PROGRESSING CAVITY PUMP WITH HEAT MANAGEMENT SYSTEM

Abstract

A progressing cavity pump heat management system including a progressing cavity pump and a controller. The controller is configured to receive data relating to the temperature of materials exiting the pump and the differential pressure across the pump to determine whether corrective action is required. The controller is configured such that if the controller determines that corrective action is required, the controller institutes corrective action to seek to reduce at least one of the temperature of materials exiting the pump or differential pressure across the pump.

Description

BACKGROUND

A fluid/material consisting of more than one phase is typically termed a multi-phase fluid/material. For example, a fluid/material which is a combination of gas and liquid is typically called a two phase fluid/material, and a fluid/material which is a combination of gas, solid, and liquid may be called a tri phase fluid/material. When materials are pumped by a progressing cavity pump, liquids, liquid vapor and certain solids in the pumped material may help to lubricate the rotor/stator interface in the pump and provide heat dissipation. However, when pumping two phase, tri phase, or multi-phase materials, a relatively high presence of gas can lead to a lack of sufficient lubrication and/or lack of heat dissipation in the pump, which can cause overheating and damage, particularly to the elastomer material of the pump.

SUMMARY

Accordingly, in one embodiment the present invention is a system in which certain parameters are monitored to determine the status of the pump such that corrective action can be instituted, if necessary. In one embodiment, the invention is a progressing cavity pump heat management system including a progressing cavity pump and a controller. The controller is configured to receive data relating to the temperature of materials exiting the pump and the differential pressure across the pump to determine whether corrective action is required. The controller is configured such that if the controller determines that corrective action is required, the controller institutes corrective action to seek to reduce at least one of the temperature of materials exiting the pump or differential pressure across the pump.

In another embodiment the invention is a method for pumping materials including the steps of pumping materials through a progressing cavity pump, monitoring a temperature of materials exiting the pump, and monitoring a differential pressure across the pump. The method further includes the step of instituting corrective action if it is determined that corrective action is required based at least in part upon the monitored pressure and differential pressure.

In yet another embodiment, the invention is a method for pumping materials including the step of providing a progressing cavity pump operatively coupled to a wellhead such that the pump is configured to pump materials provided from the wellhead. The method further includes the step of operating the pump such that the pump pumps material constituting at least 80% gas by volume therethrough for at least two minutes without significant damage to the pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective, partial cutaway view of a progressing cavity pump with a heat management system; and

FIG. 2 is a flow chart illustrating one method for implementing a heat management system.

DETAILED DESCRIPTION

As shown in FIG. 1, a progressing cavity pump 10 may include a generally cylindrical stator tube 12 having a stator 14 located therein. The stator 14 has an opening or internal bore 16 extending generally axially or longitudinally therethrough in the form of a double lead helical nut to provide an internally threaded stator 14. The pump 10 includes an externally threaded rotor 18 in the form of a single lead helical screw rotationally received inside stator 14. The rotor 18 may include a single external helical lobe 20, with the pitch of the lobe 20 being twice the pitch of the internal helical grooves of the stator 14.

The rotor 18 fits within the stator bore 16 to provide a series of helical seal lines 22 where the rotor 18 and stator 14 contact each other or come in close proximity to each other. In particular, the external helical lobe 20 of the rotor 18 and the internal helical grooves of the stator 14 define the plurality of cavities 24 therebetween. The stator 14 has an inner surface 26 which the rotor 18 contacts or nearly contacts to create the cavities 24. Particularly when the rotor 18 and/or the stator 14 is an elastomer material the rotor 18 and the inner surface 26 of the stator 14 may form an interference fit therebetween to define the cavities 24.

The rotor 18 is rotationally coupled to a drive shaft 30 by a pair of gear joints 32, 34 and by a connecting rod 36. The drive shaft 30 is rotationally coupled to a motor 38. When the motor 38 rotates the drive shaft 30, the rotor 18 is rotated about its central axis and thus eccentrically rotates within the stator 14. As the rotor 18 turns within the stator 14, the cavities 24 progress from an inlet or suction end 40 of the rotor/stator pair to an outlet or discharge end 42 of the rotor/stator pair. The pump 10 includes a suction chamber 44 in fluid communication with the inlet end 40 into which fluids to be pumped may be introduced. During a single 360° revolution of the rotor 18, one set of cavities 24 is opened or created at the inlet end 40 at exactly the same rate that a second set of cavities 24 is closing or terminating at the outlet end 42 which results in a predictable, pulsationless flow of pumped material.

