Dynamically pressure-compensated source for generating controlled-waveform tube waves in a well or pipeline

Abstract

An acoustic source for use in a well or pipe includes a pulser piston disposed in an acoustic chamber, a linear actuator connected to one side of the pulser piston and a pressure compensator having a pressure outlet in fluid communication with the one side of the pulser piston. The pressure compensator has a sensor for measuring pressure in the well or pipe, a sensor for measuring compensation pressure on the one side of the piston, an hydraulic power source and a controller operatively connected to the hydraulic power source, the well or pipe pressure sensor and the compensation pressure sensor. The controller operates the hydraulic power source such that a predetermined pressure difference between the well or pipe pressure and the compensation pressure is maintained. The controller operates the linear actuator to move the pulser piston to generate acoustic waves having predetermined amplitude, phase, frequency, and waveform.

Description

DYNAMICALLY PRESSURE-COMPENSATED SOURCE FOR GENERATING CONTROLLED-WAVEFORM TUBE WAVES IN A WELL OR PIPELINEBackground

[0001] This disclosure relates to sources of controlled-waveform tube waves that may be deployed in a well or pipeline. Tube waves are used to characterize and monitor changes with time of well or pipeline integrity, identify objects inside the well or pipeline, and characterize and monitor geological formations surrounding a well, such as natural and man-made fractures.

[0002] After completion of a well, it is desirable to obtain information about the geological formations penetrated by the well, the integrity of the well casing, and the cement surrounding the well, in addition to the existence of obstructions within the well. Such information may be especially important when the formations change, for example, by reason of hydraulic stimulation, or changes in the structure of the well such as scale buildup in the well due to production processes, or the location and operation of downhole equipment such as downhole valves. After installation of a pipeline, it is desirable to obtain information about the changing integrity of the pipe, for example, as a result of corrosion or leaks, or the buildup of scale due to flow and as well as obstructions within the pipeline such as pigs.

[0003] Tube waves are low-frequency Schulte waves that propagate in the fluid inside a pipe or well. The speed of propagation and rate of attenuation of tube waves depend on the properties of the pipe or well, the properties of the fluids inside, and the properties of the surrounding formations. Thus, it is possible to estimate these properties and their changes with respect to time by measuring the properties of propagating transmitted, and reflected tube waves, e g., amplitude, phase, velocity, and attenuation.

[0004] Numerous source and detector configurations are possible depending on the specific problem being addressed. However, a practical and cost-effective configuration isto co-locate the source and a sensor or detector inside the well or pipe at a point of access at the surface or existing entry point to the pipeline.

[0005] For wells undergoing hydraulic stimulation, fluid pressure may vary from a low of a few hundred pounds per square inch (psi) to high values often exceeding 15,000 psi. For these varying pressures, the source should be dynamically pressure-compensated and adjustable for fast and slow variations in well pressure. Noise in wells or pipes may be combinations of incoherent (e.g., due to flow) and coherent (e.g., due to pumps) of varying amplitudes and frequency content. For the noisiest conditions, the source preferably should be able to generate particular waveforms, i.e., controlled, that are easily identified and extracted from the detected acoustic pressure or pressure time derivative signal (such signal including the source waveform and noise) for subsequent data processing.Summary

[0006] One aspect of the present disclosure relates to an acoustic source for use in a pressurized well or pipe. An acoustic source according to this aspect includes a piston disposed in a chamber hydraulically connected to the well or pipe, a linear actuator connected to one side of the piston and a pressure compensator having a pressure outlet in fluid communication with the one side of the piston. The pressure compensator has a sensor for measuring pressure in the well or pipe, a sensor for measuring compensation pressure on the one side of the piston, an hydraulic power source and a controller operatively connected to the hydraulic power source, the well or pipe pressure sensor and the compensation pressure sensor. The controller operates the hydraulic power source such that a pre-determined pressure difference between the well or pipe pressure and the compensation pressure is maintained. The controller operates the linear actuator to move the piston to generate acoustic waves having predetermined waveform amplitude, phase, and frequency.

