A variable inductor includes a three-limbed core first section having an inductor winding wound about a medial limb. An air gap is disposed in the medial limb. The inductor includes a second section having a control limb in which a first end of the control limb is connected to a first outer limb of the three-limbed core, and a second end of the control limb is connected to a second outer limb of the three-limbed core. A control winding is wound about the control limb. The inductor may be used in a control circuit to control a power signal driving a transducer. The inductor may be controlled by a signal derived from a comparison of a voltage phase of a power signal to the transducer and a phase of the current traversing the transducer. A system may include the control circuit, including the variable inductor, and the transducer.

The method for enhanced depth penetration of energy into a formation may include mechanically stimulating the formation at a first frequency to induce mechanical stress in the formation and directing electromagnetic radiation towards the formation while mechanically stimulating the formation.

An acoustic transducer is provided. The acoustic transducer includes a housing, a backing, a piezocomposite element adjacent the backing within the housing, and a diaphragm covering on an outward facing surface of the piezocomposite element.

According to embodiments of the disclosure, a downhole tool for taking acoustic measurements in a wellbore is provided. The tool may have an acoustic dipole transmitter with a piston made from a soft magnetic material, mounted on a centering spring between the first coil and the second coil, which moves the piston bi-directionally along a longitudinal axis when energized. The tool may also have a feedback winding on at least one of the first or second coils. The tool may also have a circuit for energizing the first and second coils which includes an input for receiving a signal responsive to the position of the piston relative to the coils and a processor for determining an output waveform used to generate an acoustic signal.

Embodiments related to addition of a variable mass load to the shell of a marine vibrator to compensate for air spring effects. An embodiment provides a marine vibrator, comprising: an outer shell; a driver disposed at least partially within the outer shell and coupled thereto; and a mass load coupled to an exterior surface of the outer shell; wherein the marine vibrator has a resonance frequency selectable based at least in part on the mass load.

In accordance with some embodiments of the present disclosure, a method of vibration control for a wellbore logging tool is disclosed. The wellbore logging tool includes an acoustic transmitter. The method may include providing a braking signal to the acoustic transmitter. The braking signal may be based, at least in part, on at least one prior vibration in the acoustic transmitter. The method may include determining a present vibration in the acoustic transmitter after the braking signal has been provided to the acoustic transmitter. The method may include determining whether to update the braking signal and, if so, updating the braking signal based, at least in part, on the present vibration in the acoustic transmitter.

This disclosure is related to marine seismic sources, for example marine seismic sources known in the art as benders. Some embodiments of this disclosure use magnetic reluctance forces to produce seismic energy. For example, pole pieces may be attached to one or more plates of a marine seismic source, and a wire coil may induce an attractive force between the pole pieces to cause deformation of the plates to produce seismic energy. Such marine seismic sources may be components of a marine seismic survey system, and may be used in a method of marine seismic surveying. Methods of making marine seismic sources are also disclosed.

A reaction mass seismic survey source that is located in an underground casing. The seismic source includes a non-planar base plate; a reaction mass located on the non-planar base plate; and a flextensional element housed in a recess of the reaction mass and configured to vibrate the non-planar base plate when actuated, to generate seismic waves underground.

The present disclosure includes a method for monitoring a subsurface formation including disposing an antenna in a horizontal wellbore, the antenna including a plurality of piezoelectric modules. A voltage signal is applied to at least one of the piezoelectric modules to cause the at least one piezoelectric modules to emit seismic energy into the subsurface formation. A resulting signal is received at a receiver. A property of the subsurface formation is determined based, at least in part, on the resulting signal.

A downhole tool for operation within a wellbore and including a transmitter array and first and second receiver arrays. The transmitter array includes a plurality of transmitters azimuthally distributed around a longitudinal axis of the downhole tool at a first axial location of the downhole tool. The first receiver array includes a plurality of first receivers azimuthally distributed around the longitudinal axis at a second axial location axially offset from the first axial location. The second receiver array includes a plurality of second receivers azimuthally distributed around the longitudinal axis at a third axial location axially offset from the first and second axial locations.