Patent Publication Number: US-10789936-B2

Title: Active noise control for hydraulic fracturing equipment

Description:
BACKGROUND 
     Heavy machinery such as hydraulic fracturing equipment (e.g., high-pressure pumps, blenders, pneumatic conveyers) used in the oil and gas industry typically emit high levels of noise ranging from about 85 dB to about 115 db. This noise (or sound, in general) propagates in the form pressure waves, which consist of a compression phase and a rarefaction phase. High noise levels pose potential health risks to oilfield workers and the public. 
     One way to attenuate the noise generated by the machinery is to modify the design of the most significant noise producing components, such as engines, exhaust, fans, and gearboxes of the machinery. Another way to attenuate the noise is to enclose the machinery within an acoustic enclosure consisting of noise absorbing material that absorbs sound waves generated by the machinery and prevent the propagation of the sound waves away from the machinery. Additionally, noise can be attenuated by placing sound walls or noise barriers around the perimeter of the job site or by placing portable sound absorption panels between the machinery and human personnel or sensitive areas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures are included to illustrate certain aspects of the embodiments, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure. 
         FIG. 1A  is a schematic diagram of a high-pressure pumping unit used in hydraulic fracturing operations. 
         FIG. 1B  illustrates a pump system used in hydraulic fracturing operations and including multiple high-pressure pumping units of  FIG. 1A . 
         FIG. 2  illustrates example noise spectra of the noise generated by a noise source of the high-pressure pumping unit of  FIG. 1A  for different rotational speeds of the noise source. 
         FIG. 3  illustrates an example noise spectrum obtained of the noise generated by the high-pressure pumping unit of  FIG. 1A  for a given operational characteristic of its one or more noise sources. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments disclosed are directed to active noise attenuation techniques for obtaining a global attenuation of the noise generated by machinery. Noise may generally refer to any undesirable sound or acoustic propagation produced by the machinery. Each component of the machinery may produce noise that may propagate as a pressure wave having a frequency, amplitude, and phase specific to the noise generating component. 
     The active noise attenuation techniques disclosed herein use noise detection devices to detect noise generated by individual noise generating components of the machinery and produce anti-noise using one or more noise mitigation devices positioned proximate each individual noise generating component. The generated anti-noise is specific to the target noise to be attenuated and has an amplitude and frequency similar to or the same as the amplitude and frequency of the target noise, but with a phase shift of about 180° compared to the target noise. When combined, the target noise and the anti-noise destructively interfere and the target noise is thereby attenuated. 
     As used herein, the term “machinery” and any variation thereof refers to heavy duty machinery or heavy moving machinery, such as machinery used in earth moving, construction, or forestry, agricultural machines, hydraulic fracturing equipment and other oilfield equipment, mining equipment, heavy duty trucks, engineering equipment, heavy hydraulics, any combination thereof, and the like. The term “machinery” and any variation thereof also refers to other machinery, such as automobile engines, transmissions, portable generators, any combination thereof, and the like. The embodiments described herein are directed primarily to attenuating noise generated by multiple machinery located adjacent each other in an open air environment in which there are no enclosures around the machinery. This is in contrast to existing noise attenuation techniques that are predominately directed to attenuating noise generated by noise sources located in a closed environment not exposed to the atmosphere. An example of a closed environment is the passenger cabin of a vehicle and the noise attenuation techniques attenuate the noise inside the passenger cabin. Multiple machinery operating in close proximity of each other causes noise generated by adjacent heavy duty machinery to reflect or bounce off each other. As a result, locating individual noise sources is difficult and less predictable as compared to noise sources located in a defined, confined space. 
     Embodiments described herein are directed to detecting the noise generated by individual noise sources located in an open air environment and in close proximity of each other. 