[0007] In some embodiments, the linear actuator comprises a hydraulic cylinder and a reversing proportional valve in signal communication with the controller. The reversing proportional valve is operable to direct hydraulic fluid from the hydraulic power source to opposed sides of an actuator piston in the linear actuator, thus allowing the actuator pistonto move in response to the direction of hydraulic fluid. Motion of the actuator piston is coupled to the pulser piston that vibrates to generate acoustic waves.

[0008] Some embodiments further comprise an electrostrictive (e.g., piezoelectrive or magnetostrictive)) actuator arranged in line with the hydraulic cylinder to move the pulser piston, wherein motion of the electrostrictive transducer is added to the motion of the hydraulic cylinder.

[0009] Some embodiments further comprise a position sensor functionally coupled to the hydraulic cylinder and in signal communication with the controller. The controller is arranged to adjust operation of the hydraulic cylinder in response to measurements of the position sensor such that the predetermined acoustic waveform amplitude, phase, frequency are generated.

[0010] In some embodiments, the pressure compensator comprises a hydraulic intensifier coupled between the hydraulic power source and the one side of the pulser piston.

[0011] Some embodiments further comprise an accumulator disposed between the hydraulic intensifier and the one side of the pulser piston. The accumulator maintains compensation pressure for slow variations in well pressure. It also absorbs pressure increases on the one side of the pulser piston during retraction or reverse motion.

[0012] Some embodiments further comprise a diverter valve disposed between the hydraulic intensifier and the accumulator. The diverter valve is operable to direct fluid flow from the hydraulic intensifier directly to the one side of the pulser piston. This embodiment bypasses the accumulator and enables pressure compensation for rapid changes in well pressure.

[0013] In some embodiments, the diverter valve is operated by the controller. The controller is operable to cause the diverter valve to direct fluid flow to the accumulator or directly to the one side of the pulser piston when a rate of change of measured well or pipe pressure exceeds a selected threshold.

[0014] In some embodiments, the predetermined waveform amplitude, phase, and frequency comprise one of pulses, sinusoidal or periodic signals, sweeps, or codes depending on the needs of subsequent analyses and / or level and type of noise.

[0015] In some embodiments, the predetermined waveform amplitude, phase, and frequency comprise a low amplitude pre-trigger dither to minimize effects of stiction on motion of the pulser piston.

[0016] A method for generating acoustic waves in a well or pipe according to another aspect of this disclosure includes measuring pressure in the well or pipe. A compensation pressure is generated based on the measured pressure and applying the compensation pressure to one side of a driven pulser piston in a first chamber to maintain a predetermined differential pressure across the driven piston. A linear actuator is operated to move or vibrate the pulser piston to generate acoustic waves having predetermined waveform amplitude, and frequency.

[0017] Some embodiments further comprise measuring a parameter related to position of the linear actuator, and changing operation of the linear actuator to cause the measured position to match a desired motion of the linear actuator and thus the pulser piston corresponding to the predetermined amplitude, phase, frequency and waveform of piston displacement and velocity.

[0018] In some embodiments, the compensation pressure is generated by a fluid pressure source apart from the well or pipe.

[0019] Some embodiments further comprise determining a rate of change of the measured well or pipe pressure and communicating the compensation pressure to an accumulator having a compressible gas on one side of a movable barrier in a chamber when the rate of change of pressure is below a selected threshold.

[0020] In some embodiments, the linear actuator comprises an hydraulic motor.

[0021] In some embodiments, the linear actuator comprises an electrostrictive transducer.

[0022] Some embodiments further comprise stopping the generating the compensation pressure while operating the linear actuator.

[0023] Some embodiments further comprise communicating fluid pressure on the one side of the pulser piston to an accumulator having a compressible gas on one side of a movable barrier in a chamber.