The pitch length of the stator 14 may be twice that of the rotor 18, and the present embodiment illustrates a rotor/stator assembly combination known as 1:2 profile elements, which means the rotor 18 has a single lead and the stator 14 has two leads. However, the present invention can also be used with any of a variety of rotor/stator configurations, including more complex progressing cavity pumps such as 9:10 designs where the rotor has nine leads and the stator has ten leads. In general, nearly any combination of leads may be used so long as the stator 14 has one more lead than the rotor 18. Progressing cavity pumps are discussed in greater detail in U.S. Pat. Nos. 2,512,764, 2,612,845, 5,722,820, 6,120,267 and 6,491,591, the entire contents of which are incorporated herein by reference.

The stator 14 can be made of any of a variety of materials, but may be made of a material that is also chemically inert and wear resistant. For example, the stator 14 may be made of elastomers, nitrile rubber, natural rubber, synthetic rubber, fluoroelastomer rubber, urethane, ethylene-propylene-diene monomer (“EPDM”) rubber, polyolefin resins, perfluoroelastomer, hydrogenated nitriles and hydrogenated nitrile rubbers, polyurethane, epichlorohydrin polymers, thermoplastic polymers, polytetrafluoroethylene (“PTFE”), polychloroprene (such as neoprene), synthetic rubber or rubber compositions, such as VITON® materials sold by E.I. du Pont de Nemours and Company located in Wilmington Del., synthetic elastomers such as HYPALON® polyolefin resins and synthetic elastomers sold by E.I. du Pont de Nemours and Company, synthetic rubber such as KALREZ® synthetic rubber sold by E.I. du Pont de Nemours and Company, tetrafluoroethylene/propylene copolymer such as AFLAS® tetrafluoroethylene/propylene copolymer sold by Asahi Glass Co., Ltd. of Tokyo, Japan, acid-olefin interpolymers such as CHEMROZ® acid-olefin interpolymers sold by Chemfax, Incorporated of Gulfport Mississippi, and various other materials.

The suction chamber 44 of the pump 10 may be directly coupled to a two phase, multi-phase or tri phase source such as a well or wellhead through which down-hole materials including liquids, solids and gases are raised/pumped. In this case the pump 10 may be positioned on the ground surface but at or adjacent to a well, wellhead, or down-well pump (or other fluid source). Reducing and maintaining well head pressure by the pump 10 will result in higher liquid production flow rates by both the pump 10 and the wellhead. Thus, during normal operation the pump 10 (along with other pumps or components in the system) may be controlled such that the well head pressure is maintained at a constant value. The rotational speed of the rotor 18 may be varied as desired in order to maintain this constant pressure.

As briefly noted above, the presence of fluids, fluid vapors and/or certain malleable solids in the pumped materials help to lubricate the junction between the rotor 18 and stator 14 (i.e. along the seal lines 22) and also help to dissipate heat that may be generated during operation due to the interference fit between the rotor 18/stator 14, and compression of the gas subject to the ideal gas law. If gas is present in the pumped materials, lubricating and cooling effects are reduced or lost. If the friction/heat build up becomes too high (i.e. in one case, if the gas constitutes over by 95% of the pumped materials by volume) the pump 10, and particularly any elastomer or similar materials of the rotor 18 and/or stator 14, can be damaged. This phenomemon can be particularly prominent when the pump 10 is used in an oil field or other wellhead or down-hole applications. In these cases pockets of gas, such as natural gas, may be introduced into the pump 10 which can cause the pump to run in a “dry” state.

