Abstract:
Gas lock resolution during operation of an electric submersible pump is provided. An example method, module, or computing hardware with software product, detects a gas lock during current operation of an electric submersible pump (ESP) and intervenes to relieve the gas lock without stopping the ESP. After sensing a gas lock condition, an example module calculates a pump speed for attempting gas lock resolution. The example module may decrease the speed of the ESP to flush the gas lock, and then reaccelerate the ESP to check that the gas lock has been eliminated. The example module may apply one or more stored motor speed patterns that iteratively seek a pump speed that succeeds in clearing the gas lock, without stopping the ESP. The example module has built-in protections to protect the ESP from thermal overload and other damage.

Description:
BACKGROUND 
       [0001]    A gas lock may occur when liquid and gas separate in the tubing above an electric submersible pump (ESP) and inside the pump itself. The ESP may be a multistage ESP with multiple ganged pumps powered by one or more motors. In the tubing, the liquid and gas characteristically separate with the gas on top and the liquid on the bottom, effectively forming a plug above the ESP against fluid flow. Inside the pump, by contrast, the situation may be reversed, with the liquid on the top and the gas on the bottom. The liquid level in the pump is based on the amount of fluid in the tubing above the ESP and the pressure that each stage produces at zero flow. The gas in the bottom of the pump is effectively a bubble preventing more fluid from entering the pump. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]    The detailed description is set forth with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. 
           [0003]    For this discussion, the devices and systems illustrated in the figures are shown as having a multiplicity of components. Various implementations of devices and systems, as described herein, may include fewer components and remain within the scope of the disclosure. Alternately, other implementations of devices and systems may include additional components, or various combinations of the described components, and remain within the scope of the disclosure. 
           [0004]      FIG. 1  is a block diagram of an example ESP system including a variable speed drive that has access to an example gas lock resolution module. 
           [0005]      FIG. 2  is a block diagram of an example ESP system including a variable speed drive that includes an example gas lock resolution module. 
           [0006]      FIG. 3  is a block diagram of an example ESP system including a variable speed drive that includes a computing device capable of running example gas lock resolution instructions from a tangible data storage medium. 
           [0007]      FIG. 4  is a diagram of an example motor speed pattern for resolving a gas lock in an ESP while the ESP is running. 
           [0008]      FIG. 5  is a block diagram of an example computing environment for the example gas lock resolution module. 
           [0009]      FIG. 6  is a flow diagram of an example process for resolving a gas lock in an example ESP while the ESP is running. 
           [0010]      FIG. 7  is flow diagram of an example process for applying a motor speed pattern to a pump motor for resolving a gas lock in an example ESP while the ESP is running. 
       
    
    
