Abstract:
Disclosed is a cleaning apparatus for any structure where caking of particles may affect productivity, particularly a subterranean formation or wellbore, characterized in that it requires no external electrical source and includes the following elements: At least one ultrasonic energy sonde for converting an alternating electric power signal at a selected voltage into ultrasound energy; At least one ultrasonic generator that conditions electrical power to the signal required to energize the ultrasonic energy sonde; At least one apparatus which converts mechanical energy into electrical energy, preferably a piezoelectric generator, in a configuration and with appropriate circuitry to provide electrical power to said ultrasonic generator(s); and A means for applying mechanical force to said apparatus to generate electricity to power said generator.

Description:
FIELD OF INVENTION  
       [0001]     This invention relates to downhole cleaning using an ultrasonic device. More particularly, this invention relates to downhole cleaning utilizing ultrasonic generator(s) powered by piezoelectric element(s), not requiring external electric power. The ultrasonic generator and piezoelectric element are placed within the completion equipment and the piezoelectric element(s) is normally in an unstrained state, generating no electrical current, but when subjected to mechanical force, it generates electricity to power the ultrasonic device.  
       BACKGROUND OF THE INVENTION  
       [0002]     Well productivity is often impaired by fine particles lodged in restrictions or caked on the wellbore. Chemical cleaning has limited effectiveness in removal of these materials. Ultrasonic devices have been shown to enhance cleaning and particle separation from liquids. Current downhole ultrasonic cleaning devices are powered by external electric sources connected to the device by wires or cables.  
         [0003]     It is known to enhance well cleaning using acoustic excitation. U.S. Pat. No. 4,280,557 discloses an apparatus for cleaning an extended number of apertured portions of the lower region of an oil well casing, which includes a sonic oscillator, a stem member in the form of an elongated elastic tube which runs along said extended number of apertured portions, said oscillator to be attached to the top end of said stem member in the region of the apertured portions to be cleaned, and means for driving said oscillator. U.S. Pat. No. 5,458,860 discloses the use of sonic energy to enhance the removal of alkaline earth scale using an aqueous solution having a pH of about 8 to 14 and comprising a chelating agent.  
         [0004]     The use of an external electric power source connected by a cable to power an electroacoustic ultrasonic energy producing transducer is disclosed in U.S. Pat. No. 5,109,922 which describes a power supply adjacent to the well and an electrical conductor means of a length sufficient to extend from ground level to at least the level of oil in the well for conducting alternating electrical power from said power supply to said transducer. U.S. Pat. No. 5,184,678 discloses an apparatus for stimulating fluid production in a producing well wherein a well stimulating tool comprising a sealed tool housing with an acoustic transducer in the housing is run into a producing well on an electric wireline and placed at a depth opposite perforations in the producing zone. Similarly, U.S. Pat. No. 5,595,243 discloses a method and apparatus for cleaning the wellbore and the near wellbore region in which a sonde is provided which is adapted to be lowered into a borehole and which includes a plurality of acoustic transducers arranged around the sonde, and wherein electrical power provided by a cable is converted to acoustic energy.  
         [0005]     The use of mechanical coupling to produce low frequency waves is disclosed in U.S. Pat. No. 4,469,175, which describes a mechanoacoustic transducer, which comprises a plurality of circumferentially spaced contiguous vibratile plate members, which are driven in phase by a rotating cylindrical cam. The cam is shaped to provide radial oscillatory displacements of the vibratile plates of sufficient amplitude to generate acoustic power density levels in liquids in the order of 100 kW or more per square foot of radiating surface of the cylindrical transducer.  
         [0006]     The use of fluid coupling to produce vibration to enhance well cementing is disclosed in U.S. Pat. No. 4,658,897. The transducer members are within a sleeve that is filled with oil and communicates vibrations from the transducer members.  
         [0007]     U.S. Pat. No. 4,788,467 discloses in combination a housing, at least one transducer disposed in the housing and having properties of receiving electrical energy and converting the electrical energy into expansions and contractions of the transducer for the pumping of oil in the oil well in accordance with such expansions and contractions, passages extending into and out of the housing at opposite ends of the housing at a position below the transducer, a piston disposed in the housing for movement in accordance with the pressure of the fluid in the oil well, and a spring supported between the piston and the housing for compression and expansion to inhibit any cavitation of the oil in the oil well as a result of such expansion and contraction of the transducer and as a result of changes in the temperature of the oil in the oil well.  
