Abstract:
An ultrasonic fracking system and methods of using the same to extract hydrocarbons from underground geological formations (e.g., oil shale, coal beds, etc.) are disclosed. The system includes piezoelectric devices that are used to produce ultrasonic mechanical vibrations and induce fractures in the geological formations. In one embodiment, a system for extracting underground hydrocarbons comprises a plurality of piezoelectric devices capable of producing mechanical waves sufficient to fracture oil shale and other geological formations, a system of delivery for innocuous proppants to create a path of least resistance for enhanced hydrocarbon flow, and a vacuum pump connected to the fractures created by the piezoelectric devices to assist in removing the hydrocarbons.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to the field of mining (e.g., extracting, drilling or recovering) hydrocarbons. Embodiments of the present invention relate to a system for extracting hydrocarbons (e.g., hydrocarbon-based fuels) from underground formations utilizing ultrasound, and methods of using the same. More specifically, embodiments of the present invention relate to a system and method for creating controlled fractures in underground geological formations, allowing the extraction of hydrocarbons trapped therein. 
       DISCUSSION OF THE BACKGROUND 
       [0002]    Increasing demands for domestic fuel sources have led to widespread attention to a technique of underground natural gas and oil exploitation called hydraulic fracturing (fracking) While the technique has merit, environmental concerns have recently arisen regarding the environmental impacts of fracking, including possible contamination of ground water, surface water, and soil, as well as the release of greenhouse gases into the atmosphere. Additionally, current fracking techniques have several inefficiencies. 
         [0003]    Natural underground oil shale and coal deposits offer an abundant supply of petroleum and natural gas resources. Many variables must be considered in the application of fracking techniques to extract these hydrocarbons. For instance, the question of whether the extraction of natural gas and hydrocarbons from a particular oil shale or coal bed formation is efficient and economical depends on the flow rate of these materials through the formation. Darcy&#39;s Law describes the flow rate of materials through porous media, which is measured in 
         [0004]    Darcy (D). The flow rates of hydrocarbons in shale and coal bed formations is low (e.g., in the 1 nD to 1 μD range), due to the low permeability of shale and coal. Fracking of such underground formations must result in a flow rate of the hydrocarbons that is sufficient to extract economically sufficient amounts of the hydrocarbons. 
         [0005]    To achieve such flow rates, wellbores are often drilled using vertical drilling techniques. In order increase flow rates to economical levels, underground formations are pumped with large amounts of water and chemicals (fracking fluids) at extreme pressures to achieve fracturing of the natural underground geologic formations. Materials known as proppants are then pumped into the newly created fractures to prop open the fractures, creating paths of least (or lower) resistance for hydrocarbons to flow. 
         [0006]    However, fracking fluids typically include a wide range of potentially hazardous chemicals (e.g., acids, buffering agents, bactericides, corrosion inhibitors, friction reducers, surfactants, gelling agents, etc.). Large amounts of these fracking fluids can be used in a fracking operation (e.g., greater than 10 6  gallons in deep oil shale deposits). A portion of the fracking fluids can find its way into water and soil by leaking through waste pipelines transporting the fluid from the well to disposal areas and from the disposal areas themselves. Also, a portion of the fracking fluid injected into the well can remain underground. The chemicals in the fracking fluid can migrate into aquifers, surface water, and soils. Thus, the use of fracking fluids can result in the contamination of these important resources. 
         [0007]    Presently, hydraulic fracturing techniques have multiple problems, including:
       Low efficiency in capturing the released hydrocarbons;   Due to economic considerations, once the flow rate of the well is past a premium flow rate, the well may be abandoned;   Capping the abandoned well may not eliminate leeching of greenhouse gases into the atmosphere;   If left uncapped, methane (CH 4 ) can leach from the well into the air, and methane is greater than 30 times more powerful in inducing greenhouse effects than CO 2 ;   Ground and surface water and soil can be polluted by fracking fluid and chemicals released from wells; and   Horizontal drilling techniques may result in seepage of natural gas into the environment, resulting in loss of potential revenue and significant risk of injury and death to local fauna.       
 
         [0014]    An additional drawback to fracking is the release of Naturally Occurring Radioactive Materials (NORMS). These NORMS are salts of radioactive species which potentially can be solubilized in the presence of water. It is conceivable that ground water bodies may then be contaminated with labile radioactive species, lending to worsening environmental damages. 
