Note: Descriptions are shown in the official language in which they were submitted.
CA 02533839 2006-11-24
METHOD OF DETERMINING A CROSS-LOAD ON A
MOBILE REPAIR UNIT FOR A WELL
This application is a divisional application of
Canadian Patent File No. 2,238,998 filed May 28, 1998.
Background Of The Invention
Field Of The Invention
The subject invention generally pertains to
equipment used for repairing wells that have already been
drilled, and more specifically pertains to mobile repair units
that frequently travel from one site to another.
Description Of Related Art
After an oil rig drills a well and installs the well
casing, the rig is dismantled and removed from the site. From
that point on, a mobile repair unit is typically used to
service the well. Servicing includes installing and removing
inner tubing strings, sucker rods, and pumps. The variety of
work requires a myriad of tools. When the tooling is not
closely associated with the mobile repair unit, the right
equipment may not be available when needed.
Moreover, the work is carried out by a company that
typically owns and operates several mobile repair units. The
units are often operating at the same time at various remote
sites. Some sites may be separated by hundreds of miles.
This makes it difficult to stay abreast of the status at each
of the sites.
Typically, a supervisor will travel from site to
site. However, this is inefficient and often critical steps
of an operation get carried out unsupervised. At times,
accidents occur in the absence of an unbiased witness.
CA 02533839 1998-05-28
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Svmmarv of the Invention
To avoid the problems of today's mobile repair
units, a first aspect of the invention is to closely associate
hydraulic and pneumatic systems with a mobile repair unit by
having them share a common power supply and monitoring system.
A second aspect of the invention is to provide a
remotely accessible mobile repair unit with the necessary
equipment to make it universally adaptable to do a variety of
work such as removing and installing an inner tubing string,
sucker rods, and pumps.
A third aspect is to provide a mobile repair unit
that senses and transmits, to a remote home base, data that
identifies the extent to which an inner tubing string was
stretched prior to flooding the well bore with fluid.
A fourth aspect is to identify from a remote
location key events, such as the time of transition of
installing steel sucker rods to installing fiberglass ones.
A fifth aspect is to restrict local operator access
to a system that monitors the operation of a mobile repair
unit so an unbiased and unaltered record can be recorded and
maintained of the complete system and activity of the mobile
repair unit.
A sixth aspect is to convey to a remote location a
record that helps explain events that led to an accident at
the work site. When the information is conveyed to a remote
site, it is not likely to be destroyed by the accident itself,
such as a fire.
CA 02533839 1998-05-28
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A seventh aspect is to remotely identify an
imbalance of a mobile repair unit caused by wind or leaning
inner tubing segments against its derrick.
An eighth aspect is to remotely distinguish between
the raising and lowering of an inner tubing string to help
establish the cause of an accident. An added benefit is to be
able to place the proper predetermined tension on a packer or
tubing another being set.
A ninth aspect is to enable one to remotely identify
when a mobile repair unit is operating for the purpose of
determining the amounts to be invoiced for the work performed.
A tenth aspect is to provide a method of alerting a
home base of a hazardous level of hydrogen sulfide gas present
at a remote work site.
These and other aspects of the invention are
provided by a self-contained mobile repair unit having a
universal set of hydraulic and pneumatic tooling for servicing
well equipment such as an inner pipe string, a sucker rod and
a pump. The repair unit and tooling share a common engine.
An extendible derrick supporting a hoist is pivotally coupled
to the frame of the repair unit. A monitor senses the load on
the derrick and conveys that information to a remote home base
where the time of critical events is identified.
Brief Description of the Drawinas
Figure 1 is a side view of a mobile repair unit with
its derrick extended. .
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Figure 2 is a schematic view of a pneumatic slip
in a locked position.
Figure 3 is a schematic view of a pneumatic slip
in an open position.
Figure 4 is a schematic illustration of a set of
hydraulic tongs.
Figure 5 is a side view of a mobile repair unit
with its derrick retracted.
Figure 6 is an electrical schematic of a monitor
circuit.
Figure 7 is an end view of an imbalanced derrick.
Figure 8 shows diaital data associated with a time
stamo.
Figure 9 illustrat-es the raisina and lowm-ring of
1; an inner tubing string.
Figure 10 shows an inner tubing being lowered.
Fiaure 11 shows an inner tubing stopped at a
predetermined depth.
Figure 12 shows an inner tubing being locked in a
conventional manner to another casing.
Figure 13 shows an inner tubing being stretched.
Figure 14 shows pre-stretched inner tubing locked
within an outer casing.
Figure 15 shows a first steel sucker rod (with a
pump) being lowered into an inner tubing string.
Figure 16 shows a second steel sucker rod being
lowered into an inner tubing string.
Figure 17 shows a first fiberglass sucker rod
being lowered into an inner tubing string.
Figure 18 shows a second fiberglass sucker rod
being lowered into an inner tubing string.