         [0008]     U.S. Pat. No. 5,554,922 discloses a system for the conversion of pressure fluctuations prevailing in a fluid distribution piping system into electrical energy, characterized in that it includes a casing, at least one chamber formed in the casing which may be linked to a fluid system and which is limited on one side by a wall which may be moved back and forth under the influence of the pressure prevailing in the fluid system, and at least one apparatus which is connected to the movable wall and which converts the mechanical energy transmitted by this into electrical energy.  
         [0009]     As mentioned above, current downhole ultrasonic cleaning devices are powered by external electric sources connected to the device by wires or cables. It would be extremely valuable in the art if there were an alternative, lower cost, simpler way to power such devices using mechanical force to generate electrical power using a piezoelectric device. In many industrial applications, particularly those involved in the drilling, completion, and workover of oil and gas production wells, equipment normally used in these applications is already designed to apply large magnitude, controlled loads or stresses from the surface or other remote location to the equipment at the bottom of the well. On the other hand delivering external electrical power as required in the prior art requires additional equipment not normally installed in the well. The prior art does not recognize the opportunity to use the available mechanical force to create electricity to power the down hole ultrasonic device.  
       SUMMARY OF THE INVENTION  
       [0010]     In accordance with the foregoing the present invention is a cleaning apparatus for any structure where caking of particles may affect productivity, characterized in that it requires no external electrical source and includes the following elements: 
    1) At least one ultrasonic sonde or horn that produces ultra high frequency pressure oscillations in a fluid when energized by an electrical signal;     2) A generator to deliver the necessary electrical signal to the sonde or horn, said generator containing appropriate circuitry to provide the appropriate voltage, power, and frequency of electrical excitation to the ultrasonic sonde in item 1);     3) At least one apparatus which converts mechanical energy into electrical energy, preferably a piezoelectric element, also placed or inserted within said structure connected to the generator described in item 2) and through it able to provide electrical excitation to the ultrasonic sonde; and     4) A means for applying mechanical force to said apparatus to generate electricity to power said mechanical electrical converter. The invention is also a method of cleaning a structure that is enclosed, or otherwise difficult to access, and where mechanical force can be applied more readily or at lower cost than electrical power, such as, for example, an enclosed tank or vessel, or a pipeline or subterranean well, such as those used for oil and gas production, using an ultrasonic source, characterized in that no external electric source is required, which includes the elements of: 
        1) Placing in the completion equipment one or more ultrasonic generator(s);     2) Placing within the completion equipment in close proximity to the ultrasonic generator(s) one or more apparatus(s) for converting mechanical force to electrical energy, preferably piezoelectric element(s), said element(s) normally in an unstrained or relaxed state; and     3) Applying mechanical force to said piezoelectric element when it is desirable to generate ultrasonic excitation to enhance well cleaning.    
       
 
     
    
     BRIEF DESCRIPTION OF THE DIAGRAMS  
       [0018]      FIG. 1  is a block diagram of the invention configured for temporary insertion into the well or other structure of fixed diameter with a packer on tubing.  
         [0019]      FIG. 2  is a diagram of the invention configured for permanent installation in the wellbore and activation by inserted tubing.  
         [0020]      FIG. 3  is a graph showing voltage vs. current for a piezo generator.  
         [0021]     FIGS.  4 ( a ) and  4 ( b ) are diagrams of compression and tension generators, respectively.  
         [0022]     FIGS.  5 ( a ) and  5 ( b ) are diagrams of parallel and transverse shear generators, respectively.  
         [0023]     FIGS.  6 ( a ) and  6 ( b ) are diagrams of series and parallel bending generators, respectively. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Piezoelectric materials transform energy from mechanical to electrical and vice-versa. Piezoelectric materials produce an electric field when exposed to a change in dimension caused by an imposed mechanical force (mechanical to electrical conversion) and conversely, an applied electric field will produce a mechanical stress (electrical to mechanical conversion). These materials can be used for sensing purposes, including actuator and sensor applications.  