     DETAILED DESCRIPTION 
     Overview 
       [0011]    This disclosure describes example gas lock resolution during operation of an electric submersible pump (ESP). Features, systems, and methods for detecting and resolving (e.g., breaking) a gas lock in an electric submersible pump (ESP), while the ESP is currently operating, are provided. An example system contains a module or a software product that senses a gas lock while a pump or an ESP string is running, and applies actions to the pump system, while still running, to remedy the gas lock and return the pump system to its full production, without fully stopping. However, the example system also contains built-in protections, so that the example module or software product prevents motors and pumps of the system from damage from the gas lock or the gas lock remedial measure applied. A pump motor can be harmed, depending on the particular configuration, for example, if it overheats, runs dry too long, undergoes too great a load, operates at too low of a voltage, and so forth. 
       Example System 
       [0012]      FIG. 1  shows an example pumping system  100  that includes an electric submersible pump (ESP)  102 , a surface controller, such as variable speed drive (VSD)  114 , and an example gas lock resolution module  104  for eliminating trapped gas (“gas lock”) that may occur while the ESP  102  is running. Gas lock causes loss of suction and fluid thrust while the pump  102  is running, effectively causing a production plug, and can foster impeller cavitation, motor degradation, and other damaging effects. 
         [0013]    The example pumping system  100 , and specifically the ESP  102 , may include a variety of functional sections and components depending on the particular application or environment in which the system  100  is used. Component sections of the example ESP  102  may include, for example, at least one pump  106 , at least one motor  108 , and at least one motor protector  110  between each pump  106  and associated motor  108 . Instances of these component sections may be coupled together to form repeating stages or segments of the example ESP  102 , referred to as an ESP string. 
         [0014]    Power is provided to the example ESP  102  via a power cable  112  connected between a pump controller, such as a variable speed drive (VSD)  114 , and the motor  108 . Other sensing and control cables  116  may also accompany the power cable  112  along its route between the VSD  114  and the motor  108  of the ESP  102 . The motor  108  in turn, drives the pump  106 , which draws in production fluid from the surrounding well. Within the pump  106 , for example a centrifugal pump, multiple impellers may rotate to impel the production fluid through a connector section  118  and through production tubing  120  to a desired collection destination on the ground surface above. 
         [0015]    The example pumping system  100  is only one example of many types of submersible pumping systems that can benefit from the features described herein. Multiple pump stages  106  and multiple motors  108  can be added to the ESP lineup to make a longer string. Additionally, the production fluids may be pumped to a collection location partly through an annulus space around the ESP  102 . The example ESP  102  can use different types of pump stages, such as centrifugal, mixed flow, radial flow stages, and so forth. 
         [0016]    In an implementation, when a gas lock occurs, the example gas lock resolution module  104  attempts to break or resolve the gas lock, for example, by strategically slowing down the speed of the ESP. The example gas lock resolution module  104  may control the variable speed drive (VSD)  114  to vary power (voltage and/or amperage) to one or more motors  108  to implement the gas lock resolution. In one scenario, slowing down the ESP  102  decreases the pressure that each stage of the ESP  102  produces, pushing the liquid level lower. As the speed decreases, the pressure that the entire pump  102  produces eventually decreases to the point at which the entire pump  102  cannot support the weight of the fluid in the production tubing  120  above it, effectively flushing all the gas from the pump  102 . At that point, the ESP  102  can be reaccelerated to a normal or nominal operating speed, and during this gas-lock-breaking process, the ESP  102  never has to stop. Enabling the ESP  102  to continue running during elimination of a gas lock has numerous advantages, including avoiding an enormous energy requirement needed to restart induction motors from a standstill, and avoiding load and wear on bearings, races, and thrust washers when the ESP string  102  has to begin moving all of the liquid above it from a standstill. Thus, resolving a gas lock while the ESP  102  is running prevents the loss of the entire lift momentum of the column of liquid in the production tubing  120  above the pump  102 , which is under significant hydrostatic pressure. 
       Example System Configurations 
       [0017]    In  FIG. 1 , the example gas lock resolution module  104  may include various components, such as a gas lock detector  122 , a lock elimination module (or logic)  124 , a motor speed (or frequency) controller  126 , and an ESP protection module  128 , for example. The gas lock resolution module  104  shown in  FIG. 1  is only one example of a gas lock breaker or resolver for use with operating ESP&#39;s  102 . Other configurations of the gas lock resolution module  104  with different components or different arrangement of components are contemplated within the scope of the representative examples described herein. 