     For the sake of explanation, embodiments are described with reference to attenuating noise generated by hydraulic fracturing equipment, such as frac blenders to combine chemicals, base fluid and proppant into specific mixes of fracturing fluids, high-horsepower frac pumps, high-horsepower engines for running the machinery, exhaust units, transmission units, cooling units, slurry mixers, and the like. However, it should be noted that embodiments disclosed herein are equally applicable to attenuating noise generated by other types of heavy machinery, without departing from the scope of the disclosure. 
     As used herein, the term “global noise attenuation” and any variation thereof refers to noise attenuation that is performed independent of the location at which the noise attenuation is desired or measured. Thus, in the case of heavy machinery operating in an open-air environment and generating noise, global noise attenuation may result in the noise being attenuated substantially at any and all locations around the heavy machinery. Stated otherwise, the resulting noise attenuation may be omnidirectional. This is in contrast to local noise attenuation in which the noise level at a predetermined or preset (specific) location around the noise source is attenuated. In this case, the noise attenuation techniques may be employed at or around the preset location. As an example, the location may be an operator compartment of a vehicle. 
     As used herein, the term “active noise attenuation” and any variation thereof refers to a method for attenuating noise by the addition of anti-noise specifically designed to attenuate the noise. The active noise reduction is a dynamic process, wherein a variation in the characteristic (e.g., amplitude, frequency, and phase) of the noise produces a real-time, or near real-time, dynamic variation in the anti-noise to cause destructive interference between the noise and the anti-noise. In contrast, passive noise attenuation techniques attenuate a preset or predetermined range of frequencies and the passive noise attenuation techniques cannot be adapted to attenuate frequencies that may arise during operation. 
       FIG. 1A  is an isometric view of an example high-pressure pumping unit  100  used in hydraulic fracturing operations. The high-pressure pumping unit  100  may be used to pump high pressure fracturing fluid into a wellbore during hydraulic fracturing operations. As illustrated, seven distinct potential noise sources (or noise producing components) may be generally identified in the high-pressure pumping unit  100 . The potential noise sources may be or include a water cooler unit  102 , an engine unit  104 , an exhaust  106 , a transmission unit  108 , an air-cooling unit  110 , a speed controller  112 , and a pumping unit  114 . It should be understood, however, that the number of potential noise sources in the high-pressure pumping unit  100  is merely an example, and more or less potential noise sources may be present. It should also be noted that  FIG. 1A  may not indicate the exact location of the noise sources, but may depict the general location of the potential noise sources of the high-pressure pumping unit  100 . 
     Typically, hydraulic fracturing operations include multiple high-pressure pumping units  100  operating in close proximity of each other. Referring briefly to  FIG. 1B , illustrated is a pump system  230  used in hydraulic fracturing operations and that includes multiple high-pressure pumping units  100 . Each high-pressure pumping units  100  may be transported using a tractor  234 . The pump system  230  may further include a plurality of water tanks  231  that feed water to a gel maker  233 . The gel maker  233  may combine water from the tanks  231  with a gelling agent to form a gel. The gel is then sent to a blender  235  where it is mixed with a proppant from a proppant feeder  237  to form fracturing fluid. 
     The fracturing fluid is then supplied from the blender  235  to a plurality of high-pressure pumping units  100 . Each high-pressure pumping unit  100  receives the fracturing fluid and discharges it to a common manifold  237  at a high pressure. The manifold  237  then directs the fracturing fluid from the high-pressure pumping units  100  to the wellbore  239 . 
     As will be understood from  FIG. 1B , multiple high-pressure pumping units  100  operate in close proximity with each other, and as a result, the noise generated by each high-pressure pumping unit  100  interferes with the noise from the other high-pressure pumping units  100 . In addition, the reflection of the noise from adjacent high-pressure pumping units  100  results in a very complex noise spectrum. Additionally, the noise spectrum also includes the noise from the high-pressure pumping units  100  that interacts with the noise generated by the gel maker  233 , blender  235 , proppant feeder  237 , and other equipment included in the pump system  230 . The example method disclosed herein for mitigating the noise generated by the high-pressure pumping units  100  may be equally applicable to mitigating the noise generated by the gel maker  233 , blender  235 , proppant feeder  237 , and other equipment included in the pump system  230 . 
