Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION:
Automated Control System For Oil Well Pump
FIELD OF THE INVENTION
The present invention relates to an automated control system for a pump used
to pump
oil from an oil well.
BACKGROUND OF THE INVENTION
Automated control systems presently in use control pumps pumping oil from an
oil
well by either increasing or decreasing the speed of the pump based upon
production flow
rates.
SUMMARY OF THE INVENTION
According to the present invention there is provided an automated control
system for
an oil well pump, comprising a pump speed sensor, a pump torque sensor, a gas
pressure
sensor, sensors adapted to collectively determine proportions of water and oil
in liquid
production flow, and a control processor adapted to receive inputs from the
pump speed
sensor, the pump torque sensor, the gas pressure sensor and the relative
proportions of water
and oil in liquid production flow. The control processor is programmed to
alter pump speed
to maximize the relative proportion of oil to water.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention will become more apparent from the
following description in which reference is made to the appended drawing, the
drawing is for
the purpose of illustration only and are not intended to in any way limit the
scope of the
invention to the particular embodiment or embodiments shown, wherein:
FIG. 1 is a schematic of the automated control system for an oil well pump.
FIG. 2 is a side plan view of oil and water level indicators.
3 0 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment, an automated control system for an oil well pump
generally identified by reference numeral 10, will now be described with
reference to FIG. 1
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and 2.
Referring to FIG. 1, a simplified example of a well site 100 is shown. A down
hole
pump including a rod string 11 in tubing 9 that drives a rotor 12 positioned
within a stator 15
that is within casing 13 down a well 14, and driven by a well head drive 16.
While a screw
pump and drive system have been shown, it will be understood that the control
system 10
described below can be adapted to many different types of hydraulic well head
drives. Well
head drive 16 is hydraulically driven by a motor 18 and hydraulic pump 17 on a
skid 19 that
drives hydraulic fluid through lines 20 in a closed loop system. A speed
sensor 21 and a
torque sensor 23 monitor the performance of well head drive 16. Speed sensor
21 may be an
inline flow meter which measures the flow of hydraulic fluid, which, in a
closed loop system,
will be directly related to the speed of well head drive 16. Torque sensor 23
measures the
torque applied by motor 18, based on the pressure of the hydraulic fluid. The
liquid that is
pumped from well 14 is pumped to a production tank 22 through line 24. The
liquid is then
allowed to separate into an oil layer 26 and a water layer 28. Sensors are
then used that
collectively detennine the proportions of water and oil in liquid production
flow, such as an
oil level indicator 30 and a water level indicator 32 as depicted. An example
of oil and water
indicators 30 and 32 is discussed below. In addition to indicators 30 and 32,
a flow meter 35
may be used to determine the amount of flow from well 14. Flow meter 35 may be
used in
with water level indicator 32 to determine the relative amounts of fluid, such
that oil level
indicator 30 would not be required. The flow meter 35 measures head pressure
to detennine
the amount of flow into tank 22, and therefore the amount of fluid in tank 22.
Because it
works off of head pressure, there will be some drift in its accuracy based on
the proportion of
water and oil, which may vary. The readings from flow meter 35, which are
transmitted
through line 58 may then be recalibrated in a control processor 42 based on
the readings from
gauges 30 and 32, instead of having to recalibrate it manually on site. The
flow of liquid into
tank 22 is determined from the changes in volume as determined by indicator
30, or from the
head flow pressure as determined by flow meter 35. To determine the amount of
water and
oil in the tank, either indicators 30 and 32 may be used, or water level
indicator 32 and flow
meter 35 may be used.
The gas that is produced by well 14 passes through line 34 connected to
wellhead 37
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and flows to pop valve 36, which may also be a flare. The gas pressure is
measured by a gas
pressure sensor 38. While releasing gas pressure to allow pump 12 to operate,
pop valve 36
also provides a back pressure, which may be useful if motor 18 uses the gas
from well 14 as
its fuel source through gas line 62, or if a tank heater 60 is used, and is
also run off the gas
from well 14 through gas line 64. There may also be a solenoid bypass valve 40
between pop
valve 36 and casing which is controlled through line 66 to reset the gas
pressure to a pressure
programmed into a control processor 42. Pop valve 36 may also be controlled to
allow more
or less gas to vent to optimize production flow.
