Patent Publication Number: US-7218997-B2

Title: Controller system for downhole applications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/704,260, filed Nov. 1, 2000 now U.S. Pat. No. 6,937,923. The aforementioned related patent application is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to closed-loop feedback systems. More specifically, the invention relates to a controller system configured to adjust the operation of peripheral devices in response to pre-selected operating variables. 
     2. Description of the Related Art 
     The production of fluids (e.g., water and hydrocarbons) from wells (e.g., coal methane beds and oil wells) involves technologies that vary depending upon the characteristic of the well. While some wells are capable of producing under naturally induced reservoir pressures, more commonly encountered are well facilities which employ some form of an artificial lift production procedure. Certain general characteristics are, however, common to most oil and gas wells. For example, during the life of any producing well, the natural reservoir pressure decreases as gases and liquids are removed from the formation. As the natural downhole pressure of a well decreases, the well bore tends to fill up with liquids, such as oil and water, which block the flow of the formation gas into the borehole and reduce the output production from the well in the case of a gas well and comprise the production fluids themselves in the case of an oil well. In such wells, it is also conventional to periodically remove the accumulated liquids by artificial lift techniques which include plunger lift devices, gas lift devices and downhole pumps. In the case of oil wells within which the natural pressure is decreased to the point that oil does not spontaneously flow to the surface due to natural downhole pressures, fluid production may be maintained by artificial lift methods such as downhole pumps and by gas injection lift techniques. In addition, certain wells are frequently stimulated into increased production by secondary recovery techniques such as the injection of water and/or gas into the formation to maintain reservoir pressure and to cause a flow of fluids from the formation into the well bore. 
     With regard to downhole pumps, some degree of flexibility is needed in operating the pump as operating conditions change. For example, it is often necessary to adjust the rate of fluid flow through the flow line in order to maintain a desired head pressure. The desired head pressure is determined according to the need to prevent gas from entering the pump in addition to maintaining fluid flow through the pump. Failure to control the head pressure can result in conditions that adversely effect the motor and/or the pump. For example, common occurrences in down hole pumping include “gas lock,” pump plugging, high motor voltage spikes, high or low motor current and other failure modes. Left unattended, these conditions can cause damage to the pump and/or motor. 
     One conventional solution to common operating problems is to use a Variable Speed Drive (VSD) to control the speed of the motor driving the pump. VSDs affect the motor speed by changing the frequency of the input signal to the motor. Increasing the frequency results in increased motor speed while decreasing the frequency decreases the motor speed. The magnitude of the speed adjustment is determined by monitoring a pressure sensor mounted on the pump. The pressure sensor measures the head pressure and transmits the pressure values back to a computer where the pressure value is compared to a predetermined target value (which may be stored in a memory device). If the measured pressure value is different from the target value, then the VSD operates to change the motor speed in order to equalize the head pressure with the target pressure. In this manner, the motor speed is periodically changed in response to continual head pressure measurements and comparisons. 
     Despite their effectiveness, the viability of VSDs is hampered by significant adverse effects that occur during their operation. One adverse effect is the introduction of harmonics. Harmonics are sinusoidal voltages or currents having frequencies that are whole multiples of the frequency at which the supply system is designed to operate (e.g., 50 Hz or 60 Hz). The harmonics are generated by switching the transistors that are part of the VSD. Harmonics are undesirable because they can cause damage to peripheral devices (e.g., household appliances such as televisions, microwaves, clocks and the like) that are serviced by the power company supplying power to the VSD. As a result, some power companies have placed restrictions on the use of VSDs. 
     In addition to the damage caused to peripheral devices, the pump motor and associated power cable may themselves be damaged. Specifically, the high peak-to-peak voltage spikes caused by switching the VSD transistors increases the motor temperature and can damage the motor power transmission cable (due to the large difference between the spike voltage and the insulation value of the cable). As a result, the chance for premature equipment failure is increased. 