[0024] In some embodiments, the linear actuator comprises a driver piston disposed in a second chamber and an electrostrictive (e.g., piezoelectric or magnetostrictive) transducer motion-coupled to the pulser piston.

[0025] Other aspects and possible advantages will be apparent from the description and claims that follow.Brief Description of the Drawings

[0026] FIG. 1. shows example configurations where tube waves are used to monitor a well or a pipeline condition and to characterize and monitor changes in geological formations penetrated by the well or objects, leaks, and other changes in the pipe.

[0027] FIG. 2 illustrates the functional layout of an example embodiment of a tube wave source according to the present disclosure, divided into three major subsystems: an acoustics subsystem, a pressure compensation subsystem, and a control subsystem.

[0028] FIG. 3 illustrates a detailed layout of the acoustics subsystem of the example embodiment in FIG. 2.

[0029] FIG. 4 illustrates a detailed layout of the pressure compensation subsystem of the example embodiment in FIG. 2.

[0030] FIG. 5 shows three examples of measured acoustic signals induced in a well having a pressure of 7000 psi using a source according to the present disclosure: (1) 1 Hz wavelet, (2) 2 Hz wavelet, and (3) 4 Hz wavelet.Detailed Description

[0031] The present disclosure is directed to embodiments of an acoustic source that can induce tube waves in a well or pipe. Like numerals in the various drawing figures represent like components.

[0032] FIG. 1 shows an example arrangement of equipment that may be used to evaluate various properties of a well (or wellbore, the two terms may be used interchangeably in this disclosure) 103 drilled through subsurface formations, or a pipeline 102 disposed underground. Surface equipment 100 may comprise an acoustic (tube wave) source, to be explained further below with reference to FIG. 2, and one or more sensors for detecting tube waves (FIG. 1) in hydraulic communication with the interior of the well 103 or pipeline 102. The source and sensor(s) may be connected to control and recording equipment (not shown separately) used to operate the source and to record and / or process signals detected by the sensor(s). The signals detected may comprise information about obstructions in the well at 107 or in the pipeline at 106 or leaks 108. The signals may also comprise information about the formations outside the well 103. An example such information may be related to includes properties of natural or induced fracture(s) 105.

[0033] The source induces tube waves 104 which propagate, transmit and reflect, along the well 103 or pipeline 102. The waveform of the induced tube waves is related to the motion (vibration) of a pulser piston (explained further below). The waveform of reflected tube waves 104B detected back at the surface equipment 100 depends on the distance traveled in the well 103 or section of the pipeline 102 being investigated, the dimensions and material used for the well or pipeline, properties of the fluid and surrounding formations, and the features, e.g., leaks and obstructions, in the well that reflect and transmit the tube waves inside the well 103 or pipeline 102.

[0034] FIG. 2 shows a functional block diagram of an example embodiment of an acoustic (tube wave) source 200 (“source” hereinafter) according to the present disclosure. The present example embodiment of the source 200 may comprise three subsystems: a control subsystem 203, a pressure compensation subsystem 205, and an acoustics subsystem 207. The source 200 may comprise an electrical power supply (e.g., connection to an electricalcable or a self-contained electrical power supply (not shown separately)) to operate the various components and subsystems in the source 200 to be described below. Description of a source according to the present disclosure as comprising three subsystems is for convenience and is not intended to limit the structure of any embodiment of a source according to the present disclosure.

[0035] The control subsystem 203 may comprise a controller 202. The controller 202 may be, for example and without limitation, a microprocessor, microcomputer, field programmable gate array, programmable logic controller, application-specific integrated circuit or any similar device or combination of such devices capable of executing stored or communicated machine instructions to operate various other devices to be explained further below. It will be appreciated by those skilled in the art that various functions attributed to the controller 202 could also be implemented using analog circuitry. The controller 202 provides output signals that may operate the various devices to be explained further below. Such devices may be, as the type of device may require, connected to the controller 202 through a driver (not shown) such as a relay or power transistor, or other device to convert operating signals from the controller 202 to a form capable of operating the particular device.