CA 02533839 1998-05-28
Description Of The Preferred Embodiment
Referring to Figure 1, a retractable, self-
5 contained mobile repair unit 20 is shown to include a truck
frame 22 supported on wheels 24, an engine 26, a hydraulic
pump 28, an air compressor 30, a first transmission 32, a
second transmission 34, a variable speed hoist 36, a block
38, an extendible derrick 40, a first hydraulic cylinder 42,
a second hydraulic cylinder 44, a first transducer 46, a
monitor 48, and retractable feet 50.
Engine 32 selectively couples to wheels 24 and
hoist 36 by way of transmissions 34 and 32, respectively.
Engine 26 also drives hydraulic pump 28 via line 29 and air
compressor 30 via line 31. Compressor 30 powers a pneumatic
slip 84 (Figures 2 and 3), and pump 28 powers a set of
hydraulic tongs 52 (Figure 4). Pump 28 also powers
cylinders 42 and 44 which respectively extend and pivot
derrick 40 to selectively place derrick 40 in a working
position (Figure 1) and in a lowered position (Figure 5)
In the working position, derrick 40 is pointed upward, but
its longitudinal centerline 54 is angularly offset from
vertical as indicated by angle 56. The angular offset
provides block 38 access to a well bore 58 without
interference with derrick pivot point 60. With angular
offset 56, the derrick framework does not interfere with the
typically rapid installation and removal of numerous inner
pipe segments 62 and sucker rods 64 (Figure 16).
Individual pipe segments 62 and sucker rods 64 are
screwed to themselves using hydraulic tongs 66 which are
schematically illustrated in Figure 4. The term "hydraulic
CA 02533839 1998-05-28
. .. 6
tongs" used herein and below refer to any hydraulic tool
that can screw together two pipes or sucker rods. An
example would include those provided by B. J. Hughes company
of Houston, Texas. In operation, pump 28 drives a hydraulic
motor 68 forward and reverse by way of valve 70.
Conceptually, motor 68 drives pinions 72 which turn wrench
element 74 relative to clamp 76. Element 74 and clamp 76
engage flats 81 on mating couplings 78 of a sucker rod or
inner pipe string of one conceived embodiment of the
invention. However, it is well within the scope of the
invention to have rotational jaws or grippers that clamp on
to a round pipe (i.e., no flats) similar in concept to a
conventional pipe wrench, but with hydraulic clampina. '"he
rotational direction of motor 68 determines assemblv or
disassembly of couplings 78. Transducer 80 is used to
provide a 0-5 VDC signal 82 that in one embodiment of the
invention indicates the applied torque to couplings 78.
Referring to Figures 2 and 3, when installing
inner pipe segments 62, pneumatic slip 84 is used to hold a
string of pipe 62 while the next segment 62' is screwed on
using tongs 66. Compressor 30 provides pressurized air
through valve 86 to rapidly clamp and release slip 84
(Figures 2 and 3, respectively) . A tank 88 helps maintain a
constant air pressure. Pressure switch 90 provides monitor
48 with a signal that indirectly indicates that repair unit
20 is in operation.
Referring back to Figure 1, weight applied to
block 38 is sensed by way of a hydraulic pad 92 that
supports the weight of derrick 40. Hydraulic pad 92 is
basically a piston within a cylinder (alternatively a
diaphragm) such as those provided M. D. Totco company of
CA 02533839 1998-05-28
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Cedar Park, Texas. Hydraulic pressure in pad 92 increases
with increasing weight on block 38. In Figure 6, first
transducer 46 converts the hydraulic pressure to a 0-5 VDC
signal 94 that is conveyed to monitor 48. Monitor 48
converts signal 94 to a digital value, stores it in a memory
96, associates it with a real time stamp, and eventually
communicates the data to a remote home base 100 by way of a
modem 98.
In the embodiment of Figure 7, two pads 92
associated with two transducers 46 and 102 are used. An
integrator 104 separates pads 92 hydraulically. The rod
side of pistons 106 and 108 each have a pressure exposed
area that is half the full face area of piston 108. Thus
chamber 110 develops a pressure that is an average c--" the
i5 pressures in racis 92. One type of integrator 104 is
provided by M. D. Totco company of Cedar Park, Texas. In
one embodiment of the invention, just one transducer 46 is
used and it is connected to port 112. In another embodiment
of the invention, two transducers 46 and 102 are used, with
transducer 102 on the right side of unit 20 coupled to port
114 and transducer 46 on the left side coupled to port 116.
Such an arrangement allows one to identify an imbalance
between the two pads 92.
Returning to Figure 6, transducers 46 and 102 are
shown coupled monitor 48. Transducer 46 indicates the
pressure on left pad 92 and transducer 102 indicates the
pressure on the right pad 92. A generator 118 driven by
engine 26 provides an output voltage proportional to the
engine speed. This output voltage is applied across a dual-
resistor voltage divider to provide a 0-5 VDC signal at
point 120 and then passes through an amplifier 122.
CA 02533839 2006-11-24
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Generator 118 represents just one of many various tachometers
that provide a feedback signal proportional to the engine
speed. Another possibility would be to have engine 26 drive
an alternator and measure its frequency. Transducer 80
provides a signal proportional to the pressure of hydraulic
pump 28, and thus proportional to the torque of tongs 66.