         [0018]      FIG. 2  shows the gas lock resolution module  104  of  FIG. 1  as part of the VSD  114  or other ESP controller, as opposed to a separate module differentiated from the VSD  114 , as in  FIG. 1 . The gas lock resolution module  104  may be built into the fabric of the VSD  114  or may be added as a retrofit or option, for example. 
         [0019]      FIG. 3  shows an example VSD  114  that contains a computing device  300 , or that has intrinsic computing powers and components. The example VSD  144  is capable of receiving tangible data storage media  302  or communicating with tangible data storage media  302  containing the gas lock resolution module  104  as an application, software, programming instructions, computer program, executable code, machine instructions, and so forth. A tangible data storage medium  302  may be an optical disk, a flash drive, a remote hard drive, a remote Internet server, and so forth. 
       Example Gas Lock Resolution 
       [0020]    Referring to  FIG. 1 , the gas lock detector  122  of the gas lock resolution module  104  can detect a gas lock in numerous ways. In an implementation, the gas lock detector  122  detects a gas lock via a surface flow meter, i.e., when flow becomes equal to zero, but the speed of the motor  108  or pump  106  does not equal zero. This technique provides a logical and sometimes easy way to detect a gas lock in the example system  100 , when downhole monitoring is difficult because of temperature, as with steam-assisted gravity drainage (SAGD), or when significant surface measurement is already available at a particular site. In some systems, a surface controller ( 114 ) can determine that the ESP  102  is still operational (still rotating or attempting to pump). 
         [0021]    The gas lock detector  122  may also detect a gas lock by changes or stabilizations in measured amperage, for example, from the VSD  114  to the ESP  102 . Depending on the specifics of the particular gas lock that has occurred and the particular pump curve, a drop and/or stabilization in measured amperage may indicate that an ESP  102  is gas locked. This technique is particularly useful for applications that have no downhole gauge. 
         [0022]    In an implementation, the gas lock detector  122  uses an increase in pump intake pressure (PIP) to diagnose a gas lock for the ESP  102 . When no flow rate measurements are available, the downhole annulus pressure near the pump  106  (hence, “pump intake pressure”) is serviceable for detecting gas lock. If the pump  106  is gas locked, the pump intake pressure, PIP, will increase, with the rate of increase dependent on the well specifics (casing size, tubing size, well productivity, etc.). A known rate of pressure increase for an individual ESP  102  and well can provide a configurable setting in a drive  114  or other surface unit that is measuring the pump intake pressure (PIP). The surface unit may also be “smart” and in an implementation can learn the rate of increase based on shut downs or changes in speeds. 
         [0023]    Combined measurements or features may also be used by the gas lock detector  122  to detect gas lock, for example, the gas lock detector  122  can use a combination of variables selected from amperage measurement, pump intake pressure, motor temperature, discharge pressure, and so forth. 
         [0024]    The gas lock detector  122  may also apply downhole flow monitoring to detect gas lock. Downhole flow measurements can indicate a gas lock directly and immediately. Downhole flow measurement can be gathered by tools such as a triple-pressure permanent gauge or an ESP gauge that has a venturi flow meter. A zero downhole flow rate while the ESP  102  is running can indicate gas lock immediately. 
         [0025]    Once a gas lock is detected, then the gas lock elimination module  124  begins implementing automatic breaking or other resolution of the gas lock. The gas lock elimination module  124  also aims to determine whether the resolution of the gas lock has been successful. 
         [0026]    In an implementation, the gas lock elimination module  124  signals the motor speed controller  126  to decrease the speed of the ESP  102  to a lower speed corresponding to a frequency of approximately 35 Hertz for approximately five minutes. Then the gas lock elimination module  124  reaccelerates the ESP  102  to a nominal speed to determine if flow at the surface is reestablished. If the intervention does not resume the flow, then in an example implementation, the ESP protection module  128  shuts down the ESP  102 . Shutting down the ESP  102  can break the gas lock (albeit this stops the ESP too) but more importantly protects the motor from overheating, from cavitation, and so forth. 
         [0027]    In an implementation, the gas lock elimination module  124  calculates an effective pump speed for resolving the gas lock. The calculation can use a downhole measurement of differential pressure (e.g., discharge pressure minus intake pressure) or an estimation of the differential pressure. The gas lock detector  122  may have access to sensor data from a downhole monitor that measures intake pressure and discharge pressure. The gas lock elimination module  124  then calculates the pump speed effective to break the gas lock. For example, the VSD  114  or other surface controller may have a nominal reference frequency (ω REF ) and may also have possession of the pressure that the installed ESP generates at zero flow, at the reference frequency (P REF ). Then, with a measured differential pressure (ΔP) during gas lock, the gas lock elimination module  124  calculates the expected effective speed to break the gas lock, as in example Equation (1): 
         [0000]    
       
