Switch mechanisms that allow a single power cable to supply electrical power to two or more downhole electrical motors alternatively and methods associated therewith

A switch mechanism is provided for inclusion in a downhole production string located in a wellbore. The switch mechanism includes an electrical power input and at least two electrical power outputs. In addition, the switch mechanism includes an actuator mechanism which is capable of being actuated from a position remote from the wellbore to selectively move between at least two positions. The movement thereby provides a selective electrical connection between the input and one of the outputs when the actuator is in one of the at least two positions.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method for use downhole to provide power to two or more pumps and more particularly relates to a switch mechanism operable to allow a single power cable to supply electrical power to two or more downhole electrical motors alternatively.

BACKGROUND

Many oil and gas wells must be provided with artificial lift in order to extract the hydrocarbons in an effective manner, otherwise the relatively low natural reservoir pressure (particularly in the middle and latter years of some wells) is not sufficient to flow the well. Conventionally, the artificial lift can be provided by a variety of methods including injection of CO2 into the well to force the hydrocarbons up to the surface and by providing downhole pumps to suck in the hydrocarbons and pump them up production tubing to the surface. An Electrical Submersible Pump (ESP) is a form of artificial lift pump designed to draw fluid from a well in the absence of pressure to suit the production rate required. Typically ESPs, in the oilfield, have been run as single units on the end of the production tubing. A power cable, attached to the electrical motor unit of the ESP extends to the surface of the well alongside the production tubing and terminates at the wellhead.

The power cable will often need to be fed through a packer (a downhole barrier adapted to seal the annular gap between the production tubing and the casing) prior to extending to the surface of the well where the power cable also needs to be fed through the wellhead. At both of these junctions, the power cable usually has to be deployed with an electrical penetrator which seals the cable into the wellhead and packer. It should be noted however that not all ESP wells use packers but all require wellheads and such a typical/conventional configuration of a well having an ESP deployed therein is shown inFIG. 1.

In more recent years, it has become more customary for an operator to want to use a dual ESP configuration, where one ESP is run on top of the other, with a spacing therebetween. This configuration allows one ESP unit to be operated or run to the end of its life and then the second ESP unit is switched on. The benefits of dual ESP systems are considerable in terms of saved workover (well completion replacement), costs and avoidance of oil well downtime.

Conventional dual ESP configurations require a dedicated power cable from each of the dual ESPs to the surface of the well and therefore two power cables are required from the ESP's to the surface.

The power cable feed for the lower ESP motor extends from a plug-in connection at the lower ESP motor, up beyond the upper ESP and is joined by the power cable feed for the upper ESP. From there, both cables extend to the surface of the well and such a typical/conventional configuration of a well having a dual ESP system deployed therein is shown inFIG. 2.

In wells where the power cable has to pass through a packer as well as through the wellhead, special electrical “penetrators” (units which seal the power cable into a steel body) are required.

Dual ESP systems therefore require two penetrators, both for the packer and for the wellheads. Unfortunately, standard wellheads and packers are manufactured with only a single penetrator and cannot be modified to accept twin penetrators. Accordingly, packers and wellheads have to be specially manufactured to suit twin penetrators.

Accordingly, for new wells, packers and wellheads can be specially ordered to accommodate the twin penetrator requirement. However, existing wells would require a conversion and this leads to significant costs due to the large variety of wellhead types and the engineering required. Furthermore, the existing customer owned and very expensive wellheads and packers would therefore be scrapped.

This extra (significant) cost plus the associated lead time in obtaining such new and special wellheads currently makes conversion to dual ESPs non-viable for many existing wells or at least, presents a barrier to conversion to duals ESP systems.

It would therefore be desirable if the existing wellhead (and packer if required) can be utilised; if this was the case then conversion to dual ESPs becomes more viable and presents a significant opportunity to improve ESP viability in all manner of wells.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a downhole switch mechanism for inclusion in a production string located in a wellbore, the downhole switch mechanism comprising:an inlet for electrical power;at least two outlets for electrical power; andan actuator mechanism which is capable of being actuated from the surface of the wellbore to selectively move between at least two positions in order to provide a selective electrical connection between the said inlet and one of the said outlets.

