
that is monitored for rotation may include an inner rotating assembly of the
rotator itself.
FIG. 5A illustrates the inner rotating assembly of a rod rotator, according to
embodiments of the present invention. The inner rotating assembly may include
one or
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more magnets 502 (or other devices, such as RFID tags) installed in one or
more
locations, and the outer housing of the rod rotator may include a switch 504
(e.g., Hall
Effect sensor, reed switch, or position/proximity sensor) for generating the
signal
indicative of the monitored rotation when the magnets pass a fixed location.
FIG. 5B illustrates the inner rotating assembly of a tubular rotator,
according to
embodiments of the present invention. The tubular rotator may include one or
more
magnets and a switch, similar to the arrangement illustrated in FIG. 5A for a
rod rotator,
for example, within a sensor assembly housing 506 of the tubular rotator.
However,
since tubular rotators are normally disposed below the wellhead and, as a
result,
exposed to downhole conditions, any electronics involved with monitoring the
rotation
may have to be isolated.
FIG. 6 illustrates an upgrade kit for a rod rotator, according to embodiments
of
the present invention. Certain rod rotators installed at a well site may not
have the
capability to monitor the rotation of a member in a reciprocating rod lift
system.
Therefore, for some embodiments, such rod rotators may be upgraded to monitor
for
rotation, as illustrated in FIG. 6. The upgrade kit generally includes a
rotation sensor
602 (e.g., Hall Effect sensor, reed switch, or position/proximity sensor) and
one or more
magnets 604 (or other devices, such as RFID tags). The magnets 604 may be
strapped
around a portion of the rotator that rotates on each stroke of the pumping
unit, and the
sensor 602 may be set at a fixed location. The signal indicative of the
monitored
rotation may be generated by the sensor 602 when the magnets 604 pass the
fixed
location. With one magnet 604, the signal generated by the sensor 602 may
indicate a
complete revolution of the member. However, with multiple magnets 604, signals
generated by the sensor 602 may indicate partial revolutions of the member.
Referring back to FIG. 4, at 430, the generated signal may be provided to a
controller (e.g., rod pump controller). At 440, the controller may determine a
number of
revolutions (cycle counts) of the member in a given period based on the
signal. For
some embodiments, the controller may generate an alarm if the signal indicates
no
change in value (or less than expected) in the number of revolutions of the
member
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within a threshold interval (e.g., hourly or daily). Furthermore, the
controller may
communicate information (e.g., related to the alarm) to a software system
located at a
central location, where information related to different wells may be
monitored. For
example, the information may be reported back to a host system through an
existing
radio infrastructure. For some embodiments, an application may be developed in
the
firmware of the controller to determine if a rotator is operational and
generate an alarm
based on operator set limits.
FIG. 7 illustrates a cable connector design 700 for monitoring the rotation of
a
member in a reciprocating rod lift system, according to embodiments of the
present
invention. Traditionally, a load cell is connected directly to a controller
for detecting the
tensional or compressional forces being imparted to a rod string at surface.
However,
when the mechanism for monitoring rotation is located in a rotator (e.g.,
rotator 704), the
rotator 704 and a load cell 706 may share a connection with a controller 702
(e.g., via a
Y-connector 708).
With the ability to monitor the rotation of a member in a reciprocating rod
lift
system, rod and tubing wear of the system may be minimized. For example, if
there is a
determination that the member is not properly rotating, efforts may be made to
correct
the issue, in order to avoid, for example, paraffin buildup. There may also be
an
improvement in the utilization of maintenance personnel, a reduction in the
causes of
lost production, and an increase in well surveillance capabilities. With the
increase in
well run life, reduction of well down time, production may increase
accordingly.
While the foregoing is directed to embodiments of the present invention, other
and further embodiments of the invention may be devised without departing from
the
basic scope thereof, and the scope thereof is determined by the claims that
follow.
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