In order to address this type situation the pump 10 may include or be integrated into a heat management system, generally designated 46. The heat management system 46 may include or implement the tracking of certain parameters and the institution of protective measures to reduce heat and temperatures in the pump 10. In one embodiment the measured parameters are: 1) the temperature of the materials exiting the pump 10 at the outlet end 42; 2) the inlet or suction pressure of the pump 10 (i.e. pressure at the suction end 40/suction chamber 44; and 3) the outlet pressure of the pump 10 (i.e. pressure at the outlet end 42).

As can be seen in FIG. 1, the pump 10 may include a discharge temperature sensor 48 to sense the temperature of the materials exiting the pump 10, an inlet pressure sensor 50 to sense the pressure of the materials entering the pump 10, and a discharge pressure sensor 52 to sense the pressure of the materials exiting the pump 10. The sensors 48, 50, 52 are operatively coupled to a controller 54, such as a programmable logic controller, processor, computer, chip, logic, CPU or the like (hereinafter termed a controller to thereby include all of these terms listed above). In this manner data relating to the sensed pressures and discharge temperature are fed to the controller 54.

In order to determine whether corrective action is required, the controller 54 calculates and tracks pressure drop across the pump 10. The pressure drop value (ΔP) is the difference between the inlet pressure, sensed by sensor 50, and outlet pressure, sensed by the sensor 52. The controller 54 may also track the outlet temperature and calculate and track a composite value of the outlet temperature and ΔP, or a composite value incorporating the outlet temperature and ΔP. When the sensed properties and/or composite value exceed certain threshold values, corrective action may be taken.

For example the controller 54 may have algorithm stored or running thereon that determines that corrective action is required when: 1) the ΔP exceeds a certain level; and/or 2) the discharge temperature exceeds a certain level; and/or 3) the composite value incorporating ΔP and discharge temperature exceeds a certain value. The control algorithm can also take into account trends and time-variable statistics to detect troublesome increases in ΔP and/or discharge temperature, and/or the composite values.

The composite value may be calculated in a variety of manners. By way of example, the composite value can be determined by calculating the average increase in ΔP over a discrete period of time, calculating the average increase in discharge temperature over discrete period of time, and multiplying those values together.

The ultimate physical quantity to be tracked can be considered to be the temperature of the stator 14 and/or rotor 18. Since the stator 14 and/or rotor 18 can be made of an elastomer material, the stator 14 and/or rotor 18 may be the first component of the pump 10 to be damaged by high temperatures. However, it can be difficult and expensive to directly measure the temperature of the stator 14 and/or rotor 18. Thus, by measuring ΔP and discharge temperature, the present system and method can provide an efficient method to inductively determine the temperature of the stator 14 and/or rotor 18.

A high ΔP means that relatively high amount of energy is being imparted to the stator 14 and/or rotor 18. However, an elastomer stator 14 and/or rotor 18 is typically of a relatively thermally insulating material, so an elastomer stator 14 and/or rotor 18 may be relatively warm, even if the materials exiting the pump 10 are not. Thus it may be important to measure not just the outlet temperature, but also the ΔP.

FIG. 2 illustrates a flow chart including various steps that may be implemented to track heat build up and take corrective steps. At the first step 60 of FIG. 2 ΔP and the outlet temperature are measured. At step 62, those properties and/or the composite value(s) are compared to initial thresholds. The thresholds tracked by the controller 52 will vary widely and depend upon, among other factors, the materials to be pumped, the nature and materials of the pump 10 (particularly the materials of the stator 14 and/or rotor 18, such as the upper thermal limits of those components), ambient pressures and temperatures, incoming temperature and pressure of the material to be pumped, and other variables. However, in one illustrative embodiment the initial threshold for ΔP is about 10 psi and the initial threshold for discharge temperature is about 120° F. The initial threshold for the composite value will vary, depending upon how it is determined.

At step 64, it is determined whether the initial thresholds are exceeded, thereby determining whether initial corrective action is required. If initial corrective action is needed, then the system proceeds to step 66 wherein the initial corrective action is implemented. The initial corrective action can be implemented in a variety of manners and can take any of a variety of forms, including slowing the pump 10, introducing liquid into the pump 10, actively cooling the pump 10, or combinations of these features. In one embodiment, in order to institute the initial corrective action the controller 52 sends a signal to the motor 38 which causes the motor 38 and pump 10 to slow down (i.e. the rate of rotation of the rotor 18 is reduced), which reduces heat build-up. The pump 10 can be slowed down as desired, but in one embodiment is slowed down by about 10%. This slow-down will typically increase the wellhead pressure above the constant pressure desired to be maintained on the wellhead, but may be a necessary step to avoid damage to the pump 10.

