CA2551326C

CA2551326C - Automated control system for oil well pump

Info

Publication number: CA2551326C
Application number: CA2551326A
Authority: CA
Inventors: Dean Schlekewy; Karion Martiniuk
Original assignee: DIRECT DATA TECHNOLOGIES Inc
Current assignee: DIRECT DATA TECHNOLOGIES Inc
Priority date: 2006-06-28
Filing date: 2006-06-28
Publication date: 2011-04-12
Anticipated expiration: 2026-06-28
Also published as: CA2551326A1

Abstract

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.

Description

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.

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 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 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.

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 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.

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 :

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 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 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 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.

Claims

1. 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 relative 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 being programmed to alter at least one of pump speed and gas pressure to maximize the relative proportion of oil to water.

2. The automated control system of claim 1, further comprising a water and oil flow sensor.

3. The automated control system of claim 1, wherein the sensors adapted to collectively determine proportions of water and oil in liquid production flow comprise sensors for determining the level of water and the level of water and oil in a production tank.

4. The automated control system of claim 3, wherein an alarm is triggered when the amount of oil and water in a production tank reaches a certain level.

5. The automated control system of claim 4, wherein the control processor is further programmed to shut down the oil well pump when the amount of oil and water in a production tank reaches a certain level.

6. The automated control system of claim 1, wherein the control processor triggers an alarm if the liquid production flow decreases by a predetermined amount.

7. The automated control system of claim 6, wherein the decrease in liquid production flow is compared to a long-term average, or a short term average of liquid production flow.

8. The automated control system of claim 1, wherein the gas pressure is altered by controlling a gas vent.

9. An automated control system for an oil well pump, comprising:
sensors adapted to collectively determine proportions of water and oil in liquid production flow; and a control processor adapted to receive inputs from the sensors, the control processor being programmed to alter pump speed to maximize the relative proportion of oil to water.