     Returning to  FIG. 1A , each noise source may produce noise having specific (or unique) characteristics (e.g., amplitude, frequency, and phase) detectable using one or more noise detection device placed adjacent the noise sources. In an example and as illustrated, the one or more noise detection devices may be or include microphones  103 ,  105 ,  107 ,  109 ,  111 ,  113 , and  115  positioned adjacent the respective noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114 . However, other noise detection devices that directly or indirectly detect noise may also be used without departing from the scope of the disclosure. In an embodiment, the microphones may be configured to detect noise generated from a specific noise source. For example, microphones  103  may be configured to detect noise generated from the water cooler  102 , microphones  105  may be configured to detect noise generated from the engine unit  104 , and so on. However, in other embodiments, one or more microphones may be configured to detect noise generated by two or more noise sources, such as acoustically overlapping noise sources. The noise generated by a particular noise source  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114  may be attenuated using anti-noise specifically designed for that noise. As mentioned above, the anti-noise may have an amplitude and frequency about the same as the amplitude and frequency of the target noise, but with a phase shift of around 180° as compared to the target noise. 
     The anti-noise may be output (generated) using one or more noise mitigation devices associated with each noise source. Specifically, the associated noise mitigation devices may be specific to the noise source and may be positioned or otherwise installed proximate each noise source such that the anti-noise produced by these associated noise mitigation devices interacts with and thereby mitigates the noise in all directions relative to the noise source. The noise mitigation devices may thus be positioned or otherwise arranged 360° around the noise source. In an example, the noise mitigation devices may be positioned such that the anti-noise generated by the noise mitigation devices destructively interferes with the noise generated by the noise sources from all directions relative to the noise sources to thereby attenuate the noise. 
     The noise mitigation devices may thus be positioned in a variety of configurations including, for example, a generally hemispherical or dome type structure enclosing or otherwise covering the high-pressure pumping unit  100 . In other examples, the noise mitigation devices may be positioned in the form of an array that encloses or otherwise covers the high-pressure pumping unit  100  and is representative of the geometric configuration of the high-pressure pumping unit  100 . In an example, the noise mitigation devices may be positioned around the noise sources via stands placed in the surrounding ground. In other examples, the noise mitigation devices may be suspended in the air around/about the noise sources. In yet other examples, the noise mitigation devices may be installed on the high-pressure pumping unit  100  via mounting brackets, and, as a result, may be a part of the high-pressure pumping unit  100 . 
     In an example and as illustrated, the noise mitigation devices may be or include speakers  202   a - 202   f ,  204   a - 204   b ,  206   a - 206   b ,  208   a - 208   b ,  210   a - 210   d ,  212   a - 212   b , and  214   a - 214   b , each being positioned proximate respective noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114 . However, other noise mitigation devices, such as active vibrating panels, dynamic acoustic dampeners, or a combination thereof and the like, may also be used without departing from the scope of the disclosure. 
     For the sake of simplicity, the speakers  202   a - 202   f ,  204   a - 204   b ,  206   a - 206   b ,  208   a - 208   b ,  210   a - 210   d ,  212   a - 212   b , and  214   a - 214   b  are illustrated positioned on only a side (e.g., a lateral side or a top side) of each respective component. However, as mentioned above, the speakers may surround the respective noise sources from any and all possible directions so that the anti-noise output therefrom interferes with the noise from the respective noise sources from all possible directions. For instance, with reference to the water cooler unit  102 , in addition to speakers  202   a - 202   f  positioned on top thereof, speakers may also be positioned to the left and right, in the front and rear, and below the water cooler unit  102 . Similarly, additional speakers may be positioned proximate the other noise sources  104 ,  106 ,  108 ,  110 ,  112 , and  114 . It should be noted that the number of speakers  202   a - 202   f ,  204   a - 204   b ,  206   a - 206   b ,  208   a - 208   b ,  210   a - 210   d ,  212   a - 212   b , and  214   a - 214   b  illustrated in  FIG. 1A  is merely an example, and that the number may be increased or decreased based on the intensity of the noise produced from the noise sources, the number of noise sources, the distribution of the noise sources, and other application and design parameters. 
