Patent Publication Number: US-2020300050-A1

Title: Frac pump automatic rate adjustment and critical plunger speed indication

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of co-pending U.S. Provisional Patent Application Ser. No. 62/821,130 filed Mar. 20, 2019 titled “FRAC PUMP AUTOMATIC RATE ADJUSTMENT AND CRITICAL PLUNGER SPEED INDICATION,” the full disclosure of which is hereby incorporated herein by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     1. Technical Field 
     This disclosure relates generally to hydraulic fracturing and more particularly to systems and methods controlling one or more pump operating parameters. 
     2. Background 
     Hydraulic fracturing operations may include a number of high pressure pumps directing fluid into a common manifold or missile. Adjustments to any of the operating pumps may impact the others, and as a result, it may be difficult to tune pumps during operations without using an iterative approach, which may be time consuming, inefficient, and could damage equipment. For example, pumps operating at a common flow rate or critical plunger speed may generate impacts on the manifold or missile at the same time, which may lead to vibrational damage. Moreover, impacts at a resonance frequency may lead to damage to wellbore equipment. 
     SUMMARY 
     The present disclosure is directed to systems and methods to automatically adjust one or more operating parameters of a pump. 
     In an embodiment, a method for regulating a pumping rate of an electrically powered hydraulic fracturing pump includes receiving a step rate one or more pumps, the step rate limit corresponding to at least one of a minimum step rate or a maximum step rate. The method also includes determining a desired pumping rate for the one or more pumps. The method further includes determining a current rate of the one or more pumps. The method includes comparing the desired pumping rate to the current rate. The method also includes determining, based at least in part on the comparison, an adjustment to the current rate. The method further includes determining the adjustment does not exceed the step rate limit. The method includes applying the adjustment to the current rate of the one or more pumps. 
     In an embodiment, a method for regulating one or more pumping rates of an electrically powered hydraulic fracturing pump system includes receiving a desired pumping rate for a first pump. The method also includes determining a current pumping rate of an adjacent or opposite second pump. The method further includes determining a difference between the desired pumping rate and the current pumping rate is within a threshold amount. The method includes applying an adjustment to the desired pumping rate. 
     In an embodiment, a hydraulic fracturing system for fracturing a subterranean formation includes a plurality of electric powered pumps, the plurality of electric powered pumps coupled to a well associated with the subterranean formation and powered by at least one electric motor, the plurality of electric powered pumps configured to pump fluid into a wellbore associated with the well at a high pressure so that the fluid passes from the wellbore into the subterranean formation and fractures the subterranean formation. The system also includes one or more sensors receiving operating information from the plurality of electric powered pumps. The system further includes a control system receiving the operating information and controlling at least one operating parameter of the plurality of electric powered pumps, wherein the control system is configured to apply respective step rates to adjust respective pumping rates for the plurality of electric powered pumps. 
     In an embodiment, adjustable minimum and maximum step changes in speed adjustment for frac pumps are incorporated into a pumping control system. 
     In an embodiment, automatic adjustments of frac pump flow rates are incorporated into a pumping control system. The adjustments may be to optimized speeds to avoid synchronization of plunger strokes with other pumps that are pumping into the same discharge manifold while holding the overall flow rate of the collective group of frac pumps constant. 
     In an embodiment, critical plunger speed indicators are incorporated into a pumping control system. The indicators may alert the frac pump operator when any manual adjustments may lead to increased individual pump rates that may result in the critical plunger speed being reached or warned that the critical speed is being approached. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Some of the features and benefits of the present disclosure having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic plan view of an embodiment of a fracturing operation, in accordance with embodiments of the present disclosure; 
         FIG. 2  is a block diagram of an embodiment of a fracturing pump, in accordance with embodiments of the present disclosure; 
         FIG. 3  is a block diagram of an embodiment of a control system utilizing with a pumping system, in accordance with embodiments of the present disclosure; 
         FIG. 4  is a flow chart of an embodiment of a method for adjusting a pump rate, in accordance with embodiments of the present disclosure; 
         FIG. 5  is a flow chart of an embodiment of a method for adjusting a pump rate, in accordance with embodiments of the present disclosure; 
         FIG. 6  is a flow chart of an embodiment of a method for adjusting a pump rate, in accordance with embodiments of the present disclosure; and 
         FIG. 7  is a flow chart of an embodiment of a method for adjusting a pump rate, in accordance with embodiments of the present disclosure. 
     
    
    
     While the disclosure will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the disclosure to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the disclosure as defined by the appended claims. 