     Therefore, there exists a need for a control system that allows for the operation of pumps and other devices without the shortcomings of the prior arts 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a closed feedback system for operating peripheral devices (e.g., a flow controller) in response to operating information (e.g., environmental conditions). Illustrative operating information includes well bore pressure, line pressure, flow rates, fluid levels, and the like. 
     In one aspect, the invention provides a feedback system for a down hole pumping system. The down hole pumping system comprises a pump and a fluid line connected to the pump. The feedback system further comprises at least one sensor disposed and configured to collect operating variable information, a flow controller disposed in the fluid line, and a control unit coupled to the sensor. The control unit is configured to control operation of the flow controller in response to input received from the at least one sensor. 
     In another aspect, a feedback system for down hole applications, comprises a down hole pumping system comprising a pump, a motor connected to the pump, a fluid outlet line connected to the pump. The feedback system further comprises a flow controller disposed in the fluid outlet line, at least one sensor configured to collect operating information, and a control unit coupled to the down hole pumping system. The control unit is configured to process the operating information received from the at least one sensor to determine an operating variable value, compare the operating variable value with a target value, and then selectively issue a control signal to the flow controller. 
     In another aspect, a computer system for down hole applications is provided. The computer system comprises a processor and a memory containing a sensor program. When executed by the processor, the sensor program causes a method to be performed, the method comprising receiving a signal from at least one sensor configured to collect operating information from a down hole pumping system, processing the operating information to determine at least one operating variable value and comparing the operating variable value with a predetermined target value contained in the memory. If a difference between the operating variable value and the predetermined target value is greater than a threshold value, a flow control signal is output to a flow controller. 
     In another aspect, a method for operating a control unit to control peripheral devices while pumping a well bore is provided. The method comprises receiving a signal from at least one sensor configured to collect operating information from a down hole pumping system, processing the operating information to determine at least one operating variable value and comparing the operating variable value with a predetermined target value contained in the memory. If a difference between the operating variable value and the predetermined target value is greater than a threshold value, a flow control signal is output to a flow controller. 
     In another aspect, a signal bearing medium contains a program which, when executed by a processor, causes a feedback control method to be performed. The method comprises receiving an operating information signal from a down hole pumping system sensor and processing the operating information signal to determine at least one operating variable value. The operating variable value is then compared with a predetermined target value and, if a difference between the operating variable value and the predetermined target value is greater than a threshold value, a flow control signal is output to a flow controller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a side view of a well bore having a pumping system disposed therein; the pumping system is coupled to a control unit. 
         FIG. 2  is a high level schematic representation of a computer system. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a closed feedback system for operating peripheral devices (e.g., a flow controller) in response to operating information (e.g., environmental conditions). Illustrative operating information includes well bore pressure, line pressure, flow rates, fluid levels, and the like. The following embodiment describes the operation of a flow controller disposed in a fluid line in response to operating variable values, e.g., pressure/flow readings taken in the flow line and the well bore. The pressure/flow measurements are then compared to target values. If necessary, the flow controller is closed or opened to control the rate of fluid flow through the line and thereby achieve the desired target values. In some situations a pump motor may be halted is the target values cannot be achieved. However, embodiments of the invention are not limited to controlling a flow controller or to measuring pressure/flow. For example, in another embodiment, motor operation variable values are measured and processed to determine the operation of a pump motor. Those skilled in the art will readily recognize other embodiments, within the scope of the invention, which use to advantage a closed loop feedback system for measuring a variety of variables in order to control peripheral devices. 
       FIG. 1  shows a side view of a well bore  105  lined with casing  110 . A submersible pumping system  115  disposed in the well bore  105  is suspended from a well head  120  by tubing  125 . The pumping system  115  comprises a pump  130  and a motor  135 . Exemplary submersible pumps are available from General Pump Manufacturer, Reda, and Centrilift. A particular pump is available from Weatherford International, Inc. as model number CBM30-MD. Exemplary motors are available from Exodyne, Hitachi, and Franklin Electric. Notably, the electric submersible pumping system  115  is merely illustrative. In other embodiments, the pump is not submersible and need not be electric. For example, the pumping system  115  may be a rod pump, a progressive cavity (PC) pump and the like. 
