ESP WITH COMMON HOUSING Technical field

This invention relates to electric submersible pumps (ESPs) of the type commonly used to provide artificial lift on oil wells that do not have sufficient pressure to produce to the surface. In particular, the invention relates to the housings used in such pumps. Background art

Figure 1 shows a known type of ESP. Such devices are well-known in the oil industry and are located downhole in oil wells and operated to pump oil to the surface. The ESP shown in Figure 1 comprises a gauge section 10 with electronics, one or more motor sections 12 (two are shown here), each of which contains a stator and a rotor mounted on a drive shaft; a protector section 14 (comprising four separate housings), a pump intake 16, and a series of pump sections 18 (four are shown here, although the number of sections can be selected according to the amount of lift and volume the pump must deliver). Each section is provided with its own housing which means that there may be as many as 11 housings in a conventional ESP system (four pump housings, two motor housings, one intake housing, and four protector section housings).

In a conventional ESP assembly, the pump housing provides containment of the pump stages and bearings and also the reaction force for compression of the pump diffuser stack. The pump intake is typically a separate construction that is fitted between the pump and protector sections of the ESP (there is an existing integral intake pump design in the conventional ESP product line but the protector assembly is still separate from this). Such protector assembly is made up of several protector bodies with internal components attached to them, separated by sections of protector housing, the whole, being made up into a protector assembly in the factory. The pump sections, intake, and protector are field assembled with flange and bolt construction into the completed ESP assembly (along with the motor).

A number of problems are associated with the prior art systems, including concentricity errors in the assembly from accumulated manufacturing tolerances, joint-related problems caused by manufacturing defects, and vibrations (arising from bearing misalignment in joint bodies, for example). However, because of the

manner of construction of such ESPs, with each section manufactured separately with its own housing, it is difficult to avoid such problems easily.

It is an object of this invention to provide a system that is less susceptible to such problems.

Disclosure of the invention

A first aspect of this invention provides an electric submersible pump, comprising: a pump section; a pump inlet section; a protector section; and

- an electric motor section including a power stage and a commutation stage; wherein a common housing is provided which extends over all of the sections of the pump.

Preferably, the common housing comprises a first part enclosing the pump, pump inlet and protector sections; a second part enclosing the power stage of the motor section; and a third part enclosing the commutation stage of the motor section.

The pump section typically comprises a diffuser stack that is held in compression by the first housing part. The components of the inlet section and the protector section can also be held in compression by the first housing part.

The housing in the region of the pump inlet section typically comprises intake openings covered with a screen.

The third housing part (covering the commutation stage) is connected to the second (covering the power stage) by means of a pinned connection. This can ensure accurate rotational alignment. The other sections can be connected by means of threaded connections.

A pump as claimed in any preceding claim, further comprising a groove in the housing for receiving a power cable.

Other aspects of the invention will be apparent from the following description.

Brief description of the drawings

Figure 1 shows a prior art ESP;

Figure 2 shows an ESP according to an embodiment of the invention; and

Figure 3 shows a detailed view of the embodiment of Figure 2. Mode(s) for carrying out the invention

Figure 2 shows an embodiment of an ESP according to the invention. This ESP comprises a single motor section 20, a protector section with a crossover and a pump inlet 22 and a single pump section 24. The overall length of the ESP is less than 12m.

Figure 3 shows a sectional view of the ESP of Figure 2, comprising (from left to right) the commutator section 20, a motor section 23, a crossover section 21 which is connected at the top of the motor section 23; a protector section connected to the crossover section, and the pump section 24 connected on top of the protector section 22. A single-piece common shaft 26 runs through all of these sections.

The motor section 20 comprises a commutation stage 30 at its lower end for controlling the motor located inside a commutation stage housing part 31. The very end of the shaft 26 is provided with a snap ring 32 against which supports the various rotating components of the ESP. The motor power stage includes a housing 34 with a stator 36 fixed to its inner surface. A rotor 38 is mounted on the shaft 26 inside the stator 36. The motor is preferably a high torque DC motor with multiple magnet rotor poles.

The shaft leads from the motor section 20, through the crossover section 21 and into the protector section 22 which serves to separate the motor and pump sections all located in a housing part 39. The protector section comprises three pressure compensating bags 40, each with an associated high speed face seal 42. The protector section will also include a pump inlet with inlet openings 43 in the housing 39 covered by a screen and other seals and filters to prevent fluids from entering the motor housing 34.

The shaft 26 leads from the protector section into the pump section 24. The pump comprises a continuation of the housing 39 having a series of diffusers 46 fixed thereto. The diffuser stack 46 and internal components of the inlet, protector and crossover are held in compression by the housing 39. Impellers 48, corresponding to the diffusers 46 are mounted on the shaft 26 so as to be

positioned adjacent the diffusers and define centrifugal pump elements. A compression nut 50 is provided at the top of the shaft in the pump section. By tightening the compression nut 50, the impellers and other components mounted on the shaft 26 are forced against each other and held in compression against the snap ring 32.

The compact ESP construction provided by this invention allows for the reduction in total number of separate housings, from as many as 11 in a conventional ESP system , to three housing sections (pump/intake/protector housing, motor housing, commutator housing). This reduction in number of housings can be facilitated by a number of features of the compact ESP design:

1. Reduced length of the pump section(s) due to reduction in the number of pump stages as a result of increased operating speeds up to 6000 rpm.

2. Reduced length of the motor section(s) due to use of high power DC motor design.

3. The functions of the pump housing(s), intake housing, and multiple protector section housings are combined into a single housing.

The reduced number of housing joints in the overall assembly means a reduction in concentricity error in the assembly from accumulated manufacturing tolerance, fewer opportunities for joint related problems caused by manufacturing defects, lower vibration levels (fewer opportunities for bearing misalignment in joint bodies).

In the ESP assembly according to the invention, the pump diffusers, intake body and protector bodies can all be held in compression with reaction force provided by the combined single housing. The completed assembly can be made in the factory rather than assembled on-site. The functions of the pump intake body (ingress of well fluid to the pump section and screening of well debris) are integrated into the housing of the compact ESP.

In the case of a large diameter compact ESP (e.g. 111mm pump section OD), installed in a small common well casing (e.g. 120mm ID), it may be necessary to partially embed the power cable in a relief groove machined in the OD of the pump/protector housing. This relief groove can vary in depth from nothing at the discharge end (top) of the pump section where the pressure differential between inside and outside of the pump is highest to 4mm deep at the

pump intake (where differential pressure is lowest) and staying at this depth for the full length of the protector section. The purpose of this relief is to provide additional space inside the 120mm casing ID to allow for the power cable.

In the compact ESP described above, both housing connections in the pump/intake/protector section and the upper housing connection in the motor section are typically formed from threaded connections. The housing joints at the bottom of the motor and top of the commutator are preferably pinned construction to provide for precise angular alignment between the motor stator and the commutator.

Other changes within the scope of the invention will be apparent.