If the incoming temperature of the material to be pumped is relatively high, then the initial corrective action may need to be instituted fairly quickly. On the other hand, if the incoming temperature of the material to be pumped is relatively low, a time lag may be instituted before the initial corrective action (i.e. slowing of the pump 10) is implemented, which allows the pump 10 to operate at higher efficiencies for longer periods of time. This time lag could also be implemented as part of the other corrective actions described below.

During the initial corrective action, discharge temperature and ΔP are continued to be measured and compared to the initial threshold values (and/or other interim values, if desired) by the controller 54 at step 68. If the initial corrective action succeeds in sufficiently lowering the parameters below the desired limits, the initial corrective action may be terminated at step 70 (i.e. the pump 10 may be allowed to return to its previous set point speed) and the system returns to step 60.

At step 72, it is determined whether the parameters exceed secondary (typically higher) thresholds. For example, in one illustrative example the secondary ΔP threshold value is about 15 psi and the second temperature threshold value is about 130° F. If at step 70 it is determined that the secondary threshold values are exceeded, secondary corrective action is instituted at step 74; otherwise initial corrective action is continued at step 66. The secondary corrective action at step 74 can take any of a variety of forms, including further slowing the pump 10, introducing liquid into the pump, actively cooling the pump, or combinations of these features.

In the illustrative example explained herein the secondary corrective action 74 includes introducing fluid into the pump 10. For example, as shown in FIG. 1, a fluid reservoir 84 may be fluidly coupled at or adjacent to the inlet 44 of the pump 10. When secondary corrective action is required a pump is operated, and/or a valve 86 is opened by the controller 54 such that fluid 88 in the reservoir 84 is introduced into the pump 10. The introduced fluid 88 immediately cools the pump 10 by providing lubrication and heat dissipation. The secondary corrective action may be instituted while the initial corrective action is also occurring; or the initial corrective action may be suspended while the secondary corrective action is implemented.

The fluid 88 can be nearly any fluid, such as water, oil, fluids being pumped by the pump 10, or the like. The amount of fluid introduced into the pump 10 can vary, but may constitute, for example, between about 1% and about 10% by volume of the materials being pumped.

FIG. 1 illustrates the fluid 88 being introduced at the inlet 44 of the pump 10. However, the fluid 88 may also be introduced at downstream areas of the pump 10. For example, the most effective cooling may be obtained by introducing fluid at the point just upstream of the point of highest heat due to compression (i.e., depending upon the situation, about halfway along the stator 14, or about ¾ or more down the length of the stator 14). This method of introducing fluid may provide more effective cooling but may also require that another port be formed in the pump 10/stator 14.

After the secondary corrective action is implemented at step 74, at step 76, it is determined whether the secondary thresholds (and/or other interim values, if desired) are exceeded. If they are not, at step 78 the secondary corrective action is terminated, and the initial corrective action is instituted/continued at step 66. On the other hand, if, at step 76, it is determined that the secondary thresholds are exceeded, the measured parameters are compared to tertiary thresholds at step 80. In the illustrative example the tertiary values are higher than the initial and secondary thresholds (i.e. about 20 psi and about 140° F. in one embodiment).

If the tertiary thresholds are not exceeded, the secondary corrective action, at step 74, is continued. Conversely, if the tertiary thresholds are exceeded, the system proceeds to step 82 wherein tertiary corrective action is implemented. The tertiary corrective action can take a variety of forms, but in the illustrative example the tertiary corrective action takes the form of shutting down the pump 10 to prevent further damage. Of course, rather than shutting down the pump, other corrective action may be utilized, and quaternary thresholds and corrective action, etc., may be instituted as desired.