         
           
             ω 
             = 
             
               
                 ω 
                 REF 
               
                
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     P 
                   
                   
                     P 
                     REF 
                   
                 
               
             
           
         
       
     
         [0028]    The gas lock elimination module  124  may implement safety factors with this strategy and example calculation. For example, the gas lock elimination module  124  may apply a speed to break the gas lock that is associated with a frequency that is approximately 1 Hertz lower (for example) than that of the calculated effective speed, or may use a percentage of the calculated effective speed, such as 90% of the calculated effective speed, to break the gas lock. This builds-in some tolerance for the variability of the densities of the fluids being pumped by the ESP  102 . 
         [0029]    Instead of measuring the differential pressure, the example gas lock elimination module  124  may estimate an effective speed for breaking the gas lock by measuring an intake pressure, and then estimating or assuming the discharge pressure, proceeding with the example calculation above in Equation (1). For example, the VSD  114  or other controller may already be in possession of a set value for the estimated discharge pressure that can be used in the example calculation of Equation (1). Or, the gas lock elimination module  124  may extend a user interface and ask for user-provided settings, such as a percentage of the intake pressure, or “%-full” entry that can be used to estimate an effective discharge pressure for breaking the gas lock. 
         [0030]      FIG. 4  shows an example motor speed pattern  400  for safely resolving a gas lock in a running ESP  102 . In an implementation, the gas lock elimination module  124  may apply smart methods, embodied in such stored motor speed patterns  400 , to determine an effective pump speed for breaking the gas lock. Without a measured intake pressure, determining a pump speed that breaks a gas lock can be guesswork. But an example gas lock elimination module  124  can find an effective pump speed by signaling the motor speed controller  126  in accordance with such an example motor speed pattern  400  to vary the motor speed of the ESP  102 . For example, the motor speed pattern  400  may vary the motor speed in increasingly deeper troughs, to find an effective gas-lock-breaking pump speed while the pump is still operational, iteratively applying progressively lower pump speeds. The pump  106  eventually arrives at a “highest” low pump speed needed to break the gas lock, without using a lower pump speed than necessary. The gas lock elimination module  124  may also use such an example motor speed pattern  400  to learn a best pump speed for dispelling a gas lock, through trial and error. 
         [0031]    In an example motor speed pattern  400 , the gas lock elimination module  124  implements a first decreased speed  402  and then reaccelerates to the nominal speed  404  of the ESP  102  to determine if the first decreased speed  402  was successful in breaking the gas lock. The increase in pump speed at the peaks of the motor speed pattern  400 , such as reacceleration peak  404 , are important between decreased-speed troughs, such as decelerations  402  and  406  in order to determine if the gas lock has been resolved. If the first decreased pump speed  402  does not work to resolve the gas lock, then a second decreased speed  406  that is lower than the first decreased speed  402 , is attempted, in an iterative approach. In an implementation, the gas lock elimination module  124  attempts a decreased speed  402  or  406 , etc., and if the decreased speed  402  works to resolve the gas lock, then the gas lock elimination module  124  remembers the speed  402 , storing the effective speed  402  in data storage. 
         [0032]    In an implementation, when the first decreased pump speed  402  of the motor speed pattern  400  does not resolved that gas lock, then the ESP protection module  128  shuts down the ESP  102  to resolve the gas lock while protecting the ESP  102 , and tries a lower speed  406  of the example motor speed pattern  400  only on the following detection of a gas lock in the ESP  102 . The gas lock elimination module  124  can thus be programmed to store effective pump speeds for resolving a gas lock, or can learn such effective pump speeds for resolving gas lock. 
         [0033]    Once the gas lock detector  122  determines that a gas lock is present and the gas lock elimination module  124  initiates a gas lock breaking technique, the gas lock elimination module  124  detects success or failure of the breaking technique and the ESP protection module  128  preserves the integrity or safety of the ESP  102  in case the gas-lock-breaking technique is unsuccessful. In an implementation, the ESP protection module  128  may provide protection if the gas locking is not broken after one trial, for example, as detected by a surface production rate after reaccelerating the ESP  102 . Then the ESP  102  is stopped for its own protection. 
