CA2314350A1 - Pump/motor assembly - Google Patents

Abstract

A pump and, in reverse operation, a motor, for pumping viscous fluids is disclosed, comprising a rotor and stator each having opposite handed threads, and a fluid path between them, one of the stator motor having a solid body, typically in the sense that it has no throughbore.

Description

1 " t nn/Motor Assembly"

2

3 This invention relates to a pump or motor assembly,

4 typically for use downhole in an oil or gas well.
6 In oil-drilling operations, artificial lift of the oil 7 from the oil bed may be necessary if the pressure of 8 the deposit is insufficient to bring the oil to the 9 surface. Downhole pumps can be used to pump the oil to the surface.

12 Pumping of very viscous fluids, such as certain 13 densities of hydrocarbons, gives particular problems in 14 the efficient operation of conventional pumps.
16 According to the present invention there is provided a 17 pump comprising a stator and a rotor, each one being 18 provided with a thread having an opposite hand with 19 respect to the thread on the other, the stator and rotor co-operating to provide, on rotation of the 21 rotor, a system for moving fluid longitudinally between 22 them, and wherein one of the stator and the rotor has a 23 solid body.

According to the present invention there is also WO 99/27256 PCT/GB98l035Z4 1 provided a motor comprising a stator and a rotor, each 2 one being provided with an opposite handed thread with 3 respect to the thread on the other, the stator and 4 rotor co-operating to provide, on fluid moving longitudinally between them, relative rotation of the 6 rotor and stator, and wherein one of the stator and the 7 rotor has a solid body.

9 The invention also provides a method of pumping viscous fluids, the method comprising passing the fluid through 11 a pump having a rotor and a stator, each one being 12 provided with an opposite handed thread with respect to 13 the thread on the other.

The method is especially suited for pumping fluids 16 having a viscosity greater than 1000Cp, and preferably 17 greater than 2000Cp.

19 The term "solid body" is used to refer particularly to the rotor or stator having no throughbore.

22 Preferably, there is working clearance between the 23 rotor and stator and one of the stator and rotor may 24 provide bearing support for the other.
26 Preferably, the rotor is threaded on its outer face and 27 rotates within the stator, which preferably is also 28 threaded on its inner face. Most preferably the thread 29 or threads are multistart, and the rotor can have a different number of starts to the stator.

32 The pump and/or motor is preferably for downhole use.

34 In one embodiment, the stator comprises an elastomer and the rotor comprises a metal such as wear-resistant 1 steel. An advantage of the use of such a combination 2 of materials is that particles such as grit or sand are 3 entrained within the moving fluid without causing 4 damage to the pump assembly. In a preferred embodiment the rotor and stator are each formed from a plastics 6 material. Other suitable materials include metals, 7 ceramics, polymers and composite materials such as 8 carbon fibre/kevlar.

The assembly may be provided as a unit or as a set of 11 parts which may be assembled insitu.

13 The invention also provides a pump having two rotors 14 and two stators arranged at opposite end portions of a housing, the end portions and the mid portions between 16 the two end portions each having an aperture for 17 throughflow of fluid, and wherein the rotors are 18 arranged with opposite handed threads with respect to 19 one another, so that upon rotation of the rotors in the housing, fluid moves between the apertures in the mid 21 portion and the apertures at the end portions.

23 According to the present invention there is also 24 provided a pump comprising a stator and a rotor, each one being provided with a thread having an opposite 26 hand with respect to the thread on the other, the 27 stator and rotor co-operating to provide, on rotation 28 of the rotor, a system for moving fluid longitudinally 29 between them, and wherein the threads of the rotor vary in angle between one end of the rotor and the other.

32 Embodiments of the invention will now be described by 33 way of example with reference to the accompanying 34 drawings in which:

wo 99nns6 rcrics9s~o3s~,4 1 Fig. 1 is a side sectional view of a first 2 embodiment of a rotor and stator of a downhole 3 pump/motor assembly according to the present 4 invention;

Fig. 2 is a side sectional view of a pump section 6 of a downhole pump assembly according to the 7 present invention;

8 Fig 3 is a side sectional view through a third 9 embodiment of a pump according to the invention;

Fig 4 is a side sectional view of a fourth 11 embodiment of a pump;

12 Fig 5 is a side sectional view of the fig 4 pump 13 operating in a reverse direction;

14 Fig 6 is a side sectional view of a fifth embodiment of a pump;

16 Fig 7 is a side sectional view of the Fig 6 pump 17 operating in a reverse direction;

18 Fig 8 is a side sectional view of a sixth 19 embodiment of a pump;

Fig 9 is a side sectional view of a seventh 21 embodiment of a pump;

22 Fig 10 is a side sectional view of eighth 23 embodiment of a pump; and, 24 Fig 11 is a side sectional view of ninth embodiment of a pump.

