Note: Descriptions are shown in the official language in which they were submitted.
CA 02861781 2014-08-29
RACK AND PINION DRIVEN GAS COMPRESSOR
FIELD OF THE INVENTION
This invention is in the field of compressors, and more specifically to gas
compressors.
BACKGROUND
During oil production, gas can accumulate in the casing lining the production
well, restricting the
flow of hydrocarbon from a formation into the production well and causing gas
locking of the
down hole pump.
If casing pressure is high in relation to the formation pressure, free gas
will enter the pump
barrel. Due to compression of the gas, sufficient pressure can build in the
pump barrel to prevent
opening of the valves, resulting in these gas locks. Additionally, this gas
back-pressure in the
hydrocarbon well's annulus can generate a restriction to oil and gas flow from
the formation into
the well bore. These issues can mean that little or nothing is pumped, thus
reducing pump
volumetric efficiency and hydrocarbon production.
If the casing pressure in wells with low formation pressure can be reduced,
gas volumes that
enter the pump banel can be minimized and hydrocarbon may more readily flow
from the
surrounding formation into the production well. This can also ease the gas
lock problems and
overall increase well production.
Gas compressors have long been used as a solution to decrease the gas-back
pressure in well
casings by capturing and compressing the vented gas into a sales line or flow
line. Gas
compressors act to draw gas from the casing side of a well and discharge the
gas into the flow
line, which is a tube connected to the annulus. This reduces gas back-pressure
downhole and on
the formation face, allowing additional oil to enter the well bore and to flow
out of the formation,
thus relieving the flow in the oil and gas delivery line. It can additionally
minimize gas entry into
the pump barrel, preventing gas locks.
Conventional cylinder style gas compressors are mounted on a pump jack and are
driven by the
walking beam of the pumping unit. As these piston style gas compressors are
mounted on a
pump jack and driven by the walking beam, they are often referred to as
walking beam
compressors. The action of the walking beam is used as the prime mover for
these compressors.
Compressors that are driven by pump jacks are typically designed to be
specific to the producer
and well, and will be chosen or designed according to considerations such as
(but not limited to)
gas flow, well casing pressure, oil delivery line pressure, pump jack model,
sucker rod stroke,
double strokes per minute, and the working schedule of the pump jack. Its
capacity is oftentimes
entirely dependent on the number of double strokes per minute of the pump jack
and the
function-pause schedule of the well pump jack. This means that the functioning
and efficiency
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of the compressor is dependent on the operation of the pump jack. As such, the
compressor
design, operation, and maintenance will be largely dictated by the pump jack
used.
Additionally, installation of the compressor on the pump jack results in
downtime of the pump
jack, meaning that production must halt while the compressor is being
installed. Installation can
take from a few days to several days, which can stall production and result in
much wasted time.
Furthermore, when the compressor is misapplied or installed incorrectly, or
when the compressor
simply malfunctions in any way, this can cause problems for the entire
operation, resulting in
further wasted time and money and loss of pump jack warranty.
It would be advantageous to have a gas compressor that allows for increased
production and
smoother well operation.
SUMMARY OF THE INVENTION
It would be advantageous to have gas compressor that allows for efficient and
smooth well
operation, regardless of the activity of a pump jack unit operating on the
same production well.
In an aspect, a gas compressor driven by a rack and pinion drive system is
provided. The gas
compressor has a piston and piston rod reciprocal within a compressor
cylinder. The piston rod
is operatively coupled to a rack gear, which is driven by a pinion that is
operatively coupled to a
motor.
In a further aspect, a method of compressing gas comprises the step of driving
a piston and
piston rod within a compressor cylinder by operating a motor coupled to a rack
and pinion
system, which in turn, is coupled to the piston rod.
The gas compressor and method of using the gas compressor can allow for
recovery of vapours
from on-site processing and storage equipment, as well as decrease gas locking
and compress
methane gas from surface casing vents into a flow line, without significantly
disrupting or
hindering well production operation due to maintenance or repair. The free gas
can be diverted
into the annulus and can be produced.
DESCRIPTION OF THE DRAWINGS
While the invention is claimed in the concluding portions hereof, preferred
embodiments are
provided in the accompanying detailed description which may be best understood
in conjunction
with the accompanying diagram, and where:
Fig. I is a side cross-sectional view of gas compressor in an aspect of the
present
invention.
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DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
A gas compressor driven by a rack and pinion drive system is provided. The gas
compressor can
be used in oil production systems and can operate independently of a pump jack
and other
surrounding equipment, and in this way, can be optimized for its best
performance, regardless of
the operation and specifications of other equipment. It can also be repaired
or replaced
independently of other equipment, so its repair or maintenance does not halt
or hinder operations.