     The speakers  202   a - 202   f ,  204   a - 204   b ,  206   a - 206   b ,  208   a - 208   b ,  210   a - 210   d ,  212   a - 212   b , and  214   a - 214   b  may be controlled/driven by a computer system  250  in communication with the high-pressure pumping unit  100 . Specifically, the computer system  250  may be configured to receive one or more signals based on to the noise detected by the microphones  103 ,  105 ,  107 ,  109 ,  111 ,  113 , and  115  (or any other noise detection devices used), generate corresponding anti-noise signals, and control (operate) the corresponding speakers  202   a - 202   f ,  204   a - 204   b ,  206   a - 206   b ,  208   a - 208   b ,  210   a - 210   d ,  212   a - 212   b , and  214   a - 214   b  to output the anti-noise. Because the anti-noise is produced specific to a given (target) noise, the computer system  250  may be configured to drive the speakers  202   a - 202   f ,  204   a - 204   b ,  206   a - 206   b ,  208   a - 208   b ,  210   a - 210   d ,  212   a - 212   b , and  214   a - 214   b  to generate anti-noise specific to the noise detected by the corresponding microphones  103 ,  105 ,  107 ,  109 ,  111 ,  113 , and  115 . For example, the computer system  250  drives the speakers  202   a - 202   f  to generate the anti-noise that attenuates the noise detected by the microphone(s)  103 , drives the speakers  204   a - 204   b  to generate the anti-noise that attenuates the noise detected by the microphone(s)  105 , and so on. 
     The computer system  250  may be located at or near the high-pressure pumping unit  100 , or may alternatively form an integral part of the high-pressure pumping unit  100 . In other embodiments, the computer system  250  may be located at a remote location and able to control the speakers  202   a - 202   f ,  204   a - 204   b ,  206   a - 206   b ,  208   a - 208   b ,  210   a - 210   d ,  212   a - 212   b , and  214   a - 214   b  via wired or wireless telecommunication means. Referring briefly to FIG.  1 B, the computer system  250  may control the overall operation of the pump system  230 . Alternatively, each high-pressure pumping unit  100  of the pump system  230  may be controlled by an individual computer system that may be the same as or similar to the computer system  250  and may communicate with the computer systems of other high-pressure pumping units  100  via wired or wireless communication means. 
     Returning to  FIG. 1A , the computer system  250  may include a processor  252 , computer-readable storage mediums such as memory  254  and storage device  256 , and an input/output device  258 . Each of the components  252 ,  254 ,  256 , and  258  may be interconnected, for example, using a system bus  260 . The processor  252  may be processing instructions for execution within the computer system  250 . In some embodiments, the processor  252  is a single-threaded processor, a multi-threaded processor, a system on a chip, a special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit), or another type of processor. The processor  252  may be capable of processing computer program code stored in the memory  254  or on the storage device  256 . The memory  254  and the storage device  256  include non-transitory mediums such as random access memory (RAM) devices, read only memory (ROM) devices, optical devices (e.g., CDs or DVDs), semiconductor memory devices (e.g., EPROM, EEPROM, flash memory devices, and others), magnetic disks (e.g., internal hard disks, removable disks, and others), and magneto optical disks. 
     The input/output device  258  may provide input/output operations for the computer system  250 . In some embodiments, the input/output device  258  can include one or more network interface devices, e.g., an Ethernet card; a serial communication device, e.g., an RS-232 port; and/or a wireless interface device, e.g., an 802.11 card, a 3G wireless modem, or a 4G wireless modem. In some embodiments, the input/output device  258  can include driver devices configured to receive input data and send output data to other input/output devices  262  including, for example, a keyboard, a pointing device (e.g., a mouse, a trackball, a tablet, a touch sensitive screen, or another type of pointing device), a printer, and display devices (e.g., a monitor, or another type of display device) for displaying information to a user. Other kinds of devices can be used to provide for interaction with the user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. In some embodiments, mobile computing devices, mobile communication devices, and other devices can be used. 