         [0025]     In the present invention a downhole ultrasonic well cleaning device is powered by an apparatus that converts mechanical force into electrical energy, preferably a piezoelectric generator. Both are installed or inserted within the completion equipment of any structure where the caking of particles may affect productivity. The preferred application is in cleaning wells and subterranean formations. The ultrasonic generator and piezoelectric element would be placed within the completion equipment (e.g. pipeline, tubing, packer, sand control screen, or other element) of a pipeline or subterranean well such as those used for oil or gas production.  FIG. 1  illustrates a configuration for temporary insertion in the well. The mechanical electrical converter  1 , ultrasonic generator  2 , and the ultrasonic sonde  3  are inserted on the end of a temporarily installed tubing  4 , which is anchored in place by a temporary packer sealing element  5 . Tension or compression as denoted by the arrow  6  is applied to this tubing from an oil field drilling rig, workover rig, or workover hoist.  
         [0026]      FIG. 2  illustrates a configuration for permanent installation. In this case the mechanical electrical converter  1 , ultrasonic generator  2 , and the ultrasonic sonde  3  are permanently affixed to the permanent production tubing of the well  4  which may be affixed with a permanent packer sealing element  5 . In this configuration the force  6  is applied to a second tubing  7  that is temporarily inserted into the bore of the permanent tubing  4 . In this configuration a flow passage  8  exists. The principle differences between the two are the passageway to allow fluid production in the second example and the arrangement of packers and alignment of tubing to allow easy removal in the first application. Other configurations could be envisioned but these diagrams capture the key elements of two broad classes.  
         [0027]     The piezoelectric element of the mechanical electrical converter is normally in a relaxed (unstrained) state and generates no electrical current, however the piezoelectric element(s) are mounted or inserted in the pipeline or well equipment in a manner which allows the operator to apply mechanical force as required. When the operator desires to generate ultrasonic excitation to enhance well cleaning, mechanical force would be applied to the piezoelectric element to generate electricity to power the ultrasonic sonde.  
         [0028]     Ultrasonic sondes convert electrical energy to ultra high frequency pressure oscillations when electrical energy is applied to the sonde at its operational resonant frequency. The operational resonant frequency and range of the sonde is determined by its design, specifically geometry and materials of construction. Various equipment manufacturers accomplish this in a number of ways. The present invention is not intended to be limited to any particular ultrasonic sonde. Suitable acoustic sondes and transducers are described, for example, in U.S. Pat. No. 5,595,243 and U.S. Pat. No. 5,184,678, both incorporated by reference herein in the entirety.  
         [0029]     The ultrasonic generator converts normal sources of electricity, such as direct current from batteries or alternating current, typically 20 to 80 Hz, to ultra high frequency alternating current to excite the operational resonant frequency of the ultrasonic sonde. The principles to be applied in designing a suitable generator for this application are known to those skilled in the art. Examples are given in U.S. Pat. No. 5,184,678 and U.S. Pat. No. 5,595,243. Use of direct current from a battery has been revealed by Y. Bar-Cohen, S. Sherrit, B. Dolgin, T. Peterson, D. Pal and J. Kroh, “Ultrasonic/Sonic Driller/Corer (USDC) With Integrated Sensors,” New Technology Report, Submitted on Aug. 30, 1999. Docket No. 20856, Item No. 0448b, Nov. 17, 1999. Provisional Patent, filed on May 3, 2000, Application No. 60/201,650. The ultrasonic generator receives input signals from the piezoelectric element when it is placed in tension or compression or it is otherwise strained.  