[0036] By way of example, and in the present embodiment, the controller 202 may generate electrical signals to control respective solenoid-operated pneumatic valves 208. The solenoid-operated pneumatic valves 208 may control application of pneumatic pressure from a compressor 214 to other devices to be further explained. The solenoid- operated pneumatic valves 208 may be electrically selectively connected to the controller 202 as required by operation of manually operated electrical switches 206. The foregoing switches 206 in some embodiments may be electronically implemented, for example, as relays or power transistors. Pneumatic pressure may be switched through the solenoid- operated pneumatic valves 208 so as to operate hydraulic valves to switch or direct hydraulic fluid flow.

[0037] Hydraulic power to operate certain devices in the source 200, explained further below, to generate acoustic waves may be provided by a hydraulic power unit 226. Thehydraulic power unit 226 may comprise (not shown separately) an electric motor, a hydraulic fluid pump connected to the rotary output of the motor and a hydraulic fluid reservoir. In the present example embodiment, the hydraulic power unit 226 may be capable of moving hydraulic fluid, for example and without limitation, at a rate of 15 gallons per minute (gpm) at pressure of 3,000 pounds per square inch (psi). Electrical power to operate the hydraulic power unit 226 may be provided by the same electrical power supply (not shown) used to operate the controller 202, and may be switched on and off by a manually operated or electronically implemented switch 204.

[0038] The pressure compensation subsystem 205 may comprise an accumulator 210 in hydraulic communication with an output of a hydraulic intensifier 216. The hydraulic intensifier 216 may be driven / controlled by electric power or by pneumatic pressure, e.g., from the compressor 214 as modified by one of the solenoid-operated pneumatic valves 208. The intensifier 216 may act to increase hydraulic fluid pressure from the hydraulic power unit 226, such fluid pressure being applied to the accumulator 210, or in some circumstances directly to a pressure compensation port 232A to a pulser 235 (part of the acoustics subsystem 207). The accumulator 210 may be of any known type of pressure accumulator, e.g., a cylinder, tank or other sealed, pressure resistant container with a movable barrier 210A disposed therein to separate a liquid side from a gas-filled, pressure- pre-charged side of the accumulator 210. The barrier 210A may be, for example, a piston movable within the container or a flexible diaphragm, for example and without limitation. Pressure in the accumulator 210 on the liquid side of the barrier 210A, may be measured by a sensor or transducer PA in signal communication with the controller 202. Pressure in the well 103 (or pipeline 102 in FIG. 1) may be measured by a pressure transducer or sensor Pw in signal communication with the controller 202. A compensation pressure sensor Pc may be in signal communication with the controller 202 and arranged to measure fluid pressure on one side of the pulser piston 232, to be explained further below.

[0039] In operation, fluid output from the hydraulic intensifier 216 discharges through a diverter valve 220 (which may be electrically, pneumatically or hydraulically operated) to the accumulator 210. An accumulator valve 212 may be closed initially so that fluid pressure may build in the accumulator 210. Once a setpoint pressure in the accumulator210 (as measured by the accumulator pressure sensor PA) is obtained, the accumulator valve 212 may be opened so that fluid pressure in the accumulator 210 is conducted to the compensation port 232A. In some embodiments, a pressure relief valve 218 may be connected to the output of the intensifier 216 to avoid damage in the event the intensifier 216 pressure becomes unsafe.

[0040] Measurements of well (or pipeline) pressure from the well pressure sensor Pw are compared in the controller 202 to measurements of compensation pressure from compensation pressure sensor Pc. The controller 202 may operate the intensifier 216 to increase compensation pressure when the well (or pipe) pressure exceeds the compensation pressure, or may operate a dump valve 222 (which may be a solenoid operated pneumatic valve) to vent or reduce compensation pressure when the well (or pipe) pressure is less than the compensation pressure. In this way, pressure differential across the pulser piston 232 may be maintained close to zero or at a minimum, thereby minimizing the amount of force necessary to drive the pulser piston 232 to vibrate against the load presented by well pressure and generate acoustic waves.

