Thermal probe for motor lead extension

An electric submersible pumping system is configured to produce fluids from a well. The submersible pumping system includes a motor drive, an electric motor driven by the motor drive, a sensor module and a power cable. An upper end of the power cable is connected to the motor drive. The electric submersible pumping system further includes a pothead connected to the motor and a motor lead extension, where an upper end of the motor lead extension is connected to the power cable and a lower end of the motor lead extension is connected to the motor through the pothead. The electric submersible pumping system includes a motor lead extension temperature sensor located in the pothead.

FIELD OF THE INVENTION

This invention relates generally to the field of submersible pumping systems, and more particularly, but not by way of limitation, to an improved monitoring system for measuring conditions within downhole pumping systems.

BACKGROUND

Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, a submersible pumping system includes a number of components, including an electric motor coupled to one or more high performance pump assemblies. Production tubing is connected to the pump assemblies to deliver the petroleum fluids from the subterranean reservoir to a storage facility on the surface.

The motor is typically an oil-filled, high capacity electric motor that can vary in length from a few feet to nearly one hundred feet, and may be rated up to hundreds of horsepower. Typically, electricity is generated on the surface and supplied to the motor through a heavy-duty power cable. The power cable typically includes several separate conductors that are individually insulated within the power cable. Power cables are often constructed in round or flat configurations.

In many applications, power is conducted from the power cable to the motor via a “motor lead extension” or “motor lead cable.” The motor lead extension typically includes one or more “leads” that are configured for connection to a mating receptacle on the motor. The leads from the motor lead extension are often retained within a motor-connector that is commonly referred to as a “pothead.” The pothead relieves the stress or strain realized between the motor and the leads from the motor lead extension. Motor lead extensions are often constructed in a “flat” configuration for use in the limited space between downhole equipment and the well casing.

The motor lead extension is a relatively fragile component and is sensitive to being overheated during use. If the motor lead extension overheats, the insulators and seals can fail, which often leads to electrical shorts that render the cable inoperable. In some cases, the failure of the motor lead extension results in additional damage to the electric submersible pumping system.

In the past, the temperature of the motor lead extension has been indirectly monitored as a function of the temperature of the motor windings, which can be measured with a thermocouple located inside the motor. Because the motor lead extension can be dozens of feet away from the motor, this indirect method of monitoring the temperature of the motor lead cable can be imprecise and unreliable. There is, therefore, a need for an improved system and method for measuring the temperature within the motor lead extension.

SUMMARY OF THE INVENTION

In one aspect, embodiments of the present disclosure are directed to an electric submersible pumping system for use in recovering wellbore fluids from a wellbore. The submersible pumping system includes a motor drive, an electric motor driven by the motor drive, a sensor module connected to the electric motor, and a power cable, where an upper end of the power cable is connected to the motor drive. The electric submersible pumping system further includes a motor lead extension and a pothead connected between the motor lead extension and the electric motor. The electric submersible pumping system includes a motor lead extension temperature sensor located outside the motor. The motor lead extension temperature sensor is configured to measure the temperature of the motor lead extension and output a motor lead extension temperature signal to the sensor module.

In another aspect, embodiments of the present disclosure are directed to an electric submersible pumping system configured to produce fluids from a well. The submersible pumping system has a motor drive, an electric motor driven by the motor drive, a sensor module, and a power cable, where a first end of the power cable is connected to the motor drive. The electric submersible pumping system further includes a pothead connected to the motor and a motor lead extension, where a first end of the motor lead extension is connected to a second end of the power cable, and where a second end of the motor lead extension is connected to the motor through the pothead. The electric submersible pumping system further includes a motor lead extension temperature sensor located in the pothead.

In yet another embodiment, the present disclosure is directed to a method for operating an electric submersible pumping system that includes an electric motor, a motor drive, a power cable connected to the motor drive, and a motor lead extension connected through a pothead between the electric motor and the power cable. The method begins with the steps of providing a motor lead extension temperature sensor external to the electric motor. Next, the method includes the step of measuring a temperature of the motor lead extension with the motor lead extension temperature sensor. Lastly, the method includes the step of outputting a motor lead extension temperature signal to a sensor module

DETAILED DESCRIPTION

In accordance with an exemplary embodiment of the present invention,FIG.1shows a front view of a downhole pumping system100attached to production tubing102. The downhole pumping system100and production tubing102are disposed in a wellbore104, which is drilled for the production of a fluid such as water or petroleum from a subterranean geologic formation106.

The wellbore104includes a casing108, which has perforations110that permit the exchange of fluids between the wellbore104and the geologic formation106. Although the downhole pumping system100is depicted in a vertical well, it will be appreciated that the downhole pumping system100can also be used in horizontal, deviated, and other non-vertical wells. Accordingly, the terms “upper” and “lower” should not be construed as limiting the disclosed embodiments to use in vertical wells.

The production tubing102connects the pumping system100to a wellhead112located on the surface114, which may be onshore or offshore. Although the pumping system100is primarily designed to pump petroleum products, it will be understood that the present invention can also be used to move other fluids. It will also be understood that, although each of the components of the pumping system100are primarily disclosed in a submersible application, some or all of these components can also be used in surface pumping operations.

The pumping system100includes a pump116, a motor118and a seal section120. The motor118is an electric motor that receives its power from a surface-based supply through a power cable122and one or more motor lead extensions124. In many embodiments, the power cable122and motor lead extension124are configured to supply the motor118with three-phase electricity from a surface-based variable speed (or variable frequency) motor drive126, which receives electricity from a power source128. The electricity is carried along separate conductors (not separately designated), which each correspond to a separate phase of the electricity. The motor lead extension124connects to the motor118through a connector130, which is often referred to as a “pothead” connector. The motor lead extension124extends into the pothead130, where it terminates in a connection to the conductor leads of the motor118. The pothead connector130relieves mechanical stresses between the motor lead extension124and the motor118, while providing a sealed connection that prevents the ingress of wellbore fluids into the motor118, motor lead extension124, or pothead130.