         [0015]    Thus, new techniques for extracting hydrocarbons that lower the costs, minimize environmental impacts, and increase the efficiency of extracting geologic hydrocarbons are needed. 
       SUMMARY OF THE INVENTION 
       [0016]    Embodiments of the present invention are generally related to systems for extracting hydrocarbons (e.g., natural gas) from underground formations utilizing ultrasonic vibrations and methods of extracting hydrocarbons using such systems. More specifically, embodiments of the present invention relate to a system and method for creating controlled fractures in underground geological formations, allowing the extraction of hydrocarbons trapped therein. 
         [0017]    In accordance with the present invention, a system for fracturing underground formations utilizing ultrasonic mechanical vibrations may comprise a plurality of piezoelectric devices for producing mechanical vibrations capable of fracturing underground geological formations, including oil shale, coal beds, sandstone, and other geological formations in which hydrocarbons may be deposited. The piezoelectric devices may be inserted into one or more wellbores, down to the position of a geological formation containing hydrocarbons, where the piezoelectric devices can be used to create ultrasonic vibrations in the wellbore to shake and expand existing fractures. The piezoelectric devices are also capable of sensing resonant vibration frequencies (typically ultrasonic) of existing fractures, which can be enlarged by pulsing the formation with the detected resonant frequency(ies). 
         [0018]    The system may also include a reversible vacuum/pump system to create a path of least or lower resistance for hydrocarbons freed from the geological formation by the fracturing system, effectively drawing the hydrocarbons toward the surface. The vacuum/pump system may be further configured to flush an innocuous or relatively harmless fluid or gas (e.g., N 2  or air) into a wellbore as a proppant to prevent the fractures in the geological formation from (1) closing up and/or (2) trapping the hydrocarbons contained therein. 
         [0019]    The fracturing system may be used in a method for extracting hydrocarbons from underground geological formations by (1) determining the resonant frequencies of the fractures present in the geological formation, (2) producing vibrations at the resonant frequencies in order to cause spreading and growth of the fractures and free the hydrocarbon deposits contained in the geological formation, (3) pumping a proppant from the surface into the fractures (e.g., through a wellbore) in order to maintain the enlarged fracture and facilitate the flow of hydrocarbons out of the formation, and (4) collecting the hydrocarbons (e.g., through the wellbore, optionally using [i] a negative pressure created in the wellbore by the vacuum/pump system and/or [ii] a higher pressure that may naturally be present in an underground hydrocarbon deposit). 
         [0020]    In one embodiment, the present invention relates to a system for fracturing underground formations, comprising (a) a plurality of piezoelectric devices, the plurality of piezoelectric devices being capable of insertion into a plurality of underground wells in the underground formation and producing and detecting a broad range of vibrational frequencies; (b) an apparatus for receiving and interpreting data from the piezoelectric devices regarding detected vibrational frequencies; and (c) an apparatus for inducing vibrations of desired frequencies in the plurality of piezoelectric devices. 
         [0021]    In another embodiment, the present invention relates to a system of extracting hydrocarbons from underground formations, comprising (a) a plurality of piezoelectric devices, the plurality of piezoelectric devices being capable of insertion into a plurality of underground wells in the underground formation and producing and detecting a broad range of vibrational frequencies; (b) an apparatus for inducing vibrations of desired frequencies in the plurality of piezoelectric devices; (c) an apparatus for pumping a proppant fluid into the plurality of underground wells; and (d) an apparatus for extracting hydrocarbons from the wells. 
         [0022]    In another embodiment, the present invention relates to a method of enlarging fractures in underground geological formations, comprising embedding a plurality of piezoelectric devices capable of producing ultrasonic mechanical vibrations having (or within) a predetermined range of frequencies in wells exposing the underground formation; and inducing the mechanical vibrations in the wells using the piezoelectric devices to fracture the underground formation. 
         [0023]    In another embodiment, the present invention relates to a method of extracting hydrocarbons from an underground geological formation, comprising (1) inserting a plurality of piezoelectric devices into a plurality of wells near a deposit of hydrocarbons in the underground formation, (2) inducing vibrations (e.g., within a predetermined frequency range) in the formation using the piezoelectric devices, (3) detecting vibrations reflected by the formation and determining the resonant frequencies of fractures in the formation, (4) inducing vibrations in the formation at the resonant frequencies using the piezoelectric devices (e.g., to shake and enlarge the existing fractures), and (5) collecting hydrocarbons released through the enlarged fractures. The method may further include flowing a proppant into the enlarged fractures to prevent them from closing or narrowing, and to aid in freeing physisorbed hydrocarbons from the underground formation. 