27 A first embodiment of a downhole pump assembly 28 comprises a solid-bodied rotor 10 surrounded by an 29 annular stator ll co-axial with and extending around the rotor Z0. The rotor 10 is externally 31 screw-threaded in a right-handed sense and the stator 32 11 is internally screw-threaded in a left-handed sense.

33 The threads of the rotor 10 and stator 11 are of equal 34 pitch and both have a double start and the crests approach each other sufficiently closely to provide 1 between them chambers within which oil can be retained 2 for upward movement on rotation of the rotor 10. Each 3 of the threads can have different starts eg 4/5.

5 The rotor 10 is connected to a motor (not shown) to

6 induce rotation of the rotor in the stator.

7

8 The performance of a pump is affected by the

9 cross-sectional area of the threads or grooves, their pitch or helix angle, and the overall length of the 11 rotor within the stator. Generally, the greater the 12 cross-section and the steeper the pitch, the greater 13 the volume, and the less the pressure developed per 14 unit length. The overall pressure head is directly proportional to the active length.

17 It has been found that use of a coarser thread on the 18 rotor/stator assembly is unexpectedly effective in 19 improving the output of the pump.
21 The embodiment shown in Figs 1 and 2 is a pump, and is 22 designed to move fluids in the direction of the arrows 23 A, B and C through the pump, and is driven by rotation 24 of the rotor in the stator. The invention also resides in the provision of a motor for driving rotation of a 26 second rotor (not shown) which motor comprises the 27 rotor 10 and stator 11 arrangement shown in the 28 drawings. The motor of the invention is driven by 29 fluid passing between the rotor and stator in the opposite direction of the arrows A, B and C, thereby 31 forcing rotation of the rotor in the stator. This 32 rotational force can be used to drive rotation of a 33 second pump (not shown) by harnessing the rotor 10 to 34 the rotor of the second pump (not shown).

wo ~r~~zs6 PCT/GB98/03524 1 The embodiment in Fig 3 shows a pump (and operated in 2 reverse, a motor) according to a third embodiment. The 3 third embodiment has an array of rotors 100 and stators 4 120 which are vertically spaced from one another by spider bearings 110 through which fluid can pass, and 6 thrust bearings 111. Fluid is pumped through the outer 7 tube 140 by rotation of the rotors 100. Alternatively, 8 if the array is to used as a motor, fluid can be driven 9 through the tube 140 in order to drive rotation of the rotors 100 relative to the stators 120.

12 A report detailing the relative performance of the Fig 13 3 pump as compared to a conventional electric 14 submersible pump (ESP) is attached as an appendix. The report makes clear that the pump of the invention 16 maintains good performance when the viscosity of the 17 fluid is increased.

19 Third party testing of the pump of the invention illustrates that it is suitable and effective for 21 pumping fluids over a very wide range of viscosity.
22 The pump was satisfactorily tested with fluid 23 viscosities ranging from 1 centipoise to several 24 thousand centipoise. When placed under load, the pump appeared to provide superior efficiency (compared to a 26 conventional centrifugal pump ESP) at viscosities 27 greater than circa 100Cp. At viscosities greater than 28 1000Cp, the pump efficiency appeared to be 29 substantially superior to an ESP. At some thousands of centipoise, the pump was still pumping efficiently with 31 no indication of distress. A conventional ESP would 32 probably be limited to very low efficiency at circa 33 1600Cp and would cease to be effective or operate at a 34 fluid viscosity lower than 2000Cp.

1 The pump is configured such that it could be directly 2 coupled to an ESP motor and thrust section as a direct 3 substitution for the existing pump end of an ESP. In 4 particular, the pump of the invention can be threaded into the housing of an ESP and keyed to the housing by 6 a spline to prevent rotation.