The heat management system described herein is effective in providing quick and efficient cooling and corrective action to a potentially overheating pump 10. In fact, the heat management system is so effective that the pump 10 may be used to pump gases, such as natural gas, as up to 100% of the pumped materials (or material entering the pump 10). Thus in addition to being used and/or positioned to pump fluids, two phase materials, tri phase materials or multi-phase materials, the pump 10 can be designed, used and/or positioned to pump gas, such as natural gas. This represents a significant change from conventional use of progressing cavity pumps which are not typically used to pump gases.

Moreover, the use of the pump 10 in conjunction with a down-hole pump allows the pump 10 to transport pumped fluids away from the well or well-head for subsequent processing (i.e. separation or the like). The use of the pump 10 in this manner reduces demands placed on the down-hole pump (i.e. reducing well-head pressure) which can prolong the life of the down-hole pump and/or allow a smaller and more inexpensive down-hole pump to be used and/or provide a higher production liquid flow rate.

In one embodiment the pump 10 may be able to continuously pump at least about 60%, or alternately at least about 80%, further alternately up to 95% or even further alternately up to 100%, gas by volume (as either pumped material or incoming material) or more for up to two minutes, or alternately up to four minutes, or further alternately up to 30 minutes or more without significant damage to the pump (i.e., the rotor 18 and stator 14 remain intact, without damage, melting, pitting, etc., which causes permanent damage requiring repair, and/or effects the performance of the pump). These levels of operation allow a pump 10 to be used in areas in which pockets of gas are present within expected ranges. In this manner, the pump 10 can be used to de-water drilling sites, and also pump materials (such as natural gas) after the de-watering is completed without having to switch pumps.

Having described the invention in detail and by reference to the preferred embodiments, it will be apparent that modifications and variations thereof are possible without departing from the scope of the invention.

Claims

1. A progressing cavity pump heat management system comprising: a progressing cavity pump; anda controller configured to receive data relating to the temperature of materials exiting the pump and the differential pressure across the pump to determine whether corrective action is required, and wherein said controller is configured such that if the controller determines that corrective action is required, said controller institutes corrective action to seek to reduce at least one of the temperature of materials exiting the pump or differential pressure across the pump.

2. The system of claim 1 further comprising a temperature sensor configured to measure the temperature of materials exiting the pump, a discharge pressure sensor configured to measure the pressure of material exiting the pump, and an inlet pressure sensor configured to measure the pressure of material entering the pump, wherein said temperature sensor, said discharge pressure sensor, and said inlet pressure sensor are operatively coupled to said controller such that said controller can thereby receive data relating to the temperature of materials exiting the pump and the differential pressure across the pump.

3. The system of claim 1 wherein said corrective action includes at least one of reducing the speed of said pump or introducing fluid into said pump.

4. The system of claim 1 wherein said controller is configured to calculate a single composite value based upon said temperature and said differential pressure, and wherein said composite value is used by said controller to determine whether corrective action is required.

5. The system of claim 1 wherein said controller determines that corrective action is required if said temperature and said differential pressure, or a composite value thereof, exceeds a predetermined threshold or thresholds.

6. The system of claim 1 wherein said corrective action is instituted to cool a stator of the progressing cavity pump.

7. The system of claim 1 wherein said controller is configured to compare said temperature and said differential pressure, or a composite value thereof, to an initial threshold or thresholds, and if such initial threshold or thresholds are exceeded, to institute a first corrective action which seeks to reduce at least one of the temperature of materials exiting the pump or the differential pressure across the pump, and wherein said controller is configured to compare said temperature and said differential pressure, or a composite value thereof, to a secondary threshold or thresholds, and if such secondary threshold or thresholds are exceeded, to institute a second corrective action which seeks to reduce at least one of the temperature of materials exiting the pump or the differential pressure across the pump and which differs from said first corrective action.

8. The system of claim 7 wherein said secondary threshold or thresholds are surpassed when at least one of said temperature, said differential pressure, or said composite value is higher than is required to surpass said initial threshold or thresholds.

