A system for near-surface subsurface imaging for detecting and characterizing subsurface heterogeneities comprises a non-contact acoustic source that senses a plurality of acoustic waves that travel through a surface; an instrument that outputs probing electromagnetic signals through the surface that interact and are affected by scattered signals of the acoustic waves and further senses vibrational modes of a subsurface below the surface; an imaging device that dynamically generates a time sequence of images of properties of the acoustic waves and maps elastic wave fields of the acoustic waves; and a processor that analyzes dynamic multi-wave data of the images to quantify spatial variations in the mechanical and viscoelastic properties of the subsurface.

Embodiments relate to marine seismic vibrators and associated methods of use. An embodiment provides a marine seismic vibrator comprising: a shell comprising endbeams and shell side portions coupled to the endbeams, wherein each of the shell side portions has a midline between the endbeams, wherein each of the shell side portions has a thinner portion at the midline to force each of the shell side portions to bend at the midline; a driver disposed within the shell; and a pair of spring elements disposed within the shell on either side of the driver, wherein the pair of spring elements are coupled to the driver and to the shell such that movement of the driver is transferred to the shell by way of the spring elements, wherein the pair of spring elements have a second mode of oscillation that provides a second resonance frequency within the operational frequency range.

In an apparatus for multi-pole acoustic logging while drilling, a N-cycle sinusoidal wave signal is generated by utilizing a signal processor, and amplified into a high-voltage sinusoidal excitation signal by utilizing a power amplifier, and output to a transmitting transducer. The signal processor simultaneously generates an enable signal. The enable signal includes a transient discharge enable signal. The power amplifier is connected with a transient discharge circuit. After the signal processor generates N cycles of a sinusoidal wave, the transient discharge enable signal enables the transient discharge circuit to discharge to release an energy storage current of a power transformer so as to eliminate a high-voltage ringing effect and improve an excitation efficiency of the transducer.

Disclosed are dipole sources and associated methods. An example system may include a dipole source a first marine seismic vibrator and a second marine seismic vibrator. The first marine seismic vibrator may include two or more sound radiating surfaces. The second marine seismic vibrator may also include two or more sound radiating surfaces. A relative position of the second marine seismic vibrator to the first marine seismic vibrator may be fixed. The first marine seismic vibrator may be positioned above the second marine seismic vibrator in a towing configuration. The system may further include a control system operable to control the dipole source such that the first marine seismic vibrator is operating substantially 180 out of phase with the second marine seismic vibrator.

Processes and systems described herein are directed to performing marine surveys with marine vibrators that emit orthogonal coded pseudo-random sweeps. In one aspect, coded pseudo-random signals are generated based on coded pseudo-random sequences. The coded pseudo-random sequences are used to activate the marine vibrators in a body of water above a subterranean formation. The activated marine vibrators generate orthogonal coded pseudo-random sweeps. A wavefield emitted from the subterranean formation in response to the orthogonal coded pseudo-random sweeps is detected at receivers located in a body of water. Seismic signals generated by the receivers may be cross-correlated with a signature of one of the orthogonal coded pseudo-random sweeps to obtain seismic data with incoherent residual noise.

Techniques are disclosed relating to acquisition and imaging for marine surveys. In some embodiments, a transition survey that uses both one or more sources of a first type (e.g., impulsive sources) and one or more sources of a second type (e.g., vibratory sources) may facilitate calibration of prior surveys that use the first type of sources with subsequent surveys that use the second type of source. In some embodiments, the different types of sources may be operated simultaneously at approximately the same location. In some embodiments, signals generated by the sources are separated, e.g., using deconvolution. The signals may then be compared to generate difference information, which in turn may be used to adjust sensor measurements from a previous or subsequent survey. In various embodiments, the disclosed techniques may improve accuracy in images of geological formations and may facilitate transitions to new types of seismic sources while maintaining continuity in 4D surveys.

A method for applying separated wave-field imaging onshore (1) by artificially creating up-going and down-going fields and (2) by using these fields in a migration algorithm. If there are any surface multiples in the data, the resulting image created using the migration algorithm will be distorted by the unknown free-surface reflection coefficient. In fact, the surface multiples may be generated with a complex series of reflection coefficients. The distortions found in the resulting image created using the migration algorithm are then removed.

Embodiments relate to marine seismic vibrators for use in seismic surveying and associated methods of use. An embodiment provides a marine seismic vibrator comprising: a shell having a spring constant selected to provide a first resonance frequency within an operational frequency range of about 1 Hz and about 300 Hz; a driver disposed within the shell and having a first end and a second end; and a spring element coupled to the shell between the first end and the second end of the driver, wherein the spring element has a second mode of oscillation that provides a second resonance frequency within the operational frequency range.

Implementations described and claimed herein provide systems and methods for isolation detection. In one implementation, an axial acoustic signal is obtained. The axial acoustic signal is captured using an axial sensor deployed in a structure in a subterranean surface. The axial acoustic signal is separated into a first wave region and a second wave region by applying velocity filtering. An axial symmetry of a portion of the structure is determined based on at least one of the first wave region or the second wave region.

Implementations described and claimed herein provide systems and methods for isolation detection. In one implementation, recorded data is obtained. The recorded data includes radial acoustic waves transmitted and received using a radial sensor of an acoustic logging tool deployed in a wellbore. Clockwise waves are separated from counterclockwise waves by converting the recorded data from a time domain to a frequency domain. The clockwise waves are shifted into shifted clockwise waves, and the counterclockwise waves are shifted into a shifted counterclockwise waves. A forward wave is generated by combining the shifted clockwise waves, and a reflected wave is generated by combining the shifted counterclockwise waves. One or more isolation regions are identified in the wellbore using the forward wave and the reflected wave.