Control processor 42 is adapted to receive inputs from pump speed sensor 21
through
line 46, pump torque sensor 23 through line 48, gas pressure sensor 38 through
line 50 and the
relative proportions of water and oil in liquid production flow through lines
52 and 54, based
on the proportions in production tank 22. Control processor 42 is programmed
to alter the
speed of the pump 21 to maximize the relative proportion of oil to water,
which is done by
sending a control signal to a mono block valve 44 through line 56, which is
used to control
the speed of well head drive 16. Mono block valve 44 adjusts the hydraulic
flow to well head
drive 16 to ensure that a constant speed is maintained, as determined by
control processor 42.
Control processor 42 may also be programmed to shut down operations if certain
levels in production tank 22. For example, an alarm may be triggered when the
total volume
reaches 155 m3 (e.g. as indicated by oil gauge board indicator 30). Control
processor 42 may
also be programmed to trigger other alarms, such as a zero flow alarm, and a
reduced flow
alarm. The zero flow alarm would be triggered if consecutive data sampling
shows a short-
term reduction in flow. For example, if the flow is sampled every 5 minutes,
and three
consecutive readings show the pump running at 10% efficiency or less, the zero
flow alarm
would be triggered and an operator may shut down the well remotely. The
reduced flow
alarm would be triggered if the flow decreases a certain amount compared with
a long-term
average. For example, a 24 hour average may be used, where the alarm is
triggered if the
current flow was, for example, 10% or more below that average. It is preferred
to program
processor 42 such that the alarm set-point is allowed to increase with the
average, but not
decrease.
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Referring to FIG. 2, an example of oil and water level indicators 30 and 32
will now
be given. The example depicted uses the H20i1 Dual Level Gauge that can be
seen at
www.h2oil.ca. An oil level float 70 is sufficiently buoyant to float on oil
layer 26, while a
water level float 72 is sufficiently buoyant to float on water layer 28, but
not sufficiently
buoyant to rise through oil layer 26. A system of cables and pulleys generally
indicated by
reference numeral 74 connects oil level float 70 and water level float 72 to
an oil level
indicator 76 and a water level indicator 78, respectively. As depicted, oil
level indicator 76
falls as oil layer 26 rises, whereas water level indicator 78 rises as water
layer 28 rises.
Indicators 76 and 78 are connected to a gaugeboard 80, which consists of a
probe that
converts the position of each indicator into an electrical signal that is then
transmitted to
control processor 42. For example, a probe similar to the RPA series of probes
sold by the
Automation Group of Scientific Technologies, Inc. of Logan, Utah may be used,
with each
indicator 76 and 78 including a magnet. However, more favourable results have
been
obtained using the M series analog linear probe by MTS Systems Corporation.
Example of a Prior Art Control Strate~y
The following is a potential trouble shooting guide based on readings taken by
the
various sensors, with a flow sensor instead of separate water and oil sensors:
gas speed torque flow
up same or up same or down down
Cause: gas build up due to pulling down fluid level, changing engine to
propane or
frozen pop valve.
Solution: try to vent gas back to previous set point if flow restored follow
automatic
program. If no increase in flow return speed to previous set point and wait
for operator to
make decision.
gas speed torque flow
same same or down same or up down
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Cause: sand in tubing or production gone from oil/water emulsion to straight
oil.
Solution: speed up pump to previous set point to try to restore flow. If flow
restored
follow automatic program. If no increase after 15 mins slow pump down to last
set speed and
wait for operator to make decision.
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gas speed torque flow
same same or up down up
Cause: suspect well broke to straight water or lighter oil.
Solution: slow well to last set speed for 15 mins then try again to follow
automatic
program.
gas speed tor ue flow
same same or up down down or zero
Cause: partial plugged perfs, broken rods, hole in tubing, wom out pump.
Solution: if flow in zero condition for 10 minutes operator remotely slow down
or
shutdown well. After alarm if conditions exists for 15 minutes with only
decrease in flow hold
speed let operator make decision with help of production team.
gas speed torque flow
down down down down or zero
Cause: partially plugged perfs, motor failure on skid.
Solution: if flow in zero condition for 10 minutes operator remotely slow down
or
shutdown well, after alarm if conditions exists for 15 minutes with only
decrease in flow
speed up pump to previous set point to try to restore flow if no increase
after 15 mins slow
pump down to last speed and follow automatic program or call field operator to
do a site visit.