     The computer system  250  may include a single processing system, or may be a part of multiple processing systems that operate in proximity or generally remote from each other and typically interact through a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), an inter-network (e.g., the Internet), a network comprising a satellite link, and peer-to-peer networks (e.g., ad hoc peer-to-peer networks). A relationship of client and server may arise by virtue of computer programs running on the respective processing systems and having a client-server relationship to each other. 
     To effectively attenuate noise produced by a noise source, it may be required to position each speaker at or within a specific distance from an associated or corresponding noise source. This distance may be determined based on the wavelength of the noise produced by the noise source. Specifically, for effective global noise attenuation, each speaker is positioned from an associated noise source at or within a distance that is half of the shortest wavelength (alternatively, the highest frequency) of noise produced from the noise source. As an example, assuming that the velocity of sound in air is around 340 meters per second (m/s), if the primary frequency of the noise generated from the water cooler unit  102  is around 30 Hz, then the wavelength of such noise is around 11.334 meters (m). Accordingly, each speaker  202   a - 202   f  associated with the water cooler unit  102  may be placed at a distance no more than around 5.667 m (i.e., 11.334/2) from the water cooler unit  102 . As another example, again assuming that the velocity of sound in air is around 340 m/s, if the frequency of the noise generated from the transmission unit  108  is around 1000 Hz, then the wavelength of the noise is around 0.34 m and each speaker  204   a - 204   b  may be placed at a distance no more than around 0.17 m (i.e., 0.34/2) from the engine unit  104 . 
     In addition, adjacent speakers associated with (or corresponding to) the same noise source may be separated from each other with a distance that is less than or equal to half the shortest wavelength of the noise produced from the noise source. Thus, as an example, the distance between the adjacent speakers of the speakers  202   a - 202   f  associated with the water cooler unit  102  may be equal to or less than half of the wavelength of the noise generated by the water cooler unit  102 . Such separation between adjacent speaker  202   a - 202   f  may amplify the anti-noise produced by the speakers  202   a - 202   f . As a result, the amplitude of the anti-noise generated by the speakers  202   a - 202   f  may be reduced. Thus, the size and power requirements of the speakers  202   a - 202   f  may be reduced as well. 
     Embodiments contemplated herein may implement the active noise attenuation techniques disclosed above in combination with passive noise attenuation techniques to provide improved noise attenuation. Passive noise attenuation techniques can be effective for mitigating noise frequencies greater than 1000 Hz. On the other hand, active noise attenuation techniques are more effective for mitigating noise frequencies less than 1000 Hz. Passive noise attenuation may be obtained by enclosing (i.e., surrounding, encasing, enveloping, etc.) one or more of the noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114  with sound absorbent (or soundproofing) materials to absorb or minimize noise reflecting back to the noise source. Either each noise source  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114  may be individually enclosed with sound absorbent (or soundproofing) materials or two or more noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114  may be together enclosed with sound absorbent (or soundproofing) materials. Examples of sound absorbent materials may include drywall (e.g., sheetrock), damped drywall (drywall incorporating a sound damping layer), sound-deadening fiberboard (also called soundboard or acoustical board), mass-loaded vinyl (MLV), insulation (e.g., fiberglass, mineral wool, foam, etc.), sound curtains, damping compounds (e.g., viscoelastic adhesive), acoustical sealant (e.g., acoustical caulk), a combination thereof and the like. 