         [0024]    The present invention advantageously improves the efficiency of extracting hydrocarbons from underground deposits in geological formations such as oil shale, coal beds, sandstone, and other geological formations that contain hydrocarbons. The current apparatus and method reduce or eliminate the need for hydraulic fluids in the process of fracking underground geological formations. Thus, the present invention reduces the costs associated with hydraulic fracturing, including the cost of the hydraulic fluid (e.g., the water and the additives, such as acids, buffering agents, bactericides, corrosion inhibitors, friction reducers, surfactants, gelling agents, etc.), the pumping and equipment costs for introducing the hydraulic fluids into wells, and the cost of storing the used hydraulic fluid once it is removed from wells. The present invention also reduces or eliminates the environmental impacts of hydraulic fracking resulting from the use of fracking fluids, since the present invention enables fracking underground without fracking fluids. These and other advantages of the present invention will become readily apparent from the detailed description of various embodiments below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a diagram showing the major components of a fracking system according to one embodiment of the present invention. 
           [0026]      FIG. 2  is a diagram of a probe head containing one or more variable window piezoelectric transducers for delivering and sensing mechanical vibrations in an underground geological formation. 
           [0027]      FIG. 3  is a schematic of an amplifier system for inducing mechanical vibrations in an array of piezoelectric devices. 
           [0028]      FIG. 4  is a flow chart of a feedback process for determining specific ranges of resonance frequencies for an underground geological formation. 
           [0029]      FIG. 5  is a diagram showing a process of extracting hydrocarbons from an underground geological formation. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Reference will now be made in detail to various embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the following embodiments, it will be understood that the descriptions are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be readily apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention. 
         [0031]    So that the manner in which various features of the present invention can be understood in detail, a more particular description of embodiments of the present invention, briefly summarized above, may be had by reference to various embodiments as described below and shown in the drawings. It is to be noted, however, that the appended drawings show illustrative embodiments encompassed within the scope of the present invention, and therefore, are not to be considered limiting, for the present invention includes additional embodiments. 
         [0032]    The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including, but not limited to. To facilitate understanding, like reference numerals have been used, where possible, to designate like elements common to the figures. For the sake of convenience and simplicity, the terms “connected to,” “coupled with,” “coupled to,” and “in communication with,” may be used interchangeably, but these terms are also generally given their art-recognized meanings 
         [0033]    The invention, in its various aspects, will be explained in greater detail below with regard to exemplary embodiments. 
         [0034]    An Exemplary Fracking System 
         [0035]    Embodiments of the present invention generally relate to a system for inducing or enlarging fractures (fracking) in underground geological formations. In one aspect, embodiments of the present invention relate to a system that includes piezoelectric devices and is capable of determining resonant frequency ranges of fractures in underground geological formations. For example, the system is capable of producing mechanical vibrations in the resonant frequency ranges in a well to induce further fracturing of the material in the underground geological formation. In one embodiment of the system, the piezoelectric devices include ultrasonic piezoelectric transducers that are capable of detecting and producing mechanical vibrations. In another embodiment, the system further includes titanium horns coupled to the piezoelectric transducers to enhance the mechanical vibrations of or from the piezoelectric transducers. 
         [0036]      FIG. 1  provides an illustration of an exemplary fracking system  100 . The system includes a housing  110  that may contain a pulser/receiver system capable of (1) producing electrical signals to be transmitted to an array of variable window piezoelectric transducers and (2) receiving and interpreting electrical signals from the piezoelectric transducers. The array of piezoelectric transducers can be contained in housing  170 , which organizes and protects the array of transducers  120  as they are introduced into an underground geological formation through a wellbore  160 . The piezoelectric transducers in the array may each be coupled to a horn assembly configured to amplify the vibrations of the coupled piezoelectric transducer. The horn assemblies are contained in the housing  170  along with the associated piezoelectric transducers. The piezoelectric transducers may be coupled to the pulser/receiver system by coupling cables  150 , configured to carry electrical signals between the pulser/receiver system and the piezoelectric transducers. The fracking system may also include components for introducing an innocuous proppant material (e.g., nitrogen gas, air, etc.) into the well bore to maintain fractures created by the fracking system in the underground geological formation, and a vacuum system for creating negative pressure in the wellbore to create a path of lower (e.g., least) resistance for the hydrocarbons released from the formation. For example, a reversible vacuum/pump system  140  that can both reduce pressure in the wellbore  160  and draw hydrocarbons toward the surface. Also, a storage tank  130  for the proppant (e.g., N 2  gas) may be coupled with the vacuum/pump system  140 , such that the proppant can be introduced into the wellbore  160  by the reversible vacuum/pump system  140 . 