8 Fig. 4 shows a further embodiment of a pump according 9 to the invention comprising an outer housing 240, an array of rotors 200 and stators 220 vertically spaced 11 from one another by spider bearings 210 through which 12 fluid can pass, and thrust bearings 211 broadly as 13 described for the Fig. 3 pump. A central spindle 201 14 extends through all rotors and spindles. The tube 240 has central inlet apertures 202 surrounded by a 16 manifold 203 for intake of fluid into the tube 240.
17 When fluid has passed through the manifold 203 and 18 apertures 202 into a central area 204 of the tube 240, 19 it is drawn by anti-clockwise rotation of the rotors 200 to separate upper and lower ends Eu, El. The fluid 21 moving into the inlet through 202 is drawn in different 22 directions due to the rotors 2001 adjacent the lower 23 end E1 being arranged in the opposite hand to the upper 24 rotors adjacent the upper end Eu. Both rotor sets rotate in the same direction, ie anticlockwise.

27 Fig. 5 shows the same arrangement but flowing in a 28 different direction and with the spindle 201 rotating 29 in a clockwise direction with the rotors 200. Fluid is drawn through ends E1 and Eu by opposite handed 31 rotation of rotors 2001 and 200u into the central area 32 204 and is expelled through the apertures 202 and the 33 manifold 203.

Fig. 6 shows an alternative embodiment to the Figs. 4 1 and 5 pump, in which an array of three upper 200u and 2 three lower 2001 rotors are provided. Clearly, 3 additional rotors can be provided in an array in order 4 to increase the capacity of the pump. Fig 7 shows the Fig 6 apparatus pumping in the other direction.
6 Operation is as described for the Fig4/FigS pumps.

8 Fig. 8 shows a further embodiment having a stepped 9 outer housing 340 with a central area 304 which is perforated to allow access to the housing 340 by an 11 inlet manifold 303 so that fluid flowing through the 12 inlet manifold 303 can enter the housing 340 at the 13 central area 304 through the perforations therein.
14 Other features of the Fig. 8 pump are shared in common with those of previous embodiments, but the Fig. 8 pump 16 has an arrangement of three upper and three lower 17 rotors, each array disposed between the central area 18 304 and the respective ends Eu and E1. The rotor in 19 each array adjacent the central portion 304 is larger than the middle rotor, which is again larger than the 21 rotor adjacent the end portion E to allow for vapour 22 fraction compression effects resulting in net 23 volumetric reduction in the fluid passing through the 24 pump from the inlet portion 304 towards the ends Eu/E1.
This factor can often arise in pumping multi-phased 26 fluids having a gaseous phase and a liquid phase, since 27 as the fluid is subjected to higher pressure as it 28 passes through the pump, the gaseous phase collapses, 29 causing pressure instabilities across the pump. The narrower diameter rotors towards the ends Eu and E1 of 31 the Fig. 8 pump can compensate for this volume 32 reduction, and keeps the pressure of the fluid 33 relatively constant as it passes through the pump.

Fig. 9 is an adaptation of the Fig. 8 pump, but the 1 rotors 300 are arranged on the spindle in different 2 hands as the spindle rotates in the same direction, and 3 the inlets are arranged at ends Eu and E1 of the 4 housing 440. Fluid is drawn through the inlets at E1 and Eu and the stepped rotor arrangement with gradually 6 decreasing diameters of rotors 400 as the fluid 7 approaches the central area 404 compensates for volume 8 reductions due to collapse of gaseous phase as the 9 pressure is increased. Fluid is discharged through manifold 403 as previously described.

12 The problem of multi-phase fluid pumping can also be 13 addressed by altering the characteristics of the vanes 14 on the rotor. Fig. 10 shows a further embodiment having a housing 540, an inlet 541 and an outlet 542, 16 and an array of rotors 500 mounted on a spindle 501 as 17 previously described. The Fig. 10 pump draws fluid 18 from its lower end 541 and ejects it through its upper 19 end 542 after passing through the various rotors 500.
Rotors 500 have vanes 505 on their outer surface which 21 are all arranged in the same handedness in the rotor 22 stack. At the lower end of the stack, rotor 5001 has 23 modified veins 505 which at their lower end 5051 are 24 arranged at a'steep angle so that they are substantially parallel to the long axis of the rotor 26 500. The angle which the vane makes with the long axis 27 of the rotor gradually increases as the vane 505 28 extends along the rotor so that at the mid-point 505m 29 of the vein, it is substantially traversing across the long axis, and at the upper end 505u, the angle of 31 inclination is again substantially transverse to the 32 longitudinal axis of the rotor. This contrasts with 33 the constant angle on the vanes of other rotors in the 34 stack. The lower rotor 5001 is disposed in a modified stator 5201 which has matching vanes 525 corresponding 1 to the shapes of the vanes 505 on the rotor 5051. The 2 graduation in the angle of the vanes 505 and the rotor 3 5051 assists with the aforementioned problem of 4 compression effects on the gaseous phase of multi-phase 5 fluids passing through the pump.