     In some embodiments, the flow path of the airflow or other exhaust from one or more noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114  may be modified to attenuate the generated noise. In other embodiments, additional noise barriers such as a masonry wall or earthwork, or a combination thereof (e.g., a wall atop an earth berm) may also be used. Active noise attenuation techniques, according to the embodiments disclosed, may then be used (or employed) to attenuate the low frequency noise that may not be attenuated using passive noise attenuation techniques. Thus, when using a combination of active and passive noise attenuation techniques, the noise (sound waves) generated by the noise source initially encounters the passive noise attenuation techniques and then encounters the active noise attenuation techniques. 
     Various pieces of equipment of the high-pressure pumping unit  100  can include rotating component parts that rotate in generating the target noise. For example, rotating component parts may be or include fans, engines, transmissions, centrifugal pumps, volumetric pumps, vacuum pumps and compressors, turbines, ventilators, centrifuges, motors, gearboxes, mixing gears, and the like. Rotating component parts can be included, for instance, in the engine unit  104 , the transmission unit  108 , the speed controller  112 , and/or the pumping unit  114 . Rotational sensors (alternatively referred to as “speed sensors”) may be used to determine the frequency of the noise generated by such rotating component parts and, as such, the frequency of the noise generated by the equipment including the rotating component parts. The rotational sensors may be or include magnetic sensors, optical sensors, a combination thereof, and the like. 
     Accordingly, in some embodiments, the microphones  105 ,  109 ,  113 , and  115  may be replaced by (or complimented with) corresponding rotational sensors (not explicitly illustrated). One or more rotational sensors may be coupled to the rotating component parts (e.g., coupled to the shaft, gears, spindles, and the like of the rotating component parts) and may measure a rotational speed and an angular position of the rotating component parts. The computer system  250  may store pre-determined noise spectra of the noise generated by each rotating component part for different values of the rotational speed of the rotating component part. Each noise spectrum includes the amplitude of the noise for different values of frequency for a given rotational speed of the rotating component part. The rotational speed is thus indicative of the frequency of the noise generated by each rotating component part. 
     During operation, the measured rotational speed is compared with the stored rotational speed to obtain the noise spectrum corresponding to the measured rotational speed. The frequency and amplitude of the anti-noise to be generated is determined from the noise spectrum and the computer system  250  may drive the speakers  204   a - 204   b ,  208   a - 208   b ,  212   a - 212   b , and  214   a - 214   b  associated with the noise source including the rotating component part to generate the corresponding anti-noise. The anti-noise generated may be shifted in phase based on the angular position measured by the rotational sensors. 
     It should be noted that the measured rotational speed may not exactly match the stored rotational speed. The measured rotational speed may be considered to match the stored rotational speed when a difference between the measured and stored rotational speeds is less than a pre-determined value (e.g., determined based on a desired standard deviation). 
       FIG. 2  illustrates example noise spectra  220  of the noise generated by a noise source of the high-pressure pumping unit  100  of  FIG. 1A  for different rotational speeds of the noise source. The noise source may be one of the noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114  of the high-pressure pumping unit  100 . During operation, and as discussed above, the measured rotational speed from the rotational sensors is matched with the different RPM values to obtain the corresponding noise spectrum. The computer system  250  may drive the speakers  204   a - 204   b ,  208   a - 208   b ,  212   a - 212   b , and  214   a - 214   b  to generate the corresponding anti-noise. 
     In other embodiments, instead of using multiple microphones  103 ,  105 ,  107 ,  109 ,  111 ,  113 , and  115  ( FIG. 1A ), a single microphone may be used to detect noise generated by two or more of the noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114  ( FIG. 1A ). In such embodiments, a pre-determined noise spectrum of the noise generated by the high-pressure pumping unit  100  may be stored in the computer system  250  ( FIG. 1A ). The noise spectrum thus includes the noise from all noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114  of the high-pressure pumping unit  100 . The noise spectrum may be compared with the noise detected by the single microphone to generate the corresponding anti-noise signal. 
       FIG. 3  illustrates an example noise spectrum  320  obtained based on the noise generated by the high-pressure pumping unit  100  of  FIG. 1A  for a given operational characteristic of the one or more noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114 . For instance, the noise spectrum  320  may be obtained when the engine unit  104  rotates at about 1900 RPM. 