The motor118converts the electrical energy into mechanical energy, which is transmitted to the pump116by one or more shafts. The pump116then transfers a portion of this mechanical energy to fluids within the wellbore104, causing the wellbore fluids to move through the production tubing102to the surface114. In some embodiments, the pump116is a turbomachine that uses one or more impellers and diffusers to convert mechanical energy into pressure head. In other embodiments, the pump116is a progressive cavity (PC) or positive displacement pump that moves wellbore fluids with one or more screws or pistons.

The seal section120shields the motor118from mechanical thrust produced by the pump116. The seal section120is also configured to prevent the introduction of contaminants from the wellbore104into the motor118, while also accommodating the thermal expansion and contraction of lubricants within the motor118. Although only one pump116, seal section120and motor118are shown, it will be understood that the downhole pumping system100could include additional pumps116, seal sections120or motors118.

The pumping system100also includes a gauge or sensor module132connected to the motor118. As depicted inFIG.1, the motor118is positioned between the sensor module132and the seal section120. In other embodiments, the sensor module132can be located elsewhere in the pumping system100, for example, between the motor118and the seal section120. The sensor module132may include internal sensors and circuits for receiving and processing signals from remote sensors configured to measure operational and environmental conditions at the pumping system100, as well as communications circuits for transmitting and receiving data from equipment located on the surface114or elsewhere in the wellbore104.

Turning toFIG.2, shown therein is a partial cross-sectional view of the motor118, sensor module132and pothead130. The motor118includes a motor housing134, a shaft136, a stator assembly138, and a rotor140. The stator assembly138is located adjacent the interior surface of the motor housing134and remains fixed relative the motor housing134. The stator assembly134includes a stator core142that is formed by passing magnet wire144through slots146in a plurality of stacked and compressed laminates148to form windings or coils.

FIG.3depicts the passage of the magnet wire144through the stator slots146. Each stator coil is created by winding a length of magnet wire144back and forth though slots in the stator core142. Each time the wire is turned 180° to be threaded back through an opposing slot146, an end turn (not shown inFIG.2) is produced, which extends beyond the length of the stator core126. In induction type motors, power (usually three-phase AC power) is provided to the windings within the stator core142, causing the stator assembly138to generate rotating magnetic fields, which induce currents and corresponding magnetic fields in the rotor140, thereby causing the rotor140and the shaft136to rotate and drive the pump116. In the case of a permanent magnet motor, three-phase AC power is provided to the windings within the stator core142, generating rotating magnetic fields as in the induction motor. The rotor140of the permanent magnet motor, however, has a set of permanent magnets which cause the rotor140to rotate in the rotating magnetic fields generated by the sequentially energized stator assembly138.

As illustrated inFIG.2, the sensor module132is configured to receive electrical power and data signals from the motor118. A wye-point or other power connection150can be used to provide power from the motor118to the sensor module132. In some embodiments, the power connection150includes leads and terminals at the interface of the motor118and sensor module132that provide an electrical connection without the need for separate wiring. The motor118includes a motor temperature sensor152that is configured to measure the temperature of the motor118. In some embodiments, the motor temperature sensor152is a thermocouple that detects the temperature of the motor lubricating oil or stator windings in the motor118. The temperature sensor152is configured to output a signal representative of the internal operating temperature of the motor118to a processing board154within the sensor module132.

Unlike prior art systems in which the temperature within the motor lead extension124is evaluated as a function of the remote temperature in the motor118, the pumping system100includes a motor lead extension temperature sensor156positioned outside the motor118. In the embodiment depicted inFIG.2, the motor lead extension temperature sensor156is positioned in the pothead130, near the leads or conductors158in the motor lead extension124. The motor lead extension temperature sensor156is connected to a terminal junction162in the motor118which feeds to the sensor module132with a sensor wire160. In some embodiments, the motor lead extension temperature sensor156is configured to be plugged directly into the conductors158within the terminal junction162. The sensor wire may be one or more electrical wire(s), or may be an optical line. The sensor wire160extends from the terminal junction162to the sensor module132through the motor118. In the embodiment depicted inFIGS.2and3, the sensor wire160is routed through the stator core142with the magnet wire144. In this way, the sensor wire160extends through one of the continuous slots146formed by the stack of aligned laminates148. The sensor ‘wire’ may be of the embodiments of an insulated electrically conductive material or material designed to transmit light. The motor lead extension temperature sensor156is configured to measure the temperature of the motor lead extension124, the motor lead extension conductors158, and the other internal components within the pothead130and motor lead extension124, and output a motor lead extension temperature signal to the sensor module132.

In comparison to the motor temperature sensor152positioned within the motor118, the motor lead extension temperature sensor156is capable of more accurately measuring the actual temperature of the interior of the motor lead extension124and internal components within the pothead130. The signal produced by the motor lead extension temperature sensor156can be received and processed by the sensor module132, which can then provide a signal to the motor drive126. In application, the motor drive126can be configured to shut down the motor118or reduce the flow of electricity through the power cable122and motor lead extension124in the event the temperature measured by the motor lead extension temperature sensor156within the pothead130exceeds the high limit setpoint. The ability to more accurately detect the temperature within the motor lead extension124presents a significant advance over prior art systems that rely on temperature sensors that are located outside the motor lead extension124or pothead130.