     Power is supplied to the motor  135  from a power supply  140  via a power cable  145 . When the motor  135  is energized, the pump  130  is actuated and operates to draw fluid from the well bore  105  into intake ports  150  at a lower end of the pump  130 . The fluid is then flowed upward through the pump  130 , through the tubing  125  and into a flow line  155  (which may be an integral part of tubing  125 ) that extends from the well head  120 . At a terminal end, the flow line  155  empties into a holding tank  160  where the fluid is deposited and later disposed of. 
     Delivery of power from the power supply  140  the motor  135  is selectively controlled by a control system  165 . The control system  165  is also coupled to a flow controller  170  and a plurality of sensors  183 A–D. In general, the control system  165  may be any combination of hardware and software configured to regulate the supply of power as well as control the operation of peripheral devices, such as the flow controller, as will be described below. 
     In one embodiment, the control system  165  comprises a disconnect switch  175  (e.g., a knife switch), a motor starter  180 , a mode switch  185 , and a computer system  190 . The disconnect switch  175  provides a main switch having an ON position and OFF position. As an initial matter, operation of the pumping system  115  requires that the disconnect switch  175  be in the ON position. In this position, power is made available to the motor starter  180  and the computer system  190 . In other embodiments, the computer system may be equipped with an alternative (or additional) power supply such as a battery pack. Subsequently, the mode switch  185  may be set to a desired position, e.g., manual, automatic or OFF. In an automatic position, the computer system  190  monitors selected variables (measured by the sensors) and provides appropriate output signals to peripheral devices, including the motor  135  and the flow controller  170 , as will be described in detail below. In a manual position, the computer system  190  is bypassed and operation of the motor  135  and the flow controller  170  is manually performed by a human operator. In either case, the motor starter  185  may then be energized (e.g., by pushing a start button) in order to initiate operation of the motor  135 . 
     In addition to regulating the supply of power to the motor  135 , the control system  165  also provides control signals to a flow controller  170  disposed in the flow line  155 . The flow controller  170  may be any device adapted to control the rate at which fluid flows through the flow line  155 . Illustratively, the flow controller  170  is a gate style flow controller. An exemplary flow controller is the F100-300 available from Fisher. Other flow controllers that may be used to advantage are available from Allen Bradley. 
     During a pumping operation, selected variables are monitored by the computer system  190 . Upon measuring the variables, the operating parameters of the motor  135  and the flow controller  170  may be changed by the computer system  190  in order to maintain target operating conditions. Measurement of the variables is facilitated by the provision of various sensors. Accordingly, a surface pressure sensor  183 A is disposed in the flow line  155 , downstream from the flow controller  170 . The sensor  183 A may be any device adapted to detect a line pressure in the flow line  155 . An exemplary sensor is the PDIG-30-P available from Precision Digital. The output from the sensor  183 A is delivered to the control system  165  via transmission cable  187 A. The type of transmission cable used is dependent upon the signal to be propagated trerethrough from the sensor  183 A. Illustratively, the signal is electrical and the transmission cable is copper wire. 
     In one embodiment, a flow rate sensor  183 C (also referred to herein as a “flow rate meter” or “flow meter”) is also disposed in the flow line  155 . In a particular embodiment, the flow rate sensor  183 C is integral to the flow controller  170 . The flow rate sensor  183 C may be any device adapted to measure a flow rate in the flow line  155 . An exemplary sensor is the 10-500 available from Flowtronics. The output from the flow meter  183 C is delivered to the control system  165  via transmission cable  187 C. Embodiments contemplate having both the sensor  183 A and the flow meter  183 C disposed in the flow line  155 . Alternatively, only one of either the sensor  183 A or the flow meter  183 C is disposed in the flow line  155 . Further, even where both the sensor  183 A and the flow meter  183 C are provided, in some applications, only one is utilized to record readings. 