Fig. 1 illustrates a gas compressor 10 in an aspect of the present invention.
The gas compressor
10 shown is a cylinder or piston-style compressor and is driven by a rack and
pinion drive
system 20. The compressor 10 could be used in various fields of endeavor and
adapted for
various uses, including for moving gas from a wellhead or casing or a
production well into a gas
sales line.
The compressor 10 has a piston rod 12 having a first end 21 and a second end
22. The first end
21 is operatively connected to a piston 13 and the second end 22 is coupled to
the rack and
pinion drive system 20. A cylinder 14 is provided within which the piston rod
12 and piston 13
can reciprocate. Also provided is at least one inlet or suction gas connection
and at least one
outlet or discharge gas connection 18, 19. In the aspect shown in Fig. I, the
inlet and outlets 18,
19 operate to both suction gas inward as well as discharge gas outward, and
could operate
automatically by, for example, detecting differential pressures, or they could
be manually
operated. However, in other aspects of the invention, there may be inlets that
act as suction gas
connections that are separate and operate independently of outlets acting as
discharge gas
connections.
The compressor piston 13 is driven by the rack and pinion drive system 20 with
the rack and
pinion system 20 being used as the prime mover for operating the compressor
10. The rack and
pinion drive mechanism 20 has a rack gear 32 and a rotating pinion 34 that
meshes with or
otherwise engages the rack gear 32. The second end 22 of the piston rod 12 is
coupled to the rack
gear 32, which reciprocates linearly through rotational motion of the pinion
34, which in tarn, is
driven by a motor 36. The rack and pinion system 20 in this way converts
rotational movement
provided by the motor 36 coupled to the pinion 34 into reciprocating linear
movement of the rack
gear 32, and thus, the piston rod 12 and piston 13.
The rack and pinion system 20 shown has a linear rack gear 32, though any type
of rack and
pinion system could be used in this system, including an endless arcuate rack
gear with
corresponding pinion, or a circular rack gear. A curved rack gear could also
he used, or any other
rack and pinion arrangement that will allow the maintenance of the pinion in
stable engagement
with the rack gear.
The motor 36 can be manufactured to be integral with the compressor 10, or can
be removable
therefrom. Many types of motors could be used to drive the compressor 10 so as
to impart
reciprocal movement of the piston rod 12 and piston 13 within the cylinder 14,
and could depend
on the type of rack and pinion system 20 used. In an aspect, the motor 36 is a
reversing electric
motor that drives the pinion 34 in alternate clockwise and counterclockwise
directions, thus
moving the rack gear 32 linearly forward and backward and in turn imparting
the necessary
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reciprocal motion to the piston rod 12 and piston 13. An electronic device
could be used for
control of the motor 36. In some aspects of the invention, a variable
frequency drive (VFD) to
allow for speed adjustments can be provided. Such speed adjustments could
operate through
open- or closed-loop control of the compressor 10. For example, pressure
readings could be
provided by a sensor, which would signal an increase in the speed of the motor
36 and thus the
operation of the compressor 10 during lower pressure readings in the cylinder
14. As the
pressure in the cylinder 14 increases to a point at or near the pressure
capacity of the cylinder 14,
the speed of the motor 36 and thus the cylinder 14 could be slowed. As a
further example,
control of the speed of the compressor 10 could be based on position of the
piston 13 or piston
rod 12 during the compressor 10 stroke, rather than using pressure readings. A
programmable
logic controller could be provided that would give instructions to slow or
quicken the compressor
10 at predetermined positions of the compressor 10 stroke. Other examples of
such speed control
would be to use load readings or amp readings to adjust speed of the
compressor 10 to efficiently
operate the compressor 10, while remaining within the compressor 10's capacity
to handle the
load.
In the compressor 10 of Figure 1, the compressor 10 is a reciprocating or
piston compressor with
the compressor 10 having a piston rod 12 operatively driven by the motor 36.
The piston rod 12
is connected to the piston 13 contained in the cylinder 14. The piston 13
acting within the
cylinder 14 can compress gas contained within the cylinder 14. As gas enters
the cylinder 14
through a suction valve 18, 19 at suction pressure, it can be compressed to
reach a desired
discharge pressure. Once the desired discharge pressure has been reached, the
gas can be
discharged through a discharge valve 18, 19. The discharged gas can then be
diverted into a
flow line and produced.