         [0037]    In one embodiment, the fracking system  100  may be configured to work in several wellbores simultaneously. Specifically, the fracking system may include one or more piezoelectric transducer arrays that can be introduced into one or more wellbores. Each transducer array can be introduced into a separate wellbore, and each array may contain variable window piezoelectric transducers that vary in the frequency ranges in which they can produce and detect vibrations. Additionally, the vacuum/pump system  140  may include a manifold with several wellbore couplings, each connected to a different wellbore. Thus, the vacuum/pump system  140  may be used to reduce pressure and introduce proppant in multiple wellbores simultaneously. In an alternative embodiment, the fracking system can be configured to operate on a single wellbore (e.g.,  160 ). 
         [0038]    Each variable window transducer array may include one or more probe heads that contain piezoelectric transducers.  FIG. 2  shows a probe head  230  that may house one or more piezoelectric transducers and associated horn assemblies (not shown). The probe head  230  can be safely introduced into a well exposing an underground geological formation containing hydrocarbon deposits (e.g., shales, coal beds, sandstone, etc.) without damage to the piezoelectric transducers and horn assemblies therein. One or more probe heads  230  can be introduced into a single wellbore. The probe head  230  may include a tough metal housing constructed of a strong metal, such as iron, titanium, tungsten, aluminum, and alloys thereof (e.g., stainless steel), which may contain additional corrosion-resistant metals (e.g., chromium, zinc, nickel, etc.) or may be coated with corrosion-resistant metals. For instance, the probe head  230  may be made of titanium or steel (e.g., surgical grade stainless steel). 
         [0039]    The piezoelectric transducers may be ultrasonic and polyphonic, able to produce a range of sonic to ultrasonic vibration frequencies upon the application of a voltage to the transducers from a pulser/receiver system that may be connected to the piezoelectric transducers via coupling cables  210  (or  150 , as shown in  FIG. 1 ). The transducers are also able to transduce mechanical vibrations into electrical signals. Thus, the piezoelectric transducers are able to act as both sensors for sonic and ultrasonic mechanical vibrations, creating electrical current upon deformation by a mechanical vibration (the piezoelectric effect), and as oscillators for generating sonic and ultrasonic mechanical vibrations, changing molecular or crystalline structure upon the application of an electrical current (electrostriction). The piezoelectric transducers contain a piezoelectric material that behaves in this manner, such as piezoelectric ceramics and crystals. The piezoelectric transducers may include one or more piezoelectric ceramics, such as lead zirconate titanate (PZT), barium titanate (BaTiO 3 ), lead titanate (PbTiO 3 ), potassium niobate (KNbO 3 ), lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), zinc oxide (Zn 2 O 3 ), and sodium tungstate (Na 2 WO 3 ); or piezoelectric crystals, such as quartz (SiO 2 ), gallium orthophosphate (GaPO 4 ), or langasite (La 3 Ga 5 SiO 14 ). In one embodiment, the piezoelectric material is PZT. 
         [0040]    The individual piezoelectric transducers within the probe head  230  can be tuned to different vibrational frequencies, depending on the structure of the transducer. For instance, the thickness of the piezoelectric material can be varied, in order to cover various and/or different frequency ranges. Additionally, a damping layer (e.g., a resin or metal layer, such as steel or aluminum) may be included in the transducer in order to widen the range of vibration frequencies that the transducer can detect and thus increase the transducer&#39;s sensitivity. 