7 Fig. 11 shows a further embodiment having a housing 640 8 containing a spindle 601 and having an inlet 641 and an 9 outlet 642. The housing 640 is stepped at 643 and 644

10 which increase in diameter as they approach the inlet

11 641. An array of rotors 600 is mounted on the spindle

12 601, and portions 643 and 644 of the housing contain

13 correspondingly larger diameters of rotors 6003 and

14 6004. The larger diameter rotors 6003 and 6004 have the same function of pressure balancing of multi-phase 16 fluids passing through the pump which have lost volume 17 due to compression of the gaseous phases.

19 An advantage of certain embodiments of pumps as shown in Figs. 4, 5, 6, 7, 8 and 9, include the effect of 21 balance of thrust caused by the equal and opposite 22 force applied by the opposite handed rotors, which 23 preferably move in the same direction on the same 24 spindle. This reduces wear on the spindle and bearing, and could, in circumstances, negate the requirement for 26 a bearing at all.

28 The embodiments of the invention described are not 29 limited to subsea or downhole use, but can be used on surface or on seabed as a pump or motor assembly which 31 may be thrust balanced as shown in Figs. 4 to 9 or 32 located in a conventional oilfield tubular. The 33 assembly of rotors can be mounted horizontally, 34 vertically or in any suitable configuration.

1 It has been found that the present invention is 2 particularly effective in pumping of very viscous 3 fluids such as certain densities of hydrocarbons, or 4 cool and cold hydrocarbons, which give particular problems in the efficient operation of conventional 6 pumps.

8 Further embodiments of the invention can be surface or 9 terrestrial mounted and can operate as pump and motor assemblies.

12 Embodiments of the invention offer superior 13 performance, efficiency and flexibility compared to a 14 conventional ESP. They be fully compatible with variable speed drive operation, preferably over a wider 16 range than is possible with a conventional ESP.

18 The relatively visco-stable performance of certain 19 embodiments makes them particularly well suited for the full range of subsea pipeline system commissioning, 21 start-up, routine operations and abnormal operations.

23 In subsea and particularly in deep water operations, 24 boosting of the oil from the sea bed to shore to a host facility or to another subsea facility may be necessary 26 if the pressure of the deposit is insufficient to bring 27 the oil to the desired location. Subsea single phase 28 and multiphase pumps according to certain embodiments 29 of the invention can be used to pump the oil to the desired location.

32 Each of the embodiments of the invention described 33 above can be adapted to be 'solids tolerant' by 34 revising the clearance between rotor and stator (at operating temperature), with respect to the dimension 1 of the solid particle contaminant in the pumped fluid.
2 Typical pump / rotor clearance of 0.010"' can be 3 increased to as much as 0.050"' with only a very minor 4 deterioration in pump efficiency and performance.
6 A stator / rotor clearance of 0.050" will permit a 7 significant sand loading with particle size up to 10' 8 microns.

Preliminary trials indicate that the pump assembly will 11 pump a variety of extreme viscosity plastic and pseudo-12 plastic 'fluids' in the viscosity range 5000Cp to many 13 tens of thousand centipoise. Considerably reduced pump 14 rotational speeds may be necessary at the higher viscosity ranges to avoid cavitation due to pump inlet 16 pipework pressure losses on the nominal 'atmospheric 17 pressure' test loop.

19 Modifications and improvements may be made without departing from the scope of the invention. For example, 21 the rotor can be in the form of an annular ring 22 surrounding a stator which is in the form of a solid 23 rod. Any feature of the invention may be combined with 24 any other feature except where mutually exclusive. In particular, any pump descibed herein can be used as a 26 motor When operated in reverse, and fluid driven 27 through it to drive rotation of the rotors rather than 28 rotation of the rotors driving throughflow of fluid.
29 Any of the pumps and.motors described herein may be used horizontally, vertically or in another 31 configuration.