         [0034]    When the gas lock resolution module  104  has access to flow monitoring (surface or downhole), it is easy to detect successful resolution of the gas lock. Without flow monitoring, however, it can be difficult to determine that the gas lock has been successfully broken. With access to a downhole gauge, a decrease in pump intake pressure (PIP) after an acceleration (e.g.,  404 ) following a gas-break attempt is a reliable indicator that the ESP  102  is pumping fluid again. Additional ways to determine that the gas lock has been broken may be also used. For example, an increase in pump discharge pressure (PDP) during the reacceleration  404  indicates that fluid is entering the tubing and that the ESP  102  is no longer gas locked. An increase in surface temperature of the pumped fluid or surface pressure of the pumped fluid, when surface measures are available, indicate that flow is reaching the surface again. The gas lock resolution module  104  may use these detection techniques, for example, when there is no downhole gauge available. 
         [0035]    The gas lock resolution module  104  may also sense an increase in amperage to the ESP  102  compared to amperage at initiation of gas locking to determine success of breaking the gas lock. If the only measured parameter available is amperage, then the amperage at the time the ESP  102  accelerates due to the onset of gas lock may be compared to the initial amperage sensed when the ESP  102  was pumping fluid. When the well starts flowing again, then the amperage being used increases as compared with the relatively load-free state of operation during gas lock. 
         [0036]    The ESP protection module  128  may implement protective measures during automated gas lock breaking. For example, during a gas lock breaking process, the protection applied may include stopping the gas lock breaking attempts when there is no success after a time limit. Or, the ESP protection module  128  may stop the ESP  102  when a downhole temperature or a motor temperature has been exceeded before successfully breaking the gas lock. Or again, the ESP protection module  128  may stop the ESP  102  upon exceeding a certain number of attempts without success. 
         [0037]      FIG. 5  shows an example computing or hardware environment, e.g., example device  300 , for hosting an embodiment of the gas lock resolution module  104 . Thus,  FIG. 3  illustrates an example device  300 , computer, computing device, programmable logic controller (PLC), or the like, that can be implemented to monitor and analyze sensor data, and control or intervene to resolve a gas lock in an ESP  102  and thereby provide improved operation, high reliability, and high-availability to an ESP string  102 . 
         [0038]    In  FIG. 5 , the example device  300  is only one example and is not intended to suggest any limitation as to scope of use or functionality of the example device  300  and/or its possible architectures  504 . Neither should the example device  300  be interpreted as having any dependency or requirement relating to any one or a combination of components illustrated in  FIG. 5 . 
         [0039]    Example device  300  includes one or more processors or processing units  506 , one or more memory components  508 , one or more input/output (I/O) devices  510 , a bus  512  that allows the various components and devices to communicate with each other, and includes local data storage  514 , among other components. 
         [0040]    The memory  508  generally represents one or more volatile data storage media. Memory component  508  can include volatile media (such as random access memory (RAM)) and/or nonvolatile media, such as read only memory (ROM), flash memory, and so forth. 
         [0041]    Bus  512  represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. Bus  512  can include wired and/or wireless buses. 
         [0042]    Local data storage  514  can include fixed media (e.g., RAM, ROM, a fixed hard drive, etc.) as well as removable media (e.g., a flash memory drive, a removable hard drive, optical disks, magnetic disks, and so forth). 
         [0043]    One or more input/output devices  510  can allow a user to enter commands and information to example device  300 , and also allow information to be presented to the user and/or other components or devices. Examples of input devices include a keyboard, a cursor control device (e.g., a mouse), a microphone, a scanner, and so forth. Examples of output devices include a display device (e.g., a monitor or projector), speakers, a printer, a network card, and so forth. 