A telephone accessible circuit 124, referred to as
a "POCKET LOGGERT'''" by Pace Scientific, Inc. of
Charlotte, North Carolina, includes four input channels 126,
128, 130 and 132; a memory 96 and a clock 134. Circuit 124
periodically samples inputs 126, 128, 130 and 132 at a user
selectable sampling rate; digitizes the readings; stores the
digitized values; and stores the time of day that the inputs
were sampled. It should be appreciated by those skilled in
the art that with the appropriate circuit, any number of
inputs can be sampled. Page Scientific provides circuits that
employ multiplexing to provide twelve input channels.
An operator at a home base 100 remote from the work
site at which repair unit 20 is operating accesses the data
stored in circuit 124 by way of a PC-based modem 98 and a
cellular phone 136. Phone 136 reads the data stored in
circuit 124 via lines 138 (RJll telephone industry standard)
and transmits the data to modem 98 by way of antennas 140 and
142. In one embodiment of the invention, phone 136 includes
a CELLULAR CONNECTION' provided by Motorola Incorporated of
Schaumburg, Illinois (a model S1936C for Series II cellular
transceivers and a model S1688E for older cellular
transceivers).
Some details worth noting about monitor 48 is that
its access by way of a modem makes monitor 48 relatively
CA 02533839 1998-05-28
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inaccessible to the crew at the job site itself. Amplifiers
122, 144, 146 and 148 condition their input signals to
provide corresponding inputs 126, 128, 130 and 132 having an
appropriate power and amplitude range. Sufficient power is
needed for RC circuits 150 which briefly (e.g., 2-10
seconds) sustain the amplitude of inputs 126, 128, 130 and
132 even after the outputs from transducers 46, 102 and 80
and the output of generator 118 drop off. This ensures the
capturing of brief spikes without having to sample and store
an excessive amount of data. A DC power supply 152 provides
a clean and precise excitation voltage to transducers 46,
102 and 80; and also supplies circuit 124 with ar,
appropriate voltage by way of voltage divider 154. Pressure
switch 90 enables power supply 152 by way of relay 156 whose
contacts i58 ciose bv coil 160 being energized by battery
_62.
Figure 8 shows an example of the data extracted
from circuit 124 and remotely displayed at PC 164. The
values plotted at a point in time indicated by numeral 166
represent repair unit 20 at rest with engine 26 idling as
shown in Figure 1. Numeral 168 showing weight on block 38
and high engine speed indicates the raising of an inner pipe
string 62 as represented by arrow 170 of Figure 9. Numeral
172 showing weight on block 38 and low engine speed
indicates the lowering of inner pipe string 62 as
represented by arrow 174 of Figure 9. Points 176, 178, 180,
182 and 184 correspond to the conditions illustrated in
Figures 10, 11, 12, 13 and 14, respectively. In Figure 10,
an inner tubing string 62 is being lowered into an outer
casing 186. In Figure 11, tubing string is stopped at a
predetermined depth. In Figure 12 tubing string 62 is
CA 02533839 1998-05-28
rotated in a conventional manner to lock its lower end 188
to outer casing 186 (note slight torque at point 190) . In
Figure 13 an upper end 192 of string 62 is raised until the
pressure parameter at right and left pads 92 reach the
predetermined limit indicated by numeral 194. In Figure 14
wedge 196 locks upper end 192 to casing 186, and block 38 is
disconnected from tubing string 62. Points 198, 200, 202
and 204 correspond to the conditions illustrated in Figures
15, 16, 17 and 18, respectively, which depict the lowering
of a string of sucker rods having a pump 77 at its lower
end. Intermediate points 199, 201 and 203 indicate tongs 66
screwina onto the first steel sucker rod 64 a second steel
sucker rods 206, a fiberglass sucker rod 208, and a second
fiberalass sucker rod 210, respectively. Note the
?5 difference in torque and the incremental weight difference
at pads 92 when changing over from steel rods to fiberglass
ones. Points 212 correspond to the windy conditions
illustrated by arrow 214 of Figure 7. The absence of data
points beyond 12:00 indicates that the windy conditions
prevented the crew from continuing, or it was Friday
afternoon.
Referring back to Figure 4, it should be noted
that transducer 80 represents any one of a variety of
devices that produce an electrical signal in response to a
change in a sensed condition. In one embodiment of the
invention, transducer 80 is actually a hydrogen sulfide gas
detector with signal 82 serving as a gas detection signal
that varies with a varying concentration of hydrogen sulfide
gas 250. An example of a hydrogen sulfide gas detector is a
CONTROLLER 8000 provided by Industrial Scientific
Corporation of Oakdale, Pennsylvania.
CA 02533839 1998-05-28
Although the invention is described with respect
to a preferred embodiment, modifications thereto will be
apparent to those skilled in the art. Therefore, the scope
of the invention is to be determined by reference to the
claims which follow.