[0041] The acoustics subsystem 207, also shown in more detail in FIG. 3, consists of a pulser 235 comprising a pulser piston 232 disposed in a pulser chamber 235A, which chamber may be a cylinder. One end of the pulser chamber 235 A has an outlet 235 Al in fluid communication with the well 103 (or pipe 102 in FIG. 2) so that movement of the pulser piston 232 may induce pressure variations, i.e., acoustic waves, in the well (103 in FIG. 1) or pipe (102 in FIG. 1) by displacement of fluid. Movement of the pulser piston 232 may be effected by a pulser driver 231 operatively connected to the pulser piston 232. The pulser driver 231 may be, for example, a linear driver or actuator, or a linear motor 230 (e.g., hydraulic or electric cylinder, or a combination of both). The acoustics subsystem 207 produces motion of the pulser piston 232 that generates the acoustic radiation into the well 103 or pipeline (102 in FIG. 1). The pulser driver 230 may also comprise an electrostrictive motor or transducer 233, to be explained further below. Motion of the linear motor 231 and the electrostrictive motor 233 may be used in combination to drive the pulser piston 232. The linear motor 231 may be used, for example, when large displacements (strokes) and low frequencies are desired. The electrostrictive (piezoelectricor magnetostrictive) motor 233 may be used when small displacements provide sufficient acoustic wave amplitude and high frequencies are needed. In some embodiments, the pulser 235 may comprise the inclusion of either or more than one of the foregoing pulser motor mechanisms connected in series, as illustrated in FIG. 3, thus enabling capability for generating a wide band of acoustic wave frequencies.

[0042] The linear motor 231 in the present embodiment may comprise a motor piston 230A disposed in a hydraulic cylinder 230 (FIG. 2). The motor piston 230A may be linked to the pulser piston 232 directly or by any other effective linkage to transfer motion of the motor piston 230A to the pulser piston 232. Motion of the motor piston 230A in some embodiments may be effected hydraulically, wherein hydraulic fluid under pressure from the hydraulic power unit 226 is conducted through a proportional directional valve assembly 228 to the motor hydraulic cylinder on opposed sides of the motor piston 230A. The proportional directional valve assembly 228 operates to apply hydraulic fluid under controllable pressure and in controllable volumes to one or the other side of the motor piston 230A to cause motion of a desired amount, desired direction and at a desired rate. Such motion enables generating acoustic waves in the well or pipe of a desired amplitude, phase, waveform, and frequency. The proportional directional valve assembly 228 may be operated, e.g., electrically by the controller 202. A position sensor 236, e.g., a linear variable differential transformer, may be used to measure the axial position of the motor piston 230 and communicate such measurements to the controller 202. The controller 202 may use such position measurements to operate the proportional directional valve assembly 228 so that the desired amplitude, phase, and frequency of the acoustic waveform, are imparted to the motion of the motor piston .

[0043] The pressure-compensation subsystem 205, also shown in more detail in FIG. 4 and as previously explained, is arranged to maintain near-zero differential pressure across the pulser piston (232 in FIG. 2), thus minimizing the load presented to the linear motor 231. Fluid pressure on one side of the pulser piston (232 in FIG. 2) results from hydraulic connection of one side of the pulser (235 in FIG. 2) to the well (103 in FIG. 1) or the pipe (102 in FIG. 2) as explained with reference to FIG. 2. Fluid pressure on the opposed side of the pulser piston (232 in FIG. 2) is supplied by the hydraulic compensation subsystem205 to the compensator port 232A. Pressure to such side of the pulser piston (232 in FIG. 2) may be obtained from the accumulator 210. The accumulator 210 may be charged by the high-pressure intensifier 216 as explained with reference to FIG. 2.

