This invention relates to a tandem system for downhole use.

In oil production the crude oil is generally lifted to the surface by means of a downhole pump driven by an electric motor. Through time the pump can develop faults which render it inoperable, and in such cases the pump and its associated equipment has to be raised to the surface and repaired or replaced. This causes expensive discontinuation of the oil recovery and withdrawal from the drill hole of great lengths of equipment.

According to the present invention there is provided a pump system for downhole use, comprising first and second pumps coupled to a conduit, the pumps being independently actuable.

The invention is also a completion assembly for downhole use including a pump system as defined in the immediately preceding paragrap .

Preferably, the pumps are coupled to the conduit in

parallel.

The invention is of especial use in a Y-tool configuration in which each of the pumps is disposed in side-by-side relationship with bypass tubing for wireline use. The bypass tubing adjacent the pumps may be unidirectional and interconnected by a coupling member to provide a straight passageway for a wireline past both pumps.

Preferably, each Y-tool includes a valve, which permits each bypass tubing to be opened or closed. Typically, the valve may be an isolation valve which may comprise an isolation sleeve, blanking plug or logging plug to close the bypass tubing. Removal of the isolation sleeve, blanking plug or logging plug opens the bypass tubing.

Preferably, the first pump is located above the second pump.

Typically, the pump system also includes a support device to support at least a portion of the weight of the pump system. Typically, the support is coupled to the upper pump and helps support the weight of the lower pump.

Preferably each of the pumps is driven by a respective motor, and preferably each of the pumps is included in a respective assembly of the pump and its associated motor. More than one motor may be drivingly connected with each pump.

Preferably also each of the pumps is actuable through an electrical supply from the surface which is

independent of the supply to the other pump.

It is conceivable that more than two pumps may be provided, each with its own remotely acruable power supply.

By virtue of the invention, failure of the first downhole pump need not necessitate lifting of the pump and its associated equipment to the surface, as the second pump can then be actuated remotely to continue the operation. The first and second pumps may be actuated simultaneously if required to increase the pumping effect.

Preferably, the pump system is coupled to and below a packer. The packer in turn is typically coupled to and below a tubing hanger and tubing bonnet. Typically, the packer, tubing hanger and tubing bonnet have dual penetrators to permit independent power supplies to each pump.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:-

Figs. 1(a) to (e) provide a sequenced side view of an ESP completion assembly having a tandem pump arrangement in accordance with the invention; and, Fig. 2 is a schematic view of a packer, tubing hanger and tubing bonnet to which the apparatus of Fig.l is coupled.

Referring to the drawings, the completion assembly of this embodiment of the invention has at an upper end portion a submersible pump packer 2, conduits 4, 6 and

a 4 inch (100mm) diameter main mandrel 8 which provides production tubing for upward passage of crude oil to the surface. Above the packer 2, the mandrel 8 and conduits 4, 6 extend up to and through a tubing hanger 51 and a tubing bonnet 52, as shown in Fig.2.

Below the packer 2 the mandrel 8 enters a 4.5 inch (114mm) diameter Wrynose twin cable cross-coupling cable protector 10 which leads to a Wrynose tandem ESP bypass tool 12 in which the passageway for oil extends in side-by-side relationship with 2.875 inch (73mm) diameter bypass tubing 14. The bypass tubing 14 provides a passageway for a wireline and is in straight-line communication with the passage through the production tubing above it.

The passageway for oil is in the form of a first assembly 16 comprising a pump 18 of conventional design whose outlet 20 communicates with the production tubing above the bypass tubing 14 through a Wrynose isolation valve 22. The isolation valve 22 may include an isolation sleeve, blanking plug or logging plug which acts as the valve member. The pump 13 is drivingly connected to a pair of conventional downhole electric motors 24, 26 through an equalisation device 28 for equalising the fluid pressure in the motors 24, 26. The combination of the assembly 16 and the bypass tubing 14 is a Y-tool as in current use downhole.

The bypass tubing 14 continues below the assembly 16 as 2.875 inch (73mm) production tubing 30 and enters a 4.5 x 2.875 inch (114 x 73mm) cross-over 32 which itself is connected to a Wrynose ESP bypass tool 34 fitted with a reduced-diameter no-go nipple. In the tool 34 the oil passageway extends side-by-side with

2.375/2.875 inch (60 x 73mm) bypass tubing 36 for wireline use. The tubing 36 is in straight-line communication with the production tubing 30. The oil passageway at the tool 34 consists of a second assembly 46 comprising a pump 38, equalisation device 40 and motors 42, 44 in the same fashion as the first assembly 16 and provides the same function and pumping output as the first assembly 16.

Hence, the pump assemblies 16, 46 are coupled in parallel to the main mandrel 8.

The first and second assemblies 16, 46 are selectively actuated from the surface through respective independent electric cables extending downwards through the conduits 4, 6.

During use, the pump 18 of the first assembly 16 is driven by the motors 24, 26 to force crude oil from a reservoir in which the assembly is situated to the surface; the motors 42, 44 and pump 38 of the second assembly are normally at rest during this period, although they can if desired be actuated to increase the overall pumping effect.

In the event of the motors 24, 26 or the pump 18 developing a fault and ceasing to operate, the isolation valve 22 is opened and the motors 42, 44 and pump 38 of the second assembly are actuated to take over the pumping function. Hence, there is no need for significant loss of production from the reservoir by withdrawal of the equipment and replacement of the faulty unit.

This embodiment of the invention therefore provides a

very substantial economic benefit in oil production by allowing pumping to continue.

Modifications and improvements may be incorporated without departing from the scope of the invention.