     DETAILED DESCRIPTION 
     The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of 
     When introducing elements of various embodiments of the present disclosure, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters and/or environmental conditions are not exclusive of other parameters/conditions of the disclosed embodiments. Additionally, it should be understood that references to “one embodiment”, “an embodiment”, “certain embodiments”, or “other embodiments” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Furthermore, reference to terms such as “above”, “below”, “upper”, “lower”, “side”, “front”, “back”, or other terms regarding orientation or direction are made with reference to the illustrated embodiments and are not intended to be limiting or exclude other orientations or directions. Additionally, recitations of steps of a method should be understood as being capable of being performed in any order unless specifically stated otherwise. Furthermore, the steps may be performed in series or in parallel unless specifically stated otherwise. 
     Various control systems may be utilized to adjust minimum and maximum step changes for hydraulic fracturing pumps. For example, the pumps may be controlled via software that sends a signal to adjust one or more components of the hydraulic fracturing pumps, such as adjusting a speed of a corresponding motor. However, systems may be limited to banks of pumps (e.g., pump groups) that are utilized during a fracturing process. As a result, an adjustment to one pump may be propagated to the entire bank of pumps, which may be undesirable. Embodiments of the present disclosure enables software to determine and manage individual minimum and maximum step changes for each pump, independent of other pumps of the group or at the well site. As a result, particularized adjustments may be made, which may improve the pumping operation. Moreover, the step values may be stored and reported in common units that are easy for an operator to understand, such as barrels per min, gals, or the like. This improves traditional reporting systems that relay information in terms of motor rpm (e.g., electric motor rpm for electric frac pumps or engine, transmission, or pump rpm for diesel frac pumps). As a result, the operator may have a better understanding of how adjustments will impact pumping operations, as it may be easier to visualize a volumetric measurement of flow rather than a rotating speed of a component of the pump. 
     Embodiments of the present disclosure provide automated adjustments to frac pump flow rates to avoid or reduce the likelihood of synchronization of plunger strokes between pumps pumping into a common side of a discharge manifold. Moreover, embodiments of the present disclosure further adjust frac pump flow rates to maintain an overall flow rate of the collective group of pumps. Such an automated process provides an improvement over current, manual, iterative processes. That is, operators may adjust flow rate of one pump, evaluate pumping conditions, adjust a different pump, and so forth until a desired operating condition is achieved. This process is inefficient and could lead to damage to pumping components. 
     In various embodiments, data obtained from previous pumping operations may be utilized to predict or otherwise anticipate frac pump critical plunger speeds for a variety of pumping operations. That is, relationships may be developed, through data analysis, to correlate certain operating conditions to one or more desirable or undesirable states of operation. In other words, data may be utilized to determine or estimate a frac pump critical plunger speed, which may be referred to the plunger speed at which conditions for pump cavitation to occur are impending, based on the speed of the pump plungers and the acceleration head of the fluid moving into the plunger bores. 
       FIG. 1  is a plan schematic vie of an embodiment of a hydraulic fracturing system  10  positioned at a well site  12 . In the illustrated embodiment, pumps  14  (which may be arranged one or more trailers, skids, or the like), making up a pumping system  16 , are used to pressurize a slurry solution for injection into a wellhead  18 . An optional hydration unit  20  receives fluid from a fluid source  22  via a line, such as a tubular, and also receives additives from an additive source  24 . In an embodiment, the fluid is water and the additives are mixed together and transferred to a blender unit  26  where proppant from a proppant source  28  may be added to form the slurry solution (e.g., fracturing slurry) which is transferred to the pumping system  16 . The pumps  14  may receive the slurry solution at a first pressure (e.g., 80 psi to 160 psi) and boost the pressure to around 15,000 psi for injection into the wellhead  18 . In certain embodiments, the pumps  14  are powered by electric motors. 
     After being discharged from the pump system  16 , a distribution system  30 , such as a missile, receives the slurry solution for injection into the wellhead  18 . The distribution system  30  consolidates the slurry solution from each of the pumps  14  and includes discharge piping  32  coupled to the wellhead  18 . In this manner, pressurized solution for hydraulic fracturing may be injected into the wellhead  18 . 
     In the illustrated embodiment, one or more sensors  34 ,  36  are arranged throughout the hydraulic fracturing system  10  to measure various properties related to fluid flow, vibration, and the like. 