         [0041]    The piezoelectric transducers may also include other known components, such as electrodes for collecting and delivering electrical current to and from the piezoelectric material, an electrical connector between the piezoelectric transducers and the coupling cables  210 , electrical wires connecting the electrodes to the electrical connector, a housing  220  for the electrical connector between the piezoelectric transducer and the coupling cables  210 , a housing for each piezoelectric transducer within the probe head  230 , etc. Ultrasonic horns (not shown) may be coupled to each of the piezoelectric transducers in a given probe head. The ultrasonic horns vibrate with the piezoelectric transducers to increase the amplitude of the mechanical vibrations created by the piezoelectric transducer. The ultrasonic horns may comprise titanium or aluminum. 
         [0042]    The piezoelectric transducers can be coupled to a pulser/receiver instrumentation system by coupling cables.  FIG. 1  shows a housing  110  for this pulser/receiver instrumentation system coupled to a transducer array  120  by coupling cables  150 . The pulser/receiver system may include a phase-coupled inverse frequency-spectrum analyzer, an attenuator, one or more amplifiers, one or more display devices, and a quarter-wave filter assembly. The pulser/receiver instrumentation system includes a pulsing system for inducing high frequency mechanical vibrations in the piezoelectric transducers and a receiving system for electrical signals created by the detection of vibrations by the piezoelectric transducers (e.g., the phase-coupled inverse frequency-spectrum analyzer). The pulser section of the system can generate short, large amplitude electric pulses of controlled energy, which are converted into short sonic to ultrasonic pulses (e.g., about 1 kHz to about 15 MHz, about 2 kHz to about 5 MHz, about 10 kHz to about 3 kHz, or any value or range of values therein) when applied to a piezoelectric transducer. The receiver section of the system can receive and interpret the electrical signals (e.g., currents) produced by the piezoelectric transducers when they are deformed by mechanical vibrations. 
         [0043]    The receiver section may include a frequency-spectrum analyzer capable of receiving and converting the electrical signals generated by the piezoelectric transducers into digital frequency data that can be displayed on a display device. Example, frequency spectrum analyzers that may be used include the Digital Mobile Radio Transmitter Tester, model no. MS8604A, manufactured by Anritsu, and the Agilent/HP 7000x series of spectrum analyzers. 
         [0044]    The pulser instrumentation system may also include one or more multi-channel amplifiers for increasing the power of the signals created by the pulser for creating mechanical vibrations in the piezoelectric transducers, thereby increasing the amplitude of the mechanical vibrations of the piezoelectric transducers. The pulser and multi-channel amplifier are capable of producing signals for inducing vibrations at multiple frequencies in multiple piezoelectric transducers simultaneously. The receiver instrumentation may also include one or more multi-channel amplifiers to amplify the voltage signals produced by the piezoelectric transducers and transmitted to the receiver instrumentation by coupling cables  150 . The amplified voltage signal can be processed and converted to digital data by the frequency-spectrum analyzer and displayed as an output on the display device. The receiver and multi-channel amplifier are capable of receiving and processing electrical signals (e.g., currents or voltages) from multiple piezoelectric transducers simultaneously. 
         [0045]      FIG. 3  is a schematic of a typical multi-channel amplifier circuit  310 , including the basic components of the amplifiers and filters. Electrical signals from one or more piezoelectric transducers  320  are received by a mixer  350 , which may combine the voltage signal of the transducer(s)  320  with a voltage from a pre-amp  340  to boost the signal. The low pass filter (LPF)  360  filters the frequency of the electrical signal from the mixer for processing in a frequency analyzer (as discussed above), and the audio amp  370  strengthens the signal from the transducer(s)  320  to enable analysis of the electrical signals produced from the piezoelectric transducer(s)  320 . These components are utilized in a feedback loop  330  that provides real-time feedback from the piezoelectric transducer(s)  320  regarding the changing resonant frequencies in the underground geological formation during the ultrasonic fracking process. The feedback loop  330  allows monitoring of the wave response of the oil shale or other material in the geological formation during the ultrasonic fracking process. 
         [0046]    The presently described embodiments of an ultrasonic fracking system are not limiting, and the invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims. It is also understood that various embodiments described herein may be utilized in combination with any other embodiment described, without departing from the scope contained herein. In addition, embodiments of the present invention are further scalable to allow for additional clients and servers, as particular applications may require. 