[0044] The pressure-compensation subsystem 205 dynamically tracks changes in well or pipe pressure, e.g., to 15,000 psi or more during operations such as hydraulic stimulation, and depending on sensors chosen for the particular expected well or pipe conditions, as low as a few hundred psi in a quiescent well or flowing pipeline. The pressure balance across the pulser piston (232 in FIG. 2) may actively managed by software (e.g., machine operating instructions in the control subsystem (203 in FIG. 2)) that accepts inputs from the well or pipe pressure sensor Pw and the compensation pressure sensor Pc.

[0045] Change in well or pipe pressure is compensated within the pulser (235 in FIG. 2) by activating the high-pressure intensifier 216. Output of the intensifier 216 may be directed to the accumulator 210 and then through the accumulator valve 212 when well or pipe pressure increases, or opening the dump valve (222 in FIG. 2) for pressure decreases. The dump valve 222 may be connected to the reservoir in the hydraulic power unit 226 through a variable orifice valve or choke 224 to reduce compensation pressure at a controlled rate. The accumulator 210 may be suitable to provide compensation pressure for slow pressure variations, e.g., less than about 1000 psi per minute, depending on the charge and discharge rates of the accumulator 210. When pressure variations are faster, e.g., several thousand psi per minute, a diverter valve 220 may be opened by the controller (202 in FIG. 2) to connect the high-pressure intensifier 216 output directly to the compensator port 232A to the pulser piston (232 in FIG. 2), whereby fast pressure changes can be tracked because smaller volumes of hydraulic fluid are moved by removing the accumulator 210 from the effective hydraulic circuit. When the hydraulic intensifier 216 is direct-connected to the pulser piston (232 in FIG. 2), the accumulator valve 212 is closed. In some embodiments, the controller (202 in FIG. 2) may be programmed to operate the diverter valve 220 and the accumulator valve 212 when measured well pressure from the well pressure sensor Pw changes at a rate above or below a selected threshold; pressure rate change above the threshold may cause the controller 202 to operate the diverter valve 220 to direct flow from the intensifier 216 to the compensation port 232A and to close theaccumulator valve 212. Opposite operation of the foregoing valves may take place when the pressure change rate falls below the selected threshold.

[0046] A possible advantage of an active pressure compensation subsystem, as explained herein, is that well or pipe pressure is directed to only one side of the pulser piston 232, the other side being compensated entirely by controlled hydraulic pressure from the hydraulic power unit 226 and intensifier 216. Such arrangement avoids communicating well or pipe pressure through any other part of the source 200, thus avoiding possible safety hazards. In the event of failure of any part of the pulser 235, the well or pipe may be fully hydraulically isolated from the source (200 in FIG. 2) by closing a single isolation valve 234. Further, by having well or pipe pressure only on one side of the pulser piston 232, the need for high-pressure moving shaft seals to isolate well fluid from the hydraulic cylinder 231 may be eliminated.

[0047] The control subsystem (203 in FIG. 2) may be programmed to activate the acoustic subsystem (207 in FIG. 2) to generate acoustic waves only when the differential pressure across the pulser piston 232 is' within a predetermined range of values.

[0048] The pulser (235 in FIG. 2) may be activated by pausing the compensation subsystem (205 in FIG. 2), Such pausing may be performed by the controller (202 in FIG. 2) operating to close the dump valve (222 in FIG. 2) and the diverter valve (220 in FIG. 2), and opening the accumulator valve (212 in FIG. 2), thus allowing changes in pressure in the pulser piston on the compensation side that are generated by the motion of the pulser piston (232 in FIG. 2) to be absorbed by the compressible gas in the accumulator (210 in FIG. 2). If the differential pressure across the pulser piston exceeds a predetermined value in either direction, the pulser (235) may be temporarily disconnected from the well or pipe by remotely closing an isolation valve 234 shown in both FIG. 2 and FIG. 3.

