EP1034375A1

EP1034375A1 - Pump/motor assembly

Info

Publication number: EP1034375A1
Application number: EP98956989A
Authority: EP
Inventors: Alastair John Simpson; Anthony Duncan Cameron
Original assignee: Triangle Engineering Consultants Ltd
Current assignee: Triangle Engineering Consultants Ltd
Priority date: 1997-11-26
Filing date: 1998-11-26
Publication date: 2000-09-13
Also published as: ID27608A; CN1279747A; GB9724899D0; BR9814911A; WO1999027256A1; AU1342199A; CA2314350A1

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

"Pump/Motor Assembly"

This invention relates to a pump or motor assembly, typically for use downhole in an oil or gas well.

In oil-drilling operations, artificial lift of the oil from the oil bed may be necessary if the pressure of the deposit is insufficient to bring the oil to the surface. Downhole pumps can be used to pump the oil to the surface.

Pumping of very viscous fluids, such as certain densities of hydrocarbons, gives particular problems in the efficient operation of conventional pumps.

According to the present invention there is provided 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.

According to the present invention there is also provided 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.

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

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

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

Preferably, there is working clearance between the rotor and stator and one of the stator and rotor may provide bearing support for the other.

Preferably, the rotor is threaded on its outer face and rotates within the stator, which preferably is also threaded on its inner face. Most preferably the thread or threads are multistart, and the rotor can have a different number of starts to the stator.

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

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

The assembly may be provided as a unit or as a set of parts which may be assembled in situ.

The invention also provides a pump 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.

According to the present invention there is also provided 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 the threads of the rotor vary in angle between one end of the rotor and the other.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a side sectional view of a first embodiment of a rotor and stator of a downhole pump/motor assembly according to the present invention; Fig. 2 is a side sectional view of a pump section of a downhole pump assembly according to the present invention; Fig 3 is a side sectional view through a third embodiment of a pump according to the invention; Fig 4 is a side sectional view of a fourth embodiment of a pump; Fig 5 is a side sectional view of the fig 4 pump operating in a reverse direction; Fig 6 is a side sectional view of a fifth embodiment of a pump; Fig 7 is a side sectional view of the Fig 6 pump operating in a reverse direction; Fig 8 is a side sectional view of a sixth embodiment of a pump; Fig 9 is a side sectional view of a seventh embodiment of a pump; Fig 10 is a side sectional view of eighth embodiment of a pump; and, Fig 11 is a side sectional view of ninth embodiment of a pump.

A first embodiment of a downhole pump assembly comprises a solid-bodied rotor 10 surrounded by an annular stator 11 co-axial with and extending around the rotor 10. The rotor 10 is externally screw-threaded in a right-handed sense and the stator 11 is internally screw-threaded in a left-handed sense. The threads of the rotor 10 and stator 11 are of equal pitch and both have a double start and the crests approach each other sufficiently closely to provide between them chambers within which oil can be retained for upward movement on rotation of the rotor 10. Each of the threads can have different starts eg 4/5.

The rotor 10 is connected to a motor (not shown) to induce rotation of the rotor in the stator.

The performance of a pump is affected by the cross-sectional area of the threads or grooves, their pitch or helix angle, and the overall length of the rotor within the stator. Generally, the greater the cross-section and the steeper the pitch, the greater the volume, and the less the pressure developed per unit length. The overall pressure head is directly proportional to the active length.

It has been found that use of a coarser thread on the rotor/stator assembly is unexpectedly effective in improving the output of the pump.

The embodiment shown in Figs 1 and 2 is a pump, and is designed to move fluids in the direction of the arrows A, B and C through the pump, and is driven by rotation of the rotor in the stator. The invention also resides in the provision of a motor for driving rotation of a second rotor (not shown) which motor comprises the rotor 10 and stator 11 arrangement shown in the drawings. The motor of the invention is driven by fluid passing between the rotor and stator in the opposite direction of the arrows A, B and C, thereby forcing rotation of the rotor in the stator. This rotational force can be used to drive rotation of a second pump (not shown) by harnessing the rotor 10 to the rotor of the second pump (not shown) . The embodiment in Fig 3 shows a pump (and operated in reverse, a motor) according to a third embodiment. The third embodiment has an array of rotors 100 and stators 120 which are vertically spaced from one another by spider bearings 110 through which fluid can pass, and thrust bearings 111. Fluid is pumped through the outer tube 140 by rotation of the rotors 100. Alternatively, if the array is to used as a motor, fluid can be driven through the tube 140 in order to drive rotation of the rotors 100 relative to the stators 120.

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

Third party testing of the pump of the invention illustrates that it is suitable and effective for pumping fluids over a very wide range of viscosity. The pump was satisfactorily tested with fluid viscosities ranging from 1 centipoise to several thousand centipoise. When placed under load, the pump appeared to provide superior efficiency (compared to a conventional centrifugal pump ESP) at viscosities greater than circa lOOCp. At viscosities greater than lOOOCp, the pump efficiency appeared to be substantially superior to an ESP. At some thousands of centipoise, the pump was still pumping efficiently with no indication of distress. A conventional ESP would probably be limited to very low efficiency at circa 1600Cp and would cease to be effective or operate at a fluid viscosity lower than 2000Cp. The pump is configured such that it could be directly coupled to an ESP motor and thrust section as a direct substitution for the existing pump end of an ESP. In particular, the pump of the invention can be threaded into the housing of an ESP and keyed to the housing by a spline to prevent rotation.