         [0044]    A user interface device may also communicate via a user interface (UI) controller  516 , which may connect with the UI device either directly or through the bus  512 . 
         [0045]    A network interface  518  can communicate with hardware, directly or indirectly, such as a VSD  114  or a variable frequency drive (VFD), sensors, flow meters, downhole gauges, valves, and so forth. The network interface  518  may also communicate with the Internet or another network, to send data or receive the gas lock resolution module  104  as instructions from a remote tangible data storage medium  302  such as a remote hard drive or a remote Internet server. 
         [0046]    A media drive/interface  520  accepts tangible data storage media  302 , such as flash drives, optical disks, removable hard drives, software products, etc. Logic, computing instructions, applications, or a software program comprising elements of the gas lock resolution module  104  may reside on removable tangible data storage media  302  readable by the media drive/interface  520 . 
         [0047]    Various techniques and the components of the gas lock resolution module  104  may be described herein in the general context of software or program modules, or the techniques and modules may be implemented in pure computing hardware. Software generally includes routines, programs, objects, components, data structures, and so forth that perform particular tasks or implement particular abstract data types. An implementation of these modules and techniques may be stored on or transmitted across some form of tangible computer readable data storage media  302 . Computer readable media can be any available data storage medium or media that is tangible and can be accessed by a computing device. Computer readable media may thus comprise computer storage media. 
         [0048]    “Computer storage media” include volatile and non-volatile, removable and non-removable tangible media implemented for storage of information such as computer readable instructions, data structures, program modules, or other data. Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other tangible medium which can be used to store the desired information, and which can be accessed by a computer or a device  300  with a processor  506  and memory  508 . 
       Representative Processes 
       [0049]      FIG. 6  shows a representative process  600  for resolving a gas lock in a running electric submersible pump (ESP). The example process  600  is shown as individual blocks. The process  600  can be implemented by hardware, or combinations of hardware and machine instructions. For example, the process  600  can be implemented by the example gas lock resolution module  104 . 
         [0050]    At block  602 , a gas lock is detected in an ESP while the ESP is running. The detection may be made directly by sensors, gauges, and meters, or inferred by changes in fluid flow, temperature, input and output pressures, pump speed, amperage consumed at a pump motor  108 , and so forth. 
         [0051]    At block  604 , the gas lock is resolved while the ESP is still running, at least by temporarily decreasing a speed of the ESP, without stopping the ESP. Strategically slowing down the pump allows the equilibrium of the gas and fluid involved in the gas lock to shift, often using the hydrostatic pressure of the fluid column over the pump to flush trapped gas and reestablish pump thrust. However, if a strategic gas lock resolution measure does not work, the process  600  may shut down the pump to protect and ESP and relieve the gas lock. 
         [0052]      FIG. 7  shows another representative process  700  for resolving a gas lock in a running electric submersible pump (ESP). The example process  700  is shown as individual blocks. The process  700  can be implemented by hardware, or combinations of hardware and machine instructions. For example, the process  700  can be implemented by the example gas lock elimination module  124 . 
         [0053]    At block  702 , a gas lock is detected in a running ESP string. 
         [0054]    At block  704 , a motor speed pattern is sent to a motor controller of the ESP. 
         [0055]    At block  706 , the motor speed pattern iteratively decelerates and reaccelerates the pump motor, with each deceleration descending to a lower pump speed than the previous pump speed deceleration. 
         [0056]    Other motor speed patterns may be applied, such as a lower pump speed and a shorter (or longer) duration of deceleration for each successive deceleration trough. 
         [0057]    At block  708 , elimination of the gas lock is tested for at each reacceleration applied by the motor speed pattern to determine if the gas lock resolution is successful. 
       CONCLUSION 
       [0058]    Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the subject matter. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.