[0049] Referring once again to FIG. 2, the control subsystem 203 manages the acoustics subsystem 207 and the pressure-compensation subsystem 205, activates the power supplies, and provides master control and monitoring of setup, pressure integrity tests, and activation of the source 200. For the remote operation of the source and access and storage of source operational data, the control subsystem 203 may be accessed through standardcomputer communications protocols. For the acoustic subsystem 207, the desired acoustic waveform may be programmed or input to the control subsystem (e g., into the controller 202) to generate and output signals that control the direction and rate of fluid flow needed by the hydraulic actuator 230 to generate the desired motion. Such motion drives the pulser piston 232, and / or the controller 202 generates voltage-current profiles for the electrostrictive actuator 233. The motion of the pulser piston 232 resulting from the hydraulic actuator and / or electrostrictive actuator motion, and thus the generated acoustic waveform, may be maintained by a closed feedback loop with inputs from the position sensor 236 measuring actual piston motion and comparing it to the desired (programmed) motion in a closed feedback loop. The controller 202 in some embodiments updates or corrects piston motion 1000 times per second. This process enables the generation of complex waveforms (pulses, continuous sinusoids, codes, sweeps, and other) with varying amplitude, phase, frequency, shape, and duration. One unique waveform complexity is to add a small amplitude pre-trigger dither to the pulser piston motion in order to minimize the effects of stiction when initiating a acoustic waveform. For the pressure-compensation subsystem 205, the control subsystem 203 monitors ambient well or pipe pressure and compensates pressure across the pulser piston 232 and actively adjusts the compensation pressure to minimize the force on the piston and the connecting shaft to the linear actuator, i.e., hydraulic cylinder, electric cylinder, or electrostrictive transducer. The control subsystem 203 may also manage many other valves, switches, and other devices that control the flow of fluids. The control subsystem 203 may also save the control signals, faults, and settings for diagnostics and subsequent analyses.

[0050] FIG. 5 graphically shows three examples of acoustic pressure wavelets radiated in a well or pipe at 7000 psi (pounds per square inch) in the time domain (upper graphs) wherein the vertical axis represents amplitude pressure time derivative, such as may be induced in a sensor such as a hydrophone, and the frequency domain (lower graphs) wherein the vertical axis represents amplitude of the frequency spectrum. These signals, with center frequencies of 1 Hz, 2 Hz, and 4 Hz, illustrate the ability of the source (200 in FIG. 2) to control the frequency content of the signals generated.

[0051] In light of the principles and example embodiments described and illustrated herein, it will be recognized that the example embodiments can be modified in arrangement and detail without departing from such principles. The foregoing discussion has focused on specific embodiments, but other configurations are also contemplated. In particular, even though expressions such as in “an embodiment," or the like are used herein, these phrases are meant to generally reference embodiment possibilities, and are not intended to limit the disclosure to particular embodiment configurations. As used herein, these terms may reference the same or different embodiments that are combinable into other embodiments. As a rule, any embodiment referenced herein is freely combinable with any one or more of the other embodiments referenced herein, and any number of features of different embodiments are combinable with one another, unless indicated otherwise. Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible within the scope of the described examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

ClaimsWhat is claimed is:

1. An acoustic source for use in a well or pipe, comprising: a pulser piston disposed in a chamber, the chamber having an outlet on one side of the piston and an inlet on the other side of the piston; a linear actuator connected to another side of the pulser piston; a pressure compensator having a pressure outlet in fluid communication with the one side of the pulser piston, the pressure compensator comprising a sensor for measuring pressure in the well or pipe, a sensor for measuring compensation pressure on the one side of the pulser piston, a hydraulic power source and a controller operatively connected to the hydraulic power source, the well or pipe pressure sensor and the compensation pressure sensor, wherein the controller is arranged to operate the hydraulic power source such that a predetermined pressure difference between the well or pipe pressure and the compensation pressure is maintained; and wherein the controller is arranged to operate the linear actuator to move the pulser piston to generate acoustic waves having predetermined amplitude, phase, frequency, and waveform.

