Abstract: An apparatus for estimating a property in a borehole penetrating the earth, the apparatus having: a carrier configured to be disposed in the borehole; and an acoustic transducer disposed at the carrier and configured to at least one of transmit and receive an acoustic wave used to estimate the property, the acoustic transducer comprising an acoustic diaphragm; wherein the acoustic diaphragm includes a surface in communication with a plurality of structural members configured to increase the rigidity of the surface, the surface being configured to interface with a medium that propagates the acoustic wave.

Abstract: Multipole acoustic logging-while-drilling (LWD) tools and associated methods are disclosed herein. In some embodiments, the disclosed acoustic LWD tool comprises a transmitter array and at least one receiver array. The transmitter array generates acoustic waves with an excitation pattern having a cutoff frequency greater than about 3 kHz. The receiver array is spaced apart from the transmitter array and is configured to detect said acoustic waves. Some of the disclosed method embodiments comprise: generating multipole acoustic waves in a fluid-filled borehole using an excitation pattern with a cutoff frequency greater than about 3 kHz; selectively detecting acoustic waves that propagate with said excitation pattern; and determining an acoustic shear wave slowness for a formation penetrated by the borehole.

Abstract: A sonde and an apparatus for the deployment thereof against a well casing is described, the sonde comprising a resilient C-shaped member and at least one sensor.

Abstract: A downhole receiver for gathering seismic and sonic data from inside a borehole includes a substantially tubular housing adapted for axial connection to a tool string, and one or more sensors. A damping element is provided to flexibly couple each sensor to the tubular housing. An actuator extends the one or more sensors substantially radially with respect to the tubular housing to clamp the sensors against the wall of the borehole. In selected embodiments, the sensors may be one or multiple component geophones, accelerometers, hydrophones, vibrometers, or the like.

Abstract: A formation logging tool having a substantially continuous central mandrel with regularly spaced mass blocks disposed thereon, at least some of the mass blocks carrying sensors such as receivers. By adopting this structure, the tool can be made to behave as a mass-spring structure and its flexural and extensional behaviour controlled such that its dispersion curve does not extend into the dispersion curve of the formation to be logged. The structure can be applied to the whole of the logging tool or just to the receiver section and/or any spacer section between the receiver and the transmitter section.

Abstract: Methods and apparatus are adapted for acquiring seismic data from an array of sensors deployed along a section of a deviated, including horizontal, wellbore for monitoring seismic and microseismic activity. The sensors may be permanently deployed in the wellbore.

Abstract: A method of seismic data processing is described in which a particular wavelet is selected from a plurality of wavelets as being most characteristic of a received seismic signal. A subtracted signal can be determined by subtracting a weighted signal of the particular wavelet from the received signal. From the subtracted signal, an additional particular wavelet can be chosen. The process of subtracting a signal and determining an additional particular one of the plurality of wavelets can be repeated until a criterion is met. The method can be repeated at several depths. The resultant spectral analysis can be used to determine, for example, an absorption coefficient.

Abstract: A sonde and an apparatus for the deployment thereof against a well casing is described, the sonde comprising a resilient C-shaped member (22) and at least one sensor (23).

Abstract: Methods and apparatus for suppression of wave energy within a fluid-filled borehole using a low pressure acoustic barrier. In one embodiment, a flexible diaphragm type device is configured as an open bottomed tubular structure for disposition in a borehole to be filled with a gas to create a barrier to wave energy, including tube waves. In another embodiment, an expandable umbrella type device is used to define a chamber in which a gas is disposed. In yet another embodiment, a reverse acting bladder type device is suspended in the borehole. Due to its reverse acting properties, the bladder expands when internal pressure is reduced, and the reverse acting bladder device extends across the borehole to provide a low pressure wave energy barrier.

Abstract: An acoustic logging tool includes external baffle assemblies forming a waveguide structure at the acoustic source. The logging tool is designed for acoustic logging of earth formation surrounding a borehole. The external baffle assemblies form a waveguide structure that is designed to increase signal to noise ratio in an acoustic logging tool using dipole or other acoustic waves. In a preferred embodiment, the acoustic logging tool includes an elongated transmitter module, and a receiver sonde having a linear array of acoustic receivers. The transmitter module includes first and second cylindrical masses spaced apart along the axis by first and second spacers. The first cylindrical mass defines a first circular facing surface and a first cylindrical outer surface. The second cylindrical mass defines a second circular facing surface and a second cylindrical outer surface.

Abstract: A method and apparatus suitable for coupling seismic or other downhole sensors to a borehole wall in high temperature and pressure environments. In one embodiment, one or more metal bellows mounted to a sensor module are inflated to clamp the sensor module within the borehole and couple an associated seismic sensor to a borehole wall. Once the sensing operation is complete, the bellows are deflated and the sensor module is unclamped by deflation of the metal bellows. In a further embodiment, a magnetic drive pump in a pump module is used to supply fluid pressure for inflating the metal bellows using borehole fluid or fluid from a reservoir. The pump includes a magnetic drive motor configured with a rotor assembly to be exposed to borehole fluid pressure including a rotatable armature for driving an impeller and an associated coil under control of electronics isolated from borehole pressure.

Abstract: The invention provides methods and apparatus for detecting seismic waves propagating through a subterranean formation surrounding a borehole. In a first embodiment, a sensor module uses the rotation of bogey wheels to extend and retract a sensor package for selective contact and magnetic coupling to casing lining the borehole. In a second embodiment, a sensor module is magnetically coupled to the casing wall during its travel and dragged therealong while maintaining contact therewith. In a third embodiment, a sensor module is interfaced with the borehole environment to detect seismic waves using coupling through liquid in the borehole. Two or more of the above embodiments may be combined within a single sensor array to provide a resulting seismic survey combining the optimum of the outputs of each embodiment into a single data set.

Abstract: A wellbore system and method for producing seismic waves in an earth formation. The system comprises a cavity containing fluid. The cavity is in a space between a wellbore tubular, which may be casing or production tubing, and the wellbore formation. A device is provided for generating pressure waves in the cavity at resonance frequencies of the cavity. The pressure waves generate seismic waves that radiate into the adjacent earth formation that may be recorded. The recorded seismic waves may be used to determine parameters of interest of the earth formation.

Abstract: A method and apparatus for controlling fluidic torque in a downhole tool is provided. One or more rotatable components of the downhole tool comprise a deformable material, such as rubber or SMA, selectively deformable in response to the flow of fluid through the downhole tool. The rotatable components may include a rotor and/or a turbine of a generator in the downhole tool. Non-rotatable components, such as the stator of the generator, may also be deformable. The rotor, the stator, and/or turbine may comprise a deformable material capable of selectively deforming in response to the flow of drilling mud through the generator. The desired deformation and/or the desired torque may be controlled by adjusting the parameters of the components.

Abstract: A sleeve for an acoustic logging tool has a structure with a window section having fewer bars than a conventional sleeve separated by a slotted region with thin circumferential slots which are stress-relieved at the ends (“dumb-bell” shaped). Steel receiver mounts are provided for hydrophone pressure sensors and this, together with the axially oriented hydrophones makes the tool less susceptible to interfering vibration.

Abstract: A downhole electrical power system provides long term electrical power in a downhole environment. In a described embodiment, a downhole electrical power system includes a power source which supplies electrical power to a well tool interconnected in a tubular string. The power source includes a voltaic cell.

Abstract: In one aspect, the invention involves an acoustic logging tool for performing acoustic investigations of subsurface geological formations. In one embodiment, the tool comprises a generally longitudinally extending tool body adapted for positioning in a borehole. At least one transmitter is mounted on the tool body to emit acoustic energy. At least one receiver is also mounted on the tool body at a location axially displaced from the at least one transmitter. The receiver is adapted to receive acoustic energy. An attenuator is also positioned along the body and includes at least one cavity having a plurality of particles disposed therein. The attenuator as disclosed herein may be applied to other logging tools for protecting tool components and enhancing measurement quality. Methods for attenuating acoustic energy transmitted through the body of an acoustic logging tool or other logging tools are also disclosed.

Abstract: A method and an apparatus are provided for matching the response of hydrophones 22 to the response of geophones 24 and significantly reducing response variations between hydrophones caused by inherent characteristics. The method includes the steps of determining a capacitance 66 for each of the hydrophones 22 in an operating environment, configuring a filter 36 based on the capacitance 66, and modifying a response of a channel of the hydrophone 22 using the filter 36. The apparatus includes an acquisition unit 20 having a geophone 24 and a hydrophone 22, a recording unit 30, a processing unit 31 and a filter 36 for correcting for variation between hydrophones 22 and changing a first order low frequency response of the hydrophone 22 to appear like a second order response like that of the geophone 24.

Abstract: In one embodiment the invention comprises a method of gathering borehole seismic data in which a borehole acoustic instrument is lowered into a borehole in the earth's surface along with a canister positioned about the instrument and a second open bottomed canister positioned below the instrument. The canisters are at least partially filled with gas after the canisters are lowered into borehole. In another embodiment the invention comprises an apparatus for reflecting tube waves in a fluid-filled borehole which includes a canister having a diameter adapted to enable the canister to be deployed within the fluid-filled borehole, and having an open lower end, and an enclosed upper end with an aperture through the upper end adapted for sealing engagement between said upper end and a conduit.

Abstract: The invention is an apparatus for generating a seismic signal in a fluid filled borehole which includes an elongated housing formed from a gas impermeable material and a controlled frequency energy source within said housing. The housing has an external shape which expands and contracts in response to variations in pressure within said housing to enhance the transmission of said seismic signal to the borehole fluid, such as pressure variations resulting from fluid resonance within said housing.

Abstract: A borehole seismic shuttle tool includes (a) a tool body having a cavity with an opening in the wall of the tool body; (b) an anchoring arm attached to the tool body and operable to anchor the tool body to the borehole wall; (c) a sensor package positioned in the cavity and mounted on resilient mounts which act to urge the sensor package in the direction of the opening, such that when the tool body is anchored to the borehole wall, the sensor package projects part way through the opening and is held against the borehole wall by the action of the resilient mounts. The tool is characterised in that when the tool body is not in contact with the borehole wall, peripheral portions of the sensor package is urged into contact with the tool body wall surrounding the opening.

Abstract: A dual mode multiple-element resonant cavity piezoceramic borehole energy source is disclosed. Thus, a source for generating detectable seismic waves in a wellbore is provided which is capable of transmitting useful signals over long distances between the source and the related receiver or receivers. A liquid-filled elongated column is provided which defines a longitudinal axis and has a resonant frequency. A resonator comprising at least one substantially cylindrical piezoelectric element having an axis approximately parallel to the axis of the borehole for inducing seismic waves in the borehole is furnished. The resonator is constructed and arranged for vibrating at the first resonant frequency, and is also constructed and arranged for vibrating at a second frequency in a hoop mode to generate seismic waves having the second frequency.

Abstract: A wellbore remote control system is disclosed which includes (1) a transmission apparatus for generating at least one acoustic transmission having a particular transmission frequency, (2) a reception apparatus which includes an electronic circuit (preferably digital) which detects and identifies the acoustic transmissions, and which provides an actuation signal to an electrically-actuated wellbore tool if a match is detected.

Abstract: Systems are disclosed for securing near vertically deployed seismic detector systems in a cased well borehole from oscillatory motion during a seismic survey. In one embodiment a generally cylindrical body member of an unsymmetrical shape having one flat side is used opposite a selectably extensible backup locking arm. In a second embodiment a generally symmetrical cylindrical body member having sets of four essentially coplanar contacting feet disposed at 90 degree circumferential spacing an opposite ends is provided. The sets of locking feet on opposite ends of the tool body member are phased 45 degrees apart circumferentially with respect to each other. Locking edges and feet may be magnetically assisted if desired.

Abstract: A method is described for providing improved seismic data to a driller to indicate position and spatial extent of a drilling target which may be up to several hundreds of feet ahead of a drill bit. In one embodiment, the method includes the steps of: survey design and data modeling, and definition of a drilling target point and a drilling interruption point; drilling down to a depth at which drilling will be interrupted; interruption of drilling; look-ahead borehole seismic survey (VSP); continuation of drilling; data processing and interpretation; coordinate update for optimum target intersection; and steering of drilling by borehole seismic data interpretation.

Abstract: A receiver section for an acoustic oil well logging tool comprised of a plurality of receiver sub-units connected longitudinally within a rigid tubular member. Each receiver sub-unit has a series of acoustic wave sensors located for receiving and detecting monopole, dipole, quadrupole and unipole waveforms. Separate channels are provided for conveying waveforms data from each receiver sub-unit to an above ground data processing unit. Each receiver sub-unit also includes a compensating sensor for detecting tool vibrations and for producing signals which are combined with waveform data in the processing unit to eliminate the effects of tool vibration.

Abstract: A seismic source and seismic detector are placed within a wellbore, and are secured in generally fixed relation within the wellbore. Multiple sources can be utilized, or multiple detectors may be utilized, within a single wellbore. Also, additional sources or detectors may be placed in adjacent wells. The source may be periodically actuated to obtain seismic data, and subsequent actuation may be directly compared with prior actuations to evaluate reservoir characteristics.

Abstract: An apparatus for logging a borehole comprises a non-rotating component and a rotating component that is flexibly attached to the non-rotating component and includes a logging head. The rotating component is centralized independently from the non-rotating component such that the rotating component remains centralized as it rotates, regardless of whether the non-rotating component is centralized. The logging head includes at least one signaling device, a hydrostatic pressure balancing system, a sealed, variable-volume fluid reservoir in fluid communication with said transducer, and a motor housed in said logging head for rotating the rotating component. The apparatus can further include a second non-rotating component suspended below the rotating component.

Abstract: A self-propelled turbo siren modulator assembly is disclosed for use in an MWD system. The turbo siren includes a fixed turbine deflector located upstream from a rotor, which in turn is located upstream from a fixed stator. Drilling mud flowing through the turbine deflector causes the rotor to rotate independent of any external drive device. The rotor and stator preferably have a similar configuration, which includes at least one lobe and at least one port so that the rotor alternatively blocks or permits mud flow through the port(s) of the stator to create a cyclical acoustic wave signal, with a frequency that depends upon the number of lobes on the rotor and the velocity of the drilling mud. Encoded measurement data is modulated on the carrier frequency wave through the use of amplitude modulation, frequency modulation or phase shift modulation, or a combination thereof to maximize data rates.

Abstract: A dipole acoustic well logging instrument including an acoustic transmitter. Receiver sections are disposed at axially spaced apart locations from the acoustic transmitter. Each receiver section includes an outer shoulder at each end adapted to be placed in acoustically isolated contact with an internal shoulder of a connector coupling when the instrument is in tension. The outer shoulders have an acoustically isolating material disposed on their surfaces. The receiver sections include an inner shoulder at each end adapted to be placed in direct contact with an external shoulder of the connector coupling when the instrument is in compression. The instrument includes one connector couplings disposed at each end of each receiver section to couple the receiver sections to each other and to the remainder of the instrument. At least one receiver element is disposed in a passage formed into each of the receiver sections.

Abstract: An acoustic well logging tool is shown having a transmitter section and a receiver section spaced apart by a semi-rigid housing. The semi-rigid housing includes a number of rigid tubular members which are joined by interlocking lobes which permit relative movement between the tubular members but which prevent the separation thereof. Gaps between the interlocking lobes are filled with a connecting material which differs significantly in acoustic impedance from the material of the remainder of the housing, whereby acoustic energy passing from the transmitter section along the body of the tool is delayed and attenuated.

Abstract: A meso-scale profiling tool has separate upward and downward focused seismic sources, separate upward looking and downward looking directional receivers and a section of the tool containing the sources and receivers adapted to rotate with respect to the remainder of the tool so that the sources and receivers are always in a proper substantially vertical orientation.

Abstract: The invention is a system for conducting a geophysical survey in a wellbore, comprising a battery-powered, self-contained borehole seismic receiver which internally digitizes and records an electrical signal generated by a transducer in the receiver, and a surface control unit which records the acoustic signature of the seismic energy source deployed at the earth's surface, controls the firing of the seismic source, and correlates the recording in the receiver to the recording of the source to determine the travel time of the seismic energy through the earth.

Abstract: The mobile seismic system according to the invention is made up by interconnecting reception sections (T1) and of anchoring sections (T2), and possibly emission sections, the assembly being suspended in the well by means of an electro-carrying cable (3). The first sections (T1), which are filled with liquid, are delimited at least partly by a wall transparent to acoustic waves. They contain each one or several hydrophones and an electronic module of acquisition of the signals picked up. The second sections (T2) comprise a body provided with retractable anchoring means (13) and with motor means, either autonomous, or connected, by a hydraulic line running along the reception system, to common motor means located preferably in a lower section so as to be used as a ballast weight. The reception system may be continuous or made up of several parts connected to each other by electric or electro-hydraulic linking means. The system is suitable for seismic prospecting in wells for example.

Abstract: The present invention relates to a method and to a system for analyzing drilling conditions and/or the behaviour of a drill string element. It comprises the stages as follows:acquisition of a signal,calculation means are operated, which determine the wavelet coefficients of segments of the signal, the segments are merged to form a homogeneous segment,a magnitude associated with each homogeneous segment is determined.The invention further relates to a system for implementing the method.

Abstract: The signal-to-noise ratio of televiewer signals from a rotary sidewall acoustic-beam scanner is improved by replacing the volume of borehole drill fluid that lies in the path of the acoustic beam with a solid medium characterized by a lower coefficient of attenuation than that of the drill fluid.

Abstract: Method and apparatus for conducting seismic surveys from a single wellbore utilizing an array of seismic detectors and an seismic source suspended downhole from the detectors on a coiled tubing. Actuation of the airgun both generates a seismic signal penetrating the adjacent lateral geological formations and a plurality of air bubbles pass up the borehole to attenuate tube wave propagation in the borehole fluid.

Abstract: The invention concern a combination well logging device adapted to be moved inside a borehole to measure the properties of geological formations through which the borehole passes.The device according to the invention comprises a series of elongate logging sections mounted end to end, including a first section adapted to be maintained with a generatrix applied against the wall of the borehole, a second section comprising a body and a measurement pad adapted to be spaced radially from the body for application against said wall, a third section adapted to be kept space from said wall, and first and second hinges connecting the second section to the first and third sections respectively in order to allow respective angles of inclination between the second section and the first and third sections.

Abstract: A seismic profiling tool is moveable on a wireline in a well bore for exploring subsurface formations adjacent the well bore at various source-receiver spacings. The tool includes at least one acoustic source, an acoustic receiver assembly, and a spacing system for providing variable spacing and relative movement between the source and receiver assembly.

Abstract: Disclosed is a sonic well tool for performing acoustic investigations of subsurface geological formations penetrated by a borehole. The well tool generally includes a longitudinally extending body for positioning in said borehole. The tool also includes a transmitter supported by the body for transmitting acoustic energy, and a receiver supported by the body for receiving acoustic energy. Finally, the tool includes an acoustic attenuation section positioned on the body between the transmitter and the receiver. This section includes one or more cavities defined by the body, inertial mass members positioned inside the cavities in a suitable manner to form a gap between the wall of the cavity and the inertial mass members, and an acoustical attenuation fluid in the gap. The method for attenuating sonic waves generally includes transmitting a sonic wave from the transmitter to the tool, passing the sonic wave through the acoustic attenuation section, and receiving attenuated wave at the receivers.

Abstract: The invention is a method and apparatus for measuring the quality of acoustic coupling between a wellbore wall and a borehole seismic sensor system. The system includes the steps of positioning the system at a desired depth in the wellbore and activating a locking mechanism powered by a DC motor. The motor then has broadband AC applied to it to cause vibration of the system. The output of at least one seismic sensor in the system is processed in a spectrum analyzer, and the result is checked for the presence or absence of natural resonance of the system. In a particular embodiment, the system response to the broadband AC is used to generate an inverse filter operator to compensate the system response to a geophysical survey for partial acoustic coupling.

Abstract: A sonic transmitter assembly for use in logging-while-drilling includes stacks of piezoelectric crystals that extend outwardly from a nodal plate member, and a generally tubular assembly that contains such stacks and has end portions that are sealingly mounted in diametrically opposed holes in a pipe member that forms a pan of the drill string. Spring mass isolator systems are employed to inhibit transmission of acoustic waves to the pipe member. Balanced mounting forces and the bilateral symmetry of the construction also inhibit transmission of acoustic waves to the pipe member, particularly waves which are asymmetric with respect to the longitudinal axis of the pipe member.

Abstract: A steerable motor system with integrated formation evaluation logging capacity is presented. The device comprises a housing, a formation resistivity logging tool, a surface signaling device, a density logging tool, a porosity logging tool and a downhole motor and drill. The formation resistivity logging tool is located below the downhole motor and is mounted within the housing wherethrough a drive shaft, extending from the downhole motor, is disposed. Power and signal cables are located within an outer shell of the housing and connect the surface signaling device with the resistivity logging tool. In an alternate embodiment, the resistivity logging tool is located between a motor stabilizer and the drill bit. The present invention allows for increased drill angle during wellbore drilling and formation evaluation.

Abstract: Sondes provided with magnets are used in wells fitted with a metallic casing. The sondes are pressed at the surface against the inner wall of the casing and taken down towards the bottom by means of a stiff driving element such as a tubing provided with thrust driving means for the longitudinal drive and lateral extensions for the lateral positioning of the sonde, or using pulling slings, etc. The wall of the sonde pressed against the casing can have the same bending radius as the casing in order to improve the coupling. The sonde can be associated with an electronic data acquisition and transmission box fastened to the tubing. Before any intervention is performed, the tubing is moved sufficiently in order to suppress any mechanical coupling with the sonde. After it has been used, the sonde can be displaced towards another point of measurement or taken up to the surface by moving the tubing.

Abstract: An apparatus for reducing or eliminating the effects of a quadrupole component of an acoustic signal received from a transversely mounted acoustic source in a drill collar of a logging while drilling tool. The apparatus includes a drill collar for supporting a drill bit, a transversely mounted transmitter situated in a first horizontal plane in the drill collar which transmits acoustic energy into an earth formation. The drill collar also houses at least one receiver mounted in a second horizontal plane in the drill collar at an angular displacement from the transmitter such that the effects of a quadrupole component of the acoustic energy detected by the receiver are rendered insignificant.

Abstract: A sidewall contact parameter tool, adapted to be disposed in a mud-filled wellbore, includes a pad assembly, in accordance with the present invention, which is adapted to cut through mudcake and measure a parameter of a formation disposed under the mudcake. The wellbore wall includes a mudcake and an earth formation disposed under the mudcake. The pad assembly includes at least one formation parameter sensor, and the formation parameter sensor includes a base portion and a knife edge portion integrally connected to the base portion. The base portion of each formation parameter sensor is adapted to contact a surface of the mudcake but the knife edge portion is adapted to cut into the mudcake and contact or penetrate a surface of the earth formation disposed under the mudcake. The knife edge portion of each sensor includes an internal space or pinhole aperture, and a parameter sensing apparatus disposed within the internal space or aperture.

Abstract: A method of using oriented seismic sensors to delineate the surface of a geologic unit having an anomalous velocity, such as salt dome is disclosed. Seismic sensors having three orthogonal axes of sensitivity are sealed in a housing and are attached to the outside of a tubing means. The tubing means is lowered into a wellbore that penetrates the geologic unit to a known depth, and a liquid such as cement is pumped through the tubing and up the annular space to fixedly attach the sensors to the geologic formation. The orientation of the sensor axes can then be calculated from an observed orientation of the reference directions of the sensor housings. Seismic wavefields are then propagated through the geologic unit and the surrounding earth, and are observed by the sensor axes of sensitivity, and are recorded and transmitted to the top of the tubing.

Abstract: A multi-mode receiver sonde having individual receiver stations. The receiver stations have transducers which have a flat frequency response over a selected bandwidth so that there is an approximately constant ratio in amplitude and substantially little phase difference between the response signal and an input acoustic signal from a liquid containing borehole.The wide-band output response signals are combined to form composite signals which represent selected borehole propagation modes. Accurate comparisons can then be made between the composite signals obtained by separate receiver stations so that changes in phase and amplitude over distance and time can be determined.In one highly preferred embodiment, the receiver sonde has a semi-rigid receiver array. The semi-rigid receiver array is adapted to decouple noise (tool-mode noise and/or road-noise) in one location within the array from other locations within the array by using compliant spacers between the receiver stations to absorb and scatter the noise.

Abstract: A borehole system for operating a downhole generator suspended on a composite coiled tubing string. The coiled tubing has at least two separate longitudinal chambers to provide separate flow paths. A fluid is pumped from the surface through one flowpath to drive a downhole turbine powered generator for operating downhole systems. A second flowpath in the tubing is used to return fluids to the surface. The non-metal environment of the composite coiled tubing provides a non-magnetic environment in which to operate wellbore devices. Data is transmitted to the surface by way of a fiber optic conductor.

Abstract: Method and apparatus for generating resonant broad band pressure waves in a fluid-filled wellbore for seismic exploration. In the preferred embodiment, a device is provided in a borehole; the device comprises a cylindrical choke body and a means at each end of the choke body for partially or completely blocking off the borehole and creating a fluid-filled borehole cavity. The fluid inside the cavity is oscillated to establish a standing pressure wave of a desired bandwidth in the fluid. The standing wave is radiated through the wellbore into the earth formation and is received by seismic detectors. The fluid is oscillated over a range of frequencies to generate more information about the earth formation.