Proposed Control Stategv
The following is a potential trouble shooting guide based on readings taken by
the
various sensors, with oil and water sensors :
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gas speed torque oil water
up same or up same or down same down
Cause: increased gas pressure holding back water.
Solution: leave gas pressure as is and follow automatic program.
gas speed torque oil water
up same or up same or down down same
Cause: increased gas pressure holding back oil.
Solution: vent gas to try and restore oil flow and then resume automatic
program. If
flow not restored hold at last set speed till operator makes action decision
with help of
production team.
gas speed torque oil water
up same or up same or down down down
Cause: increased gas pressure holding back oil and water.
Solution: vent gas to try and restore oil flow and then resume automatic
program. If
flow not restored hold at last set speed till operator makes action decision
with help of
production team.
gas speed torque oil water
same same or down same or up down same
Cause: sand in tubing or partially plugged perfs.
Solution: speed up pump to previous set point to try to restore flow. If flow
restored
follow automatic program. If no increase after 15 mins slow pump down to last
set speed and
wait for operator to make decision.
gas speed torque oil water
same same or down same or up same down
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Cause: partially plugged perfs, higher oil cut.
Solution: follow automatic program to further increase oil production.
gas speed torque oil water
same same or down same or u down down
Cause: sand in tubing or partially plugged perfs.
Solution: speed up pump to previous set point to try to restore flow. If flow
restored
follow automatic program. If no increase after 15 mins slow pump down to last
speed and
wait for operators decision.
gas speed torque oil water
same same or up
down up same
Cause: lighter (API) oil flowing into pump
Solution: follow automatic program to increase oil production.
gas speed torque oil water
same same or up down same u
Cause: increased water cut in well.
Solution: slow pump to last set speed and hold. Wait for operator to respond
to
increased water cut alarm.
gas speed torque oil water
same same or up down up up
Cause: more inflow from well.
Solution: if water cut not increased follow automatic program as is. if water
cut alarmed
slow well down to last set speed and hold till water cut alarm responded to.
gas speed torque oil water
same same or u down down or zero down or zero
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Cause: partially plugged perfs, hole in tubing, broken rods, worn pump
Solution: if flow in zero condition for 10 minutes operator remotely slow down
or
shutdown well after alarm. If conditions exists for 15 minutes with only
decrease in flow hold
set speed and wait for operators decision.
gas speed torque oil water
down down down down or zero down or zero
Cause: partially plugged perfs, motor failure on skid.
Solution: if flow in zero condition for 10 minutes operator remotely slow down
or
shutdown well, after alarm if conditions exists for 15 minutes with only
decrease in flow
speed up pump to previous set point to try to restore flow if no increase
after 15 mins slow
pump down to last speed and follow automatic program or call field operator to
do a site visit.
A comparison of the Prior Art Control Strategy with the Proposed Control
Strategy
serves to demonstrate the huge advantages provided by the Proposed Control
Strategy. Both
strategies involve an automatic program that increases pump speed
incrementally until
optimum production limits are reached, with any further increases in pump
speed bringing
reduced production. It can be seen that basing decisions upon the parameters
in the Prior Art
Control Strategy will not always be the best strategy for maximizing oil
production. It can be
seen that many conditions viewed as being negative and resulting in immediate
remedial
action under the Prior Art Control Strategy are maintained under the Proposed
Control
Strategy when a comparison of oil to water ratios indicates that the change
has beneficially
increased the relative proportion of oil.
It will be apparent that one of the key elements presented above is the
ability to
determine the relative proportions of water and oil in production tank 22. It
is therefore also
possible to apply these teachings to a system with control processor 42 only
receiving inputs
from oil and water indicators 30 and 32, or water indicator 32 and flowmeter
35 as discussed
above. By being able to determine the amount of oil being produced from the
well, decisions
are not misled by the actual production flow, such that an increase in
production flow may be
a cause for concern if the oil flow is decreasing and the water flow is
increasing, while a
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decrease in production flow may not be a cause for concern if it is only the
water flow that is
decreasing. While this is true, it is preferred to use the other sensors to be
able to determine
whether the performance of pump 21 or the pressure of any gas being released
is affecting the
production flow from well 14.
In this patent document, the word "comprising" is used in its non-limiting
sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
there be one and only one of the elements.
It will be apparent to one skilled in the art that modifications may be made
to the
illustrated embodiment without departing from the spirit and scope of the
invention as
hereinafter defined in the Claims.