     It should be appreciated that while various embodiments of the present disclosure may describe electric motors powering the pumps  14 , in embodiments, electrical generation can be supplied by various different options, as well as hybrid options. Hybrid options may include two or more of the following electric generation options: Gas turbine generators with fuel supplied by field gas, CNG, and/or LNG, diesel turbine generators, diesel engine generators, natural gas engine generators, batteries, electrical grids, and the like. Moreover, these electric sources may include a single source type unit or multiple units. For example, there may be one gas turbine generator, two gas turbines generators, two gas turbine generators coupled with one diesel engine generator, and various other configurations. 
     In various embodiments, equipment at the well site may utilize 3 phase, 60 Hz, 690V electrical power. However, it should be appreciated that in other embodiments different power specifications may be utilized, such as 4160V or at different frequencies, such as 50 Hz. Accordingly, discussions herein with a particular type of power specification should not be interpreted as limited only the particularly discussed specification unless otherwise explicitly stated. Furthermore, systems described herein are designed for use in outdoor, oilfield conditions with fluctuations in temperature and weather, such as intense sunlight, wind, rain, snow, dust, and the like. In embodiments, the components are designed in accordance with various industry standards, such as NEMA, ANSI, and NFPA. 
       FIG. 2  is a schematic diagram of an embodiment of a fracturing pump  200  that includes a reciprocating plunger  202 . It should be appreciated that the embodiment illustrated in  FIG. 2  is simplified and has removed several components for clarity with the discussion herein. A fluid inlet  204  draws low pressure fluid into a pump body  206  and movement of the plunger  202  increases the pressure as the fluid exits the outlet  208 . It should be appreciated that the illustrated embodiment is for illustrative purposes only and that other types of pumps may be used, such as centrifugal pumps and the like. As described above in various embodiments, the speed of the plunger  202  may be indicative of cavitation within the pump  200 . As would be known, cavitation refers to the formation of vacuum bubbles in a liquid in which the liquid&#39;s vapor pressure has been reached. It is the implosion of these vacuum bubbles caused by movement of the plunger which may generate shock waves. This may lead to pitting in components of the pump  200  or undesirable vibrations, both of which can decrease the life of the pump  200 . 
       FIG. 3  illustrates an example pumping configuration  300  including a plurality of pumps (P)  200  coupled to a manifold  302 . It should be appreciated that the six pumps  200  shown in  FIG. 3  are for illustrative purposes only and that other embodiments may include more or fewer pumps. Furthermore, the illustrated embodiments include a common manifold  302 , but there may be other piping configurations used in various embodiments. 
     The pumps  200  are also communicatively coupled to a control system  304  that includes a controller  306 , a memory  308 , and a processor  310 . In the illustrated embodiment, the control system  304  is coupled to each pump  200  of the plurality of pumps  200  and may be configured to individually control one or more aspects of operation of the pump  200 , such as modifying conditions of the pump itself or associated components, such as upstream valves or a motor (e.g., an electric motor, a diesel powered motor) coupled to the pump (not pictured). 
     Embodiments of the present disclosure are directed to systems and methods for monitoring and/or adjusting operation of one or more pumps  200  within a group during a fracturing operation in order to reduce the likelihood of cavitation, among other effects, without impacting an overall group flow rate. 
     For example, the pump  200  may be communicatively coupled to a controller  306  that adjusts a minimum and maximum step change for the pump  200  during speed adjustments. As would be appreciated, the step change refers to a rate of change between two different operating points, such as speed. In various embodiments, the control system  304  may include executable programming code, for example stored on the memory device  308 , that enables the pump operator to enter the minimum and maximum step rates that can be selected while increasing or decreasing pump rates as required in hydraulic fracturing. The step rates can be chosen such that no adjacent or opposite pumps connected to either the missile trailer or the suction and discharge ground manifold will have the same step changes while increasing or decreasing pump rates. As a result, operating using the control system  304  minimizes the chances of pumps running at synchronized plunger speeds that could introduce a harmonic vibration into the connected equipment system. 
     In the example described above, step changes between the pumps may be programmed as maximum and minimum values in order to reduce upsets in operation. Furthermore, changes between associated pumps (e.g., a group of pumps on one side of the manifold, opposite facing pumps across the manifold, etc.) may be adjusted in response to adjustments to one or more associated pumps. For example, in the embodiment of  FIG. 3 , the pumps  200  may be labeled with letters, such as pumps  200 A- 200 F. Each pump may have a different step change or pump rate. Embodiments of the present disclosure may be directed toward eliminating situations where pump rates of adjacent or opposite facing pumps are the same or within a threshold amount. By way of example only, a pump rate associated with the pump  200 A would be different from the pump rates for  200 B and  200 D. Similarly, a pump rate for  200 B would be different from pump rates for  200 A,  200 C, and  200 E. 