2. The acoustic source of claim 1 wherein the linear actuator comprises an actuator piston in an hydraulic cylinder and a reversing proportional valve in signal communication with the controller, the reversing proportional valve operable to direct hydraulic fluid from the hydraulic power source to opposed sides of the actuator piston, motion of the linear actuator piston coupled to the pulser piston.

3. The acoustic source of claim 2 further comprising an electrostrictive actuator arranged to move the pulser piston, the electrostrictive actuator arranged such that motion thereof is combinable with or substitutable for the motion of the linear actuator.

4. The acoustic source of claim 1 further comprising a position sensor functionally coupled to the linear actuator and in signal communication with the controller, the controller arranged to adjust operation of the linear actuator in response to measurements of theactuator position such that the predetermined amplitude, phase, frequency, and waveform are realized.

5. The acoustic source of claim 1 wherein the pressure compensator comprises a hydraulic intensifier coupled between the hydraulic power source and the one side of the pulser piston.

6. The acoustic source of claim 5 further comprising an accumulator disposed between the hydraulic intensifier and the one side of the pulser piston.

7. The acoustic source of claim 6 further comprising a diverter valve disposed between the hydraulic intensifier and the accumulator, the diverter valve operable to direct fluid flow from the hydraulic intensifier directly to the one side of the pulser piston.

8. The acoustic source of claim 7 wherein the diverter valve is operated by the controller, the controller operable to cause the diverter valve to direct fluid flow directly to the one side of the pulser piston when a rate of change of measured well or pipe pressure exceeds a selected threshold.

9. The acoustic source of claim 1 wherein the predetermined amplitude, frequency, and waveform comprise one of pulses, continuous waveforms, codes, or sweeps.

10. The acoustic source of claim 1 wherein the predetermined amplitude, phase, frequency and waveform comprise a pre-trigger dither to minimize effects of stiction on motion of the pulser piston.

11. A method for generating acoustic waves in a well or pipe, comprising: measuring pressure in the well or pipe; generating a compensation pressure based on the measured pressure and applying the compensation pressure to one side of a pulser piston in a first chamber to maintain a predetermined differential pressure across the pulser piston with respect to the well or pipe pressure; andoperating a linear actuator to move the pulser piston to generate acoustic waves having predetermined amplitude, phase, frequency, and waveform on an opposed side of the pulser piston, and fluidly communicating the acoustic waves to the well or pipe.

12. The method of claim 11 further comprising measuring a parameter related to position of the linear actuator, and changing operation of the linear actuator to cause the measured position to match a desired motion of the linear actuator corresponding to the predetermined amplitude, frequency and waveform.

13. The method of claim 11 wherein the compensation pressure is generated by a fluid pressure source apart from the well or pipe.

14. The method of claim 13 further comprising determining a rate of change of the measured pressure and communicating the compensation pressure to an accumulator having a compressible gas on one side of a movable barrier in a chamber when the rate of change is below a selected threshold.

15. The method of claim 11 wherein the linear actuator comprises an hydraulic motor.

16. The method of claim 11 wherein the linear actuator comprises an electrostrictive transducer.

17. The method of claim 11 further comprising stopping the generating the compensation pressure during the operating the linear actuator.

18. The method of claim 17 further comprising communicating fluid pressure on the one side of the pulser piston to an accumulator having a compressible gas on one side of a movable barrier in a chamber.

19. The method of claim 11 wherein the linear actuator comprises a driver piston disposed in a second chamber and a electrostrictive transducer motion-coupled to the pulser piston, the electrostrictive transducer operated to provide acoustic waves having higher frequency than obtained by moving the driver piston.

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