According to the first aspect there is provided a method of powering at least two electrically operated devices associated with or included in a production string located downhole in a wellbore via a single electrical cable, the method comprising the steps of:providing a switch mechanism in the production string, the switch mechanism being supplied with electrical power from the surface of the wellbore by means of the single electrical cable and further being coupled to at least two downhole devices; andactuating, at the surface, the switch mechanism to move between two or more positions, each position being associated with one of the said downhole devices,such that electrical power is selectively supplied from the single electrical cable to the selected downhole device.

Preferably, the switch mechanism is incorporated into the production string before it is run into the wellbore.

Preferably, the actuator mechanism further comprises a switch arm mechanism moveable between the at least two positions, and more preferably, each position is associated with one of the said electrical power outlets. Typically, the actuator mechanism is capable of being actuated from the surface, of the wellbore to selectively move the switch arm mechanism between the two positions.

Typically, the downhole devices comprise electrically operated downhole pumps and more preferably the downhole pumps are electrically submersible pumps (ESPs).

Preferably, the switch arm is actuated by means of an actuator mechanism. Preferably, the actuator mechanism is also powered from the surface. In one preferred embodiment, the actuator mechanism comprises a hydraulic fluid powered actuator mechanism and in this preferred embodiment, the actuator mechanism comprises a hydraulic cylinder and piston arrangement, wherein fluid can be injected into or withdrawn from the hydraulic cylinder in order to move the piston. In this preferred embodiment, the piston is mechanically coupled to the switch arm.

Preferably, the switch mechanism is located downhole in the wellbore below a wellhead of the wellbore, where the wellhead of the wellbore is typically located at the surface thereof. Typically, where an annular sealing device such as a packer is included in the production string, the switch mechanism is typically located below the annular sealing device.

Typically, a first branch electrical cable is arranged to connect the first outlet of the switch mechanism to a first ESP and a second branch electrical cable is arranged to connect the second outlet of the switch mechanism to a second ESP. Preferably, the single electrical cable is electrically coupled to the inlet of the switch mechanism such that the single electrical cable supplies power from the surface of the wellbore to the inlet of the switch mechanism, through the switch arm to the selected downhole ESP.

DETAILED DESCRIPTION

FIG. 3Ashows the upper portion of a typical downhole completion and production system as comprising a wellhead10located at the surface with a conventional single penetrator wellhead hanger12. A single3phase electrical cable14passes through the single penetrator12and down towards the lower half of the well shown for instance inFIG. 3B. A suitable diameter hydraulic cable16such as ¼″ diameter also passes through the single penetrator12in a conventional manner, but as is also conventional, standard single penetrator wellhead hangers12are already provided with the provision or ability to have a relatively small conduit hydraulic line such as ¼ ″ outer diameter conduit to pass through them (as well as a much larger diameter electrical cable14). As is also conventional, the electrical cable14and hydraulic line or conduit16are secured to production tubing18by means of standard cable protectors20which are provided at each joint between each length of production tubing18, that is every 30 feet. As is also conventional, a standard production packer22having a single penetrator therein is provided toward the lower half of the upper half of the completion8where the single penetrator of the packer22allows the electrical cable14(and the hydraulic conduit line16) to pass through the body of the packer22.

An embodiment of an apparatus and a method for distributing power downhole with only one electrical cable in accordance with the present invention is shown inFIG. 3BwhereFIG. 3Bgenerally shows the lower half of a downhole completion9B. The lower completion equipment9B comprises production tubing18and a pair of ESPs24BU,24BL where the production tubing18continues on to the bottom of the well to allow the transport of hydrocarbons from the bottom of the well up to the surface. The pair of ESPs24BU,24BL shown inFIG. 3Bare arranged in parallel with the production tubing18and, for the configuration shown inFIG. 3B, the pair of ESPs24BU,24BL would typically remain dormant until the hydrocarbons had been produced from the bottom of the well and can no longer be produced from that deep region. At such a point, the operator may take the decision to activate the lower ESP24BL such that it pumps hydrocarbons from its locality upwards through outlet pipe28and into the inverted Y-shaped branch joint30and then up through the rest of the production tubing18to the surface.