     A down hole pressure sensor  183 B is located at an upper end of the pumping system  115 . In particular, the sensor  183 B is positioned adjacent an upper end of the pump  130  so that the sensor  183 B remains submersed while the pump  183 B is completely submersed. Illustratively, the sensor  183 B is clamped to the flow line  155  at the outlet from the pump  130 . In such a position, the down hole pressure sensor  183 B is configured to measure the head pressure of the fluid in the well bore  105 . An exemplary sensor is the PDIG-30-P available from Precision Digital. The output from the sensor  183 B is delivered to the control system  165  via transmission cable  187 B, which is selected according to the signal to be propagated therethrough (e.g., electrical, optical, etc.). 
     Further, a motor sensor  183 D is disposed in the control system  165  and is configured to measure selected variables during operation of the motor  135 . Illustratively, such variables include current, load and voltage. In general, motor sensors include control transformers that can be electrically coupled to the power cable  145 . An exemplary sensor is the CTI available from Electric Submersible Pump. Another sensor is the Vortex available from Centrilift. The output from the sensor  183 D is delivered to the computer system  190  for processing. 
     Measurements made by the sensors  183 A–D are transmitted as propagating signals (e.g., electrical, optical or audio depending on the sensor type) to the computer system  190  where the signals are processed. Depending on the value of the variables, control signals may be output by the computer system  190  in order to adjust the operating parameters of the motor  135  and/or flow controller  170 . Accordingly, the computer system  190 , the sensors  183 A–D and the peripheral devices to be controlled (e.g., the motor  135  and the flow controller  170 ) make up a closed feedback loop. That is, the operation of the peripheral devices is dependent upon the variables being monitored and input to the computer system  190 . 
     A schematic diagram of the control system  165  is shown in  FIG. 2 . It should be noted that the control system  165  shown in  FIG. 2  is merely illustrative. In general, the control system  165  may be any combination of hardware and software configured to execute the methods of the invention. Thus, while the control system  165  is described as an integrated microprocessing system comprising one or more processors on a common bus, in some embodiments the control system  165  may include programmable logic devices, each of which is programmed to carry out specific functions. For example, a first logic device may be programmed to respond to signals from the pressure/flow sensors  183 A–C while a second logic device is programmed to respond to signals from the motor sensor unit  183 D. Persons skilled in the art will recognize other embodiments. 
     As noted above, the control system  165  generally comprises the disconnect switch  175 , the motor starter  180  and the computer system  190 . The computer system  190  includes a processor  210  connected via a bus  212  to a memory  214 , storage  216 , and a plurality of interface devices  218 ,  220 ,  222 ,  224  configured as entry/exit devices for peripheral components (e.g. end user devices and network devices). The interface devices include an A/D converter  218  configured to convert incoming analog signal from the sensors  183 A–D to digital signals recognizable by the processor  210 . A motor starter interface  220  facilitates communication between the computer system  190  and the motor starter  180 . 
     Embodiments of the invention contemplate remote access and control (e.g., wireless) of the computer system  190 . Accordingly, in one embodiment, a communications adapter  222  interfaces the computer system  190  with a network  225  (e.g., a LAN or WAN). 
     Additionally, an I/O interface  224  enables communication between the computer system  190  and input/output devices  226 . The input/output devices  226  can include any device to give input to the computer  190 . For example, a keyboard, keypad, light-pen, touch-screen, track-ball, or speech recognition unit, audio/video player, and the like could be used. In addition, the input/output devices  226  can include any conventional display screen. Although they may be separate from one another, the input/output device  226  could be combined as integrated devices. For example, a display screen with an integrated touch-screen, and a display with an integrated keyboard, or a speech recognition unit combined with a text speech converter could be used. 
     The processor  210  includes control logic  228  that reads data (or instructions) from various locations in memory  212 , I/O or other peripheral devices. The processor  210  may be any processor capable of supporting the functions of the invention. One processor that can be used to advantage is the Aquila embedded processor available from Acquila Automation. Although only one processor is shown, the computer system  190  may be a multiprocessor system in which processors operate in parallel with one another. 