     The noise spectrum  220  includes multiple peaks  323 ,  325 ,  327 ,  329 ,  331 ,  333 , and  335 , which are indicative of the noise frequencies having the highest amplitudes. For instance, these noise frequencies may correspond to the noise generated by the noise sources  102 ,  104 ,  106 ,  108 ,  110 ,  112 , and  114 . The anti-noise may be then generated for these noise frequencies. 
     Noise may be expressed as S(t)=A*sin (ωt+φ), where A represents the amplitude of the noise, ω=2πf represents the frequency of the noise, and φ represents the phase of the noise. In the noise mitigation techniques, according to embodiments disclosed, the single microphone detects the noise generated by the high-pressure pumping unit  100 . The computer system  250  processes the noise (e.g., using a spectral analyzer) to determine the amplitude and frequency of the noise. The phase may be calculated using feed forward algorithms and other known iterative methods. 
     The computer system  250  compares the detected noise against the noise spectrum  320  stored therein. Based on the comparison, the computer system  250  may identify the noise source(s) generating the noise and generate the corresponding anti-noise having the determined amplitude and frequency, and a phase that is shifted about 180° from the calculated phase. The computer system  250  may drive the speakers  202   a - 202   f ,  204   a - 204   b ,  206   a - 206   b ,  208   a - 208   b ,  210   a - 210   d ,  212   a - 212   b , and  214   a - 214   b  associated with the identified noise source to output the anti-noise. 
     In certain instances, there may be a shift in the frequency of noise as received by the computer system  250 . This shift may be due to error in transmission of the detected noise, error in processing of the received noise, etc. Accordingly, in some embodiments, the computer system  250  may compare the received frequency with a range of possible noise frequencies in the noise spectrum  220  and may determine the noise source based on the comparison (e.g., based on a pre-determined standard deviation). The computer system  250  may then drive the corresponding speakers  202   a - 202   f ,  204   a - 204   b ,  206   a - 206   b ,  208   a - 208   b ,  210   a - 210   d ,  212   a - 212   b , and  214   a - 214   b  to output the corresponding anti-noise. 
     Examples disclosed herein include: 
     A. A method for noise attenuation, comprising comparing a frequency of noise generated by a plurality of noise sources with a plurality of frequencies associated with a pre-determined noise spectrum and stored in a computer system; identifying one or more noise sources that generate the noise based on the comparison of the frequency of the noise and the plurality of frequencies stored in the computer system; generating anti-noise corresponding to the noise; and outputting the anti-noise using one or more noise mitigation devices associated with the one or more noise sources. 
     B. A system for noise attenuation, comprising a plurality of noise mitigation devices for outputting anti-noise corresponding to noise generated by a plurality of noise sources; and a computer system including a non-transitory medium readable by a processor and storing computer-readable instructions that when executed by the processor configures the computer system to: compare a frequency of the noise with a plurality of noise frequencies associated with a pre-determined noise spectrum and stored in the computer system, identify one or more noise sources that generate the noise based on the comparison of the frequency of the noise and the plurality of frequencies stored in the computer system, generate the anti-noise corresponding to the noise, and actuate one or more noise mitigation devices associated with the one or more noise sources to output the anti-noise. 
     C. A computer program product embodied in a non-transitory computer-readable medium and comprising a computer readable program code that, when executed by a computer system, causes the computer system to: compare a frequency of noise generated by a plurality of noise sources with a plurality of noise frequencies associated with a pre-determined noise spectrum and stored in the computer system; identify one or more noise sources that generate the noise based on the comparison of the frequency of the noise and the plurality of frequencies stored in the computer system; generate anti-noise corresponding to the noise; and actuate one or more noise mitigation devices associated with the one or more noise sources to output the anti-noise. 
     Each of examples A, B, and C may have one or more of the following additional elements in any combination: Element 1: further comprising detecting the noise using one or more noise detection devices. 