     Additional embodiments may provide automatic pump rate adjustment. For example, a pump operator can choose any or all of the frac pump that are connected for hydraulic fracturing operations to be active and then enter the desired total downhole pump rate for that collection of pumps into a human-machine interface (HMI) screen for pump control. The pump operator an then manually increase or decrease pump rates utilizing the feature above (e.g., adjustable minimum and maximum step rate changes) for all of the selected active frac pumps. As a result, the desired flow rate may be changed in stages or gradually to reduce the likelihood of equipment upsets. 
     Furthermore, when the pump operator gets fairly close (e.g., within a threshold) to the overall desired flow rate of the collective pumps, the control system  304  may be utilized to automatically fine tune the rates on each pump  200  such that no adjacent or oppositely positioned pumps are within 5% (adjustable) of the same crankshaft rpm (or motor rpm if an electric motor is turning the pump), while maintaining the desired constant total flow rate. Information regarding flow rates, motor rpm, crankshaft rpm, and the like may be provided to the control system via one or more sensors  312  that may be arranged around and/or on the pump, such as the sensors  34 ,  36  shown in  FIG. 1 . 
     In various embodiments, a damage accumulation calculation factor may also be incorporated into the control system  304  to adjust operation of one or more pumps  200 . The damage accumulation calculation factor provides information associated with a likelihood of damage exhibited by a pump. As a result, the control system may utilize a damage threshold to control operation and/or adjustments to the pump. For example, based at least in part the damage accumulation calculation factor, the control system could intelligently not speed up a pump exhibiting a high damage accumulation factor, and likewise apply speed increase to only those pumps with lower damage accumulation factors. The speed differentials should eliminate “superposition” of vibration (also termed as “beating phenomenon”) within the piping system due to adjacent pumps with synchronized plunger flow ripple patterns. This process could then be repeated for any more pumps that the operator would like to bring on line. 
     In various embodiments, the pump operator could use the process described above, but eliminate the task of initially increasing or decreasing pump rates manually to the desired overall flow rate of the selected active frac pumps by simply activating the control system to automatically adjust individual pump rates and fine tune as above. 
     Furthermore, embodiments of the present disclosure may include a critical plunger speed indicator. As described above, this indicator could be utilized as a form of software stored as executable instructions on the memory  308 . In various embodiments, the indicator would enable an alert to a hydraulic fracturing pump operator as to when the critical plunger speed has been reached. In certain embodiments, the critical plunger speed may be determined based on past operating conditions of a variety of pumps in a variety of circumstances. Accordingly, one or more ore measureable factors at the site may be utilized to predict and/or determine the plunger speed and analyze whether the plunger speed is within a threshold amount of a calculated and/or predetermined critical plunger speed. For example, critical plunger speed may be directly proportional to pump crankshaft rpm, at which conditions above this critical speed are favorable for pump cavitation to exist. When this pump speed is reached, the pump operator could receive a notification (e.g., a notation with text, colored lights beginning with yellow and changing to orange and red as the pump speed is increased more, auditory alarms, or the like). 
     Embodiments of the present disclosure may provide a variety of advantages of existing methods. For example, adjustable minimum and maximum step changes for frac pump speed adjustment may minimize the likelihood of pumps running at synchronized plunger speeds that could introduce a harmonic vibration into the connected equipment system. Furthermore, the above-described automatic pump rate adjustment may eliminate or reduce the likelihood of “superposition” of vibration (also termed as “beating phenomenon”) within the piping system due to adjacent and oppositely positioned pumps with synchronized plunger flow ripple patterns. Moreover, the critical plunger speed indicator may provide an alert prior to an operating condition that could lead to pump cavitation, thereby reducing the likelihood of equipment damage. 
     It should be appreciated that a variety of adjustments may be presented to the embodiments described herein. By way of example only, rather than including a large or small step between speed changes, the pump rate could simply be entered for the desired new rate. The system could then determine the proper adjustment to reach the desired new rate. Moreover, various embodiments may include a dial, physical or digital, that allows the pump operator to turn up the rate. Furthermore, there could be all three, a desired rate entry, large and small steps, and a dial. Then the pump operator can enter in speeds as is most convenient to the pump operator. 