     In a particular embodiment, memory  212  is random access memory sufficiently large to hold the necessary programming and data structures of the invention. While memory  212  is shown as a single entity, it should be understood that memory  212  may in fact comprise a plurality of modules, and that memory  212  may exist at multiple levels, from high speed registers and caches to lower speed but larger DRAM chips. 
     Memory  212  contains an operating system  229  to support execution of applications residing in memory  212 . Illustrative applications include a motor sensor unit program  230  and a pressure sensor program  232 . The programs  230 ,  232 , when executed on processor  210 , provide support for monitoring pre-selected variables and controlling the motor  135  and the flow controller  170 , respectively, in response to the variables. In addition, memory  212  also includes a data structure  234  containing the variables to be monitored. Illustratively, the data structure  234  contains pressure set points, flow rate set points, timer set points, and motor set points (e.g., current, voltage and load). The parameters contained on the data structure  234  are configurable by an operator inputting data via the input/output devices  226  while the pumping system  115  is running or idle. In addition, the parameters may include default settings that are executed at startup unless otherwise specified by an operator. The contents of the memory  212  may be permanently stored on the storage device  214  and accessed as needed. 
     Storage device  214  is preferably a Direct Access Storage Device (DASD), although it is shown as a single unit, it could be a combination of fixed and/or removable storage devices, such as fixed disc drives, floppy disc drives, tape drives, removable memory cards, or optical storage. Memory  212  and storage  214  could be part of one virtual address space spanning multiple primary and secondary storage devices. 
     In one embodiment, the invention may be implemented as a computer program-product for use with a computer system. The programs defining the functions of the preferred embodiment (e.g., programs  230 ,  232 ) can be provided to a computer via a variety of signal-bearing media, which include but are not limited to, (i) information permanently stored on non-writable storage media (e.g. read-only memory devices within a computer such as read only CD-ROM disks readable by a CD-ROM or DVD drive; (ii) alterable information stored on a writable storage media (e.g. floppy disks within diskette drive or hard-disk drive); or (iii) information conveyed to a computer by communications medium, such as through a computer or telephone network, including wireless communication. Such signal-bearing media, when carrying computer-readable instructions that direct the functions of the present invention, represent alternative embodiments of the present invention. It may also be noted that portions of the product program may be developed and implemented independently, but when combined together are embodiments of the present invention. 
     During operation of the pumping system  115 , conditions will arise which adversely effect the motor and/or the pump  130 . For example, common occurrences in down hole pumping include “gas lock,” pump plugging, high motor voltage spikes, high or low motor current and other failure modes. Left unattended, these conditions can cause damage to the pump  130  and/or motor  135 . Accordingly, the present invention provides embodiments for monitoring and responding to select operating variables. In particular, the control system  165  receives input from the sensors  183 A–D and processes the input to determine whether operating conditions are acceptable. 
     The operation of the control system  165 , during execution of the sensor program  232 , may be described with reference to  FIG. 1  and  FIG. 2 . The following discussion assumes that the disconnect switch  175  is in the ON position to and the motor  135  is energized so that the pump  130  is operating to pump fluid from the well bore  105 . In addition, it is assumed that the computer system  190  has been initialized and is configured with the appropriate timer information, pressure set points, flow rate set points and motor set points. Illustratively, the timer and set point information is permanently stored in storage  214  and written to the memory  212  by processor  210  when the computer system  190  is initialized. However, the information may also be manually provided by an operator at the time of startup. 
     Following initialization of the control system  165 , the flow controller  170  maybe in a fully open position, thereby allowing unrestricted flow of fluid through the flowline  155  into the holding tank  160 . During continued operation, the sensors  183 A–C collect information which is transmitted to the computer  190  via the respective transmission cables  187 A–C of the sensors  183 A–C. The information received from the sensors  183 A–C is then processed by the computer system  190  to determine pressure values and flow values, according to the sensor type. Specifically, the information received from the surface pressure sensor  183 A is processed to determine a fluid pressure at a point within the flowline  155  downstream from the flow controller  170 . The information received from the downhole pressure sensor  183 B is processed to determine a head pressure of the fluid within the well bore  105 . The flow meter  183 C provides information regarding a flow rate in the flow line  155 . 