         [0030]     The device for converting mechanical to electrical energy revealed in this invention is based on the phenomenon that piezoelectric elements can be used to generate electrical power when they are subjected to mechanical force, i.e. when they are placed in compression or tension and when they are strained. Piezoelectric materials include many polymers, ceramics, and molecules, such as water, which are permanently polarized. Suitable piezoelectric materials in the present invention for producing an electric field as the result of an imposed mechanical force include, for example, but are not limited to ceramic, quartz (SiO 2 ), barium titanate (BaTiO 3 ), lithium niobate, polyvinyledene difluoride (PVDF), and lead zirconate titanate (PZT). (See: http://www.mse.cornell.edu/courses/engri111//piezo.htm They are ceramic materials manufactured of specific materials and under specific conditions to impart piezoelectric properties. Other classes of materials, such as certain minerals and combinations of metal and minerals may also create the same effect and could be used in this invention. The ceramic materials are preferred because their properties are more reproducible and controllable. The property that is exploited in this invention is that when a mechanical force is applied, placing the piezoceramic in tension, compression, or inducing strain, an electrical charge is generated. The charge generated is proportional to the force applied. If designed appropriately this charge will induce an electromotive force that can supply current to power electrical devices like the generator and sonde in this invention.  
         [0031]     The material to be used in this invention will be chosen based on the relationship between the properties of the material, the mechanical design of the installation or apparatus delivering force, and the electrical properties (voltage and power) required to power the sonde. These are captured schematically in  FIG. 3 , which illustrates a typical curve of voltage produced versus current for a piezo ceramic. The value of voltage produced for a given mechanical loading is a property of the piezo ceramic know in the industry as the “g” constant. This constant is commonly known for commercially available materials suitable for this application. The maximum voltage (denoted VOC in  FIG. 3 ) is achieved if the circuit is open, i.e. no current or power is drawn from the device. As current is drawn from the device the voltage is reduced but power is generated. The maximum current is available if the circuit is closed (denoted ICC in  FIG. 3 ). The appropriate operating point (A in  FIG. 3 ) for the piezo ceramic defined by a particular stress (SOP in  FIG. 3 ) above the threshold stress for the material (S 1  in  FIG. 3 ) will deliver the required voltage and current to the generator to power the sonde at the mechanical stress the apparatus is designed to impart.  
         [0032]     The piezoelectric element in this invention is placed in a mechanical element or housing within the wellbore or inserted tubing such that mechanical force imposed on the tubing is transmitted to the element. As illustrated in  FIGS. 4-6  this mechanical force could be used to place the piezo electric element in tension or compression or to bend it. Each of these modes of operations may be useful in specific designs. For example a simple tension or compression device, as illustrated in FIGS.  4 ( a ) and ( b ), would be applicable in the application illustrated in  FIG. 1  where the apparatus is placed symmetrically in the center of the well. A shear type device as illustrated in FIGS.  5 ( a ) and ( b ) would be more applicable in the apparatus illustrated in  FIG. 2  where the ultrasonic apparatus and mechanical—electrical energy converter is place asymmetrically on one side of the well tubing.  
         [0033]     Single sheets of piezo can be energized to produce motion in the thickness, length, and width directions. They may be stretched or compressed to generate electrical output. Double or multiple ceramic elements may be used in series or parallel as required to generate the required voltage and power. Other alternatives are bending or extension of two-layer generators including extension and bending generators. Applying mechanical stress to a laminated two layer element results in electrical generation depending on the direction of the force, the direction of polarization, and the wiring of the individual layers. In the case of an extension generator, when a mechanical stress causes both layers of a suitably polarized 2-layer element to stretch (or compress), a voltage is generated which tries to return the piece to its original dimensions. Essentially, the element acts like a single sheet of piezo. The metal shim sandwiched between the two piezo layers provides mechanical strength and stiffness. Any of these or combinations thereof may be applied to deliver the voltage and power required to drive the sonde.  
         [0034]     In multi-layer generators, one example of which is a stack generator, the stack, which comprises a large number of piezo layers, is a very stiff structure with a high capacitance. It is suitable for handling high force and collecting a large volume of charge.  
         [0035]     Series operation refers to the case where supply voltage is applied across all piezo layers at once. The voltage on any individual layer is the supply voltage divided by the total number of layers. A 2-layer device wired for series operation uses only two wires, one attached to each outside electrode ( FIG. 6   a ).  
         [0036]     Parallel operation refers to the case where the supply voltage is applied to each layer individually. This means accessing and attaching wires to each layer. A 2-layer bending element wired for parallel operation requires three wires; one attached to each outside electrode and one attached to the center shim ( FIG. 6   b ).  