         [0047]    An Exemplary Method for Extracting Hydrocarbons Using Ultrasonic Fracking 
         [0048]    The present invention also concerns a method of extracting hydrocarbons from underground geological formations using ultrasonic vibrations created using piezoelectric devices (e.g., a variable window transducer array, as discussed above). One or more of the piezoelectric devices can be introduced into each of one or more wellbores so that each piezoelectric device is near a hydrocarbon deposit in the underground geological formation. Subsequently, a predetermined range of mechanical vibrations can be induced in the piezoelectric device using the pulser/receiver instrumentation to induce fractures in the geological formation and release hydrocarbons therefrom. 
         [0049]      FIG. 4  is a flowchart  400  for the general steps of ultrasonic fracking, including a feedback loop system for adjusting the frequencies used to fracture the underground geological formation. Once determined, these frequencies are used to adjust the range of ultrasonic vibrations produced from a piezoelectric device array for creating or extending fractures in the underground geological formation. 
         [0050]    The method starts at  410 , and at  420 , a range of vibrational frequencies that are predicted to induce fracturing in the underground geological formation (e.g., oil shale, coal bed, sandstone, or other geological formation that may contain hydrocarbon deposits) are introduced by piezoelectric devices into the geological formation. Vibrations of certain frequencies are absorbed by fractures in the geological formation (resonant frequencies), and thus are attenuated when they are reflected back to the piezoelectric devices. The pulser/receiver can determine the resonant frequencies of the geological formation, based on the attenuation (lower or reduced amplitude) of the resonant frequencies that are reflected back to the piezoelectric device. At  430 , the amplitudes of the resonant frequency response are determined. Determination of the resonant frequencies at  420  and of the amplitude(s) at  430  can be repeated until the resonant frequencies of the underground formation are mapped. 
         [0051]    At  440 , the pulser and amplifier instruments can be tuned to the resonant frequencies and amplitudes to enable further fracturing the underground geological formation. At  450 , controlled ultrasonic vibrations are induced in the piezoelectric transducers at the resonant frequencies of the fractures in the geological formation. These ultrasonic vibrations result in the shaking, fracturing, and/or enlarging of fractures in the geological formation. As mentioned above, the fracking system described above is capable of monitoring changes in the resonant frequencies of the fractures in the geological formation. 
         [0052]    At  460 , the pulser/receiver instrumentation of the fracking system continually or intermittently monitors changes to the resonant frequencies of the fractures in the geological formation, in order to adjust the frequency of the ultrasonic pulses to the changing resonant frequencies during the fracking process (e.g., at  420 , via feedback loop  320  in  FIG. 3 ). Thus,  FIG. 4  shows a cyclical process, wherein frequency monitoring at  460  and analysis of the resonant frequencies at  420  and  430  are ongoing, and the frequencies delivered to the piezoelectric transducers at  440  and  450  are adjusted in response to changes detected in the resonant frequency or frequencies of the geological formation. 
         [0053]    More specifically, the piezoelectric devices (e.g., a probe head) comprise an array of piezoelectric transducers that are each tuned to a different range of frequencies in the sonic to ultrasonic range of about 1 kHz to about 15 MHz (e.g., about 2 kHz to about 5 MHz, about 10 kHz to about 3 kHz, or any value or range of values therein), which generally covers the frequencies at which geological formations such as oil shale, coal beds, sandstone and other geological formations that contain hydrocarbons absorb vibrations. The piezoelectric transducers also absorb mechanical vibrations in their tuned range, and transduce the vibrations to electrical signals, which are transmitted back to the pulser/receiver instrumentation. Fractures in the geological formation will absorb the vibrations produced by the piezoelectric device at resonant frequencies, resulting in an attenuation of the vibrations at that resonant frequency. Thus, the piezoelectric transducers that are tuned for the frequency range that includes the resonant frequency will produce a weaker electrical signal when the vibrations are reflected by the geological formation. The attenuated signal allows pulser/receiver to identify the resonant frequency range. Subsequently, the pulser/receiver system may induce mechanical vibrations at the resonant frequencies (e.g., mechanical waves  240  and their associated nodal planes  250 , shown in  FIG. 2 ) by sending an electrical current to the piezoelectric transducer(s) that is tuned for the range that includes the resonant frequencies, resulting in shaking and enlargement of the fractures. For example,  FIG. 2  shows a destructive mechanical vibration  260  at the resonant frequency of a fracture in the underground formation inducing damage and enlargement of the fracture. 