9. The system of claim 8 wherein said controller is configured to compare said temperature and said differential pressure, or a composite value thereof, to a tertiary threshold or thresholds, and if such tertiary threshold or thresholds are exceeded, to institute a tertiary corrective action which differs from said primary and secondary corrective action, and wherein said tertiary threshold or thresholds are surpassed when at least one of said temperature, said differential pressure, or said composite value is higher than is required to surpass said initial threshold or thresholds or said secondary threshold or thresholds.

10. The system of claim 9 wherein said tertiary corrective action constitutes ceasing pumping operations of said pump.

11. The system of claim 1 wherein said progressing cavity pump includes a rotor, a stator, an inlet and an outlet, said rotor being rotationally disposed in said stator such that rotation of said rotor causes material in said pump to be pumped from said inlet toward said outlet.

12. The system of claim 11 wherein said rotor is an externally threaded rotor in the form of a single lead helical screw, and wherein said stator has an opening extending generally axially therethrough in the form of a double lead helical nut, and wherein said rotor is received in said opening.

13. The system of claim 11 wherein said stator is made of an elastomer material.

14. The system of claim 1 wherein said pump is coupled to a wellhead to receive materials pumped therefrom.

15. A method for pumping materials comprising the steps of: pumping materials through a progressing cavity pump;monitoring a temperature of materials exiting the pump;monitoring a differential pressure across the pump; andinstituting corrective action if it is determined that corrective action is required based at least in part upon the monitored pressure and differential pressure.

16. The method of claim 15 wherein the corrective action is instituted if said temperature and said differential pressure, or a composite value thereof, exceeds a predetermined threshold or thresholds, and wherein said corrective action leads to cooling of the progressing cavity pump.

17. The method of claim 15 wherein said corrective action includes at least one of reducing the speed of said pump, or introducing fluid into said pump, or ceasing pumping operations of said pump.

18. A method for pumping materials comprising the steps of: providing a progressing cavity pump operatively coupled to a wellhead such that said pump is configured to pump materials provided from said wellhead; andoperating said pump while actively reducing at least one of the temperature of materials exiting the pump or the differential pressure across the pump during at least part of said operation such that the pump pumps material constituting at least 80% gas by volume therethrough for at least two minutes without significant damage to the pump.

19. The method of claim 18 wherein said operating step includes monitoring the temperature of materials exiting the pump, monitoring the differential pressure across the pump, and instituting corrective action to cool the pump if it is determined that corrective action is required based upon the monitored pressure and differential pressure.

20. The method of claim 19 wherein the corrective action is required if said temperature and said differential pressure, or a composite value thereof, exceeds a predetermined threshold or thresholds, and wherein said corrective action includes at least one of reducing the speed of said pump or introducing fluid into said pump.

21. The system of claim 1 wherein said differential pressure is a pressure differential between an inlet of said pump and an outlet of said pump.

22. The system of claim 1 wherein said progressing cavity pump includes a rotor, a stator, an inlet and an outlet, said rotor being rotationally disposed in said stator such that rotation of said rotor causes material in said pump to be pumped from said inlet toward said outlet, and wherein said differential pressure is a pressure differential between an inlet of said pump located at a position upstream of said rotor and an outlet of said pump located at a position downstream of said rotor and in fluid communication with said inlet.

23. The system of claim 1 wherein said progressing cavity pump includes a rotor, a stator, an inlet and an outlet, said rotor being rotationally disposed in said stator such that rotation of said rotor causes material in said pump to be pumped from said inlet toward said outlet, and wherein said data relating to the temperature of materials exiting the pump is data relating to the temperature of material at position downstream of said rotor.

24. The system of claim 2 wherein said controller is configured to institute corrective action if the differential pressure exceeds a predetermined value.

25. The system of claim 1 wherein said controller is configured to take into consideration both: a) data relating to the temperature of said materials exiting the pump; and b) the differential pressure across the pump in determining whether corrective action is required.

26. A progressing cavity pump heat management system comprising: a controller configured to receive data relating to the temperature of materials exiting a progressing cavity pump and the differential pressure across the pump to determine whether corrective action is required, and wherein said controller is configured such that if the controller determines that corrective action is required, said controller institutes corrective action to seek to reduce at least one of the temperature of materials exiting the pump or differential pressure across the pump.