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

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

Fig. 6 shows an alternative embodiment to the Figs. 4 and 5 pump, in which an array of three upper 200u and three lower 2001 rotors are provided. Clearly, additional rotors can be provided in an array in order to increase the capacity of the pump. Fig 7 shows the Fig 6 apparatus pumping in the other direction. Operation is as described for the Fig4/Fig5 pumps.

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

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

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

Fig. 11 shows a further embodiment having a housing 640 containing a spindle 601 and having an inlet 641 and an outlet 642. The housing 640 is stepped at 643 and 644 which increase in diameter as they approach the inlet 641. An array of rotors 600 is mounted on the spindle 601, and portions 643 and 644 of the housing contain correspondingly larger diameters of rotors 6003 and 6004. The larger diameter rotors 6003 and 6004 have the same function of pressure balancing of multi-phase fluids passing through the pump which have lost volume due to compression of the gaseous phases.

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

The embodiments of the invention described are not limited to subsea or downhole use, but can be used on surface or on seabed as a pump or motor assembly which may be thrust balanced as shown in Figs. 4 to 9 or located in a conventional oilfield tubular. The assembly of rotors can be mounted horizontally, vertically or in any suitable configuration. It has been found that the present invention is particularly effective in pumping of very viscous fluids such as certain densities of hydrocarbons, or cool and cold hydrocarbons , which give particular problems in the efficient operation of conventional pumps .

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

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

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

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

Each of the embodiments of the invention described above can be adapted to be 'solids tolerant' by revising the clearance between rotor and stator (at operating temperature), with respect to the dimension of the solid particle contaminant in the pumped fluid. Typical pump / rotor clearance of 0.010" can be increased to as much as 0.050" with only a very minor deterioration in pump efficiency and performance.

A stator / rotor clearance of 0.050^" will permit a significant sand loading with particle size up to 10³ microns .

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

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

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

Rheology Test Fann 35 - 12 Speed Viscometer Test Fluid Water Glycol + HEC polymer

co x m Dynamic Viscosity - cP m

Speed Tor ( = 51 * Dial Reading ) Gamma Dynamic Viscosity -cP

3) c rpm D Cr C B A 17*rpm D Cr C B A i- 600 1229 370 224 204 1020 121 36 22 20 Viscosity cP = Tor / Gamma [dynes * sec / cm**2] * 100 m 300 1020 275 157 102 510 200 54 31 20 t σ> 200 918 230 133 77 340 270 68 39 23

180 882 275 227 122 51 306 288 90 74 40 17

100 750 173 92 51 170 441 102 54 30 Crept are Fann dial readings repeated on sample 'C after 10 days

90 719 204 170 87 41 153 470 133 111 57 27 Gives an increase in viscosity TcR/G of +- 20 %

60 638 173 142 69 26 102 625 170 139 68 25

30 500 101 46 10 51 980 198 90 20

6 255 40 179 26 102 2500 388 175 250

3 173 22 64 05 51 3400 425 125 100

18 128 18 77 00 31 4167 583 250 00

09 82 10 26 00 15 5333 667 167 00

0 3250 751 282 3 Results extrapolated to zero rpm

Sample D viscosity determined later than pump tests

Test fluid suppliers advise viscosity could increase by factor of 2

Extrapolated value 6500 / 2 = 3250 cP

Electric Motor Test Performance

J3paad | [ Katta Out ) Natts In {Poxer Factor I EfftciβncT I Currant]

TWQUE - HP- Test Readings Test Circuit

r o

to

^ ω <

Variation of Efficiency with Viscosity, for various test pressures.

co x t m m

30 e ι- m ιs» σ>

Efficiency @ 0.15, 0.25 & 0.5 Bar

Viscosity cP

Efficiency - Varying Test Pressure

0.70

0.60

_&0.50

CO 0.40

CD |θ.30 - Efficiency x 0.96 CO

H ^U0.20 - Efficiency x 0.8

H 0.10 C H 0.00 rn 500 1000 1500 2000 2500 3000 3500 co Viscosity - cP x m m t

H

Triangle Submersible Pump Motor

BCP name plate details

MPA572TFBS3G Serial number

750 W Rated output

2800 RPM

220 /240 V Voltage

6.3A Current @ V & W

D80 Frame size

3000 RPM Synchronous speed

Motor, vertical thrust bearings ???

4.0A 3.2A

Spurious test 'A' readings No logical progression

Drive

0.96 Efficiency Fenner, belt drive efficiency, correct tension

Pump Section

Thrust bearing 4800 rpm *- Adjusted speed @ 1 Bar back pressure

Technique

Volume tank Accuracy - whisky bottle effect Ammeter, tong testers 4.0Λ Motor only 4.2A Motor only

Viscosity

The Dynamic Viscosity of the test samples was determined at a maximum speed of 600 rpm. The Viscosity - Speed curves show that the viscosity is near constant at speeds in excess of 600 rpm. 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 temperature.

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.

5 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.

10 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.

15 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 lOOOCp.

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