     It should be appreciated that embodiments herein may utilize one or more values that may be experimentally determined or correlated to certain performance characteristics based on operating conditions under similar or different conditions. For example, information may be collected from hydraulic fracturing pumps operating in a variety of conditions and at different operating points (e.g., different flow rates, different pressures, different stages of maintenance cycles, etc.). Thereafter, measurements may be analyzed in view of triggering events, such as cavitation, high vibration, pump failures, or the like. Over time, information may be identified as being indicative or related to one or more triggering events. Such information may be normalized or otherwise adjusted based on other factors, such as operating conditions, to establish threshold values to utilize as indications in the embodiments described herein. For example, rather than a specific number (e.g., X rpm) the threshold may be a percentage of a measurement components (e.g., within X % of redline rpm). In various embodiments, redline rpm may refer to a maximum engine speed at which a motor is designed to operate. However, it should be appreciated that a redline may be defined as a desired maximum operating speed and may not necessarily be the maximum engine speed. 
       FIG. 4  is a flow chart of a method  400  for adjusting a pump step rate. It should be appreciated that for this method, and all methods described herein, that the steps may be performed in a different order, or in parallel, and there may be more or fewer steps unless otherwise specifically stated. In this example, a minimum and/or maxim step rate is received for one or more pumps  402 . For example, an operator may load desirable minimum and/or maximum step rates and/or a database may provide information including the information. A desired pumping rate may be determined  404 . This desired pumping rate may be associated with the set of pumps as a whole, with one individual pumps, with a subset of pumps, or the like. The desired rate may be determined by an operator and/or by a database or other information available to the controller. A current pumping rate is determined and evaluated as being different from the desired rate  406 . For example, the current pumping rate may be higher or lower. As a result, an adjustment is determined  408  in order to bring the pump to the desired rate. The adjustment is compared against the previously received limits  410 . If the adjustment exceeds the limits, then a new adjustment is computed. If the adjustment is within the limits, the adjustment is applied  412 . In this manner, automatic tuning is enabled that may be constrained within predetermined ranges. 
       FIG. 5  is a flow chart for an embodiment of a method  500  for adjusting a step rate based on adjacent or opposite pumping configurations. In this example, a desired pumping rate for a pump is determined  502 . As noted above, it may be undesirable for adjacent or opposite pumps to have similar pumping rates, therefore, embodiments also determine a current pumping rate of at least an adjacent or opposite pump  504 . The desired pumping rate is then compared to the current pumping rate or the adjacent or opposite pump  506 . The difference is evaluated against a threshold  508 , and if the rates are within the threshold, at least one of the desired rate or the current rate is modified  510  before the modification is applied to the pump  512 . If the rates are not within a threshold, the modification is applied to the pump to change the pumping rate to the desired pumping rate. 
       FIG. 6  is a flow chart of an embodiment of a method  600  for adjusting pumping rates for a group of pumps. In this example, a desired overall pumping rate for a group of pumps is determined  602 . A respective pumping rate for each pump of the groups of pumps may be determined  604 , where each pump may have a different rate. Current respective pumping rates for each pump are also determined  606 . Thereafter, an adjustment rate for each pump is determine for bringing the respective pumps to the desired overall rate  608 . The adjustment rates are evaluated against a threshold  610 . If the rate exceeds the threshold, new adjustment rates are determined. If the rate does not exceed the threshold, the adjustment is applied  612 . In this manner, individual adjustments may be made to pumps to achieve a desired overall rate. 
       FIG. 7  is a flow chart of an embodiment of a method  700  for determining a desired pumping rate, which may be based at least n part on speed, based at least in part on a calculated damage accumulation factor. This example begins with receiving a desired pumping rate and/or speed for a pump  702 . For example, an operator or database may provide information to a controller that automatically adjusts pumping rates, A damage accumulation rate may be calculated for the pump  704 . As noted above, the damage accumulation rate may be indicative of pump health and/or suitability for operation. A high damage accumulation rate may be related to a pump that preferably is not operated at high speeds, for example. The damage accumulation is evaluated against a threshold  706 , such as a value or percentage. If the damage accumulate exceeds the threshold, a warning may be provided  708 . If not, then a step rate may be determined to adjust the pump  710 . This step rate may also be evaluated against a threshold  712 . If the step rate does not exceed the threshold, then the rate is applied  714 . If it does exceed the threshold, then a new step rate may be determined. Accordingly, changes in pump operation may be made, at least in part, based on a damage accumulation rate. 
     The present disclosure described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the disclosure has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present disclosure disclosed herein and the scope of the appended claims.