33 The reader is referred to UK Application No 9724899.1 34 from which this application claims priority, and to the abstract filed herewith, each of which are incorporated by reference.

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1 l SUBSTITUTE SHEET (RULE 26) Triangle Submersible Pump Motor BCP name plate de~7s lviPA5TITFBS3G Serial number 750 W Razed output 220 / 240 V Voltage 6.3A Current (a~ V dt W
D80 Flame size 3000 RPM Synchronous speed Motor, vertical thrust bearings ???

Spurious test'A' readings No logical progression Drive 0.96 Efficiency Fenner, belt drive efficiency, cowect tension I'nmp Section Thrust bearing 4800 rpm ~- Adjusted speed (g 1 Bar back pressure Teclmiqne Volume tank Accm~acy - whisl.~r bottle effect Ammeter, tong testers 4LOA ~Nomr only 4.1A ~Ylotor onlp Viscosity The Dynamic Viscosity of the test samples was determined at a maximum speed of 600 tpm.
The V'~ity - Speed curves show that the viscosity is near constatu ax speeds is access of 600 tp<n. Consequently, the below quoted figures will be that prevailing at a pump rotational speed of 4,800 rpm. Also listed are the viscosities at zero speed and ambient temperanu~e.
Speed Viscosity - cP ,-rpm - D C B A

600 121 36 ''? =

000 , 320 7~t '~

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Claims (21)

Claims

1 A pump comprising a stator and a rotor, each one being provided with a thread having an opposite hand with respect to the thread on the other, the stator and rotor co-operating to provide, on rotation of the rotor, a system for moving fluid longitudinally between them, and wherein one of the stator and the rotor has a solid body.

2 A pump according to claim 1, wherein the rotor or stator has no throughbore.

3 A pump according to claim 1 or claim 2, wherein working clearance is provided between the rotor and stator.

4 A pump according to any preceding claim, wherein one of the stator and rotor provides bearing support for the other.

A pump according to any preceding claim, wherein the rotor is threaded on its outer face and rotates within the stator.

6 A pump according to any preceding claim, wherein the stator is threaded on its inner face.

7 A pump according to any preceding claim, wherein the thread or threads are multistart.

8 A pump according to any preceding claim, wherein the rotor threads have a different number of starts than the stator threads.

9 A pump according to any preceding claim, wherein the rotor has a solid body, and rotates within the stator.

A pump according to any preceding claim, wherein one of the rotor and stator comprises an elastomer and the other comprises a metal.

11 A pump according to any of claims 1-9, wherein the rotor and stator are each formed from a plastics material.

12 A pump according to any of claims 1-9, wherein the rotor and/or stator are formed from materials selected from the group comprising metals, ceramics, polymers and composite materials.

13 A pump according to any preceding claim, comprising an array of rotors and stators arranged in sequence such that fluid flowing through the space between one rotor and stator enters the space between another rotor and stator.

14 A pump according to any preceding claim, wherein the rotor diameter at an inlet end of the pump is different to the rotor diameter at the outlet end.

A pump according to claim 14, wherein the rotor diameter at the inlet end of the pump is larger than the rotor diameter at the outlet end.

16 A pump according to any preceding claim, having two rotors and two stators arranged at opposite end portions of a housing, the end portions and the mid portions between the two end portions each having an aperture for throughflow of fluid, and wherein the rotors are arranged with opposite handed threads with respect to one another, so that upon rotation of the rotors in the housing, fluid moves between the apertures in the mid portion and the apertures at the end portions.

17 A pump according to any preceding claim, wherein the threads of the rotor vary in angle between one end of the rotor and the other.

18 A motor comprising a stator and a rotor, each one being provided with an opposite handed thread with respect to the thread on the other, the stator and rotor co-operating to provide, on fluid moving longitudinally between them, relative rotation of the rotor and stator, and wherein one of the stator and the rotor has a solid body.

19 A method of pumping viscous fluids, the method comprising passing the fluid through a pump having a rotor and stator, each one being provided with an opposite handed thread with respect to the thread on the other.

20 A method according to claim 19, wherein the fluid has a viscosity greater than 1000Cp.

21 A method according to claim 20, wherein the viscosity of the fluid is greater than 2000Cp.