Patent Application
20130199775
The present disclosure relates to downhole pumping systems submersible in well bore fluids. More specifically, the present disclosure concerns fluid speed measurement and submersible motor control for a downhole pumping system.
Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the well bore to the surface. These fluids are generally liquids and include produced liquid hydrocarbon as well as water. One type of system used in this application employs an electrical submersible pump (ESP). ESP's are typically disposed at the end of a length of production tubing and have an electrically powered motor. Often, electrical power is supplied to the pump motor via an electrical power cable from the surface that is strapped alongside the tubing or liner.
A motor lead is secured to the lower end of the power cable, the motor lead terminating in a connector that plugs into a receptacle of the motor. This connector is typically known as a pothead connector.
Often the power cable will be run alongside communication lines that transmit and receive data between the surface and the ESP assembly. An alternate communication method involves using the power carrying lines in the power cable to serve the dual purpose of carrying power and communication signals between the surface and the ESP assembly. Either communication setup may be used to control the operation of the motor in the ESP assembly.
Typically, the pumping unit is disposed within the well bore just above where perforations are made into a hydrocarbon producing zone. This placement allows the produced fluids to flow past the outer surface of the pumping motor and provides a cooling effect to the motor.
Heat is transferred between the fluid in the well bore and the motor. Fluid in motion over the motor or motor housing serves to disperse heat from the motor more efficiently. Overheating of the motor may be a problem when fluid flow slows down or temporarily ceases. Repeated exposure to elevated motor temperatures caused by reduced fluid flow can shorten motor longevity.
The pumping system of this invention has features to measure the fluid speed of production fluids adjacent the motor assembly in an electric submersible pumping (ESP) system. A flow assurance section is included as part of an electric submersible pumping system. The flow assurance section includes a sail switch or set of sail switches that toggle at certain detected fluid speeds such as 1 ft/s or 0.5 ft/s. The fluid speed at which the flow assurance section switches power to the motor being interchangeable to best suit a given downhole environment. The toggling of the sail switches causes the power to the motor to switch on and off thereby preventing the motor from overheating. Power to the motor can be controlled by a control circuit located adjacent the pumping system or at the surface and may utilize the toggling state of the sail switches in making control decisions. The flow assurance section can be attached beneath the motor, above the pump section, or in other locations in close proximity to the ESP system. The signal from the flow assurance section can be sent to the surface as a communication on the power lines that extend to the ESP system motor or on communication lines that extend to the surface alongside or separate from the power lines.
The toggled state of the flow assurance sail switches can indicate to a surface user the fluid speed state adjacent a motor installed downhole. For example, green, yellow, and red status indicator lights or a similar representation in software can be used at the surface to alert operations personnel of the current fluid speeds adjacent the motor. This real-time indicator of downhole fluid speeds helps operations personnel to take action before a motor can overheat and fail. Additionally, the toggled state of the sail switches may be used to directly or indirectly control power to the motor. If a sail switch for a given fluid speed is toggled off, meaning the fluid flow adjacent the sail switch has a speed below that switches fluid speed, then the motor in the ESP system may be controlled based on the toggle state of that switch. Monitoring trends in fluid speed state will additionally help in determining the effect it has on motor longevity.
Some of the features and benefits of the present invention have been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:
The power cable 27 extends alongside the production tubing 23, terminating in a connector 29, commonly referred to as a pothead connector, that electrically couples the power cable 27 to the electric motor 15. The power cable 27 can extend all the way from the surface to the pothead connector 29 and have an additional splice extending downward inside the electric motor 15 housing and extending through the flow assurance section 21. Often the power cable 27 will additionally include communication lines that transmit and receive data between the surface and the ESP system 12. An alternate communication method involves using the power carrying lines in the power cable 27 to serve the dual purpose of carrying power and communication signals between the surface and the ESP system 12. Either communication setup may be used to control and monitor the operation of the motor 15 housed in the ESP system 12. Additionally, in an alternate embodiment, the ESP system 12 could be supported on coiled tubing, rather than production tubing 23. The power cable 27 could be located inside or outside the coiled tubing for that embodiment.
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In the preferred embodiment, the flow assurance section 21 is attached beneath the ESP system 12 to advantageously measure fluid speed close to the annular space 37 between the casing 14 and the motor 15. For a given installation the preference may be to position the flow assurance section 21 further beneath the motor 15 using a tubular flow assurance extension 39. This allows for the measurement of fluid speed further beneath the motor 15 which may be a more accurate position to detect speed of the fluid flowing in the annular space 37 between the flow assurance section 21 and the casing 14. Power and communication lines for the sail switches 31 can be spliced off of the power cable 27 and extend downward from pothead connector 29 inside the motor housing through the tubular flow assurance extension 39, then into the flow assurance section 21. Alternatively, the splice of the for the power and communication lines that extend to the sail switches 31 can occur anywhere within the motor housing. In some embodiments only a power or only a communication line will be required by the sail switch 31. The communications regarding the toggle state of the sail switches 31 can be sent along the power cable 27, along a separate communication cable running alongside the power cable 27 or along a completely separate communication cable. The included figures show just a few of the intended configurations.