The compressor 10 could be any type of piston-style compressor, including a
single action or
dual action compressor. Depending on the system design and type of compressor,
the cylinder
may have one or multiple suction and discharge valves. In an aspect, the
compressor 10 is a
double acting compressor whereby during the piston rod 12 up stroke, gas is
pulled from the
casing into a bottom chamber 40 of the compressor cylinder 14 through a
suction check valve 18,
19 in communication with the bottom chamber 40. Simultaneously, gas is
compressed from the
top chamber 42 through a discharge check valve 18, 19 in communication with
the top chamber
42 and into the flow line. During the piston rod 12 down stroke, gas is pulled
from the casing and
into the top chamber 42 through a second suction check valve 18, 19 and
simultaneously gas is
also being compressed from the bottom chamber 40 through a second discharge
check valve 18,
19 and into the flow line.
It is contemplated that the cylinder 14 can be sized to accommodate any
pressure or capacity,
depending on the compressor 10's use. The size of the gas compressor 10 can
vary, but since it is
not dependent on other machinery or equipment, such as a pump jack's
operation, the size can
independently be configured to compress the daily gas production at the
operator's desired casing
pressure, as needed. The cylinder 14, piston rod 12, and piston 13 could be
constructed out of
conosion-resistant materials to protect against corrosive materials which
might be found, for
example, in natural gas.
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The rack and pinion arrangement 20 and/or the compressor 10 can be made to be
mobile or
portable, to be moved to locations, for example, other oil production wells,
with minimal cost.
For example, the arrangement 20 and/or the compressor 10 can be built on a
skid so at to allow
the arrangement 20 and/or compressor 10 to be picked up, or otherwise it may
be mounted on a
5 trailer, to be moved. Various devices can be used for attachment and
detachment of the
compressor cylinder 14 and/or rack and pinion system 20 to the well casing or
any other
equipment upon which the compressor 10 or system 20 may be mounted. In an
aspect, the
compressor 10 could be connected to the gas source such as a wellhead annulus
and sales or flow
line with a pressure rated hose, which would allow for quicker installation
and portability, or the
compressor 10 could be pipe-fitted in, allowing for a more permanent
installation.
While the use of the rack and pinion drive system 20 to drive a compressor 10
is not limited to
the field of oil and gas, the rack and pinion arrangement 20 can be used for
casing gas
compression and/or removing compressed gas from oilfield tank systems.
By driving the compressor 10 with the rack and pinion system 20, the
compressor 10 no longer
needs to he mounted on a pump jack walking beam. The system 20 can be used
with and
installed on any type of pumping equipment unit, including screw pumps,
electric submersible
pumps, as well as any type of pump jack including a RotafiexTM pumping unit.
By not having to
mount to the pump jack, the compressor unit 10 can be easily moved from
location to location,
as required.
By utilizing the rack and pinion drive system 20, the volume of the compressor
10 is no longer
limited by the speed of a pump jack or by the amount of time per day the pump
jack is actually in.
operation. By not having the system 20 mounted on the pump jack, warranty
issues from the
pump jack manufacturers are eliminated as well as possible damages to the pump
jack by the
mounting and operation of a beam driven gas compressor. By utilizing the
piston style gas
compressor 10, the system can provide the flexibility of a skid mount
compressor package, along
with the low maintenance, simple design of a beam compressor.
While Fig. 1 only shows a rack and pinion drive mechanism 20 mounted on a
piston type gas
compressor 10 and driven by a reversing electric motor 36, it is contemplated
that other
equipment can be provided on or with the compressor system 10. For example,
some aspects of
the invention may incorporate a pressure sensing system to provide control for
starting, stopping,
and speed control. Other equipment that may be provided in some aspects of the
invention
include a liquid separator or scrubber for gas entering the gas compressor 10,
which can be
installed on the gas line from the well casing to the compressor 10. These
separators can remove
entrained particulates, moisture, and liquid process fluid that could cause
damage to the
compressor valves 18, 19. A pressure regulator could be provided to provide a
minimum
required by the pressure in the well casing, and a gas flow meter or counter
for the flow pumped
from the well casing. In an aspect, an electronic temperature monitoring and
automatic
overheating protection system is included and/or a pressure safety valve could
also be included.
The foregoing is considered as illustrative only of the principles of the
invention. Further, since
numerous changes and modifications will readily occur to those skilled in the
art, it is not desired
to limit the invention to the exact construction and operation shown and
described, and
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accordingly, all such suitable changes or modifications in structure or
operation which may be
resorted to are intended to fall within the scope of the claimed invention.