         [0054]    Prior to the fracking process, a series of relatively small diameter wellbores may form a horizontal x-y array on the ground surface. The wellbores may have variable depths, thereby creating a three-dimensional array of wellbores penetrating the underground geological formation. The varying depths of each wellbore may be used to create an optimized three-dimensional array of the piezoelectric transducers introduced into the wellbores. The three dimensional array may be predetermined. Ground penetrating radar, satellite-based imagery and geologic/seismic survey data can be used to topographically map the target geological formation for volume, density, composition, etc. After these data are acquired (given that the properties of each geological body or locale is unique), the correct x-y positions (±0.5 m 2 ) over the body can be identified. Precise depths for each bore hole can then be calculated. 
         [0055]    Given that the general equation for a wave function is known, calculating the frequency windows needed on a Riemannian surface (the volume of the geological formation, e.g., shale body) begins by calculating the length in the time domain, then the material-dependent impedance of the ith piezoelectric transducer array by beginning, for example, with calculating the Lagrangian: 
         [0000]        L   a   b (φ)=∫ a   b ∥{dot over (φ)}( t )∥ dt=∫   a   b (&lt;{dot over (φ)}( t )|{dot over (φ)}( t )&gt; γ(t) ) 1/2   dt  
 
         [0000]    A Fourier Transform of this to the frequency domain would then permit determination of the frequency window for the ith transducer. As indicated above, this is merely the expectation value. Real-time data from each transducer can then optimize the pulse for the ith transducer, as it relates to the NNNth transducer (NNN=next nearest neighbor), accommodating for response time of the material surrounding each. After the body volume has been calibrated, each transducer can then be fitted with the correct titanium horn, thereby allowing each transducer to constructively, polyphonically participate in generating the disruptive manifold. Following titanium-horn installation, a total signal gain can be applied until the optimal power, power spectrum, and phase characteristics of the pulse have been achieved. 
         [0056]    The piezoelectric devices may then be inserted into the wellbore to the point that they are within or near the underground geological formation. For example, a piezoelectric device connected to a fracking system  510  may be lowered through a wellbore  520  into geological formation  530  (see  FIG. 5 ). One or more piezoelectric devices (e.g., probe heads) can be inserted into a single wellbore. Once the piezoelectric devices are sufficiently close to the geological formation  530 , the ultrasonic fracking process (as described above) can commence. In the case of vertical well bores (see, e.g., wellbore  160  in  FIG. 1 ), the piezoelectric devices may be introduced into the wellbores by simply lowering them into the well. However, in the case of horizontal wells (see, e.g., wellbore  520  in  FIG. 5 ), the piezoelectric devices can be inserted into the wellbores using a drilling string or a small mechanical tunnel-traversing vehicle. 
         [0057]    As shown in  FIG. 5 , during or immediately after ultrasonic fracking, vacuum or suction may be applied to the wellbore(s)  520  to reduce pressure in the opening and upper portion of the wellbore(s)  520  to draw hydrocarbons (e.g., natural gas)  550  to the surface, where it can be collected. Additionally, an innocuous proppant (e.g., N 2  gas) may be pumped into the underground geological formation in order to aid in (1) keeping the fractures in the formation (see, e.g., fractures  540  in  FIG. 5 ) open and (2) de-sequestration of natural gas components (e.g., methane) that may be physisorbed to the material of the formation (e.g., oil shale, coal, sandstone, etc.). Disruption of the matrix of the geological material, followed by infusion and extraction of gases along the natural z-gradient of the formation (which results in greater local pressure at greater depths) is carried out as a cyclic, periodic process. For example, ultrasonic fracking, can be followed by infusing N 2  gas into the well bore  520  and then applying a vacuum to the wellbore  520  to draw hydrocarbons  550  (see  FIG. 5 ) freed from the formation by the fracking process. 
         [0058]    The presently described embodiments of a method of extracting one or more hydrocarbons (e.g., one or more gases at room temperature and atmospheric pressure, consisting essentially of carbon and hydrogen, such as natural gas, methane, ethane, propane, butane, etc.) from underground geological formations using ultrasonic vibrations are not limiting, and the invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims. 
       Conclusion/Summary  
       [0059]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. It is also understood that various embodiments described herein may be utilized in combination with any other embodiment described, without departing from the scope contained herein. In addition, embodiments of the present invention are further scalable to allow for additional clients and servers, as particular applications may require. 
         [0060]    The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.