Abstract: A method and device for generating a high amplitude sound wave is provided. The device includes a housing having an open end. A piston is slidably disposed in the open end of the housing and forms a chamber for holding a pressurized liquid. The pressurized liquid acts on the piston to move the piston relative to the housing. A latch is operable to fix the piston relative to the housing and to release the piston. Upon release of the latch, the piston moves relative to the housing to generate the sound wave. In the method of the present invention, a piston is fixed relative to a housing to form a chamber between the housing and the piston. The chamber is filled with a pressurized fluid and the piston is released to allow the pressurized fluid move the piston relative to the housing and generate the sound wave.

Abstract: A method for planning continuity logging surveys and for detecting the presence of a continuous or discontinuous low-velocity inclusion in a subterranean geological formation. To detect the presence of a continuous or discontinuous low-velocity inclusion, a seismic source is inserted into a source borehole located at either a boundary or a center of a low velocity inclusion. Seismic energy is generated coupled to the low-velocity inclusion using the seismic source. The seismic energy propagates as seismic waves through the low-velocity inclusion and is measured and recorded by at least one detector disposed in a receiver borehole. The seismic waves are analyzed for the presence of at least one seismic signature from which the distance of a discontinuity, if any, of the low-velocity inclusion with respect to the receiver borehole can be determined.

Abstract: A drill string assembly containing a section of tube with a first end. The first end directly, mechanically links a drill pipe to a drill bit and transmits rotational forces from the drill pipe to the drill bit during drilling. A spring is connected to the section of tube at a point remote from the first end of the section of tube. A mass is connected to the spring such that the mass can vibrate on the spring in an axial direction relative to the section of tube and drill string. The value of the mass and the stiffness of the spring being selected such as to cause them to act as a mechanical filter and damp longitudinal compression waves at a predetermined frequency of frequency band and received at the first end of the section of tube.

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 transducer configuration for use in acoustically imaging a target region behind an acoustically reflective layer includes a sonde having a geometrical center and constructed and arranged to support a plurality of transducers. The system includes a first transducer disposed within the sonde at a first distance from the geometrical center for generating a first acoustic pulse and for receiving a first acoustic signal. The acoustic signal comprises a first reflection from the reflective surface, a first set of fluid multiples arising from reflections between the reflective layer and a surface of the first transducer, and a first signal associated with the target area. The system also includes a second transducer disposed within the sonde at a second distance from the geometrical center for generating a second acoustic pulse and for receiving a second acoustic signal.

Abstract: A sonic or acoustic tool is disclosed which includes a transmitter with reduced transmitter spawned noise. The transmitters are either monopole or dipole depending on the orientation of ports in a chamber divided by a piston driven by an actuator. The transmitter size is limited only by the diameter of the tools itself because the transmitters are oriented within the tool parallel to the axis of the tool.

Abstract: A reverse VSP system is provided and uses a frequency-controllable modulator of an MWD tool as a downhole seismic source. The modulator has a rotor and stator arranged to provide substantially sinusoidal outputs, and is controlled to provide a "Vibroseis"-type frequency sweep (preferably from 1 Hz to 50 Hz). With the bit of the MWD tool in contact with the bottom of the borehole, the force generated by the frequency-controllable modulator will generate measurable axial compressional (P-) waves. These waves which move through the formation are detected by an array of geophones on the formation surface, and a reference signal is obtained by a kelly-mounted accelerometer or strain gauge. The reference signal and signals obtained by the geophones are processed using known signal processing techniques.

Abstract: A well tool in accordance with the invention comprises an attenuation device which attenuates tube waves associated with an elastic wave emission and/or reception set (1, 12). The attenuation device comprises a bubble generator (2) which releases into the well a gas not readily soluble in the well fluid, slightly overpressured in relation to the hydrostatic pressure, in the form of calibrated bubbles which greatly attenuate the parasitic tube waves. The attenuation device is placed above or below the elastic wave emission and/or reception set having a plurality of pickups whose signals are acquired by a local electronic module (14) and/or a source of elastic waves such as a vibrator. A bubble trap (17) is preferably associated with the bubble generator (2) in order to limit the volume of gas to be generated in situ. The invention is applicable to VSP type seismic prospecting and acoustic logging.

Abstract: An acoustic attenuator suppresses acoustic signals traveling along the body of a measurement-while-drilling (MWD) tool, making it possible to obtain acoustic measurements relating to underground formations. Shaped cavities (spherical or cylindrical) filled with a fluid have a resonance frequency that is tuned to be within the band of interest thereby attenuating acoustic signals traveling through the body at these resonance frequencies. The staggered arrangement of the cavities increases the path length for the acoustic signals and provides further attenuation. Attenuation may also be accomplished by use of a composite consisting of cylindrical layers of two different materials with thicknesses that attenuate selected frequencies. Additional attenuation is provided by lengthening the path length of a seismic signal passing through the more competent of the two materials of the composite.

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: In oil and gas production, a process known as hydraulic fracturing is often used. Hydraulic fracturing involves pumping a fluid under pressure down a well bore into a fluid reservoir. When the pressurized fluid enters the reservoir, it produces localized failures of rock within the earth known as fractures. These fractures generate elastic waves known as microseisms that travel outward from the source of the fractures in a spherical wavefront. These microseisms can be measured with sensors located near the well bore, and their source determined. The microseismic wavefront is composed of compressional and shear waves. The amplitudes of the compressional and shear waves can be detected and measured and the ratio of the shear wave amplitude to the compressional wave amplitude which is known as the S/P ratio, can be determined.

Abstract: A system for acoustically imaging a target region behind an acoustically reflective layer includes a transducer configuration for acquiring acoustic image data from the reflective layer and target region, wherein the reflective layer and target region are divided into voxels circumferentially disposed about a central point. The system includes a mechanism for processing the data comprising a transmitting transducer for transmitting a first acoustic pulse, a receiving transducer for detecting a first arrival of a first acoustic reflection signal associated with the first acoustic pulse, and a mechanism for suppressing multiple reflected signals from the acoustic reflection signal associated with the first acoustic pulse, wherein the suppressing mechanism facilitates the acquisition of image data from the target region.

Abstract: A seismic source for crosshole testing comprises a hammer rod supported by axial bearings in the ends of a cylindrical housing. Fasteners attach a down-blow hammer to the hammer rod inside the housing. A helical spring inside the housing biases the hammer rod in a downward direction. A hammer cable, attached to the upper end of the hammer rod, raises the hammer rod against gravity and spring pressure until an up-blow hammer attached to the hammer rod below the cylindrical housing strikes the bottom end cap which serves as an anvil. Relaxation of the hammer cable tension results in the down-blow hammer striking the anvil. The device provides compression waves and highly repeatable and selectable-phase shear waves. The device is simple, light and operable by a single person.

Abstract: An impulsive snap-through acoustic pulse generator may be used to generate n acoustic pulse in an aqueous environment without gas bubbles. The impulsive snap-through acoustic pulse generator includes a support structure having an open end; a resilient shell mounted to the support structure to define a chamber, and a gas vent in fluid communication with the chamber through which a gas passes for changing the pressure in the chamber so that the resilient shell transitions from a first stable state to a second stable state, thereby generating an acoustic pulse.

Abstract: An acoustic formation logging tool includes a transmitter, a receiver, a tube wave absorber, and a digital signal processing section. The transmitter includes an electromagnetic actuator based on capacitive discharge through a coil, producing an intense magnetic pressure which causes an actuator to move into an oil-filled acoustic waveguide. The actuator includes a pusher plate with holes that reduces cavitation and is capable of operation at great depths commonly encountered in oil well logging. Pulse power and spectrum of the acoustic transmitter are sufficient to measure either reflections from distant geological structures or waves propagating through the formation near the borehole. A positive acoustic pulse and a symmetric negative acoustic pulse are generated by action of the actuator on the acoustic waveguide.

Abstract: A gas gun is provided for generation of an acoustic pulse and subsequent detection of return reflections from the annulus of a well. The system includes a gas gun and a hand-held gas source. The hand-held gas source comprises: a two-part housing forming a chamber for receipt of a small CO.sub.2 gas cartridge commonly used for CO.sub.2 target pistols; means for piercing the gas cartridge and pressurizing the chamber; a coupling for releasable connection to a delivery assembly; a passageway leading from the chamber to the coupling; and a first valve in the passageway for controlling release of gas from the chamber.

Abstract: The invention relates to a device for exploring an underground formation crossed by a well inclined significantly to the vertical.

Abstract: An acoustic sensor for use as part of a drill string in a borehole has an acoustic transducer which vibrates the drill bit in contact with the rock at the end of the borehole to generate acoustic signals in the rock. These acoustic signals propogate through the rocks ahead of the drill bit and are reflected and scattered to return to an acoustic sensor contained within the drill string.

Abstract: An acoustic wave transducer useful in sonic logging while drilling a borehole through an adjacent earth formation includes an array of transducer elements mounted circumferentially around a drill collar. The elements are bonded in an elastomer ring that is received in an external groove in the collar and are protected by a shield having windows. The elements are electrically connected in parallel so that when excited by an electrical pulse, the elements generate a monopole acoustic wave that propagates out into the formation. When used as a receiver, the electrically connected array of elements detect averaged acoustic waves from the formation around the circumference of the drill collar and have minimum sensitivity to acoustic multipole waves traveling through the drill collar.

Abstract: Within the scope of operations of long-term regular monitoring of an underground area, a seismic emission-reception device is installed in a fixed position on the production site, so as to have time stable operating conditions of identical emission-reception locations, identical quality of coupling with the formations, etc. The device includes a plurality of seismic sources (S1 . . . Sn) in fixed places at the surface or buried beneath the surface, on either side of a production well (1), and at least one array of receivers (R) set in a fixed position at the surface or in at least one well. Explosive sources, hydraulic overpressure sources, electromechanical sources, etc, can be used and connected to a plant (3) providing energy using an explosive gaseous mixture, which may be a constituent taken from the monitored area, fluid under pressure transmitting hydraulic shocks or vibrations, etc, by means of buried pipes or cables (2).

Abstract: The present invention is concerned with a system for the real time location of deep boreholes while drilling. The system includes a plurality of sensors sensitive to seismic vibrations disposed in an area where a borehole is to he drilled, the sensors being adapted to selectively pick up the vibrations emitted by the drilling bit as it progresses through the rock. The data picked up by the sensors is then processed and the results are displayed in real time, thus allowing the operator to know precisely the location of the drill bit as the hole is being drilled.

Abstract: An attenuator for use in attenuating tube waves in a borehole includes a body formed from a permeable material having a rigid matrix which can be saturated with fluid. In its simplest form, the attenuator is one or more cylindrical bodies as part of a borehole acoustic logging system. Alternatively, the shape, particularly at the end regions, can be modified to reduce the amount of reflection of tube waves in the borehole. Another attenuator includes a body for placement in a borehole formed from an attenuating material, the shape of the body being selected such that the change in impedance experienced by acoustic waves in the borehole is gradual rather than abrupt. One particularly preferred shape for the body comprises one in which the diameter is greatest towards the center of the body, for example the shape formed by two cones placed base to base, or a cylinder having conically tapered ends. A number of bodies can be used where appropriate.

Abstract: The transducer comprises for example a block (1) of sensitive elements such as piled piezoelectric disks held up by a stud bolt between two ferrules and a shell (8) all in one piece, that is arranged around the piling with a concave central part (8A) extended on either side by a solid cylindrical part (8 B, 8 C). Two sleeves are arranged at the two opposite ends of the transducer and elastic elements (14) for decoupling them in relation to the vibrating block (1) are interposed. A flexible housing (18) can be placed around the shell (8) so as to insulate from the outside environment the inner volume of the transducer that can be filled with a fluid such as oil. Connecting means allow the vibrating block to be connected to an exciting voltage source. The transducer can be used for the emission of vibrations at sea or in wells and notably petroleum or gas wells for example.

Abstract: A autonomous borehole data transmission apparatus for transmitting measurement data from measuring instruments at the downhole end of a drill string by generating pressure pulses utilizing a transducer longitudinally responsive to magnetic field pulses caused by electrical pulses corresponding to the measured downhole parameters.

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: In a bore holes, a plurality of resilient members and plates are piled up alternately to form a laminate, and a deadweight is dropped onto the laminate. The resilient members are deformed due to the impact force of the dropped deadweight to cause bore hole water among the plates to be forced out in the outward direction, and elastic waves to occur in the bore hole wall.

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: An apparatus for oscillating a mass at a plurality of selective frequencies includes a source of compressible fluid and a cylinder having a bore filled with the compressible fluid. The cylinder includes a port opening to the bore, the port being connected to the source of compressible fluid. A piston slides in the bore to define a chamber. The piston is operably connected to the fluid mass to oscillate the mass. An average volume of the chamber is adjusted to change the frequency of the oscillating mass.

Abstract: A vortex chamber fluid pulser selectively produces pressure pulses in fluid flowing therethrough by the alternating insertion and retraction of a flow-disrupting tab into and out of an annular vortex chamber having an inlet and a pair of opposed axial outlets. Insertion of the tab disrupts the normally radial flow of fluid through the chamber and outlets causing the flow to become vortical; retraction of the tab causes a second pressure pulse as the flow returns to radial, sending a sequence of pressure pulses capable of carrying encoded signals to a transducer remotely located in the fluid.

Abstract: A seismic pulse generator has a tubular outer member telescopically connected to a tubular concentric inner member. The outer member has a port in its sidewall. A force allows telescopic extension from a contracted position to an extended position. An annular well fluid chamber is located between the sidewalls of the inner and outer members in communication with the port. When at the bottom of the well, the inner and outer members are in the contracted position and the well fluid chamber has a large volume. A delay means controls the rate at which the inner and outer members initially move from the contracted to the extended position. Upon lifting the inner and outer members, the delay apparatus causes the inner and outer members to at first move apart slowly, thus allowing the inner and outer members to be raised substantially together. After a predetermined time interval, the delay apparatus allows the force to move the inner and outer members quickly to the extended position.

Abstract: The current invention is an apparatus useful for generating seismic waves with an enhanced signal to noise ratio. The enhanced signal is produced at a fundamental resonant frequency, and multiples thereof, by producing a near zero acoustic pressure condition around and beyond each end of the apparatus having an intermediate acoustic source. Such a near zero acoustic pressure condition is established preferably by either (1) using two end acoustic sources to produce a destructive interference effect with the acoustic output of a third acoustic source postioned therebetween, or (2) using two active or passive end acoustic capacitors or resonators to produce a near zero impedance condition at each end of the apparatus. The enhanced signal may be produced over a range of frequencies, including both resonant and nonresonant frequencies, by creating a high impedance condition experienced by the intermediate source and hence a high acoustic pressure around the intermediate region of the apparatus.

Abstract: In a bore holes, a plurality of resilient members and plates are piled up alternately to form a laminate, and a deadweight is dropped onto the laminate. The resilient members are deformed due to the impact force of the dropped deadweight to cause bore hole water among the plates to be forced out in the outward direction, and elastic waves to occur in the bore hole wall.

Abstract: A method and apparatus for sonic logging using a measuring while drilling telemetry system as the sonic source is provided. Transducers are provided for receiving acoustic energy from the formation surrounding the borehole. The transducers produce a signal which is processed and telemetered to the surface using the measuring while drilling system.

Abstract: The orientation of vertical fractures in subsurface rock formations is determined. A cross-dipole logging tool collects four-component shear-wave seismic data through a formation interval of interest in a subsurface formation adjacent a well bore. A gyroscope is typically provided to indicate compass orientation of the logging tool. The collected seismic data are then transformed within a time window containing arrivals of the shear waves to a new coordinate system within which the motion of the shear waves becomes linear. In the new coordinate system, the shear wave data are processed to determine the presence and orientation of fractures in the formation.

Abstract: A subsurface seismic source for generating seismic waves comprises a fluid supply conduit section conducting fluid downward and having a seat for receiving a blocking body transported by said fluid. Said body blocks the fluid through said section when forced against said seat by said mud. At least one piston chamber is arranged adjacent to and connected with said section, has in one end wall at one end an opening to said section above said blocking body when forced against said seat, and comprises a biased piston closing said chamber at the other end and being driven to the corresponding other end wall when the blocking body is forced against said seat. Said blocking body is forced through said seat at a predetermined mud pressure level, thereby releasing said piston, the piston colliding against the one end wall and generating seismic waves.

Abstract: The seismic source (5) according to the invention is associated with a drill string (1) linking a drill bit to a surface installation close to the bit. It comprises a closed chamber (6) fastened inside a drill cellar (4) of the drill string. The section thereof is smaller than the inner section of the drill string, so as to allow free circulation of the drilling fluid. A reactive mass (8) may move within this chamber (6) and along the axis of drill string (1). Hydraulic or electro-mechanical means allow a strong alternating force of controlled frequency and duration to be applied to this mass. The energy necessary to the operating thereof is taken from the fluid current. This source requires no substantial modification in the usual drilling equipments. Drilling a well and performing seismic measurings may be achieved at the same time by means of the source by arranging sensors at the surface and/or in one or several adjacent wells.

Abstract: The current invention is an apparatus useful for generating seismic waves with an enhanced signal to noise ratio. The enhanced signal is produced at a fundamental resonant frequency, and multiples thereof, by producing a near zero acoustic pressure condition around and beyond each end of the apparatus having an intermediate acoustic source. Such a near zero acoustic pressure condition is established preferably by either (1) using two end acoustic sources to produce a destructive interference effect with the acoustic output of a third acoustic source postioned therebetween, or (2) using two end acoustic capacitors or resonators to produce a near zero impedance condition at each end of the apparatus. The enhanced signal may be produced over a range of frequencies, including both resonant and nonresonant frequencies, by creating a high impedance condition experienced by the intermediate source and hence a high acoustic pressure around the intermediate region of the apparatus.

Abstract: A piezoelectric film strip is wrapped a plurality of times around a flexible inert mandrel that has standoff collars on each end. The film-wrapped mandrel is hermetically sealed inside a hollow rigid inert cylinder. Electrodes provide electrical communication with the film strip which forms the active element of the transducer. Variations in hydrodynamic pressure flex the film strip in tension to generate a voltage.

Abstract: A disposable point detachably mounted on the lower end of a vertically movable hole forming elongated member with the point having an explosive charge mounted therein in order for the disposable point and explosive charge to remain in the bottom of a hole formed by the elongated member and point when they are forced into a subsurface formation which is to be seismically explored with the elongated member then being retracted.

Abstract: A sweep frequency vibrator is set forth. It has an elongate cylindrical housing closed at the top and bottom ends. On the interior, there is a reactionary mass fixed to identical upper and lower piston ends. They are received in seal isolated chambers, one being formed in a moveable plug. The plug is moved to thereby vary the spacing of the chambers. As the frequency is changed, plug is moved to assure sufficient clearance from the excursion of the reactionary mass. Hydraulic oil under pressure is delivered to control valves, one for each piston end. The two control valves and piston ends have very short flow lines. Moreover the excursion permitted for the plug assures operation without bottoming out.

Abstract: The present invention relates to an improved downhole seismic source with an epicyclic eccentric weight system for the simultaneous generation of elliptically polarized shear wave seismic energy and compression wave seismic energy coupled into a borehole. The apparatus includes a cylindrical housing and a drive means or electric motor disposed in the housing which provides rotational output to an epicyclic eccentric weight system also disposed in the housing. Expandable tapered wedging collars are used to firmly secure the motor and the epicyclic eccentric weight systems within the housing. A flexible shaft interconnects the centerline of the epicyclic cylindrical roller and the motor whereby the roller receives the rotational output from the motor. The shaft rotates in one direction and the roller rotates in the opposite direction thereby producing an epicyclic motion.

Abstract: An acoustic wave generator for telemetering signals through a drillstem comprises a sub interposed in the drillstem with a central mandrel and a piston mass disposed in sleeved relationship around the mandrel and reciprocable by hydraulic pressure fluid to impose reaction forces on the mandrel and the drillstring at selected frequencies to transmit acoustic waves through the drillstring. A control system for operating the generator includes a hydraulic pump, a control valve and a frequency control circuit which operates the control valve to effect reciprocation of the piston mass at selected frequencies for transmitting serial data from the control system through the drillstring to a receiving system. The generator is coaxially arranged in the drillstring and is operable to generate high-energy acoustic wave signals for propagation through relatively long drillstrings.

Abstract: This disclosure is directed to a displacement amplifier for forming acoustic pulses and more particularly to one which incorporates a flexible movable lightweight diaphragm of rectangular configuration. It has upper and lower ends which are connected to opposing piston rods driven by duplicate pistons and double acting cylinders. The cylinders are located at opposite ends of the diaphragm or membrane. They are supported in an elongate tool which positions the flexible membrane in a generally rectangular window. This enables the membrane to flex as the pistons are driven, thereby enabling the flexure of the membrane to form dipole source for radially directed compression waves transmitted from the membrane in the window.

Abstract: Methods are provided for making use of an apparatus for generating vibrational energy in a borehole, the apparatus utilizes a mass and a rotary source for suspending the mass in a borehole or in casing in a borehole or in an instrument housing that may be positioned in an opened or cased borehole arranged to cause frictional contact with the surface of the rotating mass, the mass being rotatable about is rotational axis in one direction to cause it to backward whirl in the opposite direction, the centrifugal force of the whirling mass serving to generate vibrational energy that is used to obtain geophysical information as to the structure of the earth surrounding and adjacent to the borehole and for enhancing cementing and production enhancing techniques in oil or gas wells.

Abstract: A source of seismic waves operable within a borehole filled with liquid crises a module supported by a cable. The module includes means to generate a high voltage and to charge a bank of capacitors, and means to connect the capacitors across a pair of electrodes forming a spark gap. The electrodes are immersed in liquid at the same pressure as the borehole liquid and acoustically continuous with it, and are separated by a gap of width between 0.5 and 20 mm. If the gap is greater than about 5 mm, both the electrodes should be covered with insulation except at the positions where the spark is to be formed. The module can operate automatically at considerable depths and at high pressures.

Abstract: The present invention relates to an improved downhole seismic source for the simultaneous generation of elliptically polarized shear wave seismic energy and compression wave seismic energy coupled into a borehole. The source of the present invention is capable of receiving several kilowatts of energy downhole to depths of several thousand feet. An orbital vibrator, energized by a hydraulic power means is disposed within a housing. The orbital vibrator imparts an orbital motion which generates seismic wave energy in the borehole. A cable supports the hydraulic power means and the orbital vibrator at selected positions along the borehole for coupling of the seismic wave energy into the borehole.

Abstract: A downhole seismic acoustical signal source capable of selectively firing numerous, prewired explosive charges. The downhole seismic source has a firing system that uses a sequence of combinations of two conductors at a time and a downhole diode array to select and fire a single charge. The conductors are connected to a Surface Control Unit at the surface. A seismic crew on the surface can select and fire any charge through this control unit. The downhole seismic source has the ability to fire numerous explosive charges in a given downhole trip through the firing of many individual explosive charges.

Abstract: An acoustic wave energy generator comprises a body having an internal gas-pressurisable first chamber 1 adjoining a second chamber 2 into which a liquid is introduced to cover a vibratable means 4 which may be a flexible diaphragm and is mounted on the second chamber so as to close an associated opening 5 in the second chamber. After the first chamber 1 is pressurised with a first gas a common closed opening between the chambers is opened to cause communication between the chambers 1,2 to permit a shock wave emanating from the first chamber to impinge on the liquid. As a result, the vibratable means 4 is caused to vibrate so as to produce acoustic wave energy in response to the impingement of the shock wave on the liquid. By using different liquids and/or different heights of liquids in the second chamber the generator may be tuned to provide acoustic wave energy with a relatively narrow chosen frequency range or within a chosen substantially single frequency.

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.

Abstract: A seismic source for downhole use is disclosed which is formed by an outer tubular member having weighted ends which carries within a coaxially mounted tubularly shaped piezoelectric element. The piezoelectric element is cyclically driven to produce a standing wave having a frequency in the range of 0.25 to 5 kHz and a narrow bandwidth in the range of 5-50 Hz.