         [0037]     In the present invention the ultrasonic generator and piezoelectric elements would be attached or installed in a structure or wellbore during completion. This could be accomplished in a number of ways, as would be apparent to those skilled in the art and the present invention is not intended to be limited to a particular method. The elements can be secured by, for example, welding, or cement adhesions, or by screwing in mounting brackets. (See: http://www.loadmonitors.com/services.htm)  
         [0038]     The mechanical force could be applied by several means, including, but not limited to: 1) Placing the well tubing in tension or compression; 2) Use of a second tubing inserted into or around the wells permanent tubing; or 3) Use of a mechanical device inserted into the wellbore on a non-conducting wire.  
         [0039]     In another embodiment the apparatus could be situated on sectional tubing, coiled tubing, or non-electric wireline, then inserted into the wellbore and actuated by mechanical force, by one of the methods described above.  
         [0040]     As mentioned above, the mechanical force could be applied by, for example: 1) Placing the well tubing in tension or compression; 2) Use of a second tubing inserted into or around the wells permanent tubing; or 3) Use of a mechanical device inserted into the wellbore on a non-conducting wire. Well tubing can be placed in compression using a packer or other tubing anchor to lock the tubing in place. Such packers and tubing anchors are commercial items available from a variety of vendors and widely used in well construction activities, (See, for example, http://www.bakerhughes.com/bot/service_tools/index.htm) and can be placed in tension or compression using mechanical equipment normally available on rigs and hoists used for well operations. The techniques used to place tubing in compression or tension in a controlled manner are often practiced by those skilled in the art using established techniques. The piezoelectric elements could be situated such that when either tension or compression of the tubing occurs, the piezoelectric element is subjected to force, thus generating electric power for the ultrasonic transducer.  
         [0041]     In another embodiment, a second tubing, of slightly smaller or larger diameter could be inserted into or around permanent tubing, and as it moves it would come in contact with the piezoelectric elements secured in the completion equipment, to create mechanical force, which is converted to electric power for the ultrasonic generator.  
         [0042]     In yet another embodiment, a mechanical device could be introduced into the wellbore on a non-conducting wire, and as it comes into contact with the piezoelectric element(s), the element(s) would be bent or displaced.  
         [0043]     Also within the concept of the present invention the ultrasonic sonde and piezoelectric mechanical to electrical converter could be situated on sectional tubing, or coiled tubing, and subject to compression or tension loads using the equipment and methods described above.  
         [0044]     Alternatively, a non-electric wireline could be inserted into the wellbore with a device designed to catch the mechanical electrical converter or an attachment to it. The operator would then pull on the non-electric wireline to apply a tension load to the mechanical electrical converter. This method would be limited by the strength of the non-electric wireline.  
         [0045]     When mechanical force is applied to the piezoelectric generator, the movement results in an electrical voltage which can be measured at the electrical terminals of the piezoelectric converter and used to power the ultrasonic sonde by suitable electronics, referred to herein as the generator, which are not the object of the present invention.  
         [0046]     This method can be used to clean enclosed tanks or vessels where access for other methods is limited.  
         [0047]     It can be used to clean water production or injection wells or wells used for the injection of steam or production of hot water or steam from subterranean geothermal deposits.  
         [0048]     Variations might include: 
        Positioning of the respective elements (generator or oscillator) with respect to each other.     Nature of the electrical circuitry used to transmit the electrical energy generated to the sonic oscillator.     Materials of construction of the various elements.     Frequency of operation of the ultrasonic sonde.     Whether the sonde is operated in a steady or pulsed mode.     Characteristics of the electrical energy generated—voltage, current, and power.     Methods for positioning the elements in the structure to be cleaned.     Size of the various pieces of equipment.     The orientation of the equipment in the enclosure to be cleaned. This includes the direction in which the respective elements are pointed and whether they are mounted symmetrically or asymmetrically within the enclosure.     In cases where a tubing element or non-electric wireline element is used to apply mechanical force it may be inserted in the bore of a larger tubing or alternatively in the annulus between concentric tubing or casing strings.     Mechanical force may be applied to the element from any direction.        
 
         [0060]     The invention as described is intended only as a means of illustration and should not be construed as limiting the scope of the invention in any way. Those skilled in the art will recognize many variations that may be made without departing from the spirit of the disclosed invention.