In an alternate configuration of the flow assurance section 21, the sail switch paddles 33 can be on the exterior of the flow assurance section 21 housing. In the preferred embodiment the sail switch paddles 33 are on the interior of the flow assurance section 21 housing so that the sail switch paddles 33 have the benefit of being better protected during installation. In another configuration the sail switches 31 can be positioned on the motor 15, seal/equalizer 17, or pump 19, protective railings positioned to protect the sail switches 31 in this configuration.
An embodiment can have a splice from the power cable 27 extending from the pothead connector 29 alongside the motor 15 to the flow assurance section 21. In another embodiment a splice from the power cable 27 can extend alongside the pothead connector 29, alongside the motor 15, and alongside the flow assurance extension into the flow assurance section 21. In some embodiments, the flow assurance section 21 can use power from the power cable 27 as needed.
An alternate positioning of the flow assurance section 21 is in the production tubing 23 above the pump section 19 of the ESP system 12. The flow assurance section 21 can connect to the power line 27 and any corresponding communication lines with a connector similar to the pothead connector 29 that connects the power line 27 to the motor 15. This position of the flow assurance section 21 measures the speed of fluid after it passes by motor 15, the fluid inlets 25, and the pump 19. This installation position is farther away from the motor and the speed being measured is of production fluid after passing through pump 19; however, this position may still be advantageous for certain downhole environments. An alternate embodiment of the ESP system 12 may have the flow assurance section 21 installed above the pump 19 and another flow assurance section 21 installed below the motor 15. In this type of installation surface equipment may have multiple fluid speed indicators and in some embodiments the controller may utilize the toggling states of the various sail switches 31 to control the motor 15 or perform other control functions.
The sail switches in the flow assurance section 21 toggle at certain detected fluid speeds such as 1 ft/s, 0.5 ft/s, or 0.3 ft/s. The fluid speed being detected would typically represent reduced fluid speeds for a given downhole installation. Potential causes of reduced fluid speed past the motor 15 may include: gas ingestion in the pump, gas locking in the pump, sand erosion in the pump, changes in well productivity, a closed surface valve that controls flow off of the production tubing, unexpected well performance, a hole in the production tubing, deposition or build up from scale on the pump or tubing, sand, asphaltenes, or other reasons. Reduced fluid speed for any of these reasons and others not mentioned could cause the motor 15 to overheat. The use of sail switches in a flow assurance section 21 to alert operations personnel or to autonomously switch power off to the motor 15 can avoid damage that would be caused if the motor 15 were to overheat.
The flow assurance section 21 can alert operations personnel and also act autonomously to increased fluid speeds detected by the sail switches 31. For example, if a sail switch 31 in the flow assurance section 21 initially caused power to be switched off to the motor 15, it could likewise cause power to be switched back on to the motor 15 when the fluid speed increases and the sail switch 31 is again toggled. Likewise, any alerts that have been made to surface equipment or to operations personnel can be turned off when fluid speed increases. Surface equipment and operations personnel can also be notified of faster fluid speeds, as detected by the sail switches 31, that have a positive effect on the cooling of the motor 15.
In the preferred installation having multiple sail switches 31 positioned in the flow assurance section 21, each sail, switch will detect a certain fluid speed. For example, one sail switch can detect 1 ft/s while another detects 0.5 ft/s. Each switch can alert surface equipment or operations personnel as to its toggled state. In some embodiments multiple sail switches 31 of the same detection rate may be used for redundancy. For example, if one of the sail switches is damaged during installation, the second sail switch could then be used.
Alternatively, one sail switch 31 could have two or more positions and offer two or more output signals to infer two or more differing fluid speed states. These outputs could be used similarly to the methods described above to alert surface equipment and operations personnel and autonomously switch power off and on to the motor 15. For example, movement of sail switch paddle 33 to a first position may represent a fluid speed above one fluid speed, such as 0.5 ft/s, and movement of sail switch paddle 33 to a second position may represent a fluid speed above another fluid speed, such as 1 ft/s.
If an ESP is installed in perforations or with perforations above and below the ESP there can be uncertainty regarding fluid speed past the motor. This invention is capable of assuring that minimum fluid speeds are achieved and that the motor may safely operate.
There are other uses of the flow assurance section 21. These uses include: tracking when a well is producing or not, tracking well fluid speeds over time, preventing the overheating of other downhole equipment that may be susceptible to heat when fluid speeds are low. More specific examples include: tracking a motors heat exposure and corresponding insulation life, tracking fluid speed to cool the thrust bearing in the seal section, or tracking fluid speed past a rod driven PCP where the PCP elastomers could melt. With other forms of lift there may still exist further benefits of installing a flow assurance section 21. For example, tracking the production rate of a well or tracking when a well is producing or not producing over a period of time. Another benefit may exist when the flow assurance section 21 is installed in a PCP or rod pump installation. In this type of installation, for example, if the pump operates with no fluid movement, line pressure can build and result in bursting of equipment either in the well or on the surface. Having a flow assurance section 21 can provide the benefit of alerting to this condition before it becomes more serious.
In view of the foregoing, electric submersible pumping systems that are capable of operating in downhole environments are provided as embodiments of the present invention. For example, motor longevity may be improved by using an ESP system with an integrated flow assurance mechanism as illustrated in the above described embodiments.