     Element 2: wherein a noise source of the plurality of noise sources comprises rotating equipment, the pre-determined noise spectrum pertains to a plurality of pre-determined noise spectra stored in the computer system, and each pre-determined noise spectra includes frequencies generated by the noise source at different rotational speeds, the method further comprising: measuring a rotational speed of the noise source using a rotational sensor; and comparing the measured rotational speed with the different rotational speeds in the noise spectrum and thereby determining a frequency of the noise source. Element 3: further comprising positioning the one or more noise mitigation devices proximate each noise source such that the anti-noise destructively interferes with the noise in some or all directions relative to the plurality of noise sources to thereby attenuate the noise. Element 4: wherein the plurality of noise sources comprises heavy machinery located in an open air environment. Element 5: wherein each noise mitigation device is associated with a corresponding one of the plurality of noise sources and outputting the anti-noise further comprises outputting anti-noise with each noise mitigation device specific to the noise generated by the corresponding one of the plurality of noise sources. Element 6: wherein each noise mitigation device is associated with a corresponding one of the plurality of noise sources and the method further comprises: positioning each noise mitigation device associated with corresponding one of the plurality noise sources at a distance less than or equal to half of a shortest wavelength of the noise generated by the corresponding one of the plurality noise sources. 
     Element 7: further comprising one or more noise detection devices. Element 8: wherein a noise source of the plurality of noise sources comprises rotating equipment, the pre-determined noise spectrum pertains to a plurality of pre-determined noise spectra stored in the computer system, and each pre-determined noise spectra includes noise frequencies generated by the noise source at different rotational speeds, and wherein the computer system is configured to: obtain a rotational speed of the noise source measured using a rotational sensor; and compare the measured rotational speed with the different rotational speeds in the noise spectrum and thereby determine a frequency of the noise source. Element 9: wherein the plurality of noise mitigation devices are positioned proximate each noise source such that the anti-noise destructively interferes with the noise in some or all directions relative to the plurality of noise sources to thereby attenuate the noise. Element 10: wherein the plurality of noise sources comprises heavy machinery located in an open air environment. Element 11: wherein each noise mitigation device is associated with a corresponding one of the plurality of noise sources and the computer system actuates each noise mitigation device to output the anti-noise specific to the noise generated by the corresponding one of the plurality of noise sources. Element 12: wherein each noise mitigation device is associated with a corresponding one of the plurality of noise sources and each noise mitigation device associated with corresponding one of the plurality noise sources is positioned at a distance less than or equal to half of a shortest wavelength of the noise generated by the corresponding one of the plurality noise sources. Element 13: further comprising one or more passive noise attenuation techniques for attenuating part of the noise generated by the plurality of noise sources. 
     Element 14: wherein executing the program code further causes the computer system to detect the noise generated by the plurality of noise sources using one or more noise detection devices. Element 15: wherein a noise source of the plurality of noise sources comprises rotating equipment, the pre-determined noise spectrum pertains to a plurality of pre-determined noise spectra stored in the computer system, and each pre-determined noise spectra includes noise frequencies generated by the noise source at different rotational speeds, and wherein executing the program code further causes the computer system to: obtain a rotational speed of the noise source measured using a rotational sensor; and compare the measured rotational speed with the different rotational speeds in the noise spectrum and thereby determine a noise frequency of the noise source. Element 16: wherein executing the program code further causes the computer system to actuate the one or more noise mitigation devices that are positioned proximate each noise source such that the anti-noise generated by the one or more noise mitigation devices destructively interferes with the noise in some or all directions relative to the plurality of noise sources to thereby attenuate the noise. Element 17: each noise mitigation device is associated with a corresponding one of the plurality of noise sources, and executing the program code further causes the computer system to actuate the one or more noise mitigation devices to output anti-noise with each noise mitigation device specific to the noise generated by the corresponding one of the plurality of noise sources. 
     Therefore, the present disclosure is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present disclosure. The embodiments illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces.