Abstract: Devices, systems and methods for navigating and determining the location of downhole oil and gas wellbore tools are disclosed. The devices, systems, and methods may include a drone including an ultrasound transceiver that generates and receives an ultrasonic signal that interacts with the environment external to the drone and detects, utilizing a processer associated therewith, changes the environment external to the drone. The speed and location of the drone may be determined using the processor. Alternatively, an electromagnetic field generator that generates a field that interacts with the environment external to the drone. When the drone moves through the wellbore, the environment external to the drone constantly changes. Based on this changing environment, the speed and location of the drone is determined using the present devices, systems and methods.

Abstract: A method for characterizing a hydraulic fracture in a subsurface formation includes inducing a pressure change in a borehole drilled through the subsurface formation. At least one of pressure and a time derivative of pressure is measured in the borehole for a selected length of time. At least one physical parameter of at least one fracture is determined using the measured pressure and/or the time derivative of pressure. A method for characterizing hydraulic fracturing rate uses microseismic event count measured through the borehole and its real-time implementation.

Abstract: A downhole tool includes a tubular having an outer surface and an inner surface defining a flowbore having a longitudinal axis and a backpressure valve arranged in the flowbore. The backpressure valve includes a flapper valve including a hinge end, a cantilevered end, a first side and an opposing second side pivotally mounted to the inner surface at the hinge end to selectively extend across the flowbore, and a locking system mounted to the inner surface adjacent to the hinge end of the flapper valve in the flowbore. The flapper valve is pivotable between a first position, wherein the flapper valve is free to pivot relative to the inner surface between an open configuration and a closed configuration, and a second position, wherein the hinge end of the flapper valve activates the locking system to lock the flapper valve in the open configuration.

Abstract: In a method for processing a turbomachine airfoil element, the airfoil element comprises a metallic substrate having: an airfoil extending from a first end to a second end; and a cooling passageway system extending through the airfoil. The method comprises: applying an external vibration to an area of the airfoil element targeting internal fouling of the cooling passageway system; flushing the cooling passageway system; and imaging the cooling passageway system.

Abstract: Some aspects of what is described here relate to seismic data analysis techniques. A seismic excitation is generated in a first directional wellbore section in a subterranean region. A seismic response associated with the seismic excitation is detected in a second directional wellbore section in the subterranean region. Seismic response data based on the seismic response are analyzed to identify a location of a fracture treatment injection wellbore in the subterranean region.

Abstract: A seismic wave generating tool, such as a spark gap, of an electric arc generation device includes an upper part and a lower part defining a discharge chamber between them, at least one retaining arm connecting the upper part to the lower part, first and second electrodes respectively associated with the upper and lower parts and arranged in the discharge chamber. The retaining arm comprises an electrically insulating part facing the electrodes. The tool includes a first deployable device implementing a current return and connecting the upper part to the lower part. The first deployable device is configured to be in a retracted state and in a deployed state in which it is at a distance from the discharge chamber.

Abstract: An example method may include selecting a proposed pulse. A minimum phase wavelet may be generated based, at least in part, on the proposed pulse. A pulse signal within a wellbore may be generated based, at least in part, on the minimum phase wavelet. An echo signal corresponding to the pulse signal from at least a portion of the wellbore may be received, wherein the echo signal is indicative of a wellbore property.

Abstract: An acoustic transducer, such as a bender bar, having ferroelectric actuation elements that are designed to optimize a predetermined deflection mode shape. The acoustic transducers may include one or more rounded modally shaped actuation elements or weighted actuation elements. Modal shaping of the actuation elements allows for specific targeting of modes which most efficiently radiate acoustic energy.

Abstract: A downhole magnetic clamping system for a tool is provided. The clamping system may include a first permanent magnet, and a yoke, movably positioned next to the first permanent magnet and movable to at least two positions, a first position in which a magnetic attraction force produced by the first permanent magnet on structures exterior to the tool is reduced relative to a second position. In addition, the clamping system may further include a non-linear resilient member applying a resilient force to the yoke in the direction of the second position. Further, the clamping system may include an electro-magnetic coil, operable in a first and second direction to initiate movement of the yoke between the first position and the second position.

Abstract: Communication apparatus comprises a first transceiver unit (205A) and a signal processing device (106) configured to receive a signal from the first transceiver unit and to produce a signal for transmission by the first transceiver unit. A cable (201A) connects the first transceiver unit to the signal processing device. The first transceiver unit comprises a housing; a first pair of transducers (204T, 204R) located at, or adjacent, a first end of the housing, and a second set of transducers (206T, 206R) located at, or adjacent, an opposite end of the housing.

Abstract: A multitude of seismic sources are formed into a linear array which can be permanently cemented within a wellbore. The seismic sources can be orbital vibrators that are electrically connected and protected from the cementing by use of pieces of drill pipe and tubing that are interconnected and provide a container for electrical connection of the seismic sources and provide surface access through a surface vault.

Abstract: The present disclosure relates to increasing the output power of a clamped seismic or acoustic source disposed in a wellbore without damaging the borehole/casing/cement. One or more sources are provided and carried on a conveyance mechanism. The conveyance mechanism may be a wireline, a coiled tubing, or a drill pipe. The one or more sources are run into and/or out of the wellbore and temporarily disposed at various locations within the wellbore. The one or more sources are temporarily clamped to the wellbore at the various locations using distributed clamping, and a source signal is generated by the distributed clamped source. The distributed clamping device may have multiple clamping mechanisms along an increased length of the source or a continuous clamping mechanism along an increased length of the source.

Abstract: A method has been disclosed for determining a position of a water/cement boundary in an annular area between two concentric pipes in a hydrocarbon well. The method comprises the steps of running a well tool (10) into a central pipe of the well, where the well tool (10) comprises a tool housing (11), a pulse generator (14) and a signal recorder (16) provided within the housing (11); generating an electromagnetic pulse by means of the pulse generator, thereby providing physical vibrations in the central pipe of the well; recording reflected acoustic signals from the well by means of the signal recorder (16); repeating the generating and recording steps for different vertical positions of the pulse generator in the well; organizing the recorded signals in a two-dimensional representation; filtering the organized recorded signals in order to identify, in the two-dimensional representation, a hyperbola (B); and providing an apex of the hyperbola (B) as the determined position of the water/cement boundary.

Abstract: An air, fuel, and inert fluid or liquid water mixture is injected into a resonance chamber forming micro-packets. The air and fuel mixture in the micro-packets form micro-explosions in a combustion chamber where acoustic and electromagnetic energy are absorbed by the inert fluid instead of thermal energy. A standing wave is created in the central resonance chamber by the micro-explosions. Interfering waves are in phase increasing energy in the air, fuel and water mixture. Acoustic energy is transferred from the hot combustion gases to the colder inert fluid or water. A thermal equilibrium is reached without substantial energy transfer from the hot body to the cold body. Efficient combustion is achieved with reduced carbon emissions. The heat generated from the combustion may be used to produce work by any conventional device, such as a steam engine or turbine or generate heat for a building.

Abstract: A test head for testing a workpiece has an ultrasonic transducer configuration with a plurality of ultrasonic transducers. The test head further contains a carrier matched to a surface contour of the workpiece, a damping layer arranged on the carrier, and a flexible conductor foil configuration, which is arranged on the damping layer and has a number of electrically separated conductor tracks which corresponds to the number of transducer elements. The transducer elements are arranged on the conductor tracks alongside one another in at least one row, and in each case are electrically contact-connected to one of the conductor tracks.

Abstract: A seismic source configured to generate seismic waves underground. The source includes a tank configured to be buried underground, the tank having a cavity; an actuation mechanism provided inside the cavity, wherein the actuation mechanism is configured to have at least one movable part that moves back and forth to generate a seismic wave having a desired frequency; and a first fluid provided inside the cavity and around the actuation mechanism and configured to transform the back and forth movement of the at least one movable part into a varying pressure that directly acts on walls of the tank.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may operate to rotate a rotatable driving member having at least one driving lobe, and to periodically contact at least one cam on a unitary driven member with the at least one driving lobe during rotation of the rotatable driving member, to set the driven member in motion. This motion can be used to launch an acoustic wave along an axis substantially orthogonal to the axis of rotation of the driving member, where the driving member disposed completely within the driven member. The signature of the acoustic wave can be at least partially determined by the profile of the cam and the rotation rate of the driving member. Additional apparatus, systems, and methods are disclosed.

Abstract: Measurements made by a transducer assembly for downhole imaging are affected by reverberations between the transducer and the window on the outside of the assembly. The reverberations result in a stationary noise on the image. Hardware solutions to improve signal-to-noise ratio includes using a composite transducer, adjusting the distance between the transducer and the window. SNR can also be improved by processing techniques that include stacking, fitting a sinusoid to the reverberation, by envelope peak detection, and by applying a notch filter.

Abstract: Downhole seismic sources that may be compatible measurement-while-drilling systems. The downhole seismic sources are integrated into drill string components, including drill collars of the bottom hole assembly. The downhole seismic sources may generate a low swept frequency signal suitable for imaging around the drill-string and ahead of the drill bit. Integrated downhole seismic systems including a downhole seismic source, receivers and optionally data processing capabilities. The integrated systems may be configured to determine the distance and orientation of bed boundaries, including ahead of the drill bit up to about 200 m to 500 m in depth. Methods for downhole seismic, including single well and cross-well seismic. The methods may include obtaining seismic information ahead of the drill bit.

Abstract: A container data center includes a container, a plurality of power supplies, an electric switch system, a plurality of normally closed switches, an alarm device, and a controller. The electric switch system is received in the container. The plurality of normally closed switches are connected between the power supplies and the electric switch system. Each normally closed switch is connected with a corresponding one of the power supplies in series. The controller is connected to the normally closed switches and the alarm device, configured for receiving earthquake information containing an earthquake intensity, and configured for controlling the alarm device to activate alarms and controlling some of the normally closed switches or all the normally closed switches to open when the earthquake intensity is equal to or greater than a predetermined earthquake intensity.

Abstract: Measurements made by a transducer assembly for downhole imaging are affected by reverberations between the transducer and the window on the outside of the assembly. The reverberations result in a stationary noise on the image. Hardware solutions to improve signal-to-noise ratio includes using a composite transducer, adjusting the distance between the transducer and the window. SNR can also be improved by processing techniques that include stacking, fitting a sinusoid to the reverberation, by envelope peak detection, and by applying a notch filter.

Abstract: The present disclosure provides embodiments seismic energy sources configured to generate enhanced shear wave energy in order to more accurately determine the distribution and orientation of fractures in subterranean formations. At least one seismic energy source includes an elongate rod having a first end and a second end, a detonator coupled to the first end, and a bull plug coupled to the second end. An explosive is helically-wrapped about the elongate rod continuously from the first end to the second end and configured to detonate such that a time-delayed detonation is achieved which induces increased shear wave energy in the surrounding formations.

Abstract: An apparatus disclosed herein includes a shell movably coupled to a base. The shell defines a chamber, and a counterweight is disposed in the chamber. A first spring is coupled to the shell and a first end of the counterweight, and a second spring is coupled to the shell and a second end of the counterweight. The first spring is oriented at a first angle, and the second spring is oriented at a second angle different than the first angle. The example apparatus further includes an actuator coupled to the first spring or the second spring. The actuator is to oscillate the counterweight to enable the shell to provide an acoustic signal.

Abstract: An acoustic energy source for imparting acoustic energy into the Earth's subsurface includes an electrically driven transducer coupled to a source of swept frequency alternating current. A tunable Helmholtz resonator is disposed proximate the transducer. In one example, the resonator has a tuning device configured to maintain a resonant frequency substantially equal to an instantaneous frequency of the alternating current. The tuning device includes an actuator coupled to a sleeve, wherein the sleeve is disposed over selected numbers of openings in a wall of a tube on the resonator. The transducer and the resonator are disposed in a wellbore drilled through rock formations. The wellbore has a plurality of layers of fluid therein, each layer thereof having a different density and/or viscosity.

Abstract: A seismic energy source includes an inlet aperture and an inlet pipe in fluid communication with an outlet of the inlet aperture at an inlet end of the inlet pipe. The inlet pipe is in fluid communication with an accumulator at an outlet end of the inlet pipe. An outlet pipe is in fluid communication with the accumulator at an inlet end of the outlet pipe and is connected to an outlet valve at an outlet end of the outlet pipe. The outlet valve is actuated by fluid pressure in the outlet pipe. An actuation pressure of the valve, and diameter, length and material properties of the outlet pipe are selected to cause a reflected water pressure wave resulting from closure of the valve to travel within the outlet pipe at a selected velocity. Motion of the seismic source through the water provides water pressure to operate the source.

Abstract: A seismic gun system for surveying underground geological topology, the seismic gun system comprising a projectile, a seismic gun body, a barrel, and a guide tube. The projectile includes an outer tubular jacket and a frangible material in its interior. A exterior surface of the tubular jacket is textured to regulate tubular jacket disruption. The barrel includes a breach end and a muzzle end. The breach end is connectable to the seismic gun body for receiving the projectile into said barrel and said muzzle end directing the projectile towards the bottom of a bore hole. The guide tube has an upper end and a terminal end. The upper end of the guide tube is connectable to the muzzle end of the barrel. The guide tube has walls to direct the projectile towards the bottom of the bore hole when aimed therein.

Abstract: An apparatus and method for providing a downhole acoustic source is disclosed. The acoustic source includes a piston configured to oscillate in an axial direction of the acoustic source and produce an acoustic signal in a medium in contact with an exterior surface of the piston, and an elastomer disposed on an interior side of the piston, an acoustic impedance of the elastomer selected to match an acoustic impedance of the piston. A permanent magnet is configured to provide a permanent magnetic field oriented in the axial direction, and a coil disposed on an interior side of the piston produces an alternating magnetic field in the region of the permanent magnetic field. The elastomer may be, for example, a silicon rubber, a silicone jelly, and a silicone oil. A plurality of acoustic sources may be arranged to produce an acoustic dipole configuration or an acoustic quadrupole configuration.

Abstract: A system and method is provided for communicating with a device disposed in a wellbore. Signals are sent through the Earth via signal pulses. The pulses are created by a seismic vibrator and processed by a receiver disposed in the wellbore. The receiver is in communication with the device and transfers data, such as command and control signal, to the device.

Abstract: An acoustic isolator section for an acoustic well logging tool, the isolator section comprising: an isolator comprising: (i) an isolator body; (ii) a mass; (iii) a resiliently deformable portion formed integrally with the isolator body; (iv) a movement limiter.

Abstract: A seismic gun system for surveying underground geological topology, the seismic gun system comprising a projectile, a seismic gun body, a barrel, and a guide tube. The projectile includes an outer tubular jacket and a frangible material in its interior. A exterior surface of the tubular jacket is textured to regulate tubular jacket disruption. The barrel includes a breach end and a muzzle end. The breach end is connectable to the seismic gun body for receiving the projectile into said barrel and said muzzle end directing the projectile towards the bottom of a bore hole. The guide tube has an upper end and a terminal end. The upper end of the guide tube is connectable to the muzzle end of the barrel. The guide tube has walls to direct the projectile towards the bottom of the bore hole when aimed therein.

Abstract: A seismic gun assembly comprising a barrel and guide tube assembly for delivering a projectile to the bottom of a bore hole with a non-line-of-sight section. The guide tube being either a large diameter guide tube or a tight fitted guide tube. The large diameter guide tube allowing the projectile to perform shallow angle bounces to reach the bottom of a non-line-of-sight bore hole. The tight fitted guide tube allows the projectile to ride the inner wall of the guide tube to reach the bottom of a non-line-of-sight bore hole. The projectile comprises an outer jacket and a frangible core. The seismic gun barrel assembly additionally comprises a fluid exclusion puck for preventing fluids from entering the guide tube, a suppressing collar for suppressing seismic noise, and a method for modulating recoil.

Abstract: Acoustics-based methods and devices to characterize a gas kick during drilling an oil, gas, or gas condensate well are described. A pressure wave may be generated by abruptly changing the drilling mud pressure in the well, for example at the well head. The pressure wave is allowed to travel down the well, reflect from the well bottom and reach the well head again. Pressure is monitored during this process and a pressure peak is identified. The gas kick is characterized using the width of the pressure peak and time elapsed from the onset of pressure change and appearance of the peak. Negative pressure wave is preferred and may be generated by opening of a fast-acting valve located in the outlet pathway of the drilling mud fluid.

Abstract: An attenuation apparatus, system, and method are disclosed. The attenuator is attached to a pipe and includes a housing that includes an inner sleeve and an outer sleeve. The attenuator includes one or more masses, to resonate when exposed to waves including acoustic frequency components.

Abstract: A seismic source signal generator includes a mass, a primary accumulator and a secondary accumulator, the secondary accumulator having an internal volume smaller than an internal volume of the primary accumulator. A method for generating a signal using a seismic vibrator includes operating the seismic vibrator using hydraulic fluid, damping hydraulic pressure deviations in the hydraulic fluid using a first accumulator in hydraulic communication with the hydraulic fluid, and damping pressure deviations in the hydraulic fluid using a second accumulator in hydraulic communication with the hydraulic fluid, the second accumulator having an internal volume smaller than an internal volume of the first accumulator.

Abstract: A method of conducting a seismic survey comprising using at least one seismic source operable to emit an acoustic signal comprises: —providing a first receiver line extending in a first direction across a region of the ground to be surveyed; —locating at least one seismic receiver at a point on the first receiver line, the seismic i receiver(s) being adapted to record reflected acoustic signals emitted by the seismic source(s); —providing a first pre-determined shot line having a plurality of shot points along its length, extending in a second direction and along which the seismic source(s) is movable; —operating the or one of the seismic source(s) to emit an acoustic signal at a first shot point on the pre-determined shot line, the reflection of the acoustic signal being recorded by the or one of the seismic receiver(s); and —operating the or one of the seismic source(s) to emit another acoustic signal at a second shot point on the pre-determined shot line, the reflection of the another acoustic signal being

Abstract: A seismic gun assembly comprising a barrel and guide tube assembly for delivering a projectile to the bottom of a bore hole with a non-line-of-sight section. The guide tube being either a large diameter guide tube or a tight fitted guide tube. The large diameter guide tube allowing the projectile to perform shallow angle bounces to reach the bottom of a non-line-of-sight bore hole. The tight fitted guide tube allows the projectile to ride the inner wall of the guide tube to reach the bottom of a non-line-of-sight bore hole. The projectile comprises an outer jacket and a frangible core. The seismic gun barrel assembly additionally comprises a fluid exclusion puck for preventing fluids from entering the guide tube, a suppressing collar for suppressing seismic noise, and a method for modulating recoil.

Abstract: A vibration source (10) includes an armature bar (12) having a major length dimension, and a driver (20A) positioned about the armature bar. The driver (20A) is movably coupled to the armature bar (12), and includes an electromagnet (40). During operation the electromagnet (40) is activated such that the driver (20A) moves with respect to the armature bar (12) and a vibratory signal is generated in the armature bar. A described method for generating a vibratory signal in an object includes positioning the vibration source (10) in an opening of the object, coupling the armature bar (12) to a surface of the object within the opening, and activating the electromagnet (40) of the driver (20A) such that the driver moves with respect to the armature bar (12) and a vibratory signal is generated in the armature bar and the object.

Abstract: A well system and associated method can include an acoustic generator which can be used to excite a formation with acoustic waves transmitted from the acoustic generator. Another well system and associated method can include an acoustic generator which can transmit acoustic waves into cement surrounding a casing. Another well system and associated method can include an acoustic generator which can be used to transmit acoustic waves into an annulus surrounding a well screen during or after a gravel packing operation. Another well system and associated method can include an acoustic generator which can be connected in a drill string in close proximity to a drill bit, with the acoustic generator transmitting acoustic waves into a formation ahead of the bit.

Abstract: An apparatus for generating seismic body waves in a hydrocarbon reservoir includes a closed-loop borehole source having a resonant cavity for generating resonant energy, a drive source and a control unit. The drive source injects pressure pulses to the resonant cavity at a predetermined or selectable pressure and frequency. The fluid circulates between the cavity and the drive source in a closed-loop fashion. In another embodiment, the borehole source utilizes a smart or controllable material that is responsive to an applied excitation field. The cavity includes an excitation coil for providing an excitation field that changes a material property of the smart fluid. The control unit is programmed to adjust operating parameters to produce seismic waves having a selected frequency and amplitude. In one embodiment, a control unit adjusts operating parameters in response to measured parameters of interest or surface commands.

Abstract: The current invention provides an improved method of increasing well yield and enhancing oil production. The method comprises the steps of lowering a vibroacoustic downhole emitter into a well down to a production layer depth and performing acoustic impact on the formation. The impact is implemented by a multiple frequency signal containing at least two simple harmonic components whose frequencies and amplitudes meet the resonance overlapping condition.

Abstract: A system and method for microseismic fracture mapping using seismic source timing measurements for velocity calibration is disclosed. The system may include a seismic source coupled to a wireline and a seismic source trigger, a sensor capable of detecting a first signal from the seismic source trigger, a transmitter coupled to the sensor, capable of transmitting a time value associated with the first signal, a receiver capable of detecting an event generated by the seismic source; and an analyzer capable of calculating a microseismic velocity of the event. In one embodiment, a first signal is transmitted through a wireline to trigger a seismic source. The first signal is detected, and a first time value associated with the first signal is transmitted. An event associated with the seismic source is detected and a second signal associated with the event is transmitted to an analyzer.

Abstract: An acoustic isolator for attenuating through-tool acoustic signals comprises a plurality of u-shaped link members, where each link member has two sets of ears. A plurality of yoke members are adapted to fit between cooperating sets of ears. A plurality of pins connect the plurality of u-shaped link members to the plurality of yoke members for providing limited flexural compliance. The isolator may be made from metallic and/or composite materials.

Abstract: A seismic source signal generator includes a mass, a primary accumulator and a secondary accumulator, the secondary accumulator having an internal volume smaller than an internal volume of the primary accumulator. A method for generating a signal using a seismic vibrator includes operating the seismic vibrator using hydraulic fluid, damping hydraulic pressure deviations in the hydraulic fluid using a first accumulator in hydraulic communication with the hydraulic fluid, and damping pressure deviations in the hydraulic fluid using a second accumulator in hydraulic communication with the hydraulic fluid, the second accumulator having an internal volume smaller than an internal volume of the first accumulator.

Abstract: A vibration source (10) includes an armature bar (12) having a major length dimension, and a driver (20A) positioned about the armature bar. The driver (20A) is movably coupled to the armature bar (12), and includes an electromagnet (40). During operation the electromagnet (40) is activated such that the driver (20A) moves with respect to the armature bar (12) and a vibratory signal is generated in the armature bar. A described method for generating a vibratory signal in an object includes positioning the vibration source (10) in an opening of the object, coupling the armature bar (12) to a surface of the object within the opening, and activating the electromagnet (40) of the driver (20A) such that the driver moves with respect to the armature bar (12) and a vibratory signal is generated in the armature bar and the object.

Abstract: Elastodynamic waves are generated by a tool having a hammer rotatably connected with a housing by a first hinge and an actuator arm rotatably connected with the hammer by a second hinge. An axial force applied to the actuator arm by a drive shaft and spring is translated and amplified to a radial impact force by rotation of the hammer around the first hinge. The tool may also include a stabilizer arm connected to the actuator arm by a third hinge, and connected to the housing by a fourth hinge. The housing may be an acoustic wireline tool cylinder having an opening that permits the hammer mass to extend outside the housing when rotated in a first direction. The housing may also include a second opening that permits the hammer mass to extend outside the housing when rotated in a second direction, and a third opening that permits the hammer mass to extend outside the housing when rotated between the first and second openings.

Abstract: A downhole tool, having a central axis defined, may selectively include a sensor section including one or more arms connected to the tool body with an open/close mechanism. The open/close mechanism is configured to move in a radial direction with respect to the axis of the tool body. The tool also includes at least one sensor attached to the arm, and the tool may include at least one transmitter section on the tool. The transmitter is configured to transmit acoustic energy to a formation.

Abstract: An acoustic source for delivering acoustic energy to a ground formation, particularly a rock formation, the source including (a) a solenoid to generate an electromagnetic field, (b) a bullet positioned within the influence of the electromagnetic field, (c) a casing surrounding and enclosing the solenoid and bullet so that both the solenoid and the bullet are protected from the surrounding environment, in use the solenoid being electrically energized to cause the bullet to be propelled by electromagnetic force so that the bullet impacts an anvil portion of the casing in contact with the ground formation is provided.

Abstract: Acoustic measurements made in a borehole using a multipole source are used for imaging a near-borehole geological formation structure and determination of its orientation. The signal to noise ratio (as defined by the ratio of the signal radiated into the formation to the axially propagating signal) depends upon the type of source (force or volume) and its position in the borehole (on the tool, in the fluid or on the borehole wall).

Abstract: A system, method and device may be used to monitor acoustic energy in a borehole. Electromagnetic energy is used to energize a resonant circuit incorporating a sensor. The sensor modulates the electromagnetic energy in accordance with received acoustic energy and transmits the modulated energy so that it may be received and processed in order to obtain the desired measurements.

Abstract: A method for seismic exploration using nonlinear conversions between electromagnetic and seismic energy, with particular attention to the electromagnetic source waveform used. According to the invention, seismic returns from a source waveform are correlated with a reference waveform, with both waveforms custom designed to minimize both correlation side lobes and interference from linear electroseismic effects. A waveform element is selected which may be sequenced by a binary or similar digital code embodying the desired custom design to generate an input sweep with the needed depth penetration and noise suppression. Correlation of the seismic response with the reference waveform in a data processing step mathematically aggregates the seismic response from the input sweep into a single wavelet. Preferred binary digital codes include prescribed variations of maximal length shift-register sequences. Also, an apparatus for generating the desired waveforms.