A hydraulic switch module26B is conveniently located close to the upper ESP24BU.

In general, the hydraulic switch26B can be actuated with hydraulic fluid supplied through the hydraulic line16from the surface to move an electrical connector or switch arm38such that the electrical power delivered through the electrical cable14can be delivered to either the upper ESP24BU or the lower ESP BL. More details of the hydraulic switch26are shown inFIGS. 4A,4B and4C and will now be described.

FIG. 4Ashows the hydraulic switch26as comprising a single acting piston32with a heavy duty return spring33located within a hydraulic fluid cylinder or piston chamber34. The hydraulic line16(which is purged before use) extends from the surface down to the switch module26B and connects directly to the piston chamber34. Accordingly, hydraulic fluid from the surface can be delivered through the hydraulic line16U and injected into the piston chamber34or withdrawn from it in order to move the position of the piston head32to the left or right of the position shown inFIG. 4A. The outer end of the piston32is mechanically coupled at location36to a driver mechanism in the form of a switch arm38shown in dotted lines inFIGS. 4B and 4C. The switch arm38is electrically coupled via contacts A, B and C to the three phases of the electrical cable14. Accordingly, movement of the piston32directly moves the switch arm38and thus the switch contacts A, B and C between position1and position2.

The motor of the upper ESP24U comprises3electrical power inputs D, E, F and the motor of the lower ESP24L comprises3electrical power inputs G, H, I.

The hydraulic switch26has two configurations or positions:position1shown inFIG. 4Bwhere the switch arm38electrically couples the three phases A, B and C of the electric cable14to the three phases D, E and F of the upper ESP24U. In this position, the three phases G, H and I of the lower ESP24L are shown as being isolated. Accordingly, position1provides full power to and operation of the upper ESP24U whilst the lower ESP24L remains dormant.position2of the switch arm38is shown inFIG. 4Cwhere the switch arm38has been moved by the piston32via the mechanical coupling36such that the three phases A, B and C of the electric cable14are now electrically coupled to the three phases G, H and I of the lower ESP24L. Accordingly, position2provides full power to and operation of the lower ESP24L whilst the upper ESP24U becomes dormant.

Consequently, the operator can, from the surface, select which of the two ESPs24BL,24BU to operate by actuating the hydraulic switch24B with surface control equipment to move the piston32against the return spring33to move the switch arm38to the desired position1or2, all the while only having to run one electric cable from the surface down to the dual ESPs24BU,24BL. The operator can lock the pressure in the hydraulic fluid at the surface to hold the position1or2of the switch arm38.

An alternative lower half of the completion9C is shown inFIG. 3Cwhere the lower ESP24CL constitutes the lowermost portion of the completion9C and its output feeds straight into the lowermost end of the production tubing18. As can be seen inFIG. 3C, the upper ESP24CU and the switch26C are arranged in a similar manner to the upper ESP24BU and the switch26B of the system9B ofFIG. 3B.

A further alternative arrangement of ESPs is shown in system9D inFIG. 3Dwhere only one ESP24DU is shown but where there is another lower ESP24DL located much further down the wellbore and which is supplied with electrical power via electric cable14L. The main difference, however, between the ESP24DU shown inFIG. 3Dand the ESP24BU shown inFIG. 3Bis that the hydraulic switch26D is shown as being located at the upper most end of the ESP24DU rather than being located mid-way down the ESP24BU.

FIG. 3Eshows a further alternative arrangement of ESPs24EU,24EL where the difference compared to the system9B inFIG. 3Bis that the lower ESP24EL is enclosed within a can or housing40EL. The can40EL comprises a sealed cap42E at its upper most end and the lower end of the can40EL is attached to the lower section of production tubing18L. The can40EL acts to isolate the reservoir zone served by the lower ESP24EL from the reservoir zone served by the upper ESP24EU. Accordingly, the system9E provides a dual ESP with single bypass and single can system for operation in dual zones and the hydraulics switch26E can be operated as previously described to switch on either of the ESPs24EU,24EL to pump reservoir fluid from the desired respective zone.

A further alternative arrangement of ESPs24FU,24FL is shown inFIG. 3Fwhere the system9F shown therein again comprises a pair of ESPs24FU,24FL provided with respective cans40FU,40FL where the lower end of the upper can40FU is connected to a middle section of production tubing18M and the lower end of that production tubing18M is connected to the upper end of the sealed cap42FL of the lower can40FL. The lower end of the lower can40FL is connected to the upper end of the lower production tubing section18L and the switch26F is located above the upper ESP24FU, and the sealed cap42FU of the upper can40FU. Accordingly, a first electric power cable14M branches out of the hydraulic switch26F to deliver power to the upper ESP24FU and a second electric cable14L branches out of the hydraulic switch26F to provide power to the lower ESP24L but, as with the previous embodiments, only one electric cable14U and one hydraulic conduit16U are required to be run from surface to the downhole hydraulic switch26F. Accordingly, the system9F shown inFIG. 3Fprovides redundancy in a single zone reservoir in that reservoir fluids can be pumped up through the lower production string18L by either the lower ESP24FL or the upper ESP24FU and up through the upper production string18U and therefore redundancy is provided if either ESP24FL,24FU were to fail.

Accordingly, the embodiments described herein provide the great advantage that power can be remotely switched between an upper ESP24U and a lower ESP24L where the power is supplied via one electric cable14and this provides the further advantage that only one power cable14is required to penetrate the wellhead10and therefore allows existing standard wellhead equipment10to remain in place, unlike the prior art dual ESP system shown inFIG. 2. Furthermore, if a packer is present, only single penetrators are required at both the wellhead10and packer22, meaning both of these penetrators and the associated wellhead10and packer22are standard equipment which thereby minimises the costs and manpower required to install the system (unlike the non-standard wellhead hanger/bonnet twin penetrator and the non-standard production packer having a twin penetrator shown inFIG. 2).

Importantly, although an additional hydraulic line16to surface is required over a prior art single ESP system such as that shown inFIG. 1, conventional wellheads10and packers22are already furnished with small bore feedthrough porting for various applications to allow hydraulic lines such as line10to be passed therethrough. Furthermore, as the cost of rig time is so high, the switch26and the associated cabling and conduit arrangement will have the added benefit of significant time saving.

Importantly, it should be noted that the downhole switch26can be located anywhere under the wellhead10but, the lower it is positioned in the well, the less cable14is deployed downhole which means lower cabling costs. In fact, the choice to position the switch26directly under the wellhead10, or at the upper dual ESP24U will differ from case to case. Cable14is more vulnerable the deeper it goes so some users may wish to double the cable14on the underside of the wellhead10to maximize the reliability of the system and to avoid the potential failure on the cable14leading to both ESP units24U,24L being inoperable. Typically, if a packer22is used the cable14below the packer22is more vulnerable to downhole conditions than the cable14above the packer. Accordingly, the choice of positioning the switch26above or below the packer22will be made on a case by case basis depending on the operator's requirements.

If desired, the switch26could be modified by those skilled in the art without departing from the scope of the invention to provide third and fourth positions to allow further ESPs24to be added if, for instance, a triple or quadruple ESP24system was required by an operator.

Accordingly, the key benefits of embodiments of the present invention are:1. Only one power cable14to surface is required and thus the cable14cost is potentially halved;2. Only require a single penetrator at packer22and thus a standard ESP packer22can be used;3. Only require a single penetrator12at wellhead10and thus a standard ESP wellhead10can be used, giving greater flexibility for hanger size;4. Standard protector clamps20can be used (in the case of a deep set switch26);5. Minimal cost and disruption to convert to dual ESPs24U,24L thus benefiting from improved cost improvements on well production; and6. Brings in the potential to deploy more than two ESPs24U,24L downhole such as triple ESP systems or quadruple ESP systems.

Modifications and improvements may be made to the embodiments hereinbefore described without departing from the scope of the invention. For instance, the hydraulically operated switch26could be modified or replaced with an electrical solenoid actuator that could be operated from the surface by, for instance, modulating instructions/control signals onto the three phase electrical supply provided through the electrical cable14and this would have the advantage that the hydraulic line16could then be omitted and such an electrical solenoid actuator could be powered from the electrical cable14itself.