     The calculated pressure/flow values are then compared to the pressure/flow setpoints contained in the data structure  234 . A control signal is then selectively issued by the computer system  190 , depending on the outcome of the comparison. In general, the computer system  190  takes steps to issue a control signal to the flow controller  170  in the event of a difference between the pressure/flow values and the pressure/flow setpoints. In some embodiments, the difference between the pressure/flow values to the pressure/flow setpoints must be greater than a threshold value before the control signal is sent. Such a threshold allows for a degree of tolerance which avoids issuing control signals when only a nominal difference exists between the actual and desired operating conditions. In any case, issuance of a control signal is said to be “selective” in that issuance depends on the outcome of the comparison between the measured pressure/flow values and the pressure/flow setpoints. 
     An issued control signal results in an adjustment to the flow controller  170 . As described above, the flow controller  170  may initially be in a fully open position. Thus, a first control signal issued by the computer system  190  may be configured to close the flow controller  170 . The degree to which the flow controller  170  is closed is selected according to the desired pressure within the flowline  155 . More particularly, the setting of the flow controller  170  is selected to allow a high pumping speed while inhibiting gas flow into the pump  130 . Subsequent readings from the sensors  183 A–C are used to continually adjust the position of the flow controller  170  in order to maintain the desired pressure. 
     A typical operating pressure may be between about 25 psi and about 50 psi. During a pumping operations the pressure on the pump may vary due to changing conditions in the well for  105 . By adjusting the setting of the flow controller  170  according to the feedback loop of the present invention, the pressure experienced by the pump may be maintained within desired limits. 
     It should be noted that while one embodiment measures the head pressure of fluid in the well bore  105  as well as the line pressure in the flow line  155 , other embodiments measure only the head pressure (i.e., the well bore fluid pressure taken by sensor  183 B) or only line pressure (i.e., taken by the surface sensor  183 A). As between the two, the down hole sensor  183 B is preferred. The surface sensor  183 A merely provides additional information useful for identifying, for example, failure modes due to gas lock that would prevent fluid from flowing through the flow line  155 . In the case of a submersible pump, however, the down hole sensor  183 B provides important information about the head pressure of the fluid over the intake  150 , which in many cases is necessary to maintain proper operation of the pump  130 . 
     In addition to pressure and flow measurements received from the sensors  183 A–C, readings from the motor sensor  183 D are also used to advantage. Operating conditions are often experienced which can cause significant damage to the motor  135 . For example, solids may enter the pump  130  and create drag stress on the motor  135 . In the case of gas lock, the lack of fluid flowing through the pumping system  115  causes the motor  135  to run an extremely low loads. Therefore, the operating information collected by the motor sensor  183 D is processed by the computer system  190  to determine whether the motor  135  is operating within preset limits (as defined by the motor set points). If the motor  135  is operating outside of the present limits, adjustments are made to the flow controller  170  in attempt to stabilize the operation of the motor  135 . Consider, for example, a situation in which the computer system  190  determines a motor current below the motor current setpoint, indicating a possible gas lock. Corrective action by the computer system  190  may include signaling the flow controller  170  to close. This has the effect of increasing the pressure on the pump  130 , thereby causing the gas to exit the pump  130  and flow upwardly through the well bore  105  between the pumping system  115  and the casing  110 . The pumping system  115  may then continue to operate normally. 
     In some cases, however, the corrective action taken by the computer system  190  may not be effective in alleviating the undesirable condition. In such cases, it may be necessary to halt the operation of the motor  135  to avoid damage thereto. A determination of when to halt the operation of the motor  135  is facilitated by the timer information contained in the data structure  234 . The timer information defines a delay period during which the corrective action is taken. If the undesirable condition has not been resolved at the expiration of the delay period, operation of the motor